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GREAT ASTRONOMERS

by

SIR ROBERT S. BALL D.Sc. LL.D. F.R.S.

Lowndean Professor of Astronomy and Geometry in the
University of Cambridge

Author of "In Starry Realms" "In the High Heavens" etc.

WITH NUMEROUS ILLUSTRATIONS


[PLATE: GREENWICH OBSERVATORY.]




PREFACE.


It has been my object in these pages to present the life of each
astronomer in such detail as to enable the reader to realise in
some degree the man's character and surroundings; and I have
endeavoured to indicate as clearly as circumstances would permit
the main features of the discoveries by which he has become known.

There are many types of astronomers--from the stargazer who merely
watches the heavens, to the abstract mathematician who merely
works at his desk; it has, consequently, been necessary in the
case of some lives to adopt a very different treatment from that
which seemed suitable for others.

While the work was in progress, some of the sketches appeared in
"Good Words." The chapter on Brinkley has been chiefly derived from
an article on the "History of Dunsink Observatory," which was
published on the occasion of the tercentenary celebration of the
University of Dublin in 1892, and the life of Sir William Rowan
Hamilton is taken, with a few alterations and omissions, from an
article contributed to the "Quarterly Review" on Graves' life of
the great mathematician. The remaining chapters now appear for
the first time. For many of the facts contained in the sketch of
the late Professor Adams, I am indebted to the obituary notice
written by my friend Dr. J. W. L. Glaisher, for the Royal Astronomical
Society; while with regard to the late Sir George Airy, I have a
similar acknowledgment to make to Professor H. H. Turner. To my
friend Dr. Arthur A. Rambaut I owe my hearty thanks for his
kindness in aiding me in the revision of the work.

R.S.B.
The Observatory, Cambridge.
October, 1895




CONTENTS.


INTRODUCTION.

PTOLEMY.

COPERNICUS.

TYCHO BRAHE.

GALILEO.

KEPLER.

ISAAC NEWTON.

FLAMSTEED.

HALLEY.

BRADLEY.

WILLIAM HERSCHEL.

LAPLACE.

BRINKLEY.

JOHN HERSCHEL.

THE EARL OF ROSSE.

AIRY.

HAMILTON.

LE VERRIER.

ADAMS.




LIST OF ILLUSTRATIONS.

THE OBSERVATORY, GREENWICH.

PTOLEMY.

PTOLEMY'S PLANETARY SCHEME.

PTOLEMY'S THEORY OF THE MOVEMENT OF MARS.

THORN, FROM AN OLD PRINT.

COPERNICUS.

FRAUENBURG, FROM AN OLD PRINT.

EXPLANATION OF PLANETARY MOVEMENTS.

TYCHO BRAHE.

TYCHO'S CROSS STAFF.

TYCHO'S "NEW STAR" SEXTANT OF 1572.

TYCHO'S TRIGONIC SEXTANT.

TYCHO'S ASTRONOMIC SEXTANT.

TYCHO'S EQUATORIAL ARMILLARY.

THE GREAT AUGSBURG QUADRANT.

TYCHO'S "NEW SCHEME OF THE TERRESTRIAL SYSTEM," 1577.

URANIBORG AND ITS GROUNDS.

GROUND-PLAN OF THE OBSERVATORY.

THE OBSERVATORY OF URANIBORG, ISLAND OF HVEN.

EFFIGY ON TYCHO'S TOMB AT PRAGUE.
  By Permission of Messrs. A. & C. Black.

TYCHO'S MURAL QUADRANT, URANIBORG.

GALILEO'S PENDULUM.

GALILEO.

THE VILLA ARCETRI.

FACSIMILE SKETCH OF LUNAR SURFACE BY GALILEO.

CREST OF GALILEO'S FAMILY.

KEPLER'S SYSTEM OF REGULAR SOLIDS.

KEPLER.

SYMBOLICAL REPRESENTATION OF THE PLANETARY SYSTEM.

THE COMMEMORATION OF THE RUDOLPHINE TABLES.

WOOLSTHORPE MANOR.

TRINITY COLLEGE, CAMBRIDGE.

DIAGRAM OF A SUNBEAM.

ISAAC NEWTON.

SIR ISAAC NEWTON'S LITTLE REFLECTOR.

SIR ISAAC NEWTON'S SUN-DIAL.

SIR ISAAC NEWTON'S TELESCOPE.

SIR ISAAC NEWTON'S ASTROLABE.

SIR ISAAC NEWTON'S SUN-DIAL IN THE ROYAL SOCIETY.

FLAMSTEED'S HOUSE.

FLAMSTEED.

HALLEY.

GREENWICH OBSERVATORY IN HALLEY'S TIME.

7, NEW KING STREET, BATH.
   From a Photograph by John Poole, Bath.

WILLIAM HERSCHEL.

CAROLINE HERSCHEL.

STREET VIEW, HERSCHEL HOUSE, SLOUGH.
   From a Photograph by Hill & Saunders, Eton.

GARDEN VIEW, HERSCHEL HOUSE, SLOUGH.
   From a Photograph by Hill & Saunders, Eton.

OBSERVATORY, HERSCHEL HOUSE, SLOUGH.
   From a Photograph by Hill & Saunders, Eton.

THE 40-FOOT TELESCOPE, HERSCHEL HOUSE, SLOUGH.
   From a Photograph by Hill & Saunders, Eton.

LAPLACE.

THE OBSERVATORY, DUNSINK.
   From a Photograph by W. Lawrence, Dublin.

ASTRONOMETER MADE BY SIR JOHN HERSCHEL.

SIR JOHN HERSCHEL.

NEBULA IN SOUTHERN HEMISPHERE.

THE CLUSTER IN THE CENTAUR.

OBSERVATORY AT FELDHAUSEN.

GRANITE COLUMN AT FELDHAUSEN.

THE EARL OF ROSSE.

BIRR CASTLE.
   From a Photograph by W. Lawrence, Dublin.

THE MALL, PARSONSTOWN.
   From a Photograph by W. Lawrence, Dublin.

LORD ROSSE'S TELESCOPE.
   From a Photograph by W. Lawrence, Dublin.

ROMAN CATHOLIC CHURCH, PARSONSTOWN.
   From a Photograph by W. Lawrence, Dublin.

AIRY.
   From a Photograph by E.P. Adams, Greenwich.

HAMILTON.

ADAMS.

THE OBSERVATORY, CAMBRIDGE.




INTRODUCTION.


Of all the natural sciences there is not one which offers such
sublime objects to the attention of the inquirer as does the science
of astronomy. From the earliest ages the study of the stars has
exercised the same fascination as it possesses at the present day.
Among the most primitive peoples, the movements of the sun, the moon,
and the stars commanded attention from their supposed influence on
human affairs.

The practical utilities of astronomy were also obvious in primeval
times. Maxims of extreme antiquity show how the avocations of the
husbandman are to be guided by the movements of the heavenly bodies.
The positions of the stars indicated the time to plough, and the time
to sow. To the mariner who was seeking a way across the trackless
ocean, the heavenly bodies offered the only reliable marks by which
his path could be guided. There was, accordingly, a stimulus both
from intellectual curiosity and from practical necessity to follow
the movements of the stars. Thus began a search for the causes of
the ever-varying phenomena which the heavens display.

Many of the earliest discoveries are indeed prehistoric. The great
diurnal movement of the heavens, and the annual revolution of the
sun, seem to have been known in times far more ancient than those to
which any human monuments can be referred. The acuteness of the
early observers enabled them to single out the more important of the
wanderers which we now call planets. They saw that the star-like
objects, Jupiter, Saturn, and Mars, with the more conspicuous Venus,
constituted a class of bodies wholly distinct from the fixed stars
among which their movements lay, and to which they bear such a
superficial resemblance. But the penetration of the early
astronomers went even further, for they recognized that Mercury also
belongs to the same group, though this particular object is seen so
rarely. It would seem that eclipses and other phenomena were
observed at Babylon from a very remote period, while the most ancient
records of celestial observations that we possess are to be found in
the Chinese annals.

The study of astronomy, in the sense in which we understand the word,
may be said to have commenced under the reign of the Ptolemies at
Alexandria. The most famous name in the science of this period is
that of Hipparchus who lived and worked at Rhodes about the year
160BC. It was his splendid investigations that first wrought the
observed facts into a coherent branch of knowledge. He recognized
the primary obligation which lies on the student of the heavens to
compile as complete an inventory as possible of the objects which are
there to be found. Hipparchus accordingly commenced by undertaking,
on a small scale, a task exactly similar to that on which modern
astronomers, with all available appliances of meridian circles, and
photographic telescopes, are constantly engaged at the present day.
He compiled a catalogue of the principal fixed stars, which is of
special value to astronomers, as being the earliest work of its kind
which has been handed down. He also studied the movements of the sun
and the moon, and framed theories to account for the incessant
changes which he saw in progress. He found a much more difficult
problem in his attempt to interpret satisfactorily the complicated
movements of the planets. With the view of constructing a theory
which should give some coherent account of the subject, he made many
observations of the places of these wandering stars. How great were
the advances which Hipparchus accomplished may be appreciated if we
reflect that, as a preliminary task to his more purely astronomical
labours, he had to invent that branch of mathematical science by
which alone the problems he proposed could be solved. It was for
this purpose that he devised the indispensable method of calculation
which we now know so well as trigonometry. Without the aid rendered
by this beautiful art it would have been impossible for any really
important advance in astronomical calculation to have been effected.

But the discovery which shows, beyond all others, that Hipparchus
possessed one of the master-minds of all time was the detection of
that remarkable celestial movement known as the precession of the
equinoxes. The inquiry which conducted to this discovery involved a
most profound investigation, especially when it is remembered that in
the days of Hipparchus the means of observation of the heavenly
bodies were only of the rudest description, and the available
observations of earlier dates were extremely scanty. We can but look
with astonishment on the genius of the man who, in spite of such
difficulties, was able to detect such a phenomenon as the precession,
and to exhibit its actual magnitude. I shall endeavour to explain
the nature of this singular celestial movement, for it may be said to
offer the first instance in the history of science in which we find
that combination of accurate observation with skilful interpretation,
of which, in the subsequent development of astronomy, we have so many
splendid examples.

The word equinox implies the condition that the night is equal to the
day. To a resident on the equator the night is no doubt equal to the
day at all times in the year, but to one who lives on any other part
of the earth, in either hemisphere, the night and the day are not
generally equal. There is, however, one occasion in spring, and
another in autumn, on which the day and the night are each twelve
hours at all places on the earth. When the night and day are equal
in spring, the point which the sun occupies on the heavens is termed
the vernal equinox. There is similarly another point in which the
sun is situated at the time of the autumnal equinox. In any
investigation of the celestial movements the positions of these two
equinoxes on the heavens are of primary importance, and Hipparchus,
with the instinct of genius, perceived their significance, and
commenced to study them. It will be understood that we can always
define the position of a point on the sky with reference to the
surrounding stars. No doubt we do not see the stars near the sun
when the sun is shining, but they are there nevertheless. The
ingenuity of Hipparchus enabled him to determine the positions of
each of the two equinoxes relatively to the stars which lie in its
immediate vicinity. After examination of the celestial places of
these points at different periods, he was led to the conclusion that
each equinox was moving relatively to the stars, though that movement
was so slow that twenty five thousand years would necessarily elapse
before a complete circuit of the heavens was accomplished. Hipparchus
traced out this phenomenon, and established it on an impregnable
basis, so that all astronomers have ever since recognised the
precession of the equinoxes as one of the fundamental facts of
astronomy. Not until nearly two thousand years after Hipparchus had
made this splendid discovery was the explanation of its cause given
by Newton.

From the days of Hipparchus down to the present hour the science of
astronomy has steadily grown. One great observer after another has
appeared from time to time, to reveal some new phenomenon with regard
to the celestial bodies or their movements, while from time to time
one commanding intellect after another has arisen to explain the true
import of the facts of observations. The history of astronomy thus
becomes inseparable from the history of the great men to whose
labours its development is due.

In the ensuing chapters we have endeavoured to sketch the lives and
the work of the great philosophers, by whose labours the science of
astronomy has been created. We shall commence with Ptolemy, who,
after the foundations of the science had been laid by Hipparchus,
gave to astronomy the form in which it was taught throughout the
Middle Ages. We shall next see the mighty revolution in our
conceptions of the universe which are associated with the name of
Copernicus. We then pass to those periods illumined by the genius of
Galileo and Newton, and afterwards we shall trace the careers of
other more recent discoverers, by whose industry and genius the
boundaries of human knowledge have been so greatly extended. Our
history will be brought down late enough to include some of the
illustrious astronomers who laboured in the generation which has just
passed away.




PTOLEMY.


[PLATE: PTOLEMY.]

The career of the famous man whose name stands at the head of this
chapter is one of the most remarkable in the history of human
learning. There may have been other discoverers who have done more
for science than ever Ptolemy accomplished, but there never has been
any other discoverer whose authority on the subject of the movements
of the heavenly bodies has held sway over the minds of men for so
long a period as the fourteen centuries during which his opinions
reigned supreme. The doctrines he laid down in his famous book, "The
Almagest," prevailed throughout those ages. No substantial addition
was made in all that time to the undoubted truths which this work
contained. No important correction was made of the serious errors
with which Ptolemy's theories were contaminated. The authority of
Ptolemy as to all things in the heavens, and as to a good many things
on the earth (for the same illustrious man was also a diligent
geographer), was invariably final.

Though every child may now know more of the actual truths of the
celestial motions than ever Ptolemy knew, yet the fact that his work
exercised such an astonishing effect on the human intellect for some
sixty generations, shows that it must have been an extraordinary
production. We must look into the career of this wonderful man to
discover wherein lay the secret of that marvellous success which made
him the unchallenged instructor of the human race for such a
protracted period.

Unfortunately, we know very little as to the personal history of
Ptolemy. He was a native of Egypt, and though it has been sometimes
conjectured that he belonged to the royal families of the same name,
yet there is nothing to support such a belief. The name, Ptolemy,
appears to have been a common one in Egypt in those days. The time
at which he lived is fixed by the fact that his first recorded
observation was made in 127 AD, and his last in 151 AD. When we add
that he seems to have lived in or near Alexandria, or to use his own
words, "on the parallel of Alexandria," we have said everything that
can be said so far as his individuality is concerned.

Ptolemy is, without doubt, the greatest figure in ancient astronomy.
He gathered up the wisdom of the philosophers who had preceded him.
He incorporated this with the results of his own observations, and
illumined it with his theories. His speculations, even when they
were, as we now know, quite erroneous, had such an astonishing
verisimilitude to the actual facts of nature that they commanded
universal assent. Even in these modern days we not unfrequently find
lovers of paradox who maintain that Ptolemy's doctrines not only seem
true, but actually are true.

In the absence of any accurate knowledge of the science of mechanics,
philosophers in early times were forced to fall back on certain
principles of more or less validity, which they derived from their
imagination as to what the natural fitness of things ought to be.
There was no geometrical figure so simple and so symmetrical as a
circle, and as it was apparent that the heavenly bodies pursued
tracks which were not straight lines, the conclusion obviously
followed that their movements ought to be circular. There was no
argument in favour of this notion, other than the merely imaginary
reflection that circular movement, and circular movement alone, was
"perfect," whatever "perfect" may have meant. It was further
believed to be impossible that the heavenly bodies could have any
other movements save those which were perfect. Assuming this, it
followed, in Ptolemy's opinion, and in that of those who came after
him for fourteen centuries, that all the tracks of the heavenly
bodies were in some way or other to be reduced to circles.

Ptolemy succeeded in devising a scheme by which the apparent changes
that take place in the heavens could, so far as he knew them, be
explained by certain combinations of circular movement. This seemed
to reconcile so completely the scheme of things celestial with the
geometrical instincts which pointed to the circle as the type of
perfect movement, that we can hardly wonder Ptolemy's theory met with
the astonishing success that attended it. We shall, therefore, set
forth with sufficient detail the various steps of this famous
doctrine.

Ptolemy commences with laying down the undoubted truth that the shape
of the earth is globular. The proofs which he gives of this
fundamental fact are quite satisfactory; they are indeed the same
proofs as we give today. There is, first of all, the well-known
circumstance of which our books on geography remind us, that when an
object is viewed at a distance across the sea, the lower part of the
object appears cut off by the interposing curved mass of water.

The sagacity of Ptolemy enabled him to adduce another argument,
which, though not quite so obvious as that just mentioned,
demonstrates the curvature of the earth in a very impressive manner
to anyone who will take the trouble to understand it. Ptolemy
mentions that travellers who went to the south reported, that, as
they did so, the appearance of the heavens at night underwent a
gradual change. Stars that they were familiar with in the northern
skies gradually sank lower in the heavens. The constellation of the
Great Bear, which in our skies never sets during its revolution round
the pole, did set and rise when a sufficient southern latitude had
been attained. On the other hand, constellations new to the
inhabitants of northern climes were seen to rise above the southern
horizon. These circumstances would be quite incompatible with the
supposition that the earth was a flat surface. Had this been so, a
little reflection will show that no such changes in the apparent
movements of the stars would be the consequence of a voyage to the
south. Ptolemy set forth with much insight the significance of this
reasoning, and even now, with the resources of modern discoveries to
help us, we can hardly improve upon his arguments.

Ptolemy, like a true philosopher disclosing a new truth to the world,
illustrated and enforced his subject by a variety of happy
demonstrations. I must add one of them, not only on account of its
striking nature, but also because it exemplifies Ptolemy's
acuteness. If the earth were flat, said this ingenious reasoner,
sunset must necessarily take place at the same instant, no matter in
what country the observer may happen to be placed. Ptolemy, however,
proved that the time of sunset did vary greatly as the observer's
longitude was altered. To us, of course, this is quite obvious;
everybody knows that the hour of sunset may have been reached in
Great Britain while it is still noon on the western coast of
America. Ptolemy had, however, few of those sources of knowledge
which are now accessible. How was he to show that the sun actually
did set earlier at Alexandria than it would in a city which lay a
hundred miles to the west? There was no telegraph wire by which
astronomers at the two Places could communicate. There was no
chronometer or watch which could be transported from place to place;
there was not any other reliable contrivance for the keeping of
time. Ptolemy's ingenuity, however, pointed out a thoroughly
satisfactory method by which the times of sunset at two places could
be compared. He was acquainted with the fact, which must indeed have
been known from the very earliest times, that the illumination of the
moon is derived entirely from the sun. He knew that an eclipse of
the moon was due to the interposition of the earth which cuts off the
light of the sun. It was, therefore, plain that an eclipse of the
moon must be a phenomenon which would begin at the same instant from
whatever part of the earth the moon could be seen at the time.
Ptolemy, therefore, brought together from various quarters the local
times at which different observers had recorded the beginning of a
lunar eclipse. He found that the observers to the west made the time
earlier and earlier the further away their stations were from
Alexandria. On the other hand, the eastern observers set down the
hour as later than that at which the phenomenon appeared at
Alexandria. As these observers all recorded something which indeed
appeared to them simultaneously, the only interpretation was, that
the more easterly a place the later its time. Suppose there were a
number of observers along a parallel of latitude, and each noted the
hour of sunset to be six o'clock, then, since the eastern times are
earlier than western times, 6 p.m. at one station A will correspond
to 5 p.m. at a station B sufficiently to the west. If, therefore,
it is sunset to the observer at A, the hour of sunset will not yet be
reached for the observer at B. This proves conclusively that the
time of sunset is not the same all over the earth. We have, however,
already seen that the apparent time of sunset would be the same from
all stations if the earth were flat. When Ptolemy, therefore,
demonstrated that the time of sunset was not the same at various
places, he showed conclusively that the earth was not flat.

As the same arguments applied to all parts of the earth where Ptolemy
had either been himself, or from which he could gain the necessary
information, it followed that the earth, instead of being the flat
plain, girdled with an illimitable ocean, as was generally supposed,
must be in reality globular. This led at once to a startling
consequence. It was obvious that there could be no supports of any
kind by which this globe was sustained; it therefore followed that
the mighty object must be simply poised in space. This is indeed an
astonishing doctrine to anyone who relies on what merely seems the
evidence of the senses, without giving to that evidence its due
intellectual interpretation. According to our ordinary experience,
the very idea of an object poised without support in space, appears
preposterous. Would it not fall? we are immediately asked. Yes,
doubtless it could not remain poised in any way in which we try the
experiment. We must, however, observe that there are no such ideas
as upwards or downwards in relation to open space. To say that a
body falls downwards, merely means that it tries to fall as nearly as
possible towards the centre of the earth. There is no one direction
along which a body will tend to move in space, in preference to any
other. This may be illustrated by the fact that a stone let fall at
New Zealand will, in its approach towards the earth's centre, be
actually moving upwards as far as any locality in our hemisphere is
concerned. Why, then, argued Ptolemy, may not the earth remain
poised in space, for as all directions are equally upward or equally
downward, there seems no reason why the earth should require any
support? By this reasoning he arrives at the fundamental conclusion
that the earth is a globular body freely lying in space, and
surrounded above, below, and on all sides by the glittering stars of
heaven.

The perception of this sublime truth marks a notable epoch in the
history of the gradual development of the human intellect. No doubt,
other philosophers, in groping after knowledge, may have set forth
certain assertions that are more or less equivalent to this
fundamental truth. It is to Ptolemy we must give credit, however,
not only for announcing this doctrine, but for demonstrating it by
clear and logical argument. We cannot easily project our minds back
to the conception of an intellectual state in which this truth was
unfamiliar. It may, however, be well imagined that, to one who
thought the earth was a flat plain of indefinite extent, it would be
nothing less than an intellectual convulsion for him to be forced to
believe that he stood upon a spherical earth, forming merely a
particle relatively to the immense sphere of the heavens.

What Ptolemy saw in the movements of the stars led him to the
conclusion that they were bright points attached to the inside of a
tremendous globe. The movements of this globe which carried the
stars were only compatible with the supposition that the earth
occupied its centre. The imperceptible effect produced by a change
in the locality of the observer on the apparent brightness of the
stars made it plain that the dimensions of the terrestrial globe must
be quite insignificant in comparison with those of the celestial
sphere. The earth might, in fact, be regarded as a grain of sand
while the stars lay upon a globe many yards in diameter.

So tremendous was the revolution in human knowledge implied by this
discovery, that we can well imagine how Ptolemy, dazzled as it were
by the fame which had so justly accrued to him, failed to make one
further step. Had he made that step, it would have emancipated the
human intellect from the bondage of fourteen centuries of servitude
to a wholly monstrous notion of this earth's importance in the scheme
of the heavens. The obvious fact that the sun, the moon, and the
stars rose day by day, moved across the sky in a glorious
never-ending procession, and duly set when their appointed courses
had been run, demanded some explanation. The circumstance that the
fixed stars preserved their mutual distances from year to year, and
from age to age, appeared to Ptolemy to prove that the sphere which
contained those stars, and on whose surface they were believed by him
to be fixed, revolved completely around the earth once every day. He
would thus account for all the phenomena of rising and setting
consistently with the supposition that our globe was stationary.
Probably this supposition must have appeared monstrous, even to
Ptolemy. He knew that the earth was a gigantic object, but, large as
it may have been, he knew that it was only a particle in comparison
with the celestial sphere, yet he apparently believed, and certainly
succeeded in persuading other men to believe, that the celestial
sphere did actually perform these movements.

Ptolemy was an excellent geometer. He knew that the rising and the
setting of the sun, the moon, and the myriad stars, could have been
accounted for in a different way. If the earth turned round
uniformly once a day while poised at the centre of the sphere of the
heavens, all the phenomena of rising and setting could be completely
explained. This is, indeed, obvious after a moment's reflection.
Consider yourself to be standing on the earth at the centre of the
heavens. There are stars over your head, and half the contents of
the heavens are visible, while the other half are below your
horizon. As the earth turns round, the stars over your head will
change, and unless it should happen that you have taken up your
position at either of the poles, new stars will pass into your view,
and others will disappear, for at no time can you have more than half
of the whole sphere visible. The observer on the earth would,
therefore, say that some stars were rising, and that some stars were
setting. We have, therefore, two totally distinct methods, each of
which would completely explain all the observed facts of the diurnal
movement. One of these suppositions requires that the celestial
sphere, bearing with it the stars and other celestial bodies, turns
uniformly around an invisible axis, while the earth remains
stationary at the centre. The other supposition would be, that it is
the stupendous celestial sphere which remains stationary, while the
earth at the centre rotates about the same axis as the celestial
sphere did before, but in an opposite direction, and with a uniform
velocity which would enable it to complete one turn in twenty-four
hours. Ptolemy was mathematician enough to know that either of these
suppositions would suffice for the explanation of the observed
facts. Indeed, the phenomena of the movements of the stars, so far
as he could observe them, could not be called upon to pronounce which
of these views was true, and which was false.

Ptolemy had, therefore, to resort for guidance to indirect lines of
reasoning. One of these suppositions must be true, and yet it
appeared that the adoption of either was accompanied by a great
difficulty. It is one of his chief merits to have demonstrated that
the celestial sphere was so stupendous that the earth itself was
absolutely insignificant in comparison therewith. If, then, this
stupendous sphere rotated once in twenty-four hours, the speed with
which the movement of some of the stars must be executed would be so
portentous as to seem well-nigh impossible. It would, therefore,
seem much simpler on this ground to adopt the other alternative, and
to suppose the diurnal movements were due to the rotation of the
earth. Here Ptolemy saw, or at all events fancied he saw, objections
of the weightiest description. The evidence of the senses appeared
directly to controvert the supposition that this earth is anything
but stationary. Ptolemy might, perhaps, have dismissed this
objection on the ground that the testimony of the senses on such a
matter should be entirely subordinated to the interpretation which
our intelligence would place upon the facts to which the senses
deposed. Another objection, however, appeared to him to possess the
gravest moment. It was argued that if the earth were rotating, there
is nothing to make the air participate in this motion, mankind would
therefore be swept from the earth by the furious blasts which would
arise from the movement of the earth through an atmosphere at rest.
Even if we could imagine that the air were carried round with the
earth, the same would not apply, so thought Ptolemy, to any object
suspended in the air. So long as a bird was perched on a tree, he
might very well be carried onward by the moving earth, but the moment
he took wing, the ground would slip from under him at a frightful
pace, so that when he dropped down again he would find himself at a
distance perhaps ten times as great as that which a carrier-pigeon or
a swallow could have traversed in the same time. Some vague delusion
of this description seems even still to crop up occasionally. I
remember hearing of a proposition for balloon travelling of a very
remarkable kind. The voyager who wanted to reach any other place in
the same latitude was simply to ascend in a balloon, and wait there
till the rotation of the earth conveyed the locality which happened
to be his destination directly beneath him, whereupon he was to let
out the gas and drop down! Ptolemy knew quite enough natural
philosophy to be aware that such a proposal for locomotion would be
an utter absurdity; he knew that there was no such relative shift
between the air and the earth as this motion would imply. It
appeared to him to be necessary that the air should lag behind, if
the earth had been animated by a movement of rotation. In this he
was, as we know, entirely wrong. There were, however, in his days no
accurate notions on the subject of the laws of motion.

Assiduous as Ptolemy may have been in the study of the heavenly
bodies, it seems evident that he cannot have devoted much thought to
the phenomena of motion of terrestrial objects. Simple, indeed, are
the experiments which might have convinced a philosopher much less
acute than Ptolemy, that, if the earth did revolve, the air must
necessarily accompany it. If a rider galloping on horseback tosses a
ball into the air, it drops again into his hand, just as it would
have done had he been remaining at rest during the ball's flight; the
ball in fact participates in the horizontal motion, so that though it
really describes a curve as any passer-by would observe, yet it
appears to the rider himself merely to move up and down in a straight
line. This fact, and many others similar to it, demonstrate clearly
that if the earth were endowed with a movement of rotation, the
atmosphere surrounding it must participate in that movement. Ptolemy
did not know this, and consequently he came to the conclusion that
the earth did not rotate, and that, therefore, notwithstanding the
tremendous improbability of so mighty an object as the celestial
sphere spinning round once in every twenty-four hours, there was no
course open except to believe that this very improbable thing did
really happen. Thus it came to pass that Ptolemy adopted as the
cardinal doctrine of his system a stationary earth poised at the
centre of the celestial sphere, which stretched around on all sides
at a distance so vast that the diameter of the earth was an
inappreciable point in comparison therewith.

Ptolemy having thus deliberately rejected the doctrine of the earth's
rotation, had to make certain other entirely erroneous suppositions.
It was easily seen that each star required exactly the same period
for the performance of a complete revolution of the heavens. Ptolemy
knew that the stars were at enormous distances from the earth, though
no doubt his notions on this point came very far short of what we
know to be the reality. If the stars had been at very varied
distances, then it would be so wildly improbable that they should all
accomplish their revolutions in the same time, that Ptolemy came to
the conclusion that they must be all at the same distance, that is,
that they must be all on the surface of a sphere. This view, however
erroneous, was corroborated by the obvious fact that the stars in the
constellations preserved their relative places unaltered for
centuries. Thus it was that Ptolemy came to the conclusion that they
were all fixed on one spherical surface, though we are not informed
as to the material of this marvellous setting which sustained the
stars like jewels.

Nor should we hastily pronounce this doctrine to be absurd. The
stars do appear to lie on the surface of a sphere, of which the
observer is at the centre; not only is this the aspect which the
skies present to the untechnical observer, but it is the aspect in
which the skies are presented to the most experienced astronomer of
modern days. No doubt he knows well that the stars are at the most
varied distances from him; he knows that certain stars are ten times,
or a hundred times, or a thousand times, as far as other stars.
Nevertheless, to his eye the stars appear on the surface of the
sphere, it is on that surface that his measurements of the relative
places of the stars are made; indeed, it may be said that almost all
the accurate observations in the observatory relate to the places of
the stars, not as they really are, but as they appear to be projected
on that celestial sphere whose conception we owe to the genius of
Ptolemy.

This great philosopher shows very ingeniously that the earth must be
at the centre of the sphere. He proves that, unless this were the
case, each star would not appear to move with the absolute uniformity
which does, as a matter of fact, characterise it. In all these
reasonings we cannot but have the most profound admiration for the
genius of Ptolemy, even though he had made an error so enormous in
the fundamental point of the stability of the earth. Another error
of a somewhat similar kind seemed to Ptolemy to be demonstrated. He
had shown that the earth was an isolated object in space, and being
such was, of course, capable of movement. It could either be turned
round, or it could be moved from one place to another. We know that
Ptolemy deliberately adopted the view that the earth did not turn
round; he had then to investigate the other question, as to whether
the earth was animated by any movement of translation. He came to
the conclusion that to attribute any motion to the earth would be
incompatible with the truths at which he had already arrived. The
earth, argued Ptolemy, lies at the centre of the celestial sphere.
If the earth were to be endowed with movement, it would not lie
always at this point, it must, therefore, shift to some other part of
the sphere. The movements of the stars, however, preclude the
possibility of this; and, therefore, the earth must be as devoid of
any movement of translation as it is devoid of rotation. Thus it was
that Ptolemy convinced himself that the stability of the earth, as it
appeared to the ordinary senses, had a rational philosophical
foundation.

Not unfrequently it is the lot of the philosophers to contend against
the doctrines of the vulgar, but when it happens, as in the case of
Ptolemy's researches, that the doctrines of the vulgar are
corroborated by philosophical investigation which bear the stamp of
the highest authority, it is not to be wondered at that such
doctrines should be deemed well-nigh impregnable. In this way we
may, perhaps, account for the remarkable fact that the theories of
Ptolemy held unchallenged sway over the human intellect for the vast
period already mentioned.

Up to the present we have been speaking only of those primary motions
of the heavens, by which the whole sphere appeared to revolve once
every twenty-four hours. We have now to discuss the remarkable
theories by which Ptolemy endeavoured to account for the monthly
movement of the moon, for the annual movement of the sun, and for the
periodic movements of the planets which had gained for them the
titles of the wandering stars.

Possessed with the idea that these movements must be circular, or
must be capable, directly or indirectly, of being explained by
circular movements, it seemed obvious to Ptolemy, as indeed it had
done to previous astronomers, that the track of the moon through the
stars was a circle of which the earth is the centre. A similar
movement with a yearly period must also be attributed to the sun, for
the changes in the positions of the constellations in accordance with
the progress of the seasons, placed it beyond doubt that the sun made
a circuit of the celestial sphere, even though the bright light of
the sun prevented the stars in its vicinity, from being seen in
daylight. Thus the movements both of the sun and the moon, as well
as the diurnal rotation of the celestial sphere, seemed to justify
the notion that all celestial movements must be "perfect," that is to
say, described uniformly in those circles which were the only perfect
curves.

The simplest observations, however, show that the movements of the
planets cannot be explained in this simple fashion. Here the
geometrical genius of Ptolemy shone forth, and he devised a scheme by
which the apparent wanderings of the planets could be accounted for
without the introduction of aught save "perfect" movements.

To understand his reasoning, let us first set forth clearly those
facts of observation which require to be explained. I shall take, in
particular, two planets, Venus and Mars, as these illustrate, in the
most striking manner, the peculiarities of the inner and the outer
planets respectively. The simplest observations would show that
Venus did not move round the heavens in the same fashion as the sun
or the moon. Look at the evening star when brightest, as it appears
in the west after sunset. Instead of moving towards the east among
the stars, like the sun or the moon, we find, week after week, that
Venus is drawing in towards the sun, until it is lost in the
sunbeams. Then the planet emerges on the other side, not to be seen
as an evening star, but as a morning star. In fact, it was plain
that in some ways Venus accompanied the sun in its annual movement.
Now it is found advancing in front of the sun to a certain limited
distance, and now it is lagging to an equal extent behind the sun.

[FIG. 1. PTOLEMY'S PLANETARY SCHEME.]

These movements were wholly incompatible with the supposition that
the journeys of Venus were described by a single motion of the kind
regarded as perfect. It was obvious that the movement was connected
in some strange manner with the revolution of the sun, and here was
the ingenious method by which Ptolemy sought to render account of
it. Imagine a fixed arm to extend from the earth to the sun, as
shown in the accompanying figure (Fig. 1), then this arm will move
round uniformly, in consequence of the sun's movement. At a point P
on this arm let a small circle be described. Venus is supposed to
revolve uniformly in this small circle, while the circle itself is
carried round continuously by the movement of the sun. In this way
it was possible to account for the chief peculiarities in the
movement of Venus. It will be seen that, in consequence of the
revolution around P, the spectator on the earth will sometimes see
Venus on one side of the sun, and sometimes on the other side, so
that the planet always remains in the sun's vicinity. By properly
proportioning the movements, this little contrivance simulated the
transitions from the morning star to the evening star. Thus the
changes of Venus could be accounted for by a Combination of the
"perfect" movement of P in the circle which it described uniformly
round the earth, combined with the "perfect" motion of Venus in the
circle which it described uniformly around the moving centre.

In a precisely similar manner Ptolemy rendered an explanation of the
fitful apparitions of Mercury. Now just on one side of the sun, and
now just on the other, this rarely-seen planet moved like Venus on a
circle whereof the centre was also carried by the line joining the
sun and the earth. The circle, however, in which Mercury actually
revolved had to be smaller than that of Venus, in order to account
for the fact that Mercury lies always much closer to the sun than the
better-known planet.

[FIG. 2. PTOLEMY'S THEORY OF THE MOVEMENT OF MARS.]

The explanation of the movement of an outer planet like Mars could
also be deduced from the joint effect of two perfect motions. The
changes through which Mars goes are, however, so different from the
movements of Venus that quite a different disposition of the circles
is necessary. For consider the facts which characterise the
movements of an outer planet such as Mars. In the first place, Mars
accomplishes an entire circuit of the heaven. In this respect, no
doubt, it may be said to resemble the sun or the moon. A little
attention will, however, show that there are extraordinary
irregularities in the movement of the planet. Generally speaking, it
speeds its way from west to east among the stars, but sometimes the
attentive observer will note that the speed with which the planet
advances is slackening, and then it will seem to become stationary.
Some days later the direction of the planet's movement will be
reversed, and it will be found moving from the east towards the
west. At first it proceeds slowly and then quickens its pace, until
a certain speed is attained, which afterwards declines until a second
stationary position is reached. After a due pause the original
motion from west to east is resumed, and is continued until a similar
cycle of changes again commences. Such movements as these were
obviously quite at variance with any perfect movement in a single
circle round the earth. Here, again, the geometrical sagacity of
Ptolemy provided him with the means of representing the apparent
movements of Mars, and, at the same time, restricting the explanation
to those perfect movements which he deemed so essential. In Fig. 2
we exhibit Ptolemy's theory as to the movement of Mars. We have, as
before, the earth at the centre, and the sun describing its circular
orbit around that centre. The path of Mars is to be taken as
exterior to that of the sun. We are to suppose that at a point
marked M there is a fictitious planet, which revolves around the
earth uniformly, in a circle called the DEFERENT. This point M,
which is thus animated by a perfect movement, is the centre of a
circle which is carried onwards with M, and around the circumference
of which Mars revolves uniformly. It is easy to show that the
combined effect of these two perfect movements is to produce exactly
that displacement of Mars in the heavens which observation
discloses. In the position represented in the figure, Mars is
obviously pursuing a course which will appear to the observer as a
movement from west to east. When, however, the planet gets round to
such a position as R, it is then moving from east to west in
consequence of its revolution in the moving circle, as indicated by
the arrow-head. On the other hand, the whole circle is carried
forward in the opposite direction. If the latter movement be less
rapid than the former, then we shall have the backward movement of
Mars on the heavens which it was desired to explain. By a proper
adjustment of the relative lengths of these arms the movements of the
planet as actually observed could be completely accounted for.

The other outer planets with which Ptolemy was acquainted, namely,
Jupiter and Saturn, had movements of the same general character as
those of Mars. Ptolemy was equally successful in explaining the
movements they performed by the supposition that each planet had
perfect rotation in a circle of its own, which circle itself had
perfect movement around the earth in the centre.

It is somewhat strange that Ptolemy did not advance one step further,
as by so doing he would have given great simplicity to his system. He
might, for instance, have represented the movements of Venus equally
well by putting the centre of the moving circle at the sun itself,
and correspondingly enlarging the circle in which Venus revolved. He
might, too, have arranged that the several circles which the outer
planets traversed should also have had their centres at the sun. The
planetary system would then have consisted of an earth fixed at the
centre, of a sun revolving uniformly around it, and of a system of
planets each describing its own circle around a moving centre placed
in the sun. Perhaps Ptolemy had not thought of this, or perhaps he
may have seen arguments against it. This important step was,
however, taken by Tycho. He considered that all the planets revolved
around the sun in circles, and that the sun itself, bearing all these
orbits, described a mighty circle around the earth. This point
having been reached, only one more step would have been necessary to
reach the glorious truths that revealed the structure of the solar
system. That last step was taken by Copernicus.




COPERNICUS


[PLATE: THORN, FROM AN OLD PRINT.]

The quaint town of Thorn, on the Vistula, was more than two centuries
old when Copernicus was born there on the 19th of February, 1473. The
situation of this town on the frontier between Prussia and Poland,
with the commodious waterway offered by the river, made it a place of
considerable trade. A view of the town, as it was at the time of the
birth of Copernicus, is here given. The walls, with their
watch-towers, will be noted, and the strategic importance which the
situation of Thorn gave to it in the fifteenth century still belongs
thereto, so much so that the German Government recently constituted
the town a fortress of the first class.

Copernicus, the astronomer, whose discoveries make him the great
predecessor of Kepler and Newton, did not come from a noble family,
as certain other early astronomers have done, for his father was a
tradesman. Chroniclers are, however, careful to tell us that one of
his uncles was a bishop. We are not acquainted with any of those
details of his childhood or youth which are often of such interest in
other cases where men have risen to exalted fame. It would appear
that the young Nicolaus, for such was his Christian name, received
his education at home until such time as he was deemed sufficiently
advanced to be sent to the University at Cracow. The education that
he there obtained must have been in those days of a very primitive
description, but Copernicus seems to have availed himself of it to
the utmost. He devoted himself more particularly to the study of
medicine, with the view of adopting its practice as the profession of
his life. The tendencies of the future astronomer were, however,
revealed in the fact that he worked hard at mathematics, and, like
one of his illustrious successors, Galileo, the practice of the art
of painting had for him a very great interest, and in it he obtained
some measure of success.

By the time he was twenty-seven years old, it would seem that
Copernicus had given up the notion of becoming a medical
practitioner, and had resolved to devote himself to science. He was
engaged in teaching mathematics, and appears to have acquired some
reputation. His growing fame attracted the notice of his uncle the
bishop, at whose suggestion Copernicus took holy orders, and he was
presently appointed to a canonry in the cathedral of Frauenburg, near
the mouth of the Vistula.

To Frauenburg, accordingly, this man of varied gifts retired.
Possessing somewhat of the ascetic spirit, he resolved to devote his
life to work of the most serious description. He eschewed all
ordinary society, restricting his intimacies to very grave and
learned companions, and refusing to engage in conversation of any
useless kind. It would seem as if his gifts for painting were
condemned as frivolous; at all events, we do not learn that he
continued to practise them. In addition to the discharge of his
theological duties, his life was occupied partly in ministering
medically to the wants of the poor, and partly with his researches in
astronomy and mathematics. His equipment in the matter of
instruments for the study of the heavens seems to have been of a very
meagre description. He arranged apertures in the walls of his house
at Allenstein, so that he could observe in some fashion the passage
of the stars across the meridian. That he possessed some talent for
practical mechanics is proved by his construction of a contrivance
for raising water from a stream, for the use of the inhabitants of
Frauenburg. Relics of this machine are still to be seen.

[PLATE: COPERNICUS.]

The intellectual slumber of the Middle Ages was destined to be
awakened by the revolutionary doctrines of Copernicus. It may be
noted, as an interesting circumstance, that the time at which he
discovered the scheme of the solar system has coincided with a
remarkable epoch in the world's history. The great astronomer had
just reached manhood at the time when Columbus discovered the new
world.

Before the publication of the researches of Copernicus, the orthodox
scientific creed averred that the earth was stationary, and that the
apparent movements of the heavenly bodies were indeed real
movements. Ptolemy had laid down this doctrine 1,400 years before.
In his theory this huge error was associated with so much important
truth, and the whole presented such a coherent scheme for the
explanation of the heavenly movements, that the Ptolemaic theory was
not seriously questioned until the great work of Copernicus
appeared. No doubt others, before Copernicus, had from time to time
in some vague fashion surmised, with more or less plausibility, that
the sun, and not the earth, was the centre about which the system
really revolved. It is, however, one thing to state a scientific
fact; it is quite another thing to be in possession of the train of
reasoning, founded on observation or experiment, by which that fact
may be established. Pythagoras, it appears, had indeed told his
disciples that it was the sun, and not the earth, which was the
centre of movement, but it does not seem at all certain that
Pythagoras had any grounds which science could recognise for the
belief which is attributed to him. So far as information is
available to us, it would seem that Pythagoras associated his scheme
of things celestial with a number of preposterous notions in natural
philosophy. He may certainly have made a correct statement as to
which was the most important body in the solar system, but he
certainly did not provide any rational demonstration of the fact.
Copernicus, by a strict train of reasoning, convinced those who would
listen to him that the sun was the centre of the system. It is
useful for us to consider the arguments which he urged, and by which
he effected that intellectual revolution which is always connected
with his name.

The first of the great discoveries which Copernicus made relates to
the rotation of the earth on its axis. That general diurnal
movement, by which the stars and all other celestial bodies appear to
be carried completely round the heavens once every twenty-four hours,
had been accounted for by Ptolemy on the supposition that the
apparent movements were the real movements. As we have already seen,
Ptolemy himself felt the extraordinary difficulty involved in the
supposition that so stupendous a fabric as the celestial sphere
should spin in the way supposed. Such movements required that many
of the stars should travel with almost inconceivable velocity.
Copernicus also saw that the daily rising and setting of the heavenly
bodies could be accounted for either by the supposition that the
celestial sphere moved round and that the earth remained at rest, or
by the supposition that the celestial sphere was at rest while the
earth turned round in the opposite direction. He weighed the
arguments on both sides as Ptolemy had done, and, as the result of
his deliberations, Copernicus came to an opposite conclusion from
Ptolemy. To Copernicus it appeared that the difficulties attending
the supposition that the celestial sphere revolved, were vastly
greater than those which appeared so weighty to Ptolemy as to force
him to deny the earth's rotation.

Copernicus shows clearly how the observed phenomena could be
accounted for just as completely by a rotation of the earth as by a
rotation of the heavens. He alludes to the fact that, to those on
board a vessel which is moving through smooth water, the vessel
itself appears to be at rest, while the objects on shore seem to be
moving past. If, therefore, the earth were rotating uniformly, we
dwellers upon the earth, oblivious of our own movement, would wrongly
attribute to the stars the displacement which was actually the
consequence of our own motion.

Copernicus saw the futility of the arguments by which Ptolemy had
endeavoured to demonstrate that a revolution of the earth was
impossible. It was plain to him that there was nothing whatever to
warrant refusal to believe in the rotation of the earth. In his
clear-sightedness on this matter we have specially to admire the
sagacity of Copernicus as a natural philosopher. It had been urged
that, if the earth moved round, its motion would not be imparted to
the air, and that therefore the earth would be uninhabitable by the
terrific winds which would be the result of our being carried through
the air. Copernicus convinced himself that this deduction was
preposterous. He proved that the air must accompany the earth, just
as his coat remains round him, notwithstanding the fact that he is
walking down the street. In this way he was able to show that all a
priori objections to the earth's movements were absurd, and therefore
he was able to compare together the plausibilities of the two rival
schemes for explaining the diurnal movement.

[PLATE: FRAUENBURG, FROM AN OLD PRINT.]

Once the issue had been placed in this form, the result could not be
long in doubt. Here is the question: Which is it more likely--that
the earth, like a grain of sand at the centre of a mighty globe,
should turn round once in twenty-four hours, or that the whole of
that vast globe should complete a rotation in the opposite direction
in the same time? Obviously, the former is far the more simple
supposition. But the case is really much stronger than this. Ptolemy
had supposed that all the stars were attached to the surface of a
sphere. He had no ground whatever for this supposition, except that
otherwise it would have been well-nigh impossible to have devised a
scheme by which the rotation of the heavens around a fixed earth
could have been arranged. Copernicus, however, with the just
instinct of a philosopher, considered that the celestial sphere,
however convenient from a geometrical point of view, as a means of
representing apparent phenomena, could not actually have a material
existence. In the first place, the existence of a material celestial
sphere would require that all the myriad stars should be at exactly
the same distances from the earth. Of course, no one will say that
this or any other arbitrary disposition of the stars is actually
impossible, but as there was no conceivable physical reason why the
distances of all the stars from the earth should be identical, it
seemed in the very highest degree improbable that the stars should be
so placed.

Doubtless, also, Copernicus felt a considerable difficulty as to the
nature of the materials from which Ptolemy's wonderful sphere was to
be constructed. Nor could a philosopher of his penetration have
failed to observe that, unless that sphere were infinitely large,
there must have been space outside it, a consideration which would
open up other difficult questions. Whether infinite or not, it was
obvious that the celestial sphere must have a diameter at least many
thousands of times as great as that of the earth. From these
considerations Copernicus deduced the important fact that the stars
and the other celestial bodies must all be vast objects. He was thus
enabled to put the question in such a form that it could hardly
receive any answer but the correct one. Which is it more rational to
suppose, that the earth should turn round on its axis once in
twenty-four hours, or that thousands of mighty stars should circle
round the earth in the same time, many of them having to describe
circles many thousands of times greater in circumference than the
circuit of the earth at the equator? The obvious answer pressed upon
Copernicus with so much force that he was compelled to reject
Ptolemy's theory of the stationary earth, and to attribute the
diurnal rotation of the heavens to the revolution of the earth on its
axis.

Once this tremendous step had been taken, the great difficulties
which beset the monstrous conception of the celestial sphere
vanished, for the stars need no longer be regarded as situated at
equal distances from the earth. Copernicus saw that they might lie
at the most varied degrees of remoteness, some being hundreds or
thousands of times farther away than others. The complicated
structure of the celestial sphere as a material object disappeared
altogether; it remained only as a geometrical conception, whereon we
find it convenient to indicate the places of the stars. Once the
Copernican doctrine had been fully set forth, it was impossible for
anyone, who had both the inclination and the capacity to understand
it, to withhold acceptance of its truth. The doctrine of a
stationary earth had gone for ever.

Copernicus having established a theory of the celestial movements
which deliberately set aside the stability of the earth, it seemed
natural that he should inquire whether the doctrine of a moving earth
might not remove the difficulties presented in other celestial
phenomena. It had been universally admitted that the earth lay
unsupported in space. Copernicus had further shown that it possessed
a movement of rotation. Its want of stability being thus recognised,
it seemed reasonable to suppose that the earth might also have some
other kinds of movements as well. In this, Copernicus essayed to
solve a problem far more difficult than that which had hitherto
occupied his attention. It was a comparatively easy task to show how
the diurnal rising and setting could be accounted for by the rotation
of the earth. It was a much more difficult undertaking to
demonstrate that the planetary movements, which Ptolemy had
represented with so much success, could be completely explained by
the supposition that each of those planets revolved uniformly round
the sun, and that the earth was also a planet, accomplishing a
complete circuit of the sun once in the course of a year.

[PLATE: EXPLANATION OF PLANETARY MOVEMENTS.]

It would be impossible in a sketch like the present to enter into any
detail as to the geometrical propositions on which this beautiful
investigation of Copernicus depended. We can only mention a few of
the leading principles. It may be laid down in general that, if an
observer is in movement, he will, if unconscious of the fact,
attribute to the fixed objects around him a movement equal and
opposite to that which he actually possesses. A passenger on a
canal-boat sees the objects on the banks apparently moving backward
with a speed equal to that by which he is himself advancing
forwards. By an application of this principle, we can account for
all the phenomena of the movements of the planets, which Ptolemy had
so ingeniously represented by his circles. Let us take, for
instance, the most characteristic feature in the irregularities of
the outer planets. We have already remarked that Mars, though
generally advancing from west to east among the stars, occasionally
pauses, retraces his steps for awhile, again pauses, and then resumes
his ordinary onward progress. Copernicus showed clearly how this
effect was produced by the real motion of the earth, combined with
the real motion of Mars. In the adjoining figure we represent a
portion of the circular tracks in which the earth and Mars move in
accordance with the Copernican doctrine. I show particularly the
case where the earth comes directly between the planet and the sun,
because it is on such occasions that the retrograde movement (for so
this backward movement of Mars is termed) is at its highest. Mars is
then advancing in the direction shown by the arrow-head, and the
earth is also advancing in the same direction. We, on the earth,
however, being unconscious of our own motion, attribute, by the
principle I have already explained, an equal and opposite motion to
Mars. The visible effect upon the planet is, that Mars has two
movements, a real onward movement in one direction, and an apparent
movement in the opposite direction. If it so happened that the earth
was moving with the same speed as Mars, then the apparent movement
would exactly neutralise the real movement, and Mars would seem to be
at rest relatively to the surrounding stars. Under the actual
circumstances represented, however, the earth is moving faster than
Mars, and the consequence is, that the apparent movement of the
planet backwards exceeds the real movement forwards, the net result
being an apparent retrograde movement.

With consummate skill, Copernicus showed how the applications of the
same principles could account for the characteristic movements of the
planets. His reasoning in due time bore down all opposition. The
supreme importance of the earth in the system vanished. It had now
merely to take rank as one of the planets.

The same great astronomer now, for the first time, rendered something
like a rational account of the changes of the seasons. Nor did
certain of the more obscure astronomical phenomena escape his
attention.

He delayed publishing his wonderful discoveries to the world until he
was quite an old man. He had a well-founded apprehension of the
storm of opposition which they would arouse. However, he yielded at
last to the entreaties of his friends, and his book was sent to the
press. But ere it made its appearance to the world, Copernicus was
seized by mortal illness. A copy of the book was brought to him on
May 23, 1543. We are told that he was able to see it and to touch
it, but no more, and he died a few hours afterwards. He was buried
in that Cathedral of Frauenburg, with which his life had been so
closely associated.




TYCHO BRAHE.


The most picturesque figure in the history of astronomy is
undoubtedly that of the famous old Danish astronomer whose name
stands at the head of this chapter. Tycho Brahe was alike notable
for his astronomical genius and for the extraordinary vehemence of a
character which was by no means perfect. His romantic career as a
philosopher, and his taste for splendour as a Danish noble, his
ardent friendships and his furious quarrels, make him an ideal
subject for a biographer, while the magnificent astronomical work
which he accomplished, has given him imperishable fame.

The history of Tycho Brahe has been admirably told by Dr. Dreyer, the
accomplished astronomer who now directs the observatory at Armagh,
though himself a countryman of Tycho. Every student of the career of
the great Dane must necessarily look on Dr. Dreyer's work as the
chief authority on the subject. Tycho sprang from an illustrious
stock. His family had flourished for centuries, both in Sweden and
in Denmark, where his descendants are to be met with at the present
day. The astronomer's father was a privy councillor, and having
filled important positions in the Danish government, he was
ultimately promoted to be governor of Helsingborg Castle, where he
spent the last years of his life. His illustrious son Tycho was born
in 1546, and was the second child and eldest boy in a family of ten.

It appears that Otto, the father of Tycho, had a brother named
George, who was childless. George, however, desired to adopt a boy
on whom he could lavish his affection and to whom he could bequeath
his wealth. A somewhat singular arrangement was accordingly entered
into by the brothers at the time when Otto was married. It was
agreed that the first son who might be born to Otto should be
forthwith handed over by the parents to George to be reared and
adopted by him. In due time little Tycho appeared, and was
immediately claimed by George in pursuance of the compact. But it
was not unnatural that the parental instinct, which had been dormant
when the agreement was made, should here interpose. Tycho's father
and mother receded from the bargain, and refused to part with their
son. George thought he was badly treated. However, he took no
violent steps until a year later, when a brother was born to Tycho.
The uncle then felt no scruple in asserting what he believed to be
his rights by the simple process of stealing the first-born nephew,
which the original bargain had promised him. After a little time it
would seem that the parents acquiesced in the loss, and thus it was
in Uncle George's home that the future astronomer passed his
childhood.

When we read that Tycho was no more than thirteen years old at the
time he entered the University of Copenhagen, it might be at first
supposed that even in his boyish years he must have exhibited some of
those remarkable talents with which he was afterwards to astonish the
world. Such an inference should not, however, be drawn. The fact is
that in those days it was customary for students to enter the
universities at a much earlier age than is now the case. Not,
indeed, that the boys of thirteen knew more then than the boys of
thirteen know now. But the education imparted in the universities at
that time was of a much more rudimentary kind than that which we
understand by university education at present. In illustration of
this Dr. Dreyer tells us how, in the University of Wittenberg, one of
the professors, in his opening address, was accustomed to point out
that even the processes of multiplication and division in arithmetic
might be learned by any student who possessed the necessary
diligence.

It was the wish and the intention of his uncle that Tycho's education
should be specially directed to those branches of rhetoric and
philosophy which were then supposed to be a necessary preparation for
the career of a statesman. Tycho, however, speedily made it plain to
his teachers that though he was an ardent student, yet the things
which interested him were the movements of the heavenly bodies and
not the subtleties of metaphysics.

[PLATE: TYCHO BRAHE.]

On the 21st October, 1560, an eclipse of the sun occurred, which was
partially visible at Copenhagen. Tycho, boy though he was, took the
utmost interest in this event. His ardour and astonishment in
connection with the circumstance were chiefly excited by the fact
that the time of the occurrence of the phenomenon could be predicted
with so much accuracy. Urged by his desire to understand the matter
thoroughly, Tycho sought to procure some book which might explain
what he so greatly wanted to know. In those days books of any kind
were but few and scarce, and scientific books were especially
unattainable. It so happened, however, that a Latin version of
Ptolemy's astronomical works had appeared a few years before the
eclipse took place, and Tycho managed to buy a copy of this book,
which was then the chief authority on celestial matters. Young as
the boy astronomer was, he studied hard, although perhaps not always
successfully, to understand Ptolemy, and to this day his copy of the
great work, copiously annotated and marked by the schoolboy hand, is
preserved as one of the chief treasures in the library of the
University at Prague.

After Tycho had studied for about three years at the University of
Copenhagen, his uncle thought it would be better to send him, as was
usual in those days, to complete his education by a course of study
in some foreign university. The uncle cherished the hope that in
this way the attention of the young astronomer might be withdrawn
from the study of the stars and directed in what appeared to him a
more useful way. Indeed, to the wise heads of those days, the
pursuit of natural science seemed so much waste of good time which
might otherwise be devoted to logic or rhetoric or some other branch
of study more in vogue at that time. To assist in this attempt to
wean Tycho from his scientific tastes, his uncle chose as a tutor to
accompany him an intelligent and upright young man named Vedel, who
was four years senior to his pupil, and accordingly, in 1562, we find
the pair taking up their abode at the University of Leipzig.

The tutor, however, soon found that he had undertaken a most hopeless
task. He could not succeed in imbuing Tycho with the slightest taste
for the study of the law or the other branches of knowledge which
were then thought so desirable. The stars, and nothing but the
stars, engrossed the attention of his pupil. We are told that all
the money he could obtain was spent secretly in buying astronomical
books and instruments. He learned the name of the stars from a
little globe, which he kept hidden from Vedel, and only ventured to
use during the latter's absence. No little friction was at first
caused by all this, but in after years a fast and enduring friendship
grew up between Tycho and his tutor, each of whom learned to respect
and to love the other.

Before Tycho was seventeen he had commenced the difficult task of
calculating the movements of the planets and the places which they
occupied on the sky from time to time. He was not a little surprised
to find that the actual positions of the planets differed very widely
from those which were assigned to them by calculations from the best
existing works of astronomers. With the insight of genius he saw
that the only true method of investigating the movements of the
heavenly bodies would be to carry on a protracted series of
measurements of their places. This, which now seems to us so
obvious, was then entirely new doctrine. Tycho at once commenced
regular observations in such fashion as he could. His first
instrument was, indeed, a very primitive one, consisting of a simple
pair of compasses, which he used in this way. He placed his eye at
the hinge, and then opened the legs of the compass so that one leg
pointed to one star and the other leg to the other star. The compass
was then brought down to a divided circle, by which means the number
of degrees in the apparent angular distance of the two stars was
determined.

His next advance in instrumental equipment was to provide himself
with the contrivance known as the "cross-staff," which he used to
observe the stars whenever opportunity offered. It must, of course,
be remembered that in those days there were no telescopes. In the
absence of optical aid, such as lenses afford the modern observers,
astronomers had to rely on mechanical appliances alone to measure the
places of the stars. Of such appliances, perhaps the most ingenious
was one known before Tycho's time, which we have represented in the
adjoining figure.

[PLATE: TYCHO'S CROSS STAFF.]

Let us suppose that it be desired to measure the angle between two
stars, then if the angle be not too large it can be determined in the
following manner. Let the rod AB be divided into inches and parts of
an inch, and let another rod, CD, slide up and down along AB in such
a way that the two always remain perpendicular to each other.
"Sights," like those on a rifle, are placed at A and C, and there is
a pin at D. It will easily be seen that, by sliding the movable bar
along the fixed one, it must always be possible when the stars are
not too far apart to bring the sights into such positions that one
star can be seen along DC and the other along DA. This having been
accomplished, the length from A to the cross-bar is read off on the
scale, and then, by means of a table previously prepared, the value
of the required angular distance is obtained. If the angle between
the two stars were greater than it would be possible to measure in
the way already described, then there was a provision by which the
pin at D might be moved along CD into some other position, so as to
bring the angular distance of the stars within the range of the
instrument.

[PLATE: TYCHO'S "NEW STAR" SEXTANT OF 1572.
(The arms, of walnut wood, are about 5 1/2 ft. long.)]

No doubt the cross-staff is a very primitive contrivance, but when
handled by one so skilful as Tycho it afforded results of
considerable accuracy. I would recommend any reader who may have a
taste for such pursuits to construct a cross-staff for himself, and
see what measurements he can accomplish with its aid.

To employ this little instrument Tycho had to evade the vigilance of
his conscientious tutor, who felt it his duty to interdict all such
occupations as being a frivolous waste of time. It was when Vedel
was asleep that Tycho managed to escape with his cross staff and
measure the places of the heavenly bodies. Even at this early age
Tycho used to conduct his observations on those thoroughly sound
principles which lie at the foundation of all accurate modern
astronomy. Recognising the inevitable errors of workmanship in his
little instrument, he ascertained their amount and allowed for their
influence on the results which he deduced. This principle, employed
by the boy with his cross-staff in 1564, is employed at the present
day by the Astronomer Royal at Greenwich with the most superb
instruments that the skill of modern opticians has been able to
construct.

[PLATE: TYCHO'S TRIGONIC SEXTANT.
(The arms, AB and AC, are about 5 1/2 ft. long.)]

After the death of his uncle, when Tycho was nineteen years of age,
it appears that the young philosopher was no longer interfered with
in so far as the line which his studies were to take was concerned.
Always of a somewhat restless temperament, we now find that he
shifted his abode to the University of Rostock, where he speedily
made himself notable in connection with an eclipse of the moon on
28th October, 1566. Like every other astronomer of those days, Tycho
had always associated astronomy with astrology. He considered that
the phenomena of the heavenly bodies always had some significance in
connection with human affairs. Tycho was also a poet, and in the
united capacity of poet, astrologer, and astronomer, he posted up
some verses in the college at Rostock announcing that the lunar
eclipse was a prognostication of the death of the great Turkish
Sultan, whose mighty deeds at that time filled men's minds. Presently
news did arrive of the death of the Sultan, and Tycho was accordingly
triumphant; but a little later it appeared that the decease had taken
place BEFORE the eclipse, a circumstance which caused many a laugh at
Tycho's expense.

[PLATE: TYCHO'S ASTRONOMIC SEXTANT.
(Made of steel: the arms, AB, AC, measure 4 ft.)

PLATE: TYCHO'S EQUATORIAL ARMILLARY.
(The meridian circle, E B C A D, made of solid steel,
is nearly 6 ft. in diameter.)]

Tycho being of a somewhat turbulent disposition, it appears that,
while at the University of Rostock, he had a serious quarrel with
another Danish nobleman. We are not told for certain what was the
cause of the dispute. It does not, however, seem to have had any
more romantic origin than a difference of opinion as to which of them
knew the more mathematics. They fought, as perhaps it was becoming
for two astronomers to fight, under the canopy of heaven in utter
darkness at the dead of night, and the duel was honourably terminated
when a slice was taken off Tycho's nose by the insinuating sword of
his antagonist. For the repair of this injury the ingenuity of the
great instrument-maker was here again useful, and he made a
substitute for his nose "with a composition of gold and silver." The
imitation was so good that it is declared to have been quite equal to
the original. Dr. Lodge, however, pointedly observes that it does
not appear whether this remark was made by a friend or an enemy.

[PLATE: THE GREAT AUGSBURG QUADRANT.
(Built of heart of oak; the radii about 19 ft.)

PLATE: TYCHO'S "NEW SCHEME OF THE TERRESTRIAL SYSTEM," 1577.]

The next few years Tycho spent in various places ardently pursuing
somewhat varied branches of scientific study. At one time we hear of
him assisting an astronomical alderman, in the ancient city of
Augsburg, to erect a tremendous wooden machine--a quadrant of 19-feet
radius--to be used in observing the heavens. At another time we
learn that the King of Denmark had recognised the talents of his
illustrious subject, and promised to confer on him a pleasant
sinecure in the shape of a canonry, which would assist him with the
means for indulging his scientific pursuits. Again we are told that
Tycho is pursuing experiments in chemistry with the greatest energy,
nor is this so incompatible as might at first be thought with his
devotion to astronomy. In those early days of knowledge the
different sciences seemed bound together by mysterious bonds.
Alchemists and astrologers taught that the several planets were
correlated in some mysterious manner with the several metals. It
was, therefore hardly surprising that Tycho should have included a
study of the properties of the metals in the programme of his
astronomical work.

[PLATE: URANIBORG AND ITS GROUNDS.

PLATE: GROUND-PLAN OF THE OBSERVATORY.]

An event, however, occurred in 1572 which stimulated Tycho's
astronomical labours, and started him on his life's work. On the
11th of November in that year, he was returning home to supper after
a day's work in his laboratory, when he happened to lift his face to
the sky, and there he beheld a brilliant new star. It was in the
constellation of Cassiopeia, and occupied a position in which there
had certainly been no bright star visible when his attention had last
been directed to that part of the heavens. Such a phenomenon was so
startling that he found it hard to trust the evidence of his senses.
He thought he must be the subject of some hallucination. He
therefore called to the servants who were accompanying him, and asked
them whether they, too, could see a brilliant object in the direction
in which he pointed. They certainly could, and thus he became
convinced that this marvellous object was no mere creation of the
fancy, but a veritable celestial body--a new star of surpassing
splendour which had suddenly burst forth. In these days of careful
scrutiny of the heavens, we are accustomed to the occasional outbreak
of new stars. It is not, however, believed that any new star which
has ever appeared has displayed the same phenomenal brilliance as was
exhibited by the star of 1572.

This object has a value in astronomy far greater than it might at
first appear. It is true, in one sense, that Tycho discovered the
new star, but it is equally true, in a different sense, that it was
the new star which discovered Tycho. Had it not been for this
opportune apparition, it is quite possible that Tycho might have
found a career in some direction less beneficial to science than that
which he ultimately pursued.

[PLATE: THE OBSERVATORY OF URANIBORG, ISLAND OF HVEN.]

When he reached his home on this memorable evening, Tycho immediately
applied his great quadrant to the measurement of the place of the new
star. His observations were specially directed to the determination
of the distance of the object. He rightly conjectured that if it
were very much nearer to us than the stars in its vicinity, the
distance of the brilliant body might be determined in a short time by
the apparent changes in its distance from the surrounding points. It
was speedily demonstrated that the new star could not be as near as
the moon, by the simple fact that its apparent place, as compared
with the stars in its neighbourhood, was not appreciably altered when
it was observed below the pole, and again above the pole at an
interval of twelve hours. Such observations were possible, inasmuch
as the star was bright enough to be seen in full daylight. Tycho
thus showed conclusively that the body was so remote that the
diameter of the earth bore an insignificant ratio to the star's
distance. His success in this respect is the more noteworthy when we
find that many other observers, who studied the same object, came to
the erroneous conclusion that the new star was quite as near as the
moon, or even much nearer. In fact, it may be said, that with regard
to this object Tycho discovered everything which could possibly have
been discovered in the days before telescopes were invented. He not
only proved that the star's distance was too great for measurement,
but he showed that it had no proper motion on the heavens. He
recorded the successive changes in its brightness from week to week,
as well as the fluctuations in hue with which the alterations in
lustre were accompanied.

It seems, nowadays, strange to find that such thoroughly scientific
observations of the new star as those which Tycho made, possessed,
even in the eyes of the great astronomer himself, a profound
astrological significance. We learn from Dr. Dreyer that, in Tycho's
opinion, "the star was at first like Venus and Jupiter, and its
effects will therefore, first, be pleasant; but as it then became
like Mars, there will next come a period of wars, seditions,
captivity, and death of princes, and destruction of cities, together
with dryness and fiery meteors in the air, pestilence, and venomous
snakes. Lastly, the star became like Saturn, and thus will finally
come a time of want, death, imprisonment, and all kinds of sad
things!" Ideas of this kind were, however, universally entertained.
It seemed, indeed, obvious to learned men of that period that such an
apparition must forebode startling events. One of the chief theories
then held was, that just as the Star of Bethlehem announced the first
coming of Christ, so the second coming, and the end of the world, was
heralded by the new star of 1572.

The researches of Tycho on this object were the occasion of his first
appearance as an author. The publication of his book was however,
for some time delayed by the urgent remonstrances of his friends, who
thought it was beneath the dignity of a nobleman to condescend to
write a book. Happily, Tycho determined to brave the opinion of his
order; the book appeared, and was the first of a series of great
astronomical productions from the same pen.

[PLATE: EFFIGY ON TYCHO'S TOMB AT PRAGUE.]

The fame of the noble Dane being now widespread, the King of Denmark
entreated him to return to his native country, and to deliver a
course of lectures on astronomy in the University of Copenhagen. With
some reluctance he consented, and his introductory oration has been
preserved. He dwells, in fervent language, upon the beauty and the
interest of the celestial phenomena. He points out the imperative
necessity of continuous and systematic observation of the heavenly
bodies in order to extend our knowledge. He appeals to the practical
utility of the science, for what civilised nation could exist without
having the means of measuring time? He sets forth how the study of
these beautiful objects "exalts the mind from earthly and trivial
things to heavenly ones;" and then he winds up by assuring them that
"a special use of astronomy is that it enables us to draw conclusions
from the movements in the celestial regions as to human fate."

An interesting event, which occurred in 1572, distracted Tycho's
attention from astronomical matters. He fell in love. The young
girl on whom his affections were set appears to have sprung from
humble origin. Here again his august family friends sought to
dissuade him from a match they thought unsuitable for a nobleman.
But Tycho never gave way in anything. It is suggested that he did
not seek a wife among the highborn dames of his own rank from the
dread that the demands of a fashionable lady would make too great an
inroad on the time that he wished to devote to science. At all
events, Tycho's union seems to have been a happy one, and he had a
large family of children; none of whom, however, inherited their
father's talents.

[PLATE: TYCHO'S MURAL QUADRANT PICTURE, URANIBORG.]

Tycho had many scientific friends in Germany, among whom his work was
held in high esteem. The treatment that he there met with seemed to
him so much more encouraging than that which he received in Denmark
that he formed the notion of emigrating to Basle and making it his
permanent abode. A whisper of this intention was conveyed to the
large-hearted King of Denmark, Frederick II. He wisely realised how
great would be the fame which would accrue to his realm if he could
induce Tycho to remain within Danish territory and carry on there the
great work of his life. A resolution to make a splendid proposal to
Tycho was immediately formed. A noble youth was forthwith despatched
as a messenger, and ordered to travel day and night until he reached
Tycho, whom he was to summon to the king. The astronomer was in bed
on the morning of 11th February, 1576, when the message was
delivered. Tycho, of course, set off at once and had an audience of
the king at Copenhagen. The astronomer explained that what he wanted
was the means to pursue his studies unmolested, whereupon the king
offered him the Island of Hven, in the Sound near Elsinore. There he
would enjoy all the seclusion that he could desire. The king further
promised that he would provide the funds necessary for building a
house and for founding the greatest observatory that had ever yet
been reared for the study of the heavens. After due deliberation and
consultation with his friends, Tycho accepted the king's offer. He
was forthwith granted a pension, and a deed was drawn up formally
assigning the Island of Hven to his use all the days of his life.

The foundation of the famous castle of Uraniborg was laid on 30th
August, 1576. The ceremony was a formal and imposing one, in
accordance with Tycho's ideas of splendour. A party of scientific
friends had assembled, and the time had been chosen so that the
heavenly bodies were auspiciously placed. Libations of costly wines
were poured forth, and the stone was placed with due solemnity. The
picturesque character of this wonderful temple for the study of the
stars may be seen in the figures with which this chapter is
illustrated.

One of the most remarkable instruments that has ever been employed in
studying the heavens was the mural quadrant which Tycho erected in
one of the apartments of Uraniborg. By its means the altitudes of
the celestial bodies could be observed with much greater accuracy
than had been previously attainable. This wonderful contrivance is
represented on the preceding page. It will be observed that the
walls of the room are adorned by pictures with a lavishness of
decoration not usually to be found in scientific establishments.

A few years later, when the fame of the observatory at Hven became
more widely spread, a number of young men flocked to Tycho to study
under his direction. He therefore built another observatory for
their use in which the instruments were placed in subterranean rooms
of which only the roofs appeared above the ground. There was a
wonderful poetical inscription over the entrance to this underground
observatory, expressing the astonishment of Urania at finding, even
in the interior of the earth, a cavern devoted to the study of the
heavens. Tycho was indeed always fond of versifying, and he lost no
opportunity of indulging this taste whenever an occasion presented
itself.

Around the walls of the subterranean observatory were the pictures of
eight astronomers, each with a suitable inscription--one of these of
course represented Tycho himself, and beneath were written words to
the effect that posterity should judge of his work. The eighth
picture depicted an astronomer who has not yet come into existence.
Tychonides was his name, and the inscription presses the modest hope
that when he does appear he will be worthy of his great predecessor.
The vast expenses incurred in the erection and the maintenance of
this strange establishment were defrayed by a succession of grants
from the royal purse.

For twenty years Tycho laboured hard at Uraniborg in the pursuit of
science. His work mainly consisted in the determination of the
places of the moon, the planets, and the stars on the celestial
sphere. The extraordinary pains taken by Tycho to have his
observations as accurate as his instruments would permit, have justly
entitled him to the admiration of all succeeding astronomers. His
island home provided the means of recreation as well as a place for
work. He was surrounded by his family, troops of friends were not
wanting, and a pet dwarf seems to have been an inmate of his curious
residence. By way of change from his astronomical labours he used
frequently to work with his students in his chemical laboratory. It
is not indeed known what particular problems in chemistry occupied
his attention. We are told, however, that he engaged largely in the
production of medicines, and as these appear to have been dispensed
gratuitously there was no lack of patients.

Tycho's imperious and grasping character frequently brought him into
difficulties, which seem to have increased with his advancing years.
He had ill-treated one of his tenants on Hven, and an adverse
decision by the courts seems to have greatly exasperated the
astronomer. Serious changes also took place in his relations to the
court at Copenhagen. When the young king was crowned in 1596, he
reversed the policy of his predecessor with reference to Hven. The
liberal allowances to Tycho were one after another withdrawn, and
finally even his pension was stopped. Tycho accordingly abandoned
Hven in a tumult of rage and mortification. A few years later we
find him in Bohemia a prematurely aged man, and he died on the 24th
October, 1601.




GALILEO.


Among the ranks of the great astronomers it would be difficult to
find one whose life presents more interesting features and remarkable
vicissitudes than does that of Galileo. We may consider him as the
patient investigator and brilliant discoverer. We may consider him
in his private relations, especially to his daughter, Sister Maria
Celeste, a woman of very remarkable character; and we have also the
pathetic drama at the close of Galileo's life, when the philosopher
drew down upon himself the thunders of the Inquisition.

The materials for the sketch of this astonishing man are sufficiently
abundant. We make special use in this place of those charming
letters which his daughter wrote to him from her convent home. More
than a hundred of these have been preserved, and it may well be
doubted whether any more beautiful and touching series of letters
addressed to a parent by a dearly loved child have ever been
written. An admirable account of this correspondence is contained in
a little book entitled "The Private Life of Galileo," published
anonymously by Messrs. Macmillan in 1870, and I have been much
indebted to the author of that volume for many of the facts contained
in this chapter.

Galileo was born at Pisa, on 18th February, 1564. He was the eldest
son of Vincenzo de' Bonajuti de' Galilei, a Florentine noble.
Notwithstanding his illustrious birth and descent, it would seem that
the home in which the great philosopher's childhood was spent was an
impoverished one. It was obvious at least that the young Galileo
would have to be provided with some profession by which he might earn
a livelihood. From his father he derived both by inheritance and by
precept a keen taste for music, and it appears that he became an
excellent performer on the lute. He was also endowed with
considerable artistic power, which he cultivated diligently. Indeed,
it would seem that for some time the future astronomer entertained
the idea of devoting himself to painting as a profession. His
father, however, decided that he should study medicine. Accordingly,
we find that when Galileo was seventeen years of age, and had added a
knowledge of Greek and Latin to his acquaintance with the fine arts,
he was duly entered at the University of Pisa.

Here the young philosopher obtained some inkling of mathematics,
whereupon he became so much interested in this branch of science,
that he begged to be allowed to study geometry. In compliance with
his request, his father permitted a tutor to be engaged for this
purpose; but he did so with reluctance, fearing that the attention of
the young student might thus be withdrawn from that medical work
which was regarded as his primary occupation. The event speedily
proved that these anxieties were not without some justification. The
propositions of Euclid proved so engrossing to Galileo that it was
thought wise to avoid further distraction by terminating the
mathematical tutor's engagement. But it was too late for the desired
end to be attained. Galileo had now made such progress that he was
able to continue his geometrical studies by himself. Presently he
advanced to that famous 47th proposition which won his lively
admiration, and on he went until he had mastered the six books of
Euclid, which was a considerable achievement for those days.

The diligence and brilliance of the young student at Pisa did not,
however, bring him much credit with the University authorities. In
those days the doctrines of Aristotle were regarded as the embodiment
of all human wisdom in natural science as well as in everything
else. It was regarded as the duty of every student to learn
Aristotle off by heart, and any disposition to doubt or even to
question the doctrines of the venerated teacher was regarded as
intolerable presumption. But young Galileo had the audacity to think
for himself about the laws of nature. He would not take any
assertion of fact on the authority of Aristotle when he had the means
of questioning nature directly as to its truth or falsehood. His
teachers thus came to regard him as a somewhat misguided youth,
though they could not but respect the unflagging industry with which
he amassed all the knowledge he could acquire.

[PLATE: GALILEO'S PENDULUM.]

We are so accustomed to the use of pendulums in our clocks that
perhaps we do not often realise that the introduction of this method
of regulating time-pieces was really a notable invention worthy the
fame of the great astronomer to whom it was due. It appears that
sitting one day in the Cathedral of Pisa, Galileo's attention became
concentrated on the swinging of a chandelier which hung from the
ceiling. It struck him as a significant point, that whether the arc
through which the pendulum oscillated was a long one or a short one,
the time occupied in each vibration was sensibly the same. This
suggested to the thoughtful observer that a pendulum would afford the
means by which a time-keeper might be controlled, and accordingly
Galileo constructed for the first time a clock on this principle. The
immediate object sought in this apparatus was to provide a means of
aiding physicians in counting the pulses of their patients.

The talents of Galileo having at length extorted due recognition from
the authorities, he was appointed, at the age of twenty-five,
Professor of Mathematics at the University of Pisa. Then came the
time when he felt himself strong enough to throw down the gauntlet to
the adherents of the old philosophy. As a necessary part of his
doctrine on the movement of bodies Aristotle had asserted that the
time occupied by a stone in falling depends upon its weight, so that
the heavier the stone the less time would it require to fall from a
certain height to the earth. It might have been thought that a
statement so easily confuted by the simplest experiments could never
have maintained its position in any accepted scheme of philosophy.
But Aristotle had said it, and to anyone who ventured to express a
doubt the ready sneer was forthcoming, "Do you think yourself a
cleverer man than Aristotle?" Galileo determined to demonstrate in
the most emphatic manner the absurdity of a doctrine which had for
centuries received the sanction of the learned. The summit of the
Leaning Tower of Pisa offered a highly dramatic site for the great
experiment. The youthful professor let fall from the overhanging top
a large heavy body and a small light body simultaneously. According
to Aristotle the large body ought to have reached the ground much
sooner than the small one, but such was found not to be the case. In
the sight of a large concourse of people the simple fact was
demonstrated that the two bodies fell side by side, and reached the
ground at the same time. Thus the first great step was taken in the
overthrow of that preposterous system of unquestioning adhesion to
dogma, which had impeded the development of the knowledge of nature
for nearly two thousand years.

This revolutionary attitude towards the ancient beliefs was not
calculated to render Galileo's relations with the University
authorities harmonious. He had also the misfortune to make enemies
in other quarters. Don Giovanni de Medici, who was then the Governor
of the Port of Leghorn, had designed some contrivance by which he
proposed to pump out a dock. But Galileo showed up the absurdity of
this enterprise in such an aggressive manner that Don Giovanni took
mortal offence, nor was he mollified when the truths of Galileo's
criticisms were abundantly verified by the total failure of his
ridiculous invention. In various ways Galileo was made to feel his
position at Pisa so unpleasant that he was at length compelled to
abandon his chair in the University. The active exertions of his
friends, of whom Galileo was so fortunate as to have had throughout
his life an abundant supply, then secured his election to the
Professorship of Mathematics at Padua, whither he went in 1592.

[PLATE: PORTRAIT OF GALILEO.]

It was in this new position that Galileo entered on that marvellous
career of investigation which was destined to revolutionize science.
The zeal with which he discharged his professorial duties was indeed
of the most unremitting character. He speedily drew such crowds to
listen to his discourses on Natural Philosophy that his lecture-room
was filled to overflowing. He also received many private pupils in
his house for special instruction. Every moment that could be spared
from these labours was devoted to his private study and to his
incessant experiments.

Like many another philosopher who has greatly extended our knowledge
of nature, Galileo had a remarkable aptitude for the invention of
instruments designed for philosophical research. To facilitate his
practical work, we find that in 1599 he had engaged a skilled workman
who was to live in his house, and thus be constantly at hand to try
the devices for ever springing from Galileo's fertile brain. Among
the earliest of his inventions appears to have been the thermometer,
which he constructed in 1602. No doubt this apparatus in its
primitive form differed in some respects from the contrivance we call
by the same name. Galileo at first employed water as the agent, by
the expansion of which the temperature was to be measured. He
afterwards saw the advantage of using spirits for the same purpose.
It was not until about half a century later that mercury came to be
recognised as the liquid most generally suitable for the thermometer.

The time was now approaching when Galileo was to make that mighty
step in the advancement of human knowledge which followed on the
application of the telescope to astronomy. As to how his idea of
such an instrument originated, we had best let him tell us in his own
words. The passage is given in a letter which he writes to his
brother-in-law, Landucci.

"I write now because I have a piece of news for you, though whether
you will be glad or sorry to hear it I cannot say; for I have now no
hope of returning to my own country, though the occurrence which has
destroyed that hope has had results both useful and honourable. You
must know, then, that two months ago there was a report spread here
that in Flanders some one had presented to Count Maurice of Nassau a
glass manufactured in such a way as to make distant objects appear
very near, so that a man at the distance of two miles could be
clearly seen. This seemed to me so marvellous that I began to think
about it. As it appeared to me to have a foundation in the Theory of
Perspective, I set about contriving how to make it, and at length I
found out, and have succeeded so well that the one I have made is far
superior to the Dutch telescope. It was reported in Venice that I
had made one, and a week since I was commanded to show it to his
Serenity and to all the members of the senate, to their infinite
amazement. Many gentlemen and senators, even the oldest, have
ascended at various times the highest bell-towers in Venice to spy
out ships at sea making sail for the mouth of the harbour, and have
seen them clearly, though without my telescope they would have been
invisible for more than two hours. The effect of this instrument is
to show an object at a distance of say fifty miles, as if it were but
five miles."

The remarkable properties of the telescope at once commanded
universal attention among intellectual men. Galileo received
applications from several quarters for his new instrument, of which
it would seem that he manufactured a large number to be distributed
as gifts to various illustrious personages.

But it was reserved for Galileo himself to make that application of
the instrument to the celestial bodies by which its peculiar powers
were to inaugurate the new era in astronomy. The first discovery
that was made in this direction appears to have been connected with
the number of the stars. Galileo saw to his amazement that through
his little tube he could count ten times as many stars in the sky as
his unaided eye could detect. Here was, indeed, a surprise. We are
now so familiar with the elementary facts of astronomy that it is not
always easy to realise how the heavens were interpreted by the
observers in those ages prior to the invention of the telescope. We
can hardly, indeed, suppose that Galileo, like the majority of those
who ever thought of such matters, entertained the erroneous belief
that the stars were on the surface of a sphere at equal distances
from the observer. No one would be likely to have retained his
belief in such a doctrine when he saw how the number of visible stars
could be increased tenfold by means of Galileo's telescope. It would
have been almost impossible to refuse to draw the inference that the
stars thus brought into view were still more remote objects which the
telescope was able to reveal, just in the same way as it showed
certain ships to the astonished Venetians, when at the time these
ships were beyond the reach of unaided vision.

Galileo's celestial discoveries now succeeded each other rapidly.
That beautiful Milky Way, which has for ages been the object of
admiration to all lovers of nature, never disclosed its true nature
to the eye of man till the astronomer of Padua turned on it his magic
tube. The splendid zone of silvery light was then displayed as
star-dust scattered over the black background of the sky. It was
observed that though the individual stars were too small to be seen
severally without optical aid, yet such was their incredible number
that the celestial radiance produced that luminosity with which every
stargazer was so familiar.

But the greatest discovery made by the telescope in these early days,
perhaps, indeed, the greatest discovery that the telescope has ever
accomplished, was the detection of the system of four satellites
revolving around the great planet Jupiter. This phenomenon was so
wholly unexpected by Galileo that, at first, he could hardly believe
his eyes. However, the reality of the existence of a system of four
moons attending the great planet was soon established beyond all
question. Numbers of great personages crowded to Galileo to see for
themselves this beautiful miniature representing the sun with its
system of revolving planets.

Of course there were, as usual, a few incredulous people who refused
to believe the assertion that four more moving bodies had to be added
to the planetary system. They scoffed at the notion; they said the
satellites may have been in the telescope, but that they were not in
the sky. One sceptical philosopher is reported to have affirmed,
that even if he saw the moons of Jupiter himself he would not believe
in them, as their existence was contrary to the principles of
common-sense!

There can be no doubt that a special significance attached to the new
discovery at this particular epoch in the history of science. It
must be remembered that in those days the doctrine of Copernicus,
declaring that the sun, and not the earth, was the centre of the
system, that the earth revolved on its axis once a day, and that it
described a mighty circle round the sun once a year, had only
recently been promulgated. This new view of the scheme of nature had
been encountered with the most furious opposition. It may possibly
have been that Galileo himself had not felt quite confident in the
soundness of the Copernican theory, prior to the discovery of the
satellites of Jupiter. But when a picture was there exhibited in
which a number of relatively small globes were shown to be revolving
around a single large globe in the centre, it seemed impossible not
to feel that the beautiful spectacle so displayed was an emblem of
the relations of the planets to the sun. It was thus made manifest
to Galileo that the Copernican theory of the planetary system must be
the true one. The momentous import of this opinion upon the future
welfare of the great philosopher will presently appear.

It would seem that Galileo regarded his residence at Padua as a state
of undesirable exile from his beloved Tuscany. He had always a
yearning to go back to his own country and at last the desired
opportunity presented itself. For now that Galileo's fame had become
so great, the Grand Duke of Tuscany desired to have the philosopher
resident at Florence, in the belief that he would shed lustre on the
Duke's dominions. Overtures were accordingly made to Galileo, and
the consequence was that in 1616 we find him residing at Florence,
bearing the title of Mathematician and Philosopher to the Grand Duke.

Two daughters, Polissena and Virginia, and one son, Vincenzo, had
been born to Galileo in Padua. It was the custom in those days that
as soon as the daughter of an Italian gentleman had grown up, her
future career was somewhat summarily decided. Either a husband was
to be forthwith sought out, or she was to enter the convent with the
object of taking the veil as a professed nun. It was arranged that
the two daughters of Galileo, while still scarcely more than
children, should both enter the Franciscan convent of St. Matthew, at
Arcetri. The elder daughter Polissena, took the name of Sister Maria
Celeste, while Virginia became Sister Arcangela. The latter seems to
have been always delicate and subject to prolonged melancholy, and
she is of but little account in the narrative of the life of
Galileo. But Sister Maria Celeste, though never leaving the convent,
managed to preserve a close intimacy with her beloved father. This
was maintained only partly by Galileo's visits, which were very
irregular and were, indeed, often suspended for long intervals. But
his letters to this daughter were evidently frequent and
affectionate, especially in the latter part of his life. Most
unfortunately, however, all his letters have been lost. There are
grounds for believing that they were deliberately destroyed when
Galileo was seized by the Inquisition, lest they should have been
used as evidence against him, or lest they should have compromised
the convent where they were received. But Sister Maria Celeste's
letters to her father have happily been preserved, and most touching
these letters are. We can hardly read them without thinking how the
sweet and gentle nun would have shrunk from the idea of their
publication.

Her loving little notes to her "dearest lord and father," as she used
affectionately to call Galileo, were almost invariably accompanied by
some gift, trifling it may be, but always the best the poor nun had
to bestow. The tender grace of these endearing communications was
all the more precious to him from the fact that the rest of Galileo's
relatives were of quite a worthless description. He always
acknowledged the ties of his kindred in the most generous way, but
their follies and their vices, their selfishness and their
importunities, were an incessant source of annoyance to him, almost
to the last day of his life.

On 19th December, 1625, Sister Maria Celeste writes:--

"I send two baked pears for these days of vigil. But as the greatest
treat of all, I send you a rose, which ought to please you extremely,
seeing what a rarity it is at this season; and with the rose you must
accept its thorns, which represent the bitter passion of our Lord,
whilst the green leaves represent the hope we may entertain that
through the same sacred passion we, having passed through the
darkness of the short winter of our mortal life, may attain to the
brightness and felicity of an eternal spring in heaven."

When the wife and children of Galileo's shiftless brother came to
take up their abode in the philosopher's home, Sister Maria Celeste
feels glad to think that her father has now some one who, however
imperfectly, may fulfil the duty of looking after him. A graceful
note on Christmas Eve accompanies her little gifts. She hopes that--

"In these holy days the peace of God may rest on him and all the
house. The largest collar and sleeves I mean for Albertino, the
other two for the two younger boys, the little dog for baby, and the
cakes for everybody, except the spice-cakes, which are for you.
Accept the good-will which would readily do much more."

The extraordinary forbearance with which Galileo continually placed
his time, his purse, and his influence at the service of those who
had repeatedly proved themselves utterly unworthy of his countenance,
is thus commented on by the good nun.--

"Now it seems to me, dearest lord and father, that your lordship is
walking in the right path, since you take hold of every occasion that
presents itself to shower continual benefits on those who only repay
you with ingratitude. This is an action which is all the more
virtuous and perfect as it is the more difficult."

When the plague was raging in the neighbourhood, the loving
daughter's solicitude is thus shown:--

"I send you two pots of electuary as a preventive against the
plague. The one without the label consists of dried figs, walnuts,
rue, and salt, mixed together with honey. A piece of the size of a
walnut to be taken in the morning, fasting, with a little Greek
wine."

The plague increasing still more, Sister Maria Celeste obtained with
much difficulty, a small quantity of a renowned liqueur, made by
Abbess Ursula, an exceptionally saintly nun. This she sends to her
father with the words:--

"I pray your lordship to have faith in this remedy. For if you have
so much faith in my poor miserable prayers, much more may you have in
those of such a holy person; indeed, through her merits you may feel
sure of escaping all danger from the plague."

Whether Galileo took the remedy we do not know, but at all events
he escaped the plague.

[PLATE: THE VILLA ARCETRI.
Galileo's residence, where Milton visited him.]

From Galileo's new home in Florence the telescope was again directed
to the skies, and again did astounding discoveries reward the
astronomer's labours. The great success which he had met with in
studying Jupiter naturally led Galileo to look at Saturn. Here he
saw a spectacle which was sufficiently amazing, though he failed to
interpret it accurately. It was quite manifest that Saturn did not
exhibit a simple circular disc like Jupiter, or like Mars. It seemed
to Galileo as if the planet consisted of three bodies, a large globe
in the centre, and a smaller one on each side. The enigmatical
nature of the discovery led Galileo to announce it in an enigmatical
manner. He published a string of letters which, when duly
transposed, made up a sentence which affirmed that the planet Saturn
was threefold. Of course we now know that this remarkable appearance
of the planet was due to the two projecting portions of the ring.
With the feeble power of Galileo's telescope, these seemed merely
like small globes or appendages to the large central body.

The last of Galileo's great astronomical discoveries related to the
libration of the moon. I think that the detection of this phenomenon
shows his acuteness of observation more remarkably than does any one
of his other achievements with the telescope. It is well known that
the moon constantly keeps the same face turned towards the earth.
When, however, careful measurements have been made with regard to the
spots and marks on the lunar surface, it is found that there is a
slight periodic variation which permits us to see now a little to the
east or to the west, now a little to the north or to the south of
the average lunar disc.

But the circumstances which make the career of Galileo so especially
interesting from the biographer's point of view, are hardly so much
the triumphs that he won as the sufferings that he endured. The
sufferings and the triumphs were, however, closely connected, and it
is fitting that we should give due consideration to what was perhaps
the greatest drama in the history of science.

On the appearance of the immortal work of Copernicus, in which it was
taught that the earth rotated on its axis, and that the earth, like
the other planets, revolved round the sun, orthodoxy stood aghast.
The Holy Roman Church submitted this treatise, which bore the name
"De Revolutionibus Orbium Coelestium," to the Congregation of the
Index. After due examination it was condemned as heretical in 1615.
Galileo was suspected, on no doubt excellent grounds, of entertaining
the objectionable views of Copernicus. He was accordingly privately
summoned before Cardinal Bellarmine on 26th February 1616, and duly
admonished that he was on no account to teach or to defend the
obnoxious doctrines. Galileo was much distressed by this
intimation. He felt it a serious matter to be deprived of the
privilege of discoursing with his friends about the Copernican
system, and of instructing his disciples in the principles of the
great theory of whose truth he was perfectly convinced. It pained
him, however, still more to think, devout Catholic as he was, that
such suspicions of his fervent allegiance to his Church should ever
have existed, as were implied by the words and monitions of Cardinal
Bellarmine.

In 1616, Galileo had an interview with Pope Paul V., who received the
great astronomer very graciously, and walked up and down with him in
conversation for three-quarters of an hour. Galileo complained to
his Holiness of the attempts made by his enemies to embarrass him
with the authorities of the Church, but the Pope bade him be
comforted. His Holiness had himself no doubts of Galileo's
orthodoxy, and he assured him that the Congregation of the Index
should give Galileo no further trouble so long as Paul V. was in the
chair of St. Peter.

On the death of Paul V. in 1623, Maffeo Barberini was elected Pope,
as Urban VIII. This new Pope, while a cardinal, had been an intimate
friend of Galileo's, and had indeed written Latin verses in praise of
the great astronomer and his discoveries. It was therefore not
unnatural for Galileo to think that the time had arrived when, with
the use of due circumspection, he might continue his studies and his
writings, without fear of incurring the displeasure of the Church.
Indeed, in 1624, one of Galileo's friends writing from Rome, urges
Galileo to visit the city again, and added that--

"Under the auspices of this most excellent, learned, and benignant
Pontiff, science must flourish. Your arrival will be welcome to his
Holiness. He asked me if you were coming, and when, and in short, he
seems to love and esteem you more than ever."

The visit was duly paid, and when Galileo returned to Florence, the
Pope wrote a letter from which the following is an extract,
commanding the philosopher to the good offices of the young
Ferdinand, who had shortly before succeeded his father in the Grand
Duchy of Tuscany.

"We find in Galileo not only literary distinction, but also the love
of piety, and he is also strong in those qualities by which the
pontifical good-will is easily obtained. And now, when he has been
brought to this city to congratulate us on our elevation, we have
very lovingly embraced him; nor can we suffer him to return to the
country whither your liberality calls him, without an ample provision
of pontifical love. And that you may know how dear he is to us, we
have willed to give him this honourable testimonial of virtue and
piety. And we further signify that every benefit which you shall
confer upon him, imitating or even surpassing your father's
liberality, will conduce to our gratification."

The favourable reception which had been accorded to him by Pope Urban
VIII. seems to have led Galileo to expect that there might be some
corresponding change in the attitude of the Papal authorities on the
great question of the stability of the earth. He accordingly
proceeded with the preparation of the chief work of his life, "The
Dialogue of the two Systems." It was submitted for inspection by the
constituted authorities. The Pope himself thought that, if a few
conditions which he laid down were duly complied with, there could be
no objection to the publication of the work. In the first place, the
title of the book was to be so carefully worded as to show plainly
that the Copernican doctrine was merely to be regarded as an
hypothesis, and not as a scientific fact. Galileo was also
instructed to conclude the book with special arguments which had been
supplied by the Pope himself, and which appeared to his Holiness to
be quite conclusive against the new doctrine of Copernicus.

Formal leave for the publication of the Dialogue was then given to
Galileo by the Inquisitor General, and it was accordingly sent to the
press. It might be thought that the anxieties of the astronomer
about his book would then have terminated. As a matter of fact, they
had not yet seriously begun. Riccardi, the Master of the Sacred
Palace, having suddenly had some further misgivings, sent to Galileo
for the manuscript while the work was at the printer's, in order that
the doctrine it implied might be once again examined. Apparently,
Riccardi had come to the conclusion that he had not given the matter
sufficient attention, when the authority to go to press had been
first and, perhaps, hastily given. Considerable delay in the issue
of the book was the result of these further deliberations. At last,
however, in June, 1632, Galileo's great work, "The Dialogue of the
two Systems," was produced for the instruction of the world, though
the occasion was fraught with ruin to the immortal author.

[PLATE: FACSIMILE SKETCH OF LUNAR SURFACE BY GALILEO.]

The book, on its publication, was received and read with the greatest
avidity. But presently the Master of The Sacred Palace found reason
to regret that he had given his consent to its appearance. He
accordingly issued a peremptory order to sequestrate every copy in
Italy. This sudden change in the Papal attitude towards Galileo
formed the subject of a strong remonstrance addressed to the Roman
authorities by the Grand Duke of Tuscany. The Pope himself seemed to
have become impressed all at once with the belief that the work
contained matter of an heretical description. The general
interpretation put upon the book seems to have shown the authorities
that they had mistaken its true tendency, notwithstanding the fact
that it had been examined again and again by theologians deputed for
the duty. To the communication from the Grand Duke the Pope returned
answer, that he had decided to submit the book to a congregation of
"learned, grave, and saintly men," who would weigh every word in it.
The views of his Holiness personally on the subject were expressed in
his belief that the Dialogue contained the most perverse matter that
could come into a reader's hands.

The Master of the Sacred Palace was greatly blamed by the authorities
for having given his sanction to its issue. He pleaded that the book
had not been printed in the precise terms of the original manuscript
which had been submitted to him. It was also alleged that Galileo
had not adhered to his promise of inserting properly the arguments
which the Pope himself had given in support of the old and orthodox
view. One of these had, no doubt, been introduced, but, so far from
mending Galileo's case, it had made matters really look worse for the
poor philosopher. The Pope's argument had been put into the mouth of
one of the characters in the Dialogue named "Simplicio." Galileo's
enemies maintained that by adopting such a method for the expression
of his Holiness's opinion, Galileo had intended to hold the Pope
himself up to ridicule. Galileo's friends maintained that nothing
could have been farther from his intention. It seems, however,
highly probable that the suspicions thus aroused had something to say
to the sudden change of front on the part of the Papal authorities.

On 1st October, 1632, Galileo received an order to appear before the
Inquisition at Rome on the grave charge of heresy. Galileo, of
course, expressed his submission, but pleaded for a respite from
compliance with the summons, on the ground of his advanced age and
his failing health. The Pope was, however, inexorable; he said that
he had warned Galileo of his danger while he was still his friend.
The command could not be disobeyed. Galileo might perform the
journey as slowly as he pleased, but it was imperatively necessary
for him to set forth and at once.

On 20th January, 1633, Galileo started on his weary journey to Rome,
in compliance with this peremptory summons. On 13th February he was
received as the guest of Niccolini, the Tuscan ambassador, who had
acted as his wise and ever-kind friend throughout the whole affair.
It seemed plain that the Holy Office were inclined to treat Galileo
with as much clemency and consideration as was consistent with the
determination that the case against him should be proceeded with to
the end. The Pope intimated that in consequence of his respect for
the Grand Duke of Tuscany he should permit Galileo to enjoy the
privilege, quite unprecedented for a prisoner charged with heresy, of
remaining as an inmate in the ambassador's house. He ought,
strictly, to have been placed in the dungeons of the Inquisition.
When the examination of the accused had actually commenced, Galileo
was confined, not, indeed, in the dungeons, but in comfortable rooms
at the Holy Office.

By the judicious and conciliatory language of submission which
Niccolini had urged Galileo to use before the Inquisitors, they were
so far satisfied that they interceded with the Pope for his release.
During the remainder of the trial Galileo was accordingly permitted
to go back to the ambassador's, where he was most heartily welcomed.
Sister Maria Celeste, evidently thinking this meant that the whole
case was at an end, thus expresses herself:--

"The joy that your last dear letter brought me, and the having to
read it over and over to the nuns, who made quite a jubilee on
hearing its contents, put me into such an excited state that at last
I got a severe attack of headache."

In his defence Galileo urged that he had already been acquitted in
1616 by Cardinal Bellarmine, when a charge of heresy was brought
against him, and he contended that anything he might now have done,
was no more than he had done on the preceding occasion, when the
orthodoxy of his doctrines received solemn confirmation. The
Inquisition seemed certainly inclined to clemency, but the Pope was
not satisfied. Galileo was accordingly summoned again on the 21st
June. He was to be threatened with torture if he did not forthwith
give satisfactory explanations as to the reasons which led him to
write the Dialogue. In this proceeding the Pope assured the Tuscan
ambassador that he was treating Galileo with the utmost consideration
possible in consequence of his esteem and regard for the Grand Duke,
whose servant Galileo was. It was, however, necessary that some
exemplary punishment be meted out to the astronomer, inasmuch as by
the publication of the Dialogue he had distinctly disobeyed the
injunction of silence laid upon him by the decree of 1616. Nor was
it admissible for Galileo to plead that his book had been sanctioned
by the Master of the Sacred College, to whose inspection it had been
again and again submitted. It was held, that if the Master of the
Sacred College had been unaware of the solemn warning the philosopher
had already received sixteen years previously, it was the duty of
Galileo to have drawn his attention to that fact.

On the 22nd June, 1633, Galileo was led to the great hall of the
Inquisition, and compelled to kneel before the cardinals there
assembled and hear his sentence. In a long document, most
elaborately drawn up, it is definitely charged against Galileo that,
in publishing the Dialogue, he committed the essentially grave error
of treating the doctrine of the earth's motion as open to
discussion. Galileo knew, so the document affirmed, that the Church
had emphatically pronounced this notion to be contrary to Holy Writ,
and that for him to consider a doctrine so stigmatized as having any
shadow of probability in its favour was an act of disrespect to the
authority of the Church which could not be overlooked. It was also
charged against Galileo that in his Dialogue he has put the strongest
arguments into the mouth, not of those who supported the orthodox
doctrine, but of those who held the theory as to the earth's motion
which the Church had so deliberately condemned.

After due consideration of the defence made by the prisoner, it was
thereupon decreed that he had rendered himself vehemently suspected
of heresy by the Holy Office, and in consequence had incurred all the
censures and penalties of the sacred canons, and other decrees
promulgated against such persons. The graver portion of these
punishments would be remitted, if Galileo would solemnly repudiate
the heresies referred to by an abjuration to be pronounced by him in
the terms laid down.

At the same time it was necessary to mark, in some emphatic manner,
the serious offence which had been committed, so that it might serve
both as a punishment to Galileo and as a warning to others. It was
accordingly decreed that he should be condemned to imprisonment in
the Holy Office during the pleasure of the Papal authorities, and
that he should recite once a week for three years the seven
Penitential Psalms.

Then followed that ever-memorable scene in the great hall of the
Inquisition, in which the aged and infirm Galileo, the inventor of
the telescope and the famous astronomer, knelt down to abjure before
the most eminent and reverend Lords Cardinal, Inquisitors General
throughout the Christian Republic against heretical depravity. With
his hands on the Gospels, Galileo was made to curse and detest the
false opinion that the sun was the centre of the universe and
immovable, and that the earth was not the centre of the same, and
that it moved. He swore that for the future he will never say nor
write such things as may bring him under suspicion, and that if he
does so he submits to all the pains and penalties of the sacred
canons. This abjuration was subsequently read in Florence before
Galileo's disciples, who had been specially summoned to attend.

It has been noted that neither on the first occasion, in 1616, nor on
the second in 1633, did the reigning Pope sign the decrees concerning
Galileo. The contention has accordingly been made that Paul V. and
Urban VIII. are both alike vindicated from any technical
responsibility for the attitude of the Romish Church towards the
Copernican doctrines. The significance of this circumstance has been
commented on in connection with the doctrine of the infallibility of
the Pope.

We can judge of the anxiety felt by Sister Maria Celeste about her
beloved father during these terrible trials. The wife of the
ambassador Niccolini, Galileo's steadfast friend, most kindly wrote
to give the nun whatever quieting assurances the case would permit.
There is a renewed flow of these touching epistles from the daughter
to her father. Thus she sends word--

"The news of your fresh trouble has pierced my soul with grief all
the more that it came quite unexpectedly."

And again, on hearing that he had been permitted to leave Rome,
she writes--

"I wish I could describe the rejoicing of all the mothers and sisters
on hearing of your happy arrival at Siena. It was indeed most
extraordinary. On hearing the news the Mother Abbess and many of the
nuns ran to me, embracing me and weeping for joy and tenderness."

The sentence of imprisonment was at first interpreted leniently by
the Pope. Galileo was allowed to reside in qualified durance in the
archbishop's house at Siena. Evidently the greatest pain that he
endured arose from the forced separation from that daughter, whom he
had at last learned to love with an affection almost comparable with
that she bore to him. She had often told him that she never had any
pleasure equal to that with which she rendered any service to her
father. To her joy, she discovers that she can relieve him from the
task of reciting the seven Penitential Psalms which had been imposed
as a Penance:--

"I began to do this a while ago," she writes, "and it gives me much
pleasure. First, because I am persuaded that prayer in obedience to
Holy Church must be efficacious; secondly, in order to save you the
trouble of remembering it. If I had been able to do more, most
willingly would I have entered a straiter prison than the one I live
in now, if by so doing I could have set you at liberty."

[PLATE: CREST OF GALILEO'S FAMILY.]

Sister Maria Celeste was gradually failing in health, but the great
privilege was accorded to her of being able once again to embrace her
beloved lord and master. Galileo had, in fact, been permitted to
return to his old home; but on the very day when he heard of his
daughter's death came the final decree directing him to remain in his
own house in perpetual solitude.

Amid the advancing infirmities of age, the isolation from friends,
and the loss of his daughter, Galileo once again sought consolation
in hard work. He commenced his famous dialogue on Motion. Gradually,
however, his sight began to fail, and blindness was at last added to
his other troubles. On January 2nd, 1638, he writes to Diodati:--

"Alas, your dear friend and servant, Galileo, has been for the last
month perfectly blind, so that this heaven, this earth, this universe
which I by my marvellous discoveries and clear demonstrations have
enlarged a hundred thousand times beyond the belief of the wise men
of bygone ages, henceforward is for me shrunk into such a small space
as is filled by my own bodily sensations."

But the end was approaching--the great philosopher, was attacked by
low fever, from which he died on the 8th January, 1643.




KEPLER.


While the illustrious astronomer, Tycho Brahe, lay on his death-bed,
he had an interview which must ever rank as one of the important
incidents in the history of science. The life of Tycho had been
passed, as we have seen, in the accumulation of vast stores of
careful observations of the positions of the heavenly bodies. It was
not given to him to deduce from his splendid work the results to
which they were destined to lead. It was reserved for another
astronomer to distil, so to speak, from the volumes in which Tycho's
figures were recorded, the great truths of the universe which those
figures contained. Tycho felt that his work required an interpreter,
and he recognised in the genius of a young man with whom he was
acquainted the agent by whom the world was to be taught some of the
great truths of nature. To the bedside of the great Danish
astronomer the youthful philosopher was summoned, and with his last
breath Tycho besought of him to spare no labour in the performance of
those calculations, by which alone the secrets of the movements of
the heavens could be revealed. The solemn trust thus imposed was
duly accepted, and the man who accepted it bore the immortal name of
Kepler.

Kepler was born on the 27th December, 1571, at Weil, in the Duchy of
Wurtemberg. It would seem that the circumstances of his childhood
must have been singularly unhappy. His father, sprung from a
well-connected family, was but a shiftless and idle adventurer; nor
was the great astronomer much more fortunate in his other parent. His
mother was an ignorant and ill-tempered woman; indeed, the
ill-assorted union came to an abrupt end through the desertion of the
wife by her husband when their eldest son John, the hero of our
present sketch, was eighteen years old. The childhood of this lad,
destined for such fame, was still further embittered by the
circumstance that when he was four years old he had a severe attack
of small-pox. Not only was his eyesight permanently injured, but
even his constitution appears to have been much weakened by this
terrible malady.

It seems, however, that the bodily infirmities of young John Kepler
were the immediate cause of his attention being directed to the
pursuit of knowledge. Had the boy been fitted like other boys for
ordinary manual work, there can be hardly any doubt that to manual
work his life must have been devoted. But, though his body was
feeble, he soon gave indications of the possession of considerable
mental power. It was accordingly thought that a suitable sphere for
his talents might be found in the Church which, in those days, was
almost the only profession that afforded an opening for an
intellectual career. We thus find that by the time John Kepler was
seventeen years old he had attained a sufficient standard of
knowledge to entitle him to admission on the foundation of the
University at Tubingen.

In the course of his studies at this institution he seems to have
divided his attention equally between astronomy and divinity. It not
unfrequently happens that when a man has attained considerable
proficiency in two branches of knowledge he is not able to see very
clearly in which of the two pursuits his true vocation lies. His
friends and onlookers are often able to judge more wisely than he
himself can do as to which of the two lines it would be better for
him to pursue. This incapacity for perceiving the path in which
greatness awaited him, existed in the case of Kepler. Personally, he
inclined to enter the ministry, in which a promising career seemed
open to him. He yielded, however, to friends, who evidently knew him
better than he knew himself, and accepted in 1594, the important
Professorship of astronomy which had been offered to him in the
University of Gratz.

It is difficult for us in these modern days to realise the somewhat
extraordinary duties which were expected from an astronomical
professor in the sixteenth century. He was, of course, required to
employ his knowledge of the heavens in the prediction of eclipses,
and of the movements of the heavenly bodies generally. This seems
reasonable enough; but what we are not prepared to accept is the
obligation which lay on the astronomers to predict the fates of
nations and the destinies of individuals.

It must be remembered that it was the almost universal belief in
those days, that all the celestial spheres revolved in some
mysterious fashion around the earth, which appeared by far the most
important body in the universe. It was imagined that the sun, the
moon, and the stars indicated, in the vicissitudes of their
movements, the careers of nations and of individuals. Such being the
generally accepted notion, it seemed to follow that a professor who
was charged with the duty of expounding the movements of the heavenly
bodies must necessarily be looked to for the purpose of deciphering
the celestial decrees regarding the fate of man which the heavenly
luminaries were designed to announce.

Kepler threw himself with characteristic ardour into even this
fantastic phase of the labours of the astronomical professor; he
diligently studied the rules of astrology, which the fancies of
antiquity had compiled. Believing sincerely as he did in the
connection between the aspect of the stars and the state of human
affairs, he even thought that he perceived, in the events of his own
life, a corroboration of the doctrine which affirmed the influence of
the planets upon the fate of individuals.

[PLATE: KEPLER'S SYSTEM OF REGULAR SOLIDS.]

But quite independently of astrology there seem to have been many
other delusions current among the philosophers of Kepler's time. It
is now almost incomprehensible how the ablest men of a few centuries
ago should have entertained such preposterous notions, as they did,
with respect to the system of the universe. As an instance of what
is here referred to, we may cite the extraordinary notion which,
under the designation of a discovery, first brought Kepler into
fame. Geometers had long known that there were five, but no more
than five, regular solid figures. There is, for instance, the cube
with six sides, which is, of course, the most familiar of these
solids. Besides the cube there are other figures of four, eight,
twelve, and twenty sides respectively. It also happened that there
were five planets, but no more than five, known to the ancients,
namely, Mercury, Venus, Mars, Jupiter, and Saturn. To Kepler's
lively imaginations this coincidence suggested the idea that the five
regular solids corresponded to the five planets, and a number of
fancied numerical relations were adduced on the subject. The
absurdity of this doctrine is obvious enough, especially when we
observe that, as is now well known, there are two large planets, and
a host of small planets, over and above the magical number of the
regular solids. In Kepler's time, however, this doctrine was so far
from being regarded as absurd, that its announcement was hailed as a
great intellectual triumph. Kepler was at once regarded with
favour. It seems, indeed, to have been the circumstance which
brought him into correspondence with Tycho Brahe. By its means also
he became known to Galileo.

The career of a scientific professor in those early days appears
generally to have been marked by rather more striking vicissitudes
than usually befall a professor in a modern university. Kepler was a
Protestant, and as such he had been appointed to his professorship at
Gratz. A change, however, having taken place in the religious belief
entertained by the ruling powers of the University, the Protestant
professors were expelled. It seems that special influence having
been exerted in Kepler's case on account of his exceptional eminence,
he was recalled to Gratz and reinstated in the tenure of his chair.
But his pupils had vanished, so that the great astronomer was glad to
accept a post offered him by Tycho Brahe in the observatory which the
latter had recently established near Prague.

On Tycho's death, which occurred soon after, an opening presented
itself which gave Kepler the opportunity his genius demanded. He was
appointed to succeed Tycho in the position of imperial mathematician.
But a far more important point, both for Kepler and for science,
was that to him was confided the use of Tycho's observations. It was,
indeed, by the discussion of Tycho's results that Kepler was enabled
to make the discoveries which form such an important part of
astronomical history.

Kepler must also be remembered as one of the first great astronomers
who ever had the privilege of viewing celestial bodies through a
telescope. It was in 1610 that he first held in his hands one of
those little instruments which had been so recently applied to the
heavens by Galileo. It should, however, be borne in mind that the
epoch-making achievements of Kepler did not arise from any telescopic
observations that he made, or, indeed, that any one else made. They
were all elaborately deduced from Tycho's measurements of the
positions of the planets, obtained with his great instruments, which
were unprovided with telescopic assistance.

To realise the tremendous advance which science received from
Kepler's great work, it is to be understood that all the astronomers
who laboured before him at the difficult subject of the celestial
motions, took it for granted that the planets must revolve in
circles. If it did not appear that a planet moved in a fixed circle,
then the ready answer was provided by Ptolemy's theory that the
circle in which the planet did move was itself in motion, so that its
centre described another circle.

When Kepler had before him that wonderful series of observations of
the planet, Mars, which had been accumulated by the extraordinary
skill of Tycho, he proved, after much labour, that the movements of
the planet refused to be represented in a circular form. Nor would
it do to suppose that Mars revolved in one circle, the centre of
which revolved in another circle. On no such supposition could the
movements of the planets be made to tally with those which Tycho had
actually observed. This led to the astonishing discovery of the true
form of a planet's orbit. For the first time in the history of
astronomy the principle was laid down that the movement of a planet
could not be represented by a circle, nor even by combinations of
circles, but that it could be represented by an elliptic path. In
this path the sun is situated at one of those two points in the
ellipse which are known as its foci.

[PLATE: KEPLER.]

Very simple apparatus is needed for the drawing of one of those
ellipses which Kepler has shown to possess such astonishing
astronomical significance. Two pins are stuck through a sheet of
paper on a board, the point of a pencil is inserted in a loop of
string which passes over the pins, and as the pencil is moved round
in such a way as to keep the string stretched, that beautiful curve
known as the ellipse is delineated, while the positions of the pins
indicate the two foci of the curve. If the length of the loop of
string is unchanged then the nearer the pins are together, the
greater will be the resemblance between the ellipse and the circle,
whereas the more the pins are separated the more elongated does the
ellipse become. The orbit of a great planet is, in general, one of
those ellipses which approaches a nearly circular form. It
fortunately happens, however, that the orbit of Mars makes a wider
departure from the circular form than any of the other important
planets. It is, doubtless, to this circumstance that we must
attribute the astonishing success of Kepler in detecting the true
shape of a planetary orbit. Tycho's observations would not have been
sufficiently accurate to have exhibited the elliptic nature of a
planetary orbit which, like that of Venus, differed very little from
a circle.

The more we ponder on this memorable achievement the more striking
will it appear. It must be remembered that in these days we know of
the physical necessity which requires that a planet shall revolve in
an ellipse and not in any other curve. But Kepler had no such
knowledge. Even to the last hour of his life he remained in
ignorance of the existence of any natural cause which ordained that
planets should follow those particular curves which geometers know so
well. Kepler's assignment of the ellipse as the true form of the
planetary orbit is to be regarded as a brilliant guess, the truth of
which Tycho's observations enabled him to verify. Kepler also
succeeded in pointing out the law according to which the velocity of
a planet at different points of its path could be accurately
specified. Here, again, we have to admire the sagacity with which
this marvellously acute astronomer guessed the deep truth of nature.
In this case also he was quite unprovided with any reason for
expecting from physical principles that such a law as he discovered
must be obeyed. It is quite true that Kepler had some slight
knowledge of the existence of what we now know as gravitation. He
had even enunciated the remarkable doctrine that the ebb and flow of
the tide must be attributed to the attraction of the moon on the
waters of the earth. He does not, however, appear to have had any
anticipation of those wonderful discoveries which Newton was destined
to make a little later, in which he demonstrated that the laws
detected by Kepler's marvellous acumen were necessary consequences of
the principle of universal gravitation.

[PLATE: SYMBOLICAL REPRESENTATION OF THE PLANETARY SYSTEM.]

To appreciate the relations of Kepler and Tycho it is necessary to
note the very different way in which these illustrious astronomers
viewed the system of the heavens. It should be observed that
Copernicus had already expounded the true system, which located the
sun at the centre of the planetary system. But in the days of Tycho
Brahe this doctrine had not as yet commanded universal assent. In
fact, the great observer himself did not accept the new views of
Copernicus. It appeared to Tycho that the earth not only appeared to
be the centre of things celestial, but that it actually was the
centre. It is, indeed, not a little remarkable that a student of the
heavens so accurate as Tycho should have deliberately rejected the
Copernican doctrine in favour of the system which now seems so
preposterous. Throughout his great career, Tycho steadily observed
the places of the sun, the moon, and the planets, and as steadily
maintained that all those bodies revolved around the earth fixed in
the centre. Kepler, however, had the advantage of belonging to the
new school. He utilised the observations of Tycho in developing the
great Copernican theory whose teaching Tycho stoutly resisted.

Perhaps a chapter in modern science may illustrate the intellectual
relation of these great men. The revolution produced by Copernicus
in the doctrine of the heavens has often been likened to the
revolution which the Darwinian theory produced in the views held by
biologists as to life on this earth. The Darwinian theory did not at
first command universal assent even among those naturalists whose
lives had been devoted with the greatest success to the study of
organisms. Take, for instance, that great naturalist, Professor
Owen, by whose labours vast extension has been given to our knowledge
of the fossil animals which dwelt on the earth in past ages. Now,
though Owens researches were intimately connected with the great
labours of Darwin, and afforded the latter material for his
epoch-making generalization, yet Owen deliberately refused to accept
the new doctrines. Like Tycho, he kept on rigidly accumulating his
facts under the influence of a set of ideas as to the origin of
living forms which are now universally admitted to be erroneous. If,
therefore, we liken Darwin to Copernicus, and Owen to Tycho, we may
liken the biologists of the present day to Kepler, who interpreted
the results of accurate observation upon sound theoretical
principles.

In reading the works of Kepler in the light of our modern knowledge
we are often struck by the extent to which his perception of the
sublimest truths in nature was associated with the most extravagant
errors and absurdities. But, of course, it must be remembered that
he wrote in an age in which even the rudiments of science, as we now
understand it, were almost entirely unknown.

It may well be doubted whether any joy experienced by mortals is more
genuine than that which rewards the successful searcher after natural
truths. Every science-worker, be his efforts ever so humble, will be
able to sympathise with the enthusiastic delight of Kepler when at
last, after years of toil, the glorious light broke forth, and that
which he considered to be the greatest of his astonishing laws first
dawned upon him. Kepler rightly judged that the number of days which
a planet required to perform its voyage round the sun must be
connected in some manner with the distance from the planet to the
sun; that is to say, with the radius of the planet's orbit, inasmuch
as we may for our present object regard the planet's orbit as
circular.

Here, again, in his search for the unknown law, Kepler had no
accurate dynamical principles to guide his steps. Of course, we now
know not only what the connection between the planet's distance and
the planet's periodic time actually is, but we also know that it is a
necessary consequence of the law of universal gravitation. Kepler,
it is true, was not without certain surmises on the subject, but they
were of the most fanciful description. His notions of the planets,
accurate as they were in certain important respects, were mixed up
with vague ideas as to the properties of metals and the geometrical
relations of the regular solids. Above all, his reasoning was
penetrated by the supposed astrological influences of the stars and
their significant relation to human fate. Under the influence of
such a farrago of notions, Kepler resolved to make all sorts of
trials in his search for the connection between the distance of a
planet from the sun and the time in which the revolution of that
planet was accomplished.

It was quite easily demonstrated that the greater the distance of the
planet from the sun the longer was the time required for its
journey. It might have been thought that the time would be directly
proportional to the distance. It was, however, easy to show that
this supposition did not agree with the fact. Finding that this
simple relation would not do, Kepler undertook a vast series of
calculations to find out the true method of expressing the
connection. At last, after many vain attempts, he found, to his
indescribable joy, that the square of the time in which a planet
revolves around the sun was proportional to the cube of the average
distance of the planet from that body.

The extraordinary way in which Kepler's views on celestial matters
were associated with the wildest speculations, is well illustrated in
the work in which he propounded his splendid discovery just referred
to. The announcement of the law connecting the distances of the
planets from the sun with their periodic times, was then mixed up
with a preposterous conception about the properties of the different
planets. They were supposed to be associated with some profound
music of the spheres inaudible to human ears, and performed only for
the benefit of that being whose soul formed the animating spirit of
the sun.

Kepler was also the first astronomer who ever ventured to predict the
occurrence of that remarkable phenomenon, the transit of a planet in
front of the sun's disc. He published, in 1629, a notice to the
curious in things celestial, in which he announced that both of the
planets, Mercury and Venus, were to make a transit across the sun on
specified days in the winter of 1631. The transit of Mercury was
duly observed by Gassendi, and the transit of Venus also took place,
though, as we now know, the circumstances were such that it was not
possible for the phenomenon to be witnessed by any European
astronomer.

In addition to Kepler's discoveries already mentioned, with which his
name will be for ever associated, his claim on the gratitude of
astronomers chiefly depends on the publication of his famous
Rudolphine tables. In this remarkable work means are provided for
finding the places of the planets with far greater accuracy than had
previously been attainable.

Kepler, it must be always remembered, was not an astronomical
observer. It was his function to deal with the observations made by
Tycho, and, from close study and comparison of the results, to work
out the movements of the heavenly bodies. It was, in fact, Tycho who
provided as it were the raw material, while it was the genius of
Kepler which wrought that material into a beautiful and serviceable
form. For more than a century the Rudolphine tables were regarded as
a standard astronomical work. In these days we are accustomed to
find the movements of the heavenly bodies set forth with all
desirable exactitude in the NAUTICAL ALMANACK, and the similar
publication issued by foreign Governments. Let it be remembered that
it was Kepler who first imparted the proper impulse in this
direction.

[PLATE: THE COMMEMORATION OF THE RUDOLPHINE TABLES.]

When Kepler was twenty-six he married an heiress from Styria, who,
though only twenty-three years old, had already had some experience
in matrimony. Her first husband had died; and it was after her
second husband had divorced her that she received the addresses of
Kepler. It will not be surprising to hear that his domestic affairs
do not appear to have been particularly happy, and his wife died in
1611. Two years later, undeterred by the want of success in his
first venture, he sought a second partner, and he evidently
determined not to make a mistake this time. Indeed, the methodical
manner in which he made his choice of the lady to whom he should
propose has been duly set forth by him and preserved for our
edification. With some self-assurance he asserts that there were no
fewer than eleven spinsters desirous of sharing his joys and
sorrows. He has carefully estimated and recorded the merits and
demerits of each of these would-be brides. The result of his
deliberations was that he awarded himself to an orphan girl,
destitute even of a portion. Success attended his choice, and his
second marriage seems to have proved a much more suitable union than
his first. He had five children by the first wife and seven by the
second.

The years of Kepler's middle life were sorely distracted by a trouble
which, though not uncommon in those days, is one which we find it
difficult to realise at the present time. His mother, Catherine
Kepler, had attained undesirable notoriety by the suspicion that she
was guilty of witchcraft. Years were spent in legal investigations,
and it was only after unceasing exertions on the part of the
astronomer for upwards of a twelve-month that he was finally able to
procure her acquittal and release from prison.

It is interesting for us to note that at one time there was a
proposal that Kepler should forsake his native country and adopt
England as a home. It arose in this wise. The great man was
distressed throughout the greater part of his life by pecuniary
anxieties. Finding him in a strait of this description, the English
ambassador in Venice, Sir Henry Wotton, in the year 1620, besought
Kepler to come over to England, where he assured him that he would
obtain a favourable reception, and where, he was able to add,
Kepler's great scientific work was already highly esteemed. But his
efforts were unavailing; Kepler would not leave his own country. He
was then forty-nine years of age, and doubtless a home in a foreign
land, where people spoke a strange tongue, had not sufficient
attraction for him, even when accompanied with the substantial
inducements which the ambassador was able to offer. Had Kepler
accepted this invitation, he would, in transferring his home to
England, have anticipated the similar change which took place in the
career of another great astronomer two centuries later. It will be
remembered that Herschel, in his younger days, did transfer himself
to England, and thus gave to England the imperishable fame of
association with his triumphs.

The publication of the Rudolphine tables of the celestial movements
entailed much expense. A considerable part of this was defrayed by
the Government at Venice but the balance occasioned no little trouble
and anxiety to Kepler. No doubt the authorities of those days were
even less willing to spend money on scientific matters than are the
Governments of more recent times. For several years the imperial
Treasury was importuned to relieve him from his anxieties. The
effects of so much worry, and of the long journeys which were
involved, at last broke down Kepler's health completely. As we have
already mentioned, he had never been strong from infancy, and he
finally succumbed to a fever in November, 1630, at the age of
fifty-nine. He was interred at St. Peter's Church at Ratisbon.

Though Kepler had not those personal characteristics which have made
his great predecessor, Tycho Brahe, such a romantic figure, yet a
picturesque element in Kepler's character is not wanting. It was,
however, of an intellectual kind. His imagination, as well as his
reasoning faculties, always worked together. He was incessantly
prompted by the most extraordinary speculations. The great majority
of them were in a high degree wild and chimerical, but every now and
then one of his fancies struck right to the heart of nature, and an
immortal truth was brought to light.

I remember visiting the observatory of one of our greatest modern
astronomers, and in a large desk he showed me a multitude of
photographs which he had attempted but which had not been successful,
and then he showed me the few and rare pictures which had succeeded,
and by which important truths had been revealed. With a felicity of
expression which I have often since thought of, he alluded to the
contents of the desk as the "chips." They were useless, but they
were necessary incidents in the truly successful work. So it is in
all great and good work. Even the most skilful man of science
pursues many a wrong scent. Time after time he goes off on some
track that plays him false. The greater the man's genius and
intellectual resource, the more numerous will be the ventures which
he makes, and the great majority of those ventures are certain to be
fruitless. They are in fact, the "chips." In Kepler's case the
chips were numerous enough. They were of the most extraordinary
variety and structure. But every now and then a sublime discovery
was made of such a character as to make us regard even the most
fantastic of Kepler's chips with the greatest veneration and respect.



ISAAC NEWTON.


It was just a year after the death of Galileo, that an infant came
into the world who was christened Isaac Newton. Even the great fame
of Galileo himself must be relegated to a second place in comparison
with that of the philosopher who first expounded the true theory of
the universe.

Isaac Newton was born on the 25th of December (old style), 1642, at
Woolsthorpe, in Lincolnshire, about a half-mile from Colsterworth,
and eight miles south of Grantham. His father, Mr. Isaac Newton, had
died a few months after his marriage to Harriet Ayscough, the
daughter of Mr. James Ayscough, of Market Overton, in Rutlandshire.
The little Isaac was at first so excessively frail and weakly that
his life was despaired of. The watchful mother, however, tended her
delicate child with such success that he seems to have thriven better
than might have been expected from the circumstances of his infancy,
and he ultimately acquired a frame strong enough to outlast the
ordinary span of human life.

For three years they continued to live at Woolsthorpe, the widow's
means of livelihood being supplemented by the income from another
small estate at Sewstern, in a neighbouring part of Leicestershire.

[PLATE: WOOLSTHORPE MANOR.
Showing solar dial made by Newton when a boy.]

In 1645, Mrs. Newton took as a second husband the Rev. Barnabas
Smith, and on moving to her new home, about a mile from Woolsthorpe,
she entrusted little Isaac to her mother, Mrs. Ayscough. In due
time we find that the boy was sent to the public school at Grantham,
the name of the master being Stokes. For the purpose of being near
his work, the embryo philosopher was boarded at the house of Mr.
Clark, an apothecary at Grantham. We learn from Newton himself that
at first he had a very low place in the class lists of the school,
and was by no means one of those model school-boys who find favour in
the eyes of the school-master by attention to Latin grammar. Isaac's
first incentive to diligent study seems to have been derived from the
circumstance that he was severely kicked by one of the boys who was
above him in the class. This indignity had the effect of stimulating
young Newton's activity to such an extent that he not only attained
the desired object of passing over the head of the boy who had
maltreated him, but continued to rise until he became the head of the
school.

The play-hours of the great philosopher were devoted to pursuits very
different from those of most school-boys. His chief amusement was
found in making mechanical toys and various ingenious contrivances.
He watched day by day with great interest the workmen engaged in
constructing a windmill in the neighbourhood of the school, the
result of which was that the boy made a working model of the windmill
and of its machinery, which seems to have been much admired, as
indicating his aptitude for mechanics. We are told that Isaac also
indulged in somewhat higher flights of mechanical enterprise. He
constructed a carriage, the wheels of which were to be driven by the
hands of the occupant, while the first philosophical instrument he
made was a clock, which was actuated by water. He also devoted much
attention to the construction of paper kites, and his skill in this
respect was highly appreciated by his school-fellows. Like a true
philosopher, even at this stage he experimented on the best methods
of attaching the string, and on the proportions which the tail ought
to have. He also made lanthorns of paper to provide himself with
light as he walked to school in the dark winter mornings.

The only love affair in Newton's life appears to have commenced while
he was still of tender years. The incidents are thus described in
Brewster's "Life of Newton," a work to which I am much indebted in
this chapter.

"In the house where he lodged there were some female inmates, in
whose company he appears to have taken much pleasure. One of these,
a Miss Storey, sister to Dr. Storey, a physician at Buckminster, near
Colsterworth, was two or three years younger than Newton and to great
personal attractions she seems to have added more than the usual
allotment of female talent. The society of this young lady and her
companions was always preferred to that of his own school-fellows,
and it was one of his most agreeable occupations to construct for
them little tables and cupboards, and other utensils for holding
their dolls and their trinkets. He had lived nearly six years in the
same house with Miss Storey, and there is reason to believe that
their youthful friendship gradually rose to a higher passion; but the
smallness of her portion, and the inadequacy of his own fortune,
appear to have prevented the consummation of their happiness. Miss
Storey was afterwards twice married, and under the name of Mrs.
Vincent, Dr. Stukeley visited her at Grantham in 1727, at the age of
eighty-two, and obtained from her many particulars respecting the
early history of our author. Newton's esteem for her continued
unabated during his life. He regularly visited her when he went to
Lincolnshire, and never failed to relieve her from little pecuniary
difficulties which seem to have beset her family."

The schoolboy at Grantham was only fourteen years of age when his
mother became a widow for the second time. She then returned to the
old family home at Woolsthorpe, bringing with her the three children
of her second marriage. Her means appear to have been somewhat
scanty, and it was consequently thought necessary to recall Isaac
from the school. His recently-born industry had been such that he
had already made good progress in his studies, and his mother hoped
that he would now lay aside his books, and those silent meditations
to which, even at this early age, he had become addicted. It was
expected that, instead of such pursuits, which were deemed quite
useless, the boy would enter busily into the duties of the farm and
the details of a country life. But before long it became manifest
that the study of nature and the pursuit of knowledge had such a
fascination for the youth that he could give little attention to
aught else. It was plain that he would make but an indifferent
farmer. He greatly preferred experimenting on his water-wheels to
looking after labourers, while he found that working at mathematics
behind a hedge was much more interesting than chaffering about the
price of bullocks in the market place. Fortunately for humanity his
mother, like a wise woman, determined to let her boy's genius have
the scope which it required. He was accordingly sent back to
Grantham school, with the object of being trained in the knowledge
which would fit him for entering the University of Cambridge.

[PLATE: TRINITY COLLEGE, CAMBRIDGE.
Showing Newton's rooms; on the leads of the gateway he placed
his telescope.]

It was the 5th of June, 1660, when Isaac Newton, a youth of eighteen,
was enrolled as an undergraduate of Trinity College, Cambridge.
Little did those who sent him there dream that this boy was destined
to be the most illustrious student who ever entered the portals of
that great seat of learning. Little could the youth himself have
foreseen that the rooms near the gateway which he occupied would
acquire a celebrity from the fact that he dwelt in them, or that the
ante-chapel of his college was in good time to be adorned by that
noble statue, which is regarded as one of the chief art treasures of
Cambridge University, both on account of its intrinsic beauty and the
fact that it commemorates the fame of her most distinguished alumnus,
Isaac Newton, the immortal astronomer. Indeed, his advent at the
University seemed to have been by no means auspicious or brilliant.
His birth was, as we have seen, comparatively obscure, and though he
had already given indication of his capacity for reflecting on
philosophical matters, yet he seems to have been but ill-equipped
with the routine knowledge which youths are generally expected to
take with them to the Universities.

From the outset of his college career, Newton's attention seems to
have been mainly directed to mathematics. Here he began to give
evidence of that marvellous insight into the deep secrets of nature
which more than a century later led so dispassionate a judge as
Laplace to pronounce Newton's immortal work as pre-eminent above all
the productions of the human intellect. But though Newton was one of
the very greatest mathematicians that ever lived, he was never a
mathematician for the mere sake of mathematics. He employed his
mathematics as an instrument for discovering the laws of nature. His
industry and genius soon brought him under the notice of the
University authorities. It is stated in the University records that
he obtained a Scholarship in 1664. Two years later we find that
Newton, as well as many residents in the University, had to leave
Cambridge temporarily on account of the breaking out of the plague.
The philosopher retired for a season to his old home at Woolsthorpe,
and there he remained until he was appointed a Fellow of Trinity
College, Cambridge, in 1667. From this time onwards, Newton's
reputation as a mathematician and as a natural philosopher steadily
advanced, so that in 1669, while still but twenty-seven years of age,
he was appointed to the distinguished position of Lucasian Professor
of Mathematics at Cambridge. Here he found the opportunity to
continue and develop that marvellous career of discovery which formed
his life's work.

The earliest of Newton's great achievements in natural philosophy was
his detection of the composite character of light. That a beam of
ordinary sunlight is, in fact, a mixture of a very great number of
different-coloured lights, is a doctrine now familiar to every one
who has the slightest education in physical science. We must,
however, remember that this discovery was really a tremendous advance
in knowledge at the time when Newton announced it.

[PLATE: DIAGRAM OF A SUNBEAM.]

We here give the little diagram originally drawn by Newton, to
explain the experiment by which he first learned the composition of
light. A sunbeam is admitted into a darkened room through an
opening, H, in a shutter. This beam when not interfered with will
travel in a straight line to the screen, and there reproduce a bright
spot of the same shape as the hole in the shutter. If, however, a
prism of glass, A B C, be introduced so that the beam traverse it,
then it will be seen at once that the light is deflected from its
original track. There is, however, a further and most important
change which takes place. The spot of light is not alone removed to
another part of the screen, but it becomes spread out into a long
band beautifully coloured, and exhibiting the hues of the rainbow. At
the top are the violet rays, and then in descending order we have the
indigo, blue, green, yellow, orange, and red.

The circumstance in this phenomenon which appears to have
particularly arrested Newton's attention, was the elongation which
the luminous spot underwent in consequence of its passage through the
prism. When the prism was absent the spot was nearly circular, but
when the prism was introduced the spot was about five times as long
as it was broad. To ascertain the explanation of this was the first
problem to be solved. It seemed natural to suppose that it might be
due to the thickness of the glass in the prism which the light
traversed, or to the angle of incidence at which the light fell upon
the prism. He found, however, upon careful trial, that the phenomenon
could not be thus accounted for. It was not until after much patient
labour that the true explanation dawned upon him. He discovered that
though the beam of white light looks so pure and so simple, yet in
reality it is composed of differently coloured lights blended
together. These are, of course, indistinguishable in the compound
beam, but they are separated or disentangled, so to speak, by the
action of the prism. The rays at the blue end of the spectrum are
more powerfully deflected by the action of the glass than are the
rays at the red end. Thus, the rays variously coloured red, orange,
yellow, green, blue, indigo, violet, are each conducted to a
different part of the screen. In this way the prism has the effect
of exhibiting the constitution of the composite beam of light.

To us this now seems quite obvious, but Newton did not adopt it
hastily. With characteristic caution he verified the explanation by
many different experiments, all of which confirmed his discovery. One
of these may be mentioned. He made a hole in the screen at that part
on which the violet rays fell. Thus a violet ray was allowed to pass
through, all the rest of the light being intercepted, and on this
beam so isolated he was able to try further experiments. For
instance, when he interposed another prism in its path, he found, as
he expected, that it was again deflected, and he measured the amount
of the deflection. Again he tried the same experiment with one of
the red rays from the opposite end of the coloured band. He allowed
it to pass through the same aperture in the screen, and he tested the
amount by which the second prism was capable of producing deflection.
He thus found, as he had expected to find, that the second prism was
more efficacious in bending the violet rays than in bending the red
rays. Thus he confirmed the fact that the various hues of the
rainbow were each bent by a prism to a different extent, violet being
acted upon the most, and red the least.

[PLATE: ISAAC NEWTON.]

Not only did Newton decompose a white beam into its constituent
colours, but conversely by interposing a second prism with its angle
turned upwards, he reunited the different colours, and thus
reproduced the original beam of white light. In several other ways
also he illustrated his famous proposition, which then seemed so
startling, that white light was the result of a mixture of all hues
of the rainbow. By combining painters' colours in the right
proportion he did not indeed succeed in producing a mixture which
would ordinarily be called white, but he obtained a grey pigment.
Some of this he put on the floor of his room for comparison with a
piece of white paper. He allowed a beam of bright sunlight to fall
upon the paper and the mixed colours side by side, and a friend he
called in for his opinion pronounced that under these circumstances
the mixed colours looked the whiter of the two.

By repeated demonstrations Newton thus established his great
discovery of the composite character of light. He at once perceived
that his researches had an important bearing upon the principles
involved in the construction of a telescope. Those who employed the
telescope for looking at the stars, had been long aware of the
imperfections which prevented all the various rays from being
conducted to the same focus. But this imperfection had hitherto been
erroneously accounted for. It had been supposed that the reason why
success had not been attained in the construction of a refracting
telescope was due to the fact that the object glass, made as it then
was of a single piece, had not been properly shaped. Mathematicians
had abundantly demonstrated that a single lens, if properly figured,
must conduct all rays of light to the same focus, provided all rays
experienced equal refraction in passing through the glass. Until
Newton's discovery of the composition of white light, it had been
taken for granted that the several rays in a white beam were equally
refrangible. No doubt if this had been the case, a perfect telescope
could have been produced by properly shaping the object glass. But
when Newton had demonstrated that light was by no means so simple as
had been supposed, it became obvious that a satisfactory refracting
telescope was an impossibility when only a single object lens was
employed, however carefully that lens might have been wrought. Such
an objective might, no doubt, be made to conduct any one group of
rays of a particular shade to the same focus, but the rays of other
colours in the beam of white light must necessarily travel somewhat
astray. In this way Newton accounted for a great part of the
difficulties which had hitherto beset the attempts to construct a
perfect refracting telescope.

We now know how these difficulties can be, to a great extent,
overcome, by employing for the objective a composite lens made of two
pieces of glass possessing different qualities. To these achromatic
object glasses, as they are called, the great development of
astronomical knowledge, since Newton's time, is due. But it must be
remarked that, although the theoretical possibility of constructing
an achromatic lens was investigated by Newton, he certainly came to
the conclusion that the difficulty could not be removed by employing
a composite objective, with two different kinds of glass. In this
his marvellous sagacity in the interpretation of nature seems for
once to have deserted him. We can, however, hardly regret that
Newton failed to discover the achromatic objective, when we observe
that it was in consequence of his deeming an achromatic objective to
be impossible that he was led to the invention of the reflecting
telescope. Finding, as he believed, that the defects of the
telescope could not be remedied by any application of the principle
of refraction he was led to look in quite a different direction for
the improvement of the tool on which the advancement of astronomy
depended. The REFRACTION of light depended as he had found, upon the
colour of the light. The laws of REFLECTION were, however, quite
independent of the colour. Whether rays be red or green, blue or
yellow, they are all reflected in precisely the same manner from a
mirror. Accordingly, Newton perceived that if he could construct a
telescope the action of which depended upon reflection, instead of
upon refraction, the difficulty which had hitherto proved an
insuperable obstacle to the improvement of the instrument would be
evaded.

[PLATE: SIR ISAAC NEWTON'S LITTLE REFLECTOR.]

For this purpose Newton fashioned a concave mirror from a mixture of
copper and tin, a combination which gives a surface with almost the
lustre of silver. When the light of a star fell upon the surface, an
image of the star was produced in the focus of this mirror, and then
this image was examined by a magnifying eye-piece. Such is the
principle of the famous reflecting telescope which bears the name of
Newton. The little reflector which he constructed, represented in
the adjoining figure, is still preserved as one of the treasures of
the Royal Society. The telescope tube had the very modest dimension
of one inch in diameter. It was, however, the precursor of a whole
series of magnificent instruments, each outstripping the other in
magnitude, until at last the culminating point was attained in 1845,
by the construction of Lord Rosse's mammoth reflector of six feet in
aperture.

Newton's discovery of the composition of light led to an embittered
controversy, which caused no little worry to the great Philosopher.
Some of those who attacked him enjoyed considerable and, it must be
admitted, even well-merited repute in the ranks of science. They
alleged, however, that the elongation of the coloured band which
Newton had noticed was due to this, to that, or to the other--to
anything, in fact, rather than to the true cause which Newton
assigned. With characteristic patience and love of truth, Newton
steadily replied to each such attack. He showed most completely how
utterly his adversaries had misunderstood the subject, and how slight
indeed was their acquaintance with the natural phenomenon in
question. In reply to each point raised, he was ever able to cite
fresh experiments and adduce fresh illustrations, until at last his
opponents retired worsted from the combat.

It has been often a matter for surprise that Newton, throughout his
whole career, should have taken so much trouble to expose the errors
of those who attacked his views. He used even to do this when it
plainly appeared that his adversaries did not understand the subject
they were discussing. A philosopher might have said, "I know I am
right, and whether others think I am right or not may be a matter of
concern to them, but it is certainly not a matter about which I need
trouble. If after having been told the truth they elect to remain in
error, so much the worse for them; my time can be better employed
than in seeking to put such people right." This, however, was not
Newton's method. He spent much valuable time in overthrowing
objections which were often of a very futile description. Indeed, he
suffered a great deal of annoyance from the persistency, and in some
cases one might almost say from the rancour, of the attacks which
were made upon him. Unfortunately for himself, he did not possess
that capacity for sublime indifference to what men may say, which is
often the happy possession of intellects greatly inferior to his.

The subject of optics still continuing to engross Newton's attention,
he followed up his researches into the structure of the sunbeam by
many other valuable investigations in connection with light. Every
one has noticed the beautiful colours manifested in a soap-bubble.
Here was a subject which not unnaturally attracted the attention of
one who had expounded the colours of the spectrum with such success.
He perceived that similar hues were produced by other thin plates of
transparent material besides soap-bubbles, and his ingenuity was
sufficient to devise a method by which the thicknesses of the
different films could be measured. We can hardly, indeed, say that a
like success attended his interpretation of these phenomena to that
which had been so conspicuous in his explanation of the spectrum. It
implies no disparagement to the sublime genius of Newton to admit
that the doctrines he put forth as to the causes of the colours in
the soap-bubbles can be no longer accepted. We must remember that
Newton was a pioneer in accounting for the physical properties of
light. The facts that he established are indeed unquestionable, but
the explanations which he was led to offer of some of them are seen
to be untenable in the fuller light of our present knowledge.

[PLATE: SIR ISAAC NEWTON'S SUN-DIAL.]

Had Newton done nothing beyond making his wonderful discoveries in
light, his fame would have gone down to posterity as one of the
greatest of Nature's interpreters. But it was reserved for him to
accomplish other discoveries, which have pushed even his analysis of
the sunbeam into the background; it is he who has expounded the
system of the universe by the discovery of the law of universal
gravitation.

The age had indeed become ripe for the advent of the genius of
Newton. Kepler had discovered with marvellous penetration the laws
which govern the movements of the planets around the sun, and in
various directions it had been more or less vaguely felt that the
explanation of Kepler's laws, as well as of many other phenomena,
must be sought for in connection with the attractive power of
matter. But the mathematical analysis which alone could deal with
this subject was wanting; it had to be created by Newton.

At Woolsthorpe, in the year 1666, Newton's attention appears to have
been concentrated upon the subject of gravitation. Whatever may be
the extent to which we accept the more or less mythical story as to
how the fall of an apple first directed the attention of the
philosopher to the fact that gravitation must extend through space,
it seems, at all events, certain that this is an excellent
illustration of the line of reasoning which he followed. He argued
in this way. The earth attracts the apple; it would do so, no matter
how high might be the tree from which that apple fell. It would then
seem to follow that this power which resides in the earth by which it
can draw all external bodies towards it, extends far beyond the
altitude of the loftiest tree. Indeed, we seem to find no limit to
it. At the greatest elevation that has ever been attained, the
attractive power of the earth is still exerted, and though we cannot
by any actual experiment reach an altitude more than a few miles
above the earth, yet it is certain that gravitation would extend to
elevations far greater. It is plain, thought Newton, that an apple
let fall from a point a hundred miles above this earth's surface,
would be drawn down by the attraction, and would continually gather
fresh velocity until it reached the ground. From a hundred miles it
was natural to think of what would happen at a thousand miles, or at
hundreds of thousands of miles. No doubt the intensity of the
attraction becomes weaker with every increase in the altitude, but
that action would still exist to some extent, however lofty might be
the elevation which had been attained.

It then occurred to Newton, that though the moon is at a distance of
two hundred and forty thousand miles from the earth, yet the
attractive power of the earth must extend to the moon. He was
particularly led to think of the moon in this connection, not only
because the moon is so much closer to the earth than are any other
celestial bodies, but also because the moon is an appendage to the
earth, always revolving around it. The moon is certainly attracted
to the earth, and yet the moon does not fall down; how is this to be
accounted for? The explanation was to be found in the character of
the moon's present motion. If the moon were left for a moment at
rest, there can be no doubt that the attraction of the earth would
begin to draw the lunar globe in towards our globe. In the course of
a few days our satellite would come down on the earth with a most
fearful crash. This catastrophe is averted by the circumstance that
the moon has a movement of revolution around the earth. Newton was
able to calculate from the known laws of mechanics, which he had
himself been mainly instrumental in discovering, what the attractive
power of the earth must be, so that the moon shall move precisely as
we find it to move. It then appeared that the very power which makes
an apple fall at the earth's surface is the power which guides the
moon in its orbit.

[PLATE: SIR ISAAC NEWTON'S TELESCOPE.]

Once this step had been taken, the whole scheme of the universe might
almost be said to have become unrolled before the eye of the
philosopher. It was natural to suppose that just as the moon was
guided and controlled by the attraction of the earth, so the earth
itself, in the course of its great annual progress, should be guided
and controlled by the supreme attractive power of the sun. If this
were so with regard to the earth, then it would be impossible to
doubt that in the same way the movements of the planets could be
explained to be consequences of solar attraction.

It was at this point that the great laws of Kepler became especially
significant. Kepler had shown how each of the planets revolves in an
ellipse around the sun, which is situated on one of the foci. This
discovery had been arrived at from the interpretation of
observations. Kepler had himself assigned no reason why the orbit of
a planet should be an ellipse rather than any other of the infinite
number of closed curves which might be traced around the sun. Kepler
had also shown, and here again he was merely deducing the results
from observation, that when the movements of two planets were
compared together, the squares of the periodic times in which each
planet revolved were proportional to the cubes of their mean
distances from the sun. This also Kepler merely knew to be true as a
fact, he gave no demonstration of the reason why nature should have
adopted this particular relation between the distance and the
periodic time rather than any other. Then, too, there was the law by
which Kepler with unparalleled ingenuity, explained the way in which
the velocity of a planet varies at the different points of its track,
when he showed how the line drawn from the sun to the planet
described equal areas around the sun in equal times. These were the
materials with which Newton set to work. He proposed to infer from
these the actual laws regulating the force by which the sun guides
the planets. Here it was that his sublime mathematical genius came
into play. Step by step Newton advanced until he had completely
accounted for all the phenomena.

In the first place, he showed that as the planet describes equal
areas in equal times about the sun, the attractive force which the
sun exerts upon it must necessarily be directed in a straight line
towards the sun itself. He also demonstrated the converse truth,
that whatever be the nature of the force which emanated from a sun,
yet so long as that force was directed through the sun's centre, any
body which revolved around it must describe equal areas in equal
times, and this it must do, whatever be the actual character of the
law according to which the intensity of the force varies at different
parts of the planet's journey. Thus the first advance was taken in
the exposition of the scheme of the universe.

The next step was to determine the law according to which the force
thus proved to reside in the sun varied with the distance of the
planet. Newton presently showed by a most superb effort of
mathematical reasoning, that if the orbit of a planet were an ellipse
and if the sun were at one of the foci of that ellipse, the intensity
of the attractive force must vary inversely as the square of the
planet's distance. If the law had any other expression than the
inverse square of the distance, then the orbit which the planet must
follow would not be an ellipse; or if an ellipse, it would, at all
events, not have the sun in the focus. Hence he was able to show
from Kepler's laws alone that the force which guided the planets was
an attractive power emanating from the sun, and that the intensity of
this attractive power varied with the inverse square of the distance
between the two bodies.

These circumstances being known, it was then easy to show that the
last of Kepler's three laws must necessarily follow. If a number of
planets were revolving around the sun, then supposing the materials
of all these bodies were equally affected by gravitation, it can be
demonstrated that the square of the periodic time in which each
planet completes its orbit is proportional to the cube of the
greatest diameter in that orbit.

[PLATE: SIR ISAAC NEWTON'S ASTROLABE.]

These superb discoveries were, however, but the starting point from
which Newton entered on a series of researches, which disclosed many
of the profoundest secrets in the scheme of celestial mechanics. His
natural insight showed that not only large masses like the sun and
the earth, and the moon, attract each other, but that every particle
in the universe must attract every other particle with a force which
varies inversely as the square of the distance between them. If, for
example, the two particles were placed twice as far apart, then the
intensity of the force which sought to bring them together would be
reduced to one-fourth. If two particles, originally ten miles
asunder, attracted each other with a certain force, then, when the
distance was reduced to one mile, the intensity of the attraction
between the two particles would be increased one-hundred-fold. This
fertile principle extends throughout the whole of nature. In some
cases, however, the calculation of its effect upon the actual
problems of nature would be hardly possible, were it not for another
discovery which Newton's genius enabled him to accomplish. In the
case of two globes like the earth and the moon, we must remember that
we are dealing not with particles, but with two mighty masses of
matter, each composed of innumerable myriads of particles. Every
particle in the earth does attract every particle in the moon with a
force which varies inversely as the square of their distance. The
calculation of such attractions is rendered feasible by the following
principle. Assuming that the earth consists of materials
symmetrically arranged in shells of varying densities, we may then,
in calculating its attraction, regard the whole mass of the globe as
concentrated at its centre. Similarly we may regard the moon as
concentrated at the centre of its mass. In this way the earth and
the moon can both be regarded as particles in point of size, each
particle having, however, the entire mass of the corresponding
globe. The attraction of one particle for another is a much more
simple matter to investigate than the attraction of the myriad
different points of the earth upon the myriad different points of the
moon.

Many great discoveries now crowded in upon Newton. He first of all
gave the explanation of the tides that ebb and flow around our
shores. Even in the earliest times the tides had been shown to be
related to the moon. It was noticed that the tides were specially
high during full moon or during new moon, and this circumstance
obviously pointed to the existence of some connection between the
moon and these movements of the water, though as to what that
connection was no one had any accurate conception until Newton
announced the law of gravitation. Newton then made it plain that the
rise and fall of the water was simply a consequence of the attractive
power which the moon exerted upon the oceans lying upon our globe. He
showed also that to a certain extent the sun produces tides, and he
was able to explain how it was that when the sun and the moon both
conspire, the joint result was to produce especially high tides,
which we call "spring tides"; whereas if the solar tide was low,
while the lunar tide was high, then we had the phenomenon of "neap"
tides.

But perhaps the most signal of Newton's applications of the law of
gravitation was connected with certain irregularities in the
movements of the moon. In its orbit round the earth our satellite
is, of course, mainly guided by the great attraction of our globe. If
there were no other body in the universe, then the centre of the moon
must necessarily perform an ellipse, and the centre of the earth
would lie in the focus of that ellipse. Nature, however, does not
allow the movements to possess the simplicity which this arrangement
would imply, for the sun is present as a source of disturbance. The
sun attracts the moon, and the sun attracts the earth, but in
different degrees, and the consequence is that the moon's movement
with regard to the earth is seriously affected by the influence of
the sun. It is not allowed to move exactly in an ellipse, nor is the
earth exactly in the focus. How great was Newton's achievement in
the solution of this problem will be appreciated if we realise that
he not only had to determine from the law of gravitation the nature
of the disturbance of the moon, but he had actually to construct the
mathematical tools by which alone such calculations could be
effected.

The resources of Newton's genius seemed, however, to prove equal to
almost any demand that could be made upon it. He saw that each
planet must disturb the other, and in that way he was able to render
a satisfactory account of certain phenomena which had perplexed all
preceding investigators. That mysterious movement by which the pole
of the earth sways about among the stars had been long an unsolved
enigma, but Newton showed that the moon grasped with its attraction
the protuberant mass at the equatorial regions of the earth, and thus
tilted the earth's axis in a way that accounted for the phenomenon
which had been known but had never been explained for two thousand
years. All these discoveries were brought together in that immortal
work, Newton's "Principia."

Down to the year 1687, when the "Principia" was published, Newton had
lived the life of a recluse at Cambridge, being entirely occupied
with those transcendent researches to which we have referred. But in
that year he issued from his seclusion under circumstances of
considerable historical interest. King James the Second attempted an
invasion of the rights and privileges of the University of Cambridge
by issuing a command that Father Francis, a Benedictine monk, should
be received as a Master of Arts in the University, without having taken
the oaths of allegiance and supremacy. With this arbitrary command
the University sternly refused to comply. The Vice-Chancellor was
accordingly summoned to answer for an act of contempt to the authority
of the Crown. Newton was one of nine delegates who were chosen to
defend the independence of the University before the High Court.
They were able to show that Charles the Second, who had issued a
MANDAMUS under somewhat similar circumstances, had been induced after
due consideration to withdraw it. This argument appeared satisfactory,
and the University gained their case. Newton's next step in public
life was his election, by a narrow majority, as member for the
University, and during the years 1688 and 1689, he seems to have
attended to his parliamentary duties with considerable regularity.

An incident which happened in 1692 was apparently the cause of
considerable disturbance in Newton's equanimity, if not in his
health. He had gone to early morning chapel, leaving a lighted
candle among his papers on his desk. Tradition asserts that his
little dog "Diamond" upset the candle; at all events, when Newton
came back he found that many valuable papers had perished in a
conflagration. The loss of these manuscripts seems to have had a
serious effect. Indeed, it has been asserted that the distress
reduced Newton to a state of mental aberration for a considerable
time. This has, apparently, not been confirmed, but there is no
doubt that he experienced considerable disquiet, for in writing on
September 13th, 1693, to Mr. Pepys, he says:

"I am extremely troubled at the embroilment I am in, and have
neither ate nor slept well this twelve-month, nor have my former
consistency of mind."

Notwithstanding the fame which Newton had achieved, by the
publication of his, "Principia," and by all his researches, the State
had not as yet taken any notice whatever of the most illustrious man
of science that this or any other country has ever produced. Many of
his friends had exerted themselves to procure him some permanent
appointment, but without success. It happened, however, that Mr.
Montagu, who had sat with Newton in Parliament, was appointed
Chancellor of the Exchequer in 1694. Ambitious of distinction in his
new office, Mr. Montagu addressed himself to the improvement of the
current coin, which was then in a very debased condition. It
fortunately happened that an opportunity occurred of appointing a new
official in the Mint; and Mr. Montagu on the 19th of March, 1695,
wrote to offer Mr. Newton the position of warden. The salary was to
be five or six hundred a year, and the business would not require
more attendance than Newton could spare. The Lucasian professor
accepted this post, and forthwith entered upon his new duties.

The knowledge of physics which Newton had acquired by his experiments
was of much use in connection with his duties at the Mint. He
carried out the re-coinage with great skill in the course of two
years, and as a reward for his exertions, he was appointed, in 1697,
to the Mastership of the Mint, with a salary between 1,200 Pounds and
1,500 Pounds per annum. In 1701, his duties at the Mint being so
engrossing, he resigned his Lucasian professorship at Cambridge, and
at the same time he had to surrender his fellowship at Trinity
College. This closed his connection with the University of
Cambridge. It should, however, be remarked that at a somewhat
earlier stage in his career he was very nearly being appointed to an
office which might have enabled the University to retain the great
philosopher within its precincts. Some of his friends had almost
succeeded in securing his nomination to the Provostship of King's
College, Cambridge; the appointment, however, fell through, inasmuch
as the statute could not be evaded, which required that the Provost
of King's College should be in holy orders.

In those days it was often the custom for illustrious mathematicians,
when they had discovered a solution for some new and striking
problem, to publish that problem as a challenge to the world, while
withholding their own solution. A famous instance of this is found
in what is known as the Brachistochrone problem, which was solved by
John Bernouilli. The nature of this problem may be mentioned. It
was to find the shape of the curve along which a body would slide
down from one point (A) to another point (B) in the shortest time. It
might at first be thought that the straight line from A to B, as it
is undoubtedly the shortest distance between the points, would also
be the path of quickest descent; but this is not so. There is a
curved line, down which a bead, let us say, would run on a smooth
wire from A to B in a shorter time than the same bead would require
to run down the straight wire. Bernouilli's problem was to find out
what that curve must be. Newton solved it correctly; he showed that
the curve was a part of what is termed a cycloid--that is to say, a
curve like that which is described by a point on the rim of a
carriage-wheel as the wheel runs along the ground. Such was Newton's
geometrical insight that he was able to transmit a solution of the
problem on the day after he had received it, to the President of the
Royal Society.

In 1703 Newton, whose world wide fame was now established, was
elected President of the Royal Society. Year after year he was
re-elected to this distinguished position, and his tenure, which
lasted twenty-five years, only terminated with his life. It was in
discharge of his duties as President of the Royal Society that Newton
was brought into contact with Prince George of Denmark. In April,
1705, the Queen paid a visit to Cambridge as the guest of Dr.
Bentley, the then Master of Trinity, and in a court held at Trinity
Lodge on April 15th, 1705, the honour of knighthood was conferred
upon the discoverer of gravitation.

Urged by illustrious friends, who sought the promotion of knowledge,
Newton gave his attention to the publication of a new edition of the
"Principia." His duties at the Mint, however, added to the supreme
duty of carrying on his original investigations, left him but little
time for the more ordinary task of the revision. He was accordingly
induced to associate with himself for this purpose a distinguished
young mathematician, Roger Coates, a Fellow of Trinity College,
Cambridge, who had recently been appointed Plumian Professor of
Astronomy. On July 27th, 1713, Newton, by this time a favourite at
Court, waited on the Queen, and presented her with a copy of the new
edition of the "Principia."

Throughout his life Newton appears to have been greatly interested in
theological studies, and he specially devoted his attention to the
subject of prophecy. He left behind him a manuscript on the
prophecies of Daniel and the Apocalypse of St. John, and he also
wrote various theological papers. Many other subjects had from time
to time engaged his attention. He studied the laws of heat; he
experimented in pursuit of the dreams of the Alchymist; while the
philosopher who had revealed the mechanism of the heavens found
occasional relaxation in trying to interpret hieroglyphics. In the
last few years of his life he bore with fortitude a painful ailment,
and on Monday, March 20th, 1727, he died in the eighty-fifth year of
his age. On Tuesday, March 28th, he was buried in Westminster Abbey.

Though Newton lived long enough to receive the honour that his
astonishing discoveries so justly merited, and though for many years
of his life his renown was much greater than that of any of his
contemporaries, yet it is not too much to say that, in the years
which have since elapsed, Newton's fame has been ever steadily
advancing, so that it never stood higher than it does at this moment.

We hardly know whether to admire more the sublime discoveries at
which he arrived, or the extraordinary character of the intellectual
processes by which those discoveries were reached. Viewed from
either standpoint, Newton's "Principia" is incomparably the greatest
work on science that has ever yet been produced.

[PLATE: SIR ISAAC NEWTON'S SUN-DIAL IN THE ROYAL SOCIETY.]




FLAMSTEED.


Among the manuscripts preserved at Greenwich Observatory are certain
documents in which Flamsteed gives an account of his own life. We
may commence our sketch by quoting the following passage from this
autobiography:--"To keep myself from idleness, and to recreate
myself, I have intended here to give some account of my life, in my
youth, before the actions thereof, and the providences of God
therein, be too far passed out of my memory; and to observe the
accidents of all my years, and inclinations of my mind, that
whosoever may light upon these papers may see I was not so wholly
taken up, either with my father's business or my mathematics, but
that I both admitted and found time for other as weighty
considerations."

The chief interest which attaches to the name of Flamsteed arises
from the fact that he was the first of the illustrious series of
Astronomers Royal who have presided over Greenwich Observatory. In
that capacity Flamsteed was able to render material assistance to
Newton by providing him with the observations which his lunar theory
required.

John Flamsteed was born at Denby, in Derbyshire, on the 19th of
August, 1646. His mother died when he was three years old, and the
second wife, whom his father took three years later, only lived until
Flamsteed was eight, there being also two younger sisters. In his
boyhood the future astronomer tells us that he was very fond of those
romances which affect boy's imagination, but as he writes, "At twelve
years of age I left all the wild ones and betook myself to read the
better sort of them, which, though they were not probable, yet
carried no seeming impossibility in the picturing." By the time
Flamsteed was fifteen years old he had embarked in still more serious
work, for he had read Plutarch's "Lives," Tacitus' "Roman History,"
and many other books of a similar description. In 1661 he became ill
with some serious rheumatic affection, which obliged him to be
withdrawn from school. It was then for the first time that he
received the rudiments of a scientific education. He had, however,
attained his sixteenth year before he made any progress in
arithmetic. He tells us how his father taught him "the doctrine of
fractions," and "the golden rule of three"--lessons which he seemed
to have learned easily and quickly. One of the books which he read
at this time directed his attention to astronomical instruments, and
he was thus led to construct for himself a quadrant, by which he
could take some simple astronomical observations. He further
calculated a table to give the sun's altitudes at different hours,
and thus displayed those tastes for practical astronomy which he
lived to develop so greatly. It appears that these scientific
studies were discountenanced by his father, who designed that his son
should follow a business career. Flamsteed's natural inclination,
however, forced him to prosecute astronomical work, notwithstanding
the impediments that lay in his path. Unfortunately, his
constitutional delicacy seems to have increased, and he had just
completed his eighteenth year, "when," to use his own words, "the
winter came on and thrust me again into the chimney, whence the heat
and the dryness of the preceding summer had happily once before
withdrawn me. But, it not being a fit season for physic, it was
thought fit to let me alone this winter, and try the skill of another
physician on me in the spring."

It appears that at this time a quack named Valentine Greatrackes, was
reputed to have effected most astonishing cures in Ireland merely by
the stroke of his hands, without the application of any medicine
whatever. Flamsteed's father, despairing of any remedy for his son
from the legitimate branch of the profession, despatched him to
Ireland on August 26th, 1665, he being then, as recorded with
astronomical accuracy, "nineteen years, six days, and eleven hours
old." The young astronomer, accompanied by a friend, arrived on a
Tuesday at Liverpool but the wind not being favourable, they remained
there till the following Friday, when a shift of the wind to the east
took place. They embarked accordingly on a vessel called the SUPPLY
at noon, and on Saturday night came in sight of Dublin. Ere they
could land, however, they were nearly being wrecked on Lambay
Island. This peril safely passed, there was a long delay for
quarantine before they were at last allowed on shore. On Thursday,
September 6th, they set out from Dublin, where they had been
sojourning at the "Ship" Hotel, in Dame Street, towards Assaune,
where Greatrackes received his patients.

[PLATE: FLAMSTEED'S HOUSE.]

Flamsteed gives an interesting account of his travels in Ireland.
They dined at Naas on the first day, and on September 8th they
reached Carlow, a town which is described as one of the fairest they
saw on their journey. By Sunday morning, September 10th, having lost
their way several times, they reached Castleton, called commonly Four
Mile Waters. Flamsteed inquired of the host in the inn where they
might find a church, but was told that the minister lived twelve
miles away, and that they had no sermon except when he came to
receive his tithes once a year, and a woman added that "they had
plenty enough of everything necessary except the word of God." The
travellers accordingly went on to Cappoquin, which lies up the river
Blackwater, on the road to Lismore, eight miles from Youghal. Thence
they immediately started on foot to Assaune. About a mile from
Cappoquin, and entering into the house of Mr. Greatrackes, they saw
him touch several patients, "whereof some were nearly cured, others
were on the mending hand, and some on whom his strokes had no
effect." Flamsteed was touched by the famous quack on the afternoon
of September 11th, but we are hardly surprised to hear his remark
that "he found not his disease to stir." Next morning the astronomer
came again to see Mr. Greatrackes, who had "a kind of majestical yet
affable presence, and a composed carriage." Even after the third
touching had been submitted to, no benefit seems to have been
derived. We must, however record, to the credit of Mr. Greatrackes,
that he refused to accept any payment from Flamsteed, because he was
a stranger.

Finding it useless to protract his stay any longer, Flamsteed and his
friend set out on their return to Dublin. In the course of his
journey he seems to have been much impressed with Clonmel, which he
describes as an "exceedingly pleasantly seated town." But in those
days a journey to Ireland was so serious an enterprise that when
Flamsteed did arrive safely back at Derby after an absence of a
month, he adds, "For God's providence in this journey, His name be
praised, Amen."

As to the expected benefits to his health from the expedition we may
quote his own words: "In the winter following I was indifferent
hearty, and my disease was not so violent as it used to be at that
time formerly. But whether through God's mercy I received this
through Mr. Greatrackes' touch, or my journey and vomiting at sea, I
am uncertain; but, by some circumstances, I guess that I received a
benefit from both."

It is evident that by this time Flamsteed's interest in all
astronomical matters had greatly increased. He studied the
construction of sun-dials, he formed a catalogue of seventy of the
fixed stars, with their places on the heavens, and he computed the
circumstances of the solar eclipse which was to happen on June 22nd,
1666. It is interesting to note that even in those days the
doctrines of the astrologers still found a considerable degree of
credence, and Flamsteed spent a good deal of his time in astrological
studies and computations. He investigated the methods of casting a
nativity, but a suspicion, or, indeed, rather more than a suspicion,
seems to have crossed his mind as to the value of these astrological
predictions, for he says in fine, "I found astrology to give
generally strong conjectural hints, not perfect declarations."

All this time, however, the future Astronomer Royal was steadily
advancing in astronomical inquiries of a recondite nature. He had
investigated the obliquity of the ecliptic with extreme care, so far
as the circumstances of astronomical observation would at that time
permit. He had also sought to discover the sun's distance from the
earth in so far as it could be obtained by determining when the moon
was exactly half illuminated, and he had measured, with much
accuracy, the length of the tropical year. It will thus be seen
that, even at the age of twenty, Flamsteed had made marked progress,
considering how much his time had been interfered with by ill-health.

Other branches of astronomy began also to claim his attention. We
learn that in 1669 and 1670 he compared the planets Jupiter and Mars
with certain fixed stars near which they passed. His instrumental
means, though very imperfect, were still sufficient to enable him to
measure the intervals on the celestial sphere between the planets and
the stars. As the places of the stars were known, Flamsteed was thus
able to obtain the places of the planets. This is substantially the
way in which astronomers of the present day still proceed when they
desire to determine the places of the planets, inasmuch as, directly
or indirectly those places are always obtained relatively to the
fixed stars. By his observations at this early period, Flamsteed
was, it is true, not able to obtain any great degree of accuracy; he
succeeded, however, in proving that the tables by which the places of
the planets were ordinarily given were not to be relied upon.

[PLATE: FLAMSTEED.]

Flamsteed's labours in astronomy and in the allied branches of
science were now becoming generally known, and he gradually came to
correspond with many distinguished men of learning. One of the first
occasions which brought the talents of the young astronomer into fame
was the publication of some calculations concerning certain
astronomical phenomena which were to happen in the year 1670. In the
monthly revolution of the moon its disc passes over those stars which
lie along its track. The disappearance of a star by the
interposition of the moon is called an "occultation." Owing to the
fact that our satellite is comparatively near us, the position which
the moon appears to occupy on the heavens varies from different parts
of the earth, it consequently happens that a star which would be
occulted to an observer in one locality, would often not be occulted
to an observer who was situated elsewhere. Even when an occultation
is visible from both places, the times at which the star disappears
from view will, generally speaking, be different. Much calculation
is therefore necessary to decide the circumstances under which the
occultations of stars may be visible from any particular station.
Having a taste for such computations, Flamsteed calculated the
occultations which were to happen in the year 1670, it being the case
that several remarkable stars would be passed over by the moon during
this year. Of course at the present time, we find such information
duly set forth in the NAUTICAL ALMANAC, but a couple of centuries ago
there was no such source of astronomical knowledge as is now to be
found in that invaluable publication, which astronomers and
navigators know so well. Flamsteed accordingly sent the results of
his work to the President of the Royal Society. The paper which
contained them was received very favourably, and at once brought
Flamsteed into notice among the most eminent members of that
illustrious body, one of whom, Mr. Collins, became through life his
faithful friend and constant correspondent. Flamsteed's father was
naturally gratified with the remarkable notice which his son was
receiving from the great and learned; accordingly he desired him to
go to London, that he might make the personal acquaintance of those
scientific friends whom he had only known by correspondence
previously. Flamsteed was indeed glad to avail himself of this
opportunity. Thus he became acquainted with Dr. Barrow, and
especially with Newton, who was then Lucasian Professor of
Mathematics at Cambridge. It seems to have been in consequence of
this visit to London that Flamsteed entered himself as a member of
Jesus College, Cambridge. We have but little information as to his
University career, but at all events he took his degree of M.A. on
June 5th, 1674.

Up to this time it would seem that Flamsteed had been engaged, to a
certain extent, in the business carried on by his father. It is true
that he does not give any explicit details, yet there are frequent
references to journeys which he had to take on business matters. But
the time now approached when Flamsteed was to start on an independent
career, and it appears that he took his degree in Cambridge with the
object of entering into holy orders, so that he might settle in a
small living near Derby, which was in the gift of a friend of his
father, and would be at the disposal of the young astronomer. This
scheme was, however, not carried out, but Flamsteed does not tell us
why it failed, his only remark being, that "the good providence of
God that had designed me for another station ordered it otherwise."

Sir Jonas Moore, one of the influential friends whom Flamsteed's
talents had attracted, seems to have procured for him the position of
king's astronomer, with a salary of 100 pounds per annum. A larger
salary appears to have been designed at first for this office, which
was now being newly created, but as Flamsteed was resolved on taking
holy orders, a lesser salary was in his case deemed sufficient. The
building of the observatory, in which the first Astronomer Royal was
to be installed, seems to have been brought about, or, at all events,
its progress was accelerated, in a somewhat curious manner.

A Frenchman, named Le Sieur de S. Pierre, came over to London to
promulgate a scheme for discovering longitudes, then a question of
much importance. He brought with him introductions to distinguished
people, and his mission attracted a great deal of attention. The
proposals which he made came under Flamsteed's notice, who pointed
out that the Frenchman's projects were quite inapplicable in the
present state of astronomical science, inasmuch as the places of the
stars were not known with the degree of accuracy which would be
necessary if such methods were to be rendered available. Flamsteed
then goes on to say:--"I heard no more of the Frenchman after this;
but was told that my letters had been shown King Charles. He was
startled at the assertion of the fixed stars' places being false in
the catalogue, and said, with some vehemence, he must have them anew
observed, examined, and corrected, for the use of his seamen."

The first question to be settled was the site for the new
observatory. Hyde Park and Chelsea College were both mentioned as
suitable localities, but, at Sir Christopher Wren's suggestion,
Greenwich Hill was finally resolved upon. The king made a grant of
five hundred pounds of money. He gave bricks from Tilbury Fort,
while materials, in the shape of wood, iron, and lead, were available
from a gatehouse demolished in the Tower. The king also promised
whatever further material aid might be shown to be necessary. The
first stone of the Royal Observatory was laid on August 10th, 1675,
and within a few years a building was erected in which the art of
modern practical astronomy was to be created. Flamsteed strove with
extraordinary diligence, and in spite of many difficulties, to obtain
a due provision of astronomical instruments, and to arrange for the
carrying on of his observations. Notwithstanding the king's
promises, the astronomer was, however, but scantily provided with
means, and he had no assistants to help him in his work. It follows
that all the observations, as well as the reductions, and, indeed,
all the incidental work of the observatory, had to be carried on by
himself alone. Flamsteed, as we have seen, had, however, many
staunch friends. Sir Jonas Moore in particular at all times rendered
him most valuable assistance, and encouraged him by the warm sympathy
and keen interest which he showed in astronomy. The work of the
first Astronomer Royal was frequently interrupted by recurrent
attacks of the complaints to which we have already referred. He says
himself that "his distempers stick so close that that he cannot
remove them," and he lost much time by prostration from headaches, as
well as from more serious affections.

The year 1678 found him in the full tide of work in his observatory.
He was specially engaged on the problem of the earth's motion, which
he sought to derive from observations of the sun and of Venus. But
this, as well as many other astronomical researches which he
undertook, were only subsidiary to that which he made the main task
of his life, namely, the formation of a catalogue of fixed stars. At
the time when Flamsteed commenced his career, the only available
catalogue of fixed stars was that of Tycho Brahe. This work had been
published at the commencement of the seventeenth century, and it
contained about a thousand stars. The positions assigned to these
stars, though obtained with wonderful skill, considering the many
difficulties under which Tycho laboured, were quite inaccurate when
judged by our modern standards. Tycho's instruments were necessarily
most rudely divided, and he had, of course, no telescopes to aid him.
Consequently it was merely by a process of sighting that he could
obtain the places of the stars. It must further be remembered that
Tycho had no clocks, and no micrometers. He had, indeed, but little
correct knowledge of the motions of the heavenly bodies to guide
him. To determine the longitudes of a few principal stars he
conceived the ingenious idea of measuring by day the position of
Venus with respect to the sun, an observation which the exceptional
brightness of this planet rendered possible without telescopic aid,
and then by night he observed the position of Venus with regard to
the stars.

It has been well remarked by Mr. Baily, in his introduction to the
"British Catalogue of Stars," that "Flamsteed's observations, by a
fortunate combination of circumstances, commenced a new and a
brilliant era. It happened that, at that period, the powerful mind
of Newton was directed to this subject; a friendly intercourse then
existed between these two distinguished characters; and thus the
first observations that could lay any claim to accuracy were at once
brought in aid of those deep researches in which our illustrious
geometer was then engaged. The first edition of the 'Principia'
bears testimony to the assistance afforded by Flamsteed to Newton in
these inquiries; although the former considers that the
acknowledgment is not so ample as it ought to have been."

Although Flamsteed's observations can hardly be said to possess the
accuracy of those made in more recent times, when instruments so much
superior to his have been available, yet they possess an interest of
a special kind from their very antiquity. This circumstance renders
them of particular importance to the astronomer, inasmuch as they are
calculated to throw light on the proper motions of the stars.
Flamsteed's work may, indeed, be regarded as the origin of all
subsequent catalogues, and the nomenclature which he adopted, though
in some respects it can hardly be said to be very defensible, is,
nevertheless, that which has been adopted by all subsequent
astronomers. There were also a great many errors, as might be
expected in a work of such extent, composed almost entirely of
numerical detail. Many of these errors have been corrected by Baily
himself, the assiduous editor of "Flamsteed's Life and Works," for
Flamsteed was so harassed from various causes in the latter part of
his life, and was so subject to infirmities all through his career,
that he was unable to revise his computations with the care that
would have been necessary. Indeed, he observed many additional stars
which he never included in the British Catalogue. It is, as Baily
well remarks, "rather a matter of astonishment that he accomplished
so much, considering his slender means, his weak frame, and the
vexations which he constantly experienced."

Flamsteed had the misfortune, in the latter part of his life, to
become estranged from his most eminent scientific contemporaries. He
had supplied Newton with places of the moon, at the urgent
solicitation of the author of the "Principia," in order that the
lunar theory should be carefully compared with observation. But
Flamsteed appears to have thought that in Newton's further request
for similar information, he appeared to be demanding as a right that
which Flamsteed considered he was only called upon to render as a
favour. A considerable dispute grew out of this matter, and there
are many letters and documents, bearing on the difficulties which
subsequently arose, that are not, perhaps, very creditable to either
party.

Notwithstanding his feeble constitution, Flamsteed lived to the age
of seventy-three, his death occurring on the last day of the year
1719.




HALLEY.


Isaac Newton was just fourteen years of age when the birth of Edmund
Halley, who was destined in after years to become Newton's warmly
attached friend, and one of his most illustrious scientific
contemporaries, took place. There can be little doubt that the fame
as an astronomer which Halley ultimately acquired, great as it
certainly was, would have been even greater still had it not been
somewhat impaired by the misfortune that he had to shine in the same
sky as that which was illumined by the unparalleled genius of Newton.

Edmund Halley was born at Haggerston, in the Parish of St. Leonard's,
Shoreditch, on October 29th, 1656. His father, who bore the same
name as his famous son, was a soap-boiler in Winchester Street,
London, and he had conducted his business with such success that he
accumulated an ample fortune. I have been unable to obtain more than
a very few particulars with respect to the early life of the future
astronomer. It would, however, appear that from boyhood he showed
considerable aptitude for the acquisition of various kinds of
learning, and he also had some capacity for mechanical invention.
Halley seems to have received a sound education at St. Paul's School,
then under the care of Dr. Thomas Gale.

Here, the young philosopher rapidly distanced his competitors in the
various branches of ordinary school instruction. His superiority
was, however, most conspicuous in mathematical studies, and, as a
natural development of such tastes, we learn that by the time he had
left school he had already made good progress in astronomy. At the
age of seventeen he was entered as a commoner at Queen's College,
Oxford, and the reputation that he brought with him to the University
may be inferred from the remark of the writer of "Athenae
Oxonienses," that Halley came to Oxford "with skill in Latin, Greek,
and Hebrew, and such a knowledge of geometry as to make a complete
dial." Though his studies were thus of a somewhat multifarious
nature, yet it is plain that from the first his most favourite
pursuit was astronomy. His earliest efforts in practical observation
were connected with an eclipse which he observed from his father's
house in Winchester Street. It also appears that he had studied
theoretical branches of astronomy so far as to be conversant with the
application of mathematics to somewhat abstruse problems.

Up to the time of Kepler, philosophers had assumed almost as an axiom
that the heavenly bodies must revolve in circles and that the motion
of the planet around the orbit which it described must be uniform. We
have already seen how that great philosopher, after very persevering
labour, succeeded in proving that the orbits of the planets were not
circles, but that they were ellipses of small eccentricity. Kepler
was, however, unable to shake himself free from the prevailing notion
that the angular motion of the planet ought to be of a uniform
character around some point. He had indeed proved that the motion
round the focus of the ellipse in which the sun lies is not of this
description. One of his most important discoveries even related to
the fact that at some parts of its orbit a planet swings around the
sun with greater angular velocity than at others. But it so happens
that in elliptic tracks which differ but little from circles, as is
the case with all the more important planetary orbits, the motion
round the empty focus of the ellipse is very nearly uniform. It
seemed natural to assume, that this was exactly the case, in which
event each of the two foci of the ellipse would have had a special
significance in relation to the movement of the planet. The youthful
Halley, however, demonstrated that so far as the empty focus was
concerned, the movement of the planet around it, though so nearly
uniform, was still not exactly so, and at the age of nineteen, he
published a treatise on the subject which at once placed him in the
foremost rank amongst theoretical astronomers.

But Halley had no intention of being merely an astronomer with his
pen. He longed to engage in the practical work of observing. He saw
that the progress of exact astronomy must depend largely on the
determination of the positions of the stars with all attainable
accuracy. He accordingly determined to take up this branch of work,
which had been so successfully initiated by Tycho Brahe.

At the present day, astronomers of the great national observatories
are assiduously engaged in the determination of the places of the
stars. A knowledge of the exact positions of these bodies is indeed
of the most fundamental importance, not alone for the purposes of
scientific astronomy, but also for navigation and for extensive
operations of surveying in which accuracy is desired. The fact that
Halley determined to concentrate himself on this work shows clearly
the scientific acumen of the young astronomer.

Halley, however, found that Hevelius, at Dantzig, and Flamsteed, the
Astronomer Royal at Greenwich, were both engaged on work of this
character. He accordingly determined to direct his energies in a way
that he thought would be more useful to science. He resigned to the
two astronomers whom I have named the investigation of the stars in
the northern hemisphere, and he sought for himself a field hitherto
almost entirely unworked. He determined to go to the southern
hemisphere, there to measure and survey those stars which were
invisible in Europe, so that his work should supplement the labours
of the northern astronomers, and that the joint result of his labours
and of theirs might be a complete survey of the most important stars
on the surface of the heavens.

In these days, after so many ardent students everywhere have devoted
themselves to the study of Nature, it seems difficult for a beginner
to find a virgin territory in which to commence his explorations.
Halley may, however, be said to have enjoyed the privilege of
commencing to work in a magnificent region, the contents of which
were previously almost entirely unknown. Indeed none of the stars
which were so situated as to have been invisible from Tycho Brahe's
observatory at Uraniborg, in Denmark, could be said to have been
properly observed. There was, no doubt, a rumour that a Dutchman had
observed southern stars from the island of Sumatra, and certain stars
were indicated in the southern heavens on a celestial globe. On
examination, however, Halley found that no reliance could be placed
on the results which had been obtained, so that practically the field
before him may be said to have been unworked.

At the age of twenty, without having even waited to take that degree
at the university which the authorities would have been glad to
confer on so promising an undergraduate, this ardent student of
Nature sought his father's permission to go to the southern
hemisphere for the purpose of studying the stars which lie around the
southern pole. His father possessed the necessary means, and he had
likewise the sagacity to encourage the young astronomer. He was
indeed most anxious to make everything as easy as possible for so
hopeful a son. He provided him with an allowance of 300 pounds a
year, which was regarded as a very munificent provision in those
days. Halley was also furnished with letters of recommendation from
King Charles II., as well as from the directors of the East India
Company. He accordingly set sail with his instruments in the year
1676, in one of the East India Company's ships, for the island of St.
Helena, which he had selected as the scene of his labours.

[PLATE: HALLEY.]

After an uneventful voyage of three months, the astronomer landed on
St. Helena, with his sextant of five and a half feet radius, and a
telescope 24 feet long, and forthwith plunged with ardour into his
investigation of the southern skies. He met, however, with one very
considerable disappointment. The climate of this island had been
represented to him as most favourable for astronomical observation;
but instead of the pure blue skies he had been led to expect, he
found that they were almost always more or less clouded, and that
rain was frequent, so that his observations were very much
interrupted. On this account he only remained at St. Helena for a
single year, having, during that time, and in spite of many
difficulties, accomplished a piece of work which earned for him the
title of "our southern Tycho." Thus did Halley establish his fame as
an astronomer on the same lonely rock in mid-Atlantic, which nearly a
century and a-half later became the scene of Napoleon's imprisonment,
when his star, in which he believed so firmly, had irretrievably set.

On his return to England, Halley prepared a map which showed the
result of his labours, and he presented it to the king, in 1677.
Like his great predecessor Tycho, Halley did not altogether disdain
the arts of the courtier, for he endeavoured to squeeze a new
constellation into the group around the southern pole which he styled
"The Royal Oak," adding a description to the effect that the
incidents of which "The Royal Oak" was a symbol were of sufficient
importance to be inscribed on the surface of the heavens.

There is reason to think that Charles II. duly appreciated the
scientific renown which one of his subjects had achieved, and it was
probably through the influence of the king that Halley was made a
Master of Arts at Oxford on November 18th, 1678. Special reference
was made on the occasion to his observations at St. Helena, as
evidence of unusual attainments in mathematics and astronomy. This
degree was no small honour to such a young man, who, as we have seen,
quitted his university before he had the opportunity of graduating in
the ordinary manner.

On November 30th, in the same year, the astronomer received a further
distinction in being elected a Fellow of the Royal Society. From
this time forward he took a most active part in the affairs of the
Society, and the numerous papers which he read before it form a very
valuable part of that notable series of volumes known as the
"Philosophical Transactions." He was subsequently elected to the
important office of secretary to the Royal Society, and he discharged
the duties of his post until his appointment to Greenwich
necessitated his resignation.

Within a year of Halley's election as a Fellow of the Royal Society,
he was chosen by the Society to represent them in a discussion which
had arisen with Hevelius. The nature of this discussion, or rather
the fact that any discussion should have been necessary, may seem
strange to modern astronomers, for the point is one on which it would
now seem impossible for there to be any difference of opinion. We
must, however, remember that the days of Halley were, comparatively
speaking, the days of infancy as regards the art of astronomical
observation, and issues that now seem obvious were often, in those
early times, the occasions of grave and anxious consideration. The
particular question on which Halley had to represent the Royal
Society may be simply stated. When Tycho Brahe made his memorable
investigations into the places of the stars, he had no telescopes to
help him. The famous instruments at Uraniborg were merely provided
with sights, by which the telescope was pointed to a star on the same
principle as a rifle is sighted for a target. Shortly after Tycho's
time, Galileo invented the telescope. Of course every one admitted
at once the extraordinary advantages which the telescope had to
offer, so far as the mere question of the visibility of objects was
concerned. But the bearing of Galileo's invention upon what we may
describe as the measuring part of astronomy was not so immediately
obvious. If a star be visible to the unaided eye, we can determine
its place by such instruments as those which Tycho used, in which no
telescope is employed. We can, however, also avail ourselves of an
instrument in which we view the star not directly but through the
intervention of the telescope. Can the place of the star be
determined more accurately by the latter method than it can when the
telescope is dispensed with? With our present knowledge, of course,
there is no doubt about the answer; every one conversant with
instruments knows that we can determine the place of a star far more
accurately with the telescope than is possible by any mere sighting
apparatus. In fact an observer would be as likely to make an error
of a minute with the sighting apparatus in Tycho's instrument, as he
would be to make an error of a second with the modern telescope, or,
to express the matter somewhat differently, we may say, speaking
quite generally, that the telescopic method of determining the places
of the stars does not lead to errors more than one-sixtieth part as
great as which are unavoidable when we make use of Tycho's method.

But though this is so apparent to the modern astronomer, it was not
at all apparent in the days of Halley, and accordingly he was sent
off to discuss the question with the Continental astronomers.
Hevelius, as the representative of the older method, which Tycho had
employed with such success, maintained that an instrument could be
pointed more accurately at a star by the use of sights than by the
use of a telescope, and vigorously disputed the claims put forward by
those who believed that the latter method was the more suitable. On
May 14th, 1679, Halley started for Dantzig, and the energetic
character of the man may be judged from the fact that on the very
night of his arrival he commenced to make the necessary
observations. In those days astronomical telescopes had only
obtained a fractional part of the perfection possessed by the
instruments in our modern observatories, and therefore it may not be
surprising that the results of the trial were not immediately
conclusive. Halley appears to have devoted much time to the
investigation; indeed, he remained at Dantzig for more than a
twelve-month. On his return to England, he spoke highly of the skill
which Hevelius exhibited in the use of his antiquated methods, but
Halley was nevertheless too sagacious an observer to be shaken in his
preference for the telescopic method of observation.

The next year we find our young astronomer starting for a Continental
tour, and we, who complain if the Channel passage lasts more than an
hour or two, may note Halley's remark in writing to Hooke on June
15th, 1680: "Having fallen in with bad weather we took forty hours in
the journey from Dover to Calais." The scientific distinction which
he had already attained was such that he was received in Paris with
marked attention. A great deal of his time seems to have been passed
in the Paris observatory, where Cassini, the presiding genius,
himself an astronomer of well-deserved repute, had extended a hearty
welcome to his English visitor. They made observations together of
the place of the splendid comet which was then attracting universal
attention, and Halley found the work thus done of much use when he
subsequently came to investigate the path pursued by this body.
Halley was wise enough to spare no pains to derive all possible
advantages from his intercourse with the distinguished savants of the
French capital. In the further progress of his tour he visited the
principal cities of the Continent, leaving behind him everywhere the
memory of an amiable disposition and of a rare intelligence.

After Halley's return to England, in 1682, he married a young lady
named Mary Tooke, with whom he lived happily, till her death
fifty-five years later. On his marriage, he took up his abode in
Islington, where he erected his instruments and recommenced his
observations.

It has often been the good fortune of astronomers to render practical
services to humanity by their investigations, and Halley's
achievements in this respect deserve to be noted. A few years after
he had settled in England, he published an important paper on the
variation of the magnetic compass, for so the departure of the needle
from the true north is termed. This subject had indeed early engaged
his attention, and he continued to feel much interest in it up to the
end of his life. With respect to his labours in this direction, Sir
John Herschel says: "To Halley we owe the first appreciation of the
real complexity of the subject of magnetism. It is wonderful indeed,
and a striking proof of the penetration and sagacity of this
extraordinary man, that with his means of information he should have
been able to draw such conclusions, and to take so large and
comprehensive a view of the subject as he appears to have done." In
1692, Halley explained his theory of terrestrial magnetism, and
begged captains of ships to take observations of the variations of
the compass in all parts of the world, and to communicate them to the
Royal Society, "in order that all the facts may be readily available
to those who are hereafter to complete this difficult and complicated
subject."

The extent to which Halley was in advance of his contemporaries, in
the study of terrestrial magnetism, may be judged from the fact that
the subject was scarcely touched after his time till the year 1811.
The interest which he felt in it was not of a merely theoretical
kind, nor was it one which could be cultivated in an easy-chair. Like
all true investigators, he longed to submit his theory to the test of
experiment, and for that purpose Halley determined to observe the
magnetic variation for himself. He procured from King William III.
the command of a vessel called the "Paramour Pink," with which he
started for the South Seas in 1694. This particular enterprise was
not, however, successful; for, on crossing the line, some of his men
fell sick and one of his lieutenants mutinied, so that he was obliged
to return the following year with his mission unaccomplished. The
government cashiered the lieutenant, and Halley having procured a
second smaller vessel to accompany the "Paramour Pink," started once
more in September, 1699. He traversed the Atlantic to the 52nd
degree of southern latitude, beyond which his further advance was
stopped. "In these latitudes," he writes to say, "we fell in with
great islands of ice of so incredible height and magnitude, that I
scarce dare write my thoughts of it."

On his return in 1700, Halley published a general chart, showing the
variation of the compass at the different places which he had
visited. On these charts he set down lines connecting those
localities at which the magnetic variation was identical. He thus
set an example of the graphic representation of large masses of
complex facts, in such a manner as to appeal at once to the eye, a
method of which we make many applications in the present day.

But probably the greatest service which Halley ever rendered to human
knowledge was the share in which he took in bringing Newton's
"Principia" before the world. In fact, as Dr. Glaisher, writing in
1888, has truly remarked, "but for Halley the 'Principia' would not
have existed."

It was a visit from Halley in the year 1684 which seems to have first
suggested to Newton the idea of publishing the results of his
investigations on gravitation. Halley, and other scientific
contemporaries, had no doubt some faint glimmering of the great truth
which only Newton's genius was able fully to reveal. Halley had
indeed shown how, on the assumptions that the planets move in
circular orbits round the sun, and that the squares of their periodic
times are proportional to the cubes of their mean distances, it may
be proved that the force acting on each planet must vary inversely as
the square of its distance from the sun. Since, however, each of the
planets actually moves in an ellipse, and therefore, at continually
varying distances from the sun, it becomes a much more difficult
matter to account mathematically for the body's motions on the
supposition that the attractive force varies inversely as the square
of the distance. This was the question with which Halley found
himself confronted, but which his mathematical abilities were not
adequate to solve. It would seem that both Hooke and Sir Christopher
Wren were interested in the same problem; in fact, the former claimed
to have arrived at a solution, but declined to make known his
results, giving as an excuse his desire that others having tried and
failed might learn to value his achievements all the more. Halley,
however, confessed that his attempts at the solution were
unsuccessful, and Wren, in order to encourage the other two
philosophers to pursue the inquiry, offered to present a book of
forty shillings value to either of them who should in the space of
two months bring him a convincing proof of it. Such was the value
which Sir Christopher set on the Law of Gravitation, upon which the
whole fabric of modern astronomy may be said to stand.

Finding himself unequal to the task, Halley went down to Cambridge to
see Newton on the subject, and was delighted to learn that the great
mathematician had already completed the investigation. He showed
Halley that the motions of all the planets could be completely
accounted for on the hypothesis of a force of attraction directed
towards the sun, which varies inversely as the square of the distance
from that body.

Halley had the genius to perceive the tremendous importance of
Newton's researches, and he ceased not to urge upon the recluse man
of science the necessity for giving his new discoveries publication.
He paid another visit to Cambridge with the object of learning more
with regard to the mathematical methods which had already conducted
Newton to such sublime truths, and he again encouraged the latter
both to pursue his investigations, and to give some account of them
to the world. In December of the same year Halley had the
gratification of announcing to the Royal Society that Newton had
promised to send that body a paper containing his researches on
Gravitation.

It seems that at this epoch the finances of the Royal Society were at
a very low ebb. This impecuniosity was due to the fact that a book
by Willoughby, entitled "De Historia Piscium," had been recently
printed by the society at great expense. In fact, the coffers were
so low that they had some difficulty in paying the salaries of their
permanent officials. It appears that the public did not care about
the history of fishes, or at all events the volume did not meet with
the ready demand which was expected for it. Indeed, it has been
recorded that when Halley had undertaken to measure the length of a
degree of the earth's surface, at the request of the Royal Society,
it was ordered that his expenses be defrayed either in 50 pounds
sterling, or in fifty books of fishes. Thus it happened that on June
2nd, the Council, after due consideration of ways and means in
connection with the issue of the Principia, "ordered that Halley
should undertake the business of looking after the book and printing
it at his own charge," which he engaged to do.

It was, as we have elsewhere mentioned, characteristic of Newton that
he detested controversies, and he was, in fact, inclined to suppress
the third book of the "Principia" altogether rather than have any
conflict with Hooke with respect to the discoveries there
enunciated. He also thought of changing the name of the work to De
Motu Corporum Libri Duo, but upon second thoughts, he retained the
original title, remarking, as he wrote to Halley, "It will help the
sale of the book, which I ought not to diminish, now it is yours," a
sentence which shows conclusively, if further proof were necessary,
that Halley had assumed the responsibility of its publication.

Halley spared no pains in pushing forward the publication of his
illustrious friend's great work, so that in the same year he was in a
position to present a complete copy to King James II., with a proper
discourse of his own. Halley also wrote a set of Latin hexameters in
praise of Newton's genius, which he printed at the beginning of the
work. The last line of this specimen of Halley's poetic muse may be
thus rendered: "Nor mortals nearer may approach the gods."

The intimate friendship between the two greatest astronomers of the
time continued without interruption till the death of Newton. It
has, indeed, been alleged that some serious cause of estrangement
arose between them. There is, however, no satisfactory ground for
this statement; indeed, it may be regarded as effectually disposed of
by the fact that, in the year 1727, Halley took up the defence of his
friend, and wrote two learned papers in support of Newton's "System
of Chronology," which had been seriously attacked by a certain
ecclesiastic. It is quite evident to any one who has studied these
papers that Halley's friendship for Newton was as ardent as ever.

The generous zeal with which Halley adopted and defended the
doctrines of Newton with regard to the movements of the celestial
bodies was presently rewarded by a brilliant discovery, which has
more than any of his other researches rendered his name a familiar
one to astronomers. Newton, having explained the movement of the
planets, was naturally led to turn his attention to comets. He
perceived that their journeyings could be completely accounted for as
consequences of the attraction of the sun, and he laid down the
principles by which the orbit of a comet could be determined,
provided that observations of its positions were obtained at three
different dates. The importance of these principles was by no one
more quickly recognised than by Halley, who saw at once that it
provided the means of detecting something like order in the movements
of these strange wanderers. The doctrine of Gravitation seemed to
show that just as the planets revolved around the sun in ellipses, so
also must the comets. The orbit, however, in the case of the comet,
is so extremely elongated that the very small part of the elliptic
path within which the comet is both near enough and bright enough to
be seen from the earth, is indistinguishable from a parabola.
Applying these principles, Halley thought it would be instructive to
study the movements of certain bright comets, concerning which
reliable observations could be obtained. At the expense of much
labour, he laid down the paths pursued by twenty-four of these
bodies, which had appeared between the years 1337 and 1698. Amongst
them he noticed three, which followed tracks so closely resembling
each other, that he was led to conclude the so called three comets
could only have been three different appearances of the same body.
The first of these occurred in 1531, the second was seen by Kepler in
1607, and the third by Halley himself in 1682. These dates suggested
that the observed phenomena might be due to the successive returns of
one and the same comet after intervals of seventy-five or seventy-six
years. On the further examination of ancient records, Halley found
that a comet had been seen in the year 1456, a date, it will be
observed, seventy-five years before 1531. Another had been observed
seventy-six years earlier than 1456, viz., in 1380, and another
seventy-five years before that, in 1305.

As Halley thus found that a comet had been recorded on several
occasions at intervals of seventy-five or seventy-six years, he was
led to the conclusion that these several apparitions related to one
and the same object, which was an obedient vassal of the sun,
performing an eccentric journey round that luminary in a period of
seventy-five or seventy-six years. To realise the importance of this
discovery, it should be remembered that before Halley's time a comet,
if not regarded merely as a sign of divine displeasure, or as an omen
of intending disaster, had at least been regarded as a chance visitor
to the solar system, arriving no one knew whence, and going no one
knew whither.

A supreme test remained to be applied to Halley's theory. The
question arose as to the date at which this comet would be seen
again. We must observe that the question was complicated by the fact
that the body, in the course of its voyage around the sun, was
exposed to the incessant disturbing action produced by the attraction
of the several planets. The comet therefore, does not describe a
simple ellipse as it would do if the attraction of the sun were the
only force by which its movement were controlled. Each of the
planets solicits the comet to depart from its track, and though the
amount of these attractions may be insignificant in comparison with
the supreme controlling force of the sun, yet the departure from the
ellipse is quite sufficient to produce appreciable irregularities in
the comet's movement. At the time when Halley lived, no means
existed of calculating with precision the effect of the disturbance a
comet might experience from the action of the different planets.
Halley exhibited his usual astronomical sagacity in deciding that
Jupiter would retard the return of the comet to some extent. Had it
not been for this disturbance the comet would apparently have been
due in 1757 or early in 1758. But the attraction of the great planet
would cause delay, so that Halley assigned, for the date of its
re-appearance, either the end of 1758 or the beginning of 1759.
Halley knew that he could not himself live to witness the fulfilment
of his prediction, but he says: "If it should return, according to
our predictions, about the year 1758, impartial posterity will not
refuse to acknowledge that this was first discovered by an
Englishman." This was, indeed, a remarkable prediction of an event
to occur fifty-three years after it had been uttered. The way in
which it was fulfilled forms one of the most striking episodes in the
history of astronomy. The comet was first seen on Christmas Day,
1758, and passed through its nearest point to the sun on March 13th,
1759. Halley had then been lying in his grave for seventeen years,
yet the verification of his prophecy reflects a glory on his name
which will cause it to live for ever in the annals of astronomy. The
comet paid a subsequent visit in 1835, and its next appearance is due
about 1910.

Halley next entered upon a labour which, if less striking to the
imagination than his discoveries with regard to comets, is still of
inestimable value in astronomy. He undertook a series of
investigations with the object of improving our knowledge of the
movements of the planets. This task was practically finished in
1719, though the results of it were not published until after his
death in 1749. In the course of it he was led to investigate closely
the motion of Venus, and thus he came to recognise for the first time
the peculiar importance which attaches to the phenomenon of the
transit of this planet across the sun. Halley saw that the transit,
which was to take place in the year 1761, would afford a favourable
opportunity for determining the distance of the sun, and thus
learning the scale of the solar system. He predicted the
circumstances of the phenomenon with an astonishing degree of
accuracy, considering his means of information, and it is
unquestionably to the exertions of Halley in urging the importance of
the matter upon astronomers that we owe the unexampled degree of
interest taken in the event, and the energy which scientific men
exhibited in observing it. The illustrious astronomer had no hope of
being himself a witness of the event, for it could not happen till
many years after his death. This did not, however, diminish his
anxiety to impress upon those who would then be alive, the importance
of the occurrence, nor did it lead him to neglect anything which
might contribute to the success of the observations. As we now know,
Halley rather over-estimated the value of the transit of Venus, as a
means of determining the solar distance. The fact is that the
circumstances are such that the observation of the time of contact
between the edge of the planet and the edge of the sun cannot be made
with the accuracy which he had expected.

In 1691, Halley became a candidate for the Savilian Professorship of
Astronomy at Oxford. He was not, however, successful, for his
candidature was opposed by Flamsteed, the Astronomer Royal of the
time, and another was appointed. He received some consolation for
this particular disappointment by the fact that, in 1696, owing to
Newton's friendly influence, he was appointed deputy Controller of
the Mint at Chester, an office which he did not retain for long, as
it was abolished two years later. At last, in 1703, he received what
he had before vainly sought, and he was appointed to the Savilian
chair.

His observations of the eclipse of the sun, which occurred in 1715,
added greatly to Halley's reputation. This phenomenon excited
special attention, inasmuch as it was the first total eclipse of the
sun which had been visible in London since the year 1140. Halley
undertook the necessary calculations, and predicted the various
circumstances with a far higher degree of precision than the official
announcement. He himself observed the phenomenon from the Royal
Society's rooms, and he minutely describes the outer atmosphere of
the sun, now known as the corona; without, however, offering an
opinion as to whether it was a solar or a lunar appendage.

At last Halley was called to the dignified office which he of all men
was most competent to fill. On February 9th, 1720, he was appointed
Astronomer Royal in succession to Flamsteed. He found things at the
Royal Observatory in a most unsatisfactory state. Indeed, there were
no instruments, nor anything else that was movable; for such things,
being the property of Flamsteed, had been removed by his widow, and
though Halley attempted to purchase from that lady some of the
instruments which his predecessor had employed, the unhappy personal
differences which had existed between him and Flamsteed, and which,
as we have already seen, prevented his election as Savilian Professor
of Astronomy, proved a bar to the negotiation. Greenwich Observatory
wore a very different appearance in those days, from that which the
modern visitor, who is fortunate enough to gain admission, may now
behold. Not only did Halley find it bereft of instruments, we learn
besides that he had no assistants, and was obliged to transact the
whole business of the establishment single-handed.

In 1721, however, he obtained a grant of 500 pounds from the Board of
Ordnance, and accordingly a transit instrument was erected in the
same year. Some time afterwards he procured an eight-foot quadrant,
and with these instruments, at the age of sixty-four, he commenced a
series of observations on the moon. He intended, if his life was
spared, to continue his observations for a period of eighteen years,
this being, as astronomers know, a very important cycle in connection
with lunar movements. The special object of this vast undertaking
was to improve the theory of the moon's motion, so that it might
serve more accurately to determine longitudes at sea. This
self-imposed task Halley lived to carry to a successful termination,
and the tables deduced from his observations, and published after his
death, were adopted almost universally by astronomers, those of the
French nation being the only exception.

Throughout his life Halley had been singularly free from illness of
every kind, but in 1737 he had a stroke of paralysis. Notwithstanding
this, however, he worked diligently at his telescope till 1739, after
which his health began rapidly to give way. He died on January 14th,
1742, in the eighty-sixth year of his age, retaining his mental
faculties to the end. He was buried in the cemetery of the church of
Lee in Kent, in the same grave as his wife, who had died five years
previously. We are informed by Admiral Smyth that Pond, a later
Astronomer Royal, was afterwards laid in the same tomb.

Halley's disposition seems to have been generous and candid, and
wholly free from anything like jealousy or rancour. In person he was
rather above the middle height, and slight in build; his complexion
was fair, and he is said to have always spoken, as well as acted,
with uncommon sprightliness. In the eloge pronounced upon him at the
Paris Academie Des Sciences, of which Halley had been made a member
in 1719 it was said, "he possessed all the qualifications which were
necessary to please princes who were desirous of instruction, with a
great extent of knowledge and a constant presence of mind; his
answers were ready, and at the same time pertinent, judicious, polite
and sincere."

[PLATE: GREENWICH OBSERVATORY IN HALLEY'S TIME.]

Thus we find that Peter the Great was one of his most ardent
admirers. He consulted the astronomer on matters connected with
shipbuilding, and invited him to his own table. But Halley possessed
nobler qualifications than the capacity of pleasing Princes. He was
able to excite and to retain the love and admiration of his equals.
This was due to the warmth of his attachments, the unselfishness of
his devotion to his friends, and to a vein of gaiety and good-humour
which pervaded all his conversation.




BRADLEY.


James Bradley was descended from an ancient family in the county of
Durham. He was born in 1692 or 1693, at Sherbourne, in
Gloucestershire, and was educated in the Grammar School at
Northleach. From thence he proceeded in due course to Oxford, where
he was admitted a commoner at Balliol College, on March 15th, 1711.
Much of his time, while an undergraduate, was passed in Essex with
his maternal uncle, the Rev. James Pound, who was a well-known man of
science and a diligent observer of the stars. It was doubtless by
intercourse with his uncle that young Bradley became so expert in the
use of astronomical instruments, but the immortal discoveries he
subsequently made show him to have been a born astronomer.

The first exhibition of Bradley's practical skill seems to be
contained in two observations which he made in 1717 and 1718. They
have been published by Halley, whose acuteness had led him to
perceive the extraordinary scientific talents of the young
astronomer. Another illustration of the sagacity which Bradley
manifested, even at the very commencement of his astronomical career,
is contained in a remark of Halley's, who says: "Dr. Pound and his
nephew, Mr. Bradley, did, myself being present, in the last
opposition of the sun and Mars this way demonstrate the extreme
minuteness of the sun's parallax, and that it was not more than
twelve seconds nor less than nine seconds." To make the significance
of this plain, it should be observed that the determination of the
sun's parallax is equivalent to the determination of the distance
from the earth to the sun. At the time of which we are now writing,
this very important unit of celestial measurement was only very
imperfectly known, and the observations of Pound and Bradley may be
interpreted to mean that, from their observations, they had come to
the conclusion that the distance from the earth to the sun must be
more than 94 millions of miles, and less than 125 millions. We now,
of course, know that they were not exactly right, for the true
distance of the sun is about 93 millions of miles. We cannot,
however, but think that it was a very remarkable approach for the
veteran astronomer and his brilliant nephew to make towards the
determination of a magnitude which did not become accurately known
till fifty years later.

Among the earliest parts of astronomical work to which Bradley's
attention was directed, were the eclipses of Jupiter's satellites.
These phenomena are specially attractive inasmuch as they can be so
readily observed, and Bradley found it extremely interesting to
calculate the times at which the eclipses should take place, and then
to compare his observations with the predicted times. From the
success that he met with in this work, and from his other labours,
Bradley's reputation as an astronomer increased so greatly that on
November the 6th, 1718, he was elected a Fellow of the Royal Society.

Up to this time the astronomical investigations of Bradley had been
more those of an amateur than of a professional astronomer, and as it
did not at first seem likely that scientific work would lead to any
permanent provision, it became necessary for the youthful astronomer
to choose a profession. It had been all along intended that he
should enter the Church, though for some reason which is not told us,
he did not take orders as soon as his age would have entitled him to
do so. In 1719, however, the Bishop of Hereford offered Bradley the
Vicarage of Bridstow, near Ross, in Monmouthshire, and on July 25th,
1720, he having then taken priest's orders, was duly instituted in
his vicarage. In the beginning of the next year, Bradley had some
addition to his income from the proceeds of a Welsh living, which,
being a sinecure, he was able to hold with his appointment at
Bridstow. It appears, however, that his clerical occupations were
not very exacting in their demands upon his time, for he was still
able to pay long and often-repeated visits to his uncle at
Wandsworth, who, being himself a clergyman, seems to have received
occasional assistance in his ministerial duties from his astronomical
nephew.

The time, however, soon arrived when Bradley was able to make a
choice between continuing to exercise his profession as a divine, or
devoting himself to a scientific career. The Savilian Professorship
of Astronomy in the University of Oxford became vacant by the death
of Dr. John Keill. The statutes forbade that the Savilian Professor
should also hold a clerical appointment, and Mr. Pound would
certainly have been elected to the professorship had he consented to
surrender his preferments in the Church. But Pound was unwilling to
sacrifice his clerical position, and though two or three other
candidates appeared in the field, yet the talents of Bradley were so
conspicuous that he was duly elected, his willingness to resign the
clerical profession having been first ascertained.

There can be no doubt that, with such influential friends as Bradley
possessed, he would have made great advances had he adhered to his
profession as a divine. Bishop Hoadly, indeed, with other marks of
favour, had already made the astronomer his chaplain. The engrossing
nature of Bradley's interest in astronomy decided him, however, to
sacrifice all other prospects in comparison with the opening afforded
by the Savilian Professorship. It was not that Bradley found himself
devoid of interest in clerical matters, but he felt that the true
scope for such abilities as he possessed would be better found in the
discharge of the scientific duties of the Oxford chair than in the
spiritual charge of a parish. On April the 26th, 1722, Bradley read
his inaugural lecture in that new position on which he was destined
to confer such lustre.

It must, of course, be remembered that in those early days the art of
constructing the astronomical telescope was very imperfectly
understood. The only known method for getting over the peculiar
difficulties presented in the construction of the refracting
telescope, was to have it of the most portentous length. In fact,
Bradley made several of his observations with an instrument of two
hundred and twelve feet focus. In such a case, no tube could be
used, and the object glass was merely fixed at the top of a high
pole. Notwithstanding the inconvenience and awkwardness of such an
instrument, Bradley by its means succeeded in making many careful
measurements. He observed, for example, the transit of Mercury over
the sun's disc, on October 9th, 1723; he also observed the dimensions
of the planet Venus, while a comet which Halley discovered on October
the 9th, 1723, was assiduously observed at Wanstead up to the middle
of the ensuing month. The first of Bradley's remarkable
contributions to the "Philosophical Transactions" relates to this
comet, and the extraordinary amount of work that he went through in
connection therewith may be seen from an examination of his book of
Calculations which is still extant.

The time was now approaching when Bradley was to make the first of
those two great discoveries by which his name has acquired a lustre
that has placed him in the very foremost rank of astronomical
discoverers. As has been often the case in the history of science,
the first of these great successes was attained while he was pursuing
a research intended for a wholly different purpose. It had long been
recognised that as the earth describes a vast orbit, nearly two
hundred million miles in diameter, in its annual journey round the
sun, the apparent places of the stars should alter, to some extent,
in correspondence with the changes in the earth's position. The
nearer the star the greater the shift in its apparent place on the
heavens, which must arise from the fact that it was seen from
different positions in the earth's orbit. It had been pointed out
that these apparent changes in the places of the stars, due to the
movement of the earth, would provide the means of measuring the
distances of the stars. As, however, these distances are enormously
great in comparison with the orbit which the earth describes around
the sun, the attempt to determine the distances of the stars by the
shift in their positions had hitherto proved ineffectual. Bradley
determined to enter on this research once again; he thought that by
using instruments of greater power, and by making measurements of
increased delicacy, he would be able to perceive and to measure
displacements which had proved so small as to elude the skill of the
other astronomers who had previously made efforts in the same
direction. In order to simplify the investigation as much as
possible, Bradley devoted his attention to one particular star, Beta
Draconis, which happened to pass near his zenith. The object of
choosing a star in this position was to avoid the difficulties which
would be introduced by refraction had the star occupied any other
place in the heavens than that directly overhead.

We are still able to identify the very spot on which the telescope
stood which was used in this memorable research. It was erected at
the house then occupied by Molyneux, on the western extremity of Kew
Green. The focal length was 24 feet 3 inches, and the eye-glass was
3 and a half feet above the ground floor. The instrument was first
set up on November 26th, 1725. If there had been any appreciable
disturbance in the place of Beta Draconis in consequence of the
movement of the earth around the sun, the star must appear to have
the smallest latitude when in conjunction with the sun, and the
greatest when in opposition. The star passed the meridian at noon in
December, and its position was particularly noticed by Molyneux on
the third of that month. Any perceptible displacement by
parallax--for so the apparent change in position, due to the earth's
motion, is called--would would have made the star shift towards the
north. Bradley, however, when observing it on the 17th, was
surprised to find that the apparent place of the star, so far from
shifting towards the north, as they had perhaps hoped it would, was
found to lie a little more to the south than when it was observed
before. He took extreme care to be sure that there was no mistake in
his observation, and, true astronomer as he was, he scrutinized with
the utmost minuteness all the circumstances of the adjustment of his
instruments. Still the star went to the south, and it continued so
advancing in the same direction until the following March, by which
time it had moved no less than twenty seconds south from the place
which it occupied when the first observation was made. After a brief
pause, in which no apparent movement was perceptible, the star by the
middle of April appeared to be returning to the north. Early in June
it reached the same distance from the zenith which it had in
December. By September the star was as much as thirty-nine seconds
more to the north than it had been in March, then it returned towards
the south, regaining in December the same situation which it had
occupied twelve months before.

This movement of the star being directly opposite to the movements
which would have been the consequence of parallax, seemed to show
that even if the star had any parallax its effects upon the apparent
place were entirely masked by a much larger motion of a totally
different description. Various attempts were made to account for the
phenomenon, but they were not successful. Bradley accordingly
determined to investigate the whole subject in a more thorough
manner. One of his objects was to try whether the same movements
which he had observed in one star were in any similar degree
possessed by other stars. For this purpose he set up a new
instrument at Wanstead, and there he commenced a most diligent
scrutiny of the apparent places of several stars which passed at
different distances from the zenith. He found in the course of this
research that other stars exhibited movements of a similar
description to those which had already proved so perplexing. For a
long time the cause of these apparent movements seemed a mystery. At
last, however, the explanation of these remarkable phenomena dawned
upon him, and his great discovery was made.

One day when Bradley was out sailing he happened to remark that every
time the boat was laid on a different tack the vane at the top of the
boat's mast shifted a little, as if there had been a slight change in
the direction of the wind. After he had noticed this three or four
times he made a remark to the sailors to the effect that it was very
strange the wind should always happen to change just at the moment
when the boat was going about. The sailors, however, said there had
been no change in the wind, but that the alteration in the vane was
due to the fact that the boat's course had been altered. In fact,
the position of the vane was determined both by the course of the
boat and the direction of the wind, and if either of these were
altered there would be a corresponding change in the direction of the
vane. This meant, of course, that the observer in the boat which was
moving along would feel the wind coming from a point different from
that in which the wind appeared to be blowing when the boat was at
rest, or when it was sailing in some different direction. Bradley's
sagacity saw in this observation the clue to the Difficulty which had
so long troubled him.

It had been discovered before the time of Bradley that the passage of
light through space is not an instantaneous phenomenon. Light
requires time for its journey. Galileo surmised that the sun may
have reached the horizon before we see it there, and it was indeed
sufficiently obvious that a physical action, like the transmission of
light, could hardly take place without requiring some lapse of time.
The speed with which light actually travelled was, however, so rapid
that its determination eluded all the means of experimenting which
were available in those days. The penetration of Roemer had
previously detected irregularities in the observed times of the
eclipses of Jupiter's satellites, which were undoubtedly due to the
interval which light required for stretching across the
interplanetary spaces. Bradley argued that as light can only travel
with a certain speed, it may in a measure be regarded like the wind,
which he noticed in the boat. If the observer were at rest, that is
to say, if the earth were a stationary object, the direction in which
the light actually does come would be different from that in which it
appears to come when the earth is in motion. It is true that the
earth travels but eighteen miles a second, while the velocity with
which light is borne along attains to as much as 180,000 miles a
second. The velocity of light is thus ten thousand times greater
than the speed of the earth. But even though the wind blew ten
thousand times faster than the speed with which the boat was sailing
there would still be some change, though no doubt a very small
change, in the position of the vane when the boat was in progress
from the position it would have if the boat were at rest. It
therefore occurred to this most acute of astronomers that when the
telescope was pointed towards a star so as to place it apparently in
the centre of the field of view, yet it was not generally the true
position of the star. It was not, in fact, the position in which the
star would have been observed had the earth been at rest. Provided
with this suggestion, he explained the apparent movements of the
stars by the principle known as the "aberration of light." Every
circumstance was accounted for as a consequence of the relative
movements of the earth and of the light from the star. This
beautiful discovery not only established in the most forcible manner
the nature of the movement of light; not only did it illustrate the
truth of the Copernican theory which asserted that the earth revolved
around the sun, but it was also of the utmost importance in the
improvement of practical astronomy. Every observer now knows that,
generally speaking, the position which the star appears to have is
not exactly the position in which the star does actually lie. The
observer is, however, able, by the application of the principles
which Bradley so clearly laid down, to apply to an observation the
correction which is necessary to obtain from it the true place in
which the object is actually situated. This memorable achievement at
once conferred on Bradley the highest astronomical fame. He tested
his discovery in every way, but only to confirm its truth in the most
complete manner.

Halley, the Astronomer Royal, died on the 14th, January, 1742, and
Bradley was immediately pointed out as his successor. He was
accordingly appointed Astronomer Royal in February, 1742. On first
taking up his abode at Greenwich he was unable to conduct his
observations owing to the wretched condition in which he found the
instruments. He devoted himself, however, assiduously to their
repair, and his first transit observation is recorded on the 25th
July, 1742. He worked with such energy that on one day it appears
that 255 transit observations were taken by himself alone, and in
September, 1747, he had completed the series of observations which
established his second great discovery, the nutation of the earth's
axis. The way in which he was led to the detection of the nutation
is strikingly illustrative of the extreme care with which Bradley
conducted his observations. He found that in the course of a
twelve-month, when the star had completed the movement which was due
to aberration, it did not return exactly to the same position which
it had previously occupied. At first he thought this must be due to
some instrumental error, but after closer examination and repeated
study of the effect as manifested by many different stars, he came to
the conclusion that its origin must be sought in some quite different
source. The fact is that a certain change takes place in the
apparent position of the stars which is not due to the movement of
the star itself, but is rather to be attributed to changes in the
points from which the star's positions are measured.

We may explain the matter in this way. As the earth is not a sphere,
but has protuberant parts at the equator, the attraction of the moon
exercises on those protuberant parts a pulling effect which
continually changes the direction of the earth's axis, and
consequently the position of the pole must be in a state of incessant
fluctuation. The pole to which the earth's axis points on the sky
is, therefore, slowly changing. At present it happens to lie near
the Pole Star, but it will not always remain there. It describes a
circle around the pole of the Ecliptic, requiring about 25,000 years
for a complete circuit. In the course of its progress the pole will
gradually pass now near one star and now near another, so that many
stars will in the lapse of ages discharge the various functions which
the present Pole Star does for us. In about 12,000 years, for
instance, the pole will have come near the bright star, Vega. This
movement of the pole had been known for ages. But what Bradley
discovered was that the pole, instead of describing an uniform
movement as had been previously supposed, followed a sinuous course
now on one side and now on the other of its mean place. This he
traced to the fluctuations of the moon's orbit, which undergoes a
continuous change in a period of nineteen years. Thus the efficiency
with which the moon acts on the protuberant mass of the earth varies,
and thus the pole is caused to oscillate.

This subtle discovery, if perhaps in some ways less impressive than
Bradley's earlier achievements of the detection of the aberration of
light, is regarded by astronomers as testifying even in a higher
degree to his astonishing care and skill as an observer, and justly
entitles him to a unique place among the astronomers whose
discoveries have been effected by consummate practical skill in the
use of astronomical instruments.

Of Bradley's private or domestic life there is but little to tell. In
1744, soon after he became Astronomer Royal, he married a daughter of
Samuel Peach, of Chalford, in Gloucestershire. There was but one
child, a daughter, who became the wife of her cousin, Rev. Samuel
Peach, rector of Compton, Beauchamp, in Berkshire.

Bradley's last two years of life were clouded by a melancholy
depression of spirits, due to an apprehension that he should survive
his rational faculties. It seems, however, that the ill he dreaded
never came upon him, for he retained his mental powers to the close.
He died on 13th July, 1762, aged seventy, and was buried at
Michinghamton.




WILLIAM HERSCHEL.


William Herschel, one of the greatest astronomers that has ever
lived, was born at Hanover, on the 15th November, 1738. His father,
Isaac Herschel, was a man evidently of considerable ability, whose
life was devoted to the study and practice of music, by which he
earned a somewhat precarious maintenance. He had but few worldly
goods to leave to his children, but he more than compensated for this
by bequeathing to them a splendid inheritance of genius. Touches of
genius were, indeed, liberally scattered among the members of Isaac's
large family, and in the case of his forth child, William, and of a
sister several years younger, it was united with that determined
perseverance and rigid adherence to principle which enabled genius to
fulfil its perfect work.

A faithful chronicler has given us an interesting account of the way
in which Isaac Herschel educated his sons; the narrative is taken
from the recollections of one who, at the time we are speaking of,
was an unnoticed little girl five or six years old. She writes:--

"My brothers were often introduced as solo performers and assistants
in the orchestra at the Court, and I remember that I was frequently
prevented from going to sleep by the lively criticisms on music on
coming from a concert. Often I would keep myself awake that I might
listen to their animating remarks, for it made me so happy to see
them so happy. But generally their conversation would branch out on
philosophical subjects, when my brother William and my father often
argued with such warmth that my mother's interference became
necessary, when the names--Euler, Leibnitz, and Newton--sounded
rather too loud for the repose of her little ones, who had to be at
school by seven in the morning." The child whose reminiscences are
here given became afterwards the famous Caroline Herschel. The
narrative of her life, by Mrs. John Herschel, is a most interesting
book, not only for the account it contains of the remarkable woman
herself, but also because it provides the best picture we have of the
great astronomer to whom Caroline devoted her life.

This modest family circle was, in a measure, dispersed at the
outbreak of the Seven Years' War in 1756. The French proceeded to
invade Hanover, which, it will be remembered, belonged at this time
to the British dominions. Young William Herschel had already
obtained the position of a regular performer in the regimental band
of the Hanoverian Guards, and it was his fortune to obtain some
experience of actual warfare in the disastrous battle of Hastenbeck.
He was not wounded, but he had to spend the night after the battle in
a ditch, and his meditations on the occasion convinced him that
soldiering was not the profession exactly adapted to his tastes. We
need not attempt to conceal the fact that he left his regiment by the
very simple but somewhat risky process of desertion. He had, it
would seem, to adopt disguises to effect his escape. At all events,
by some means he succeeded in eluding detection and reached England
in safety. It is interesting to have learned on good authority that
many years after this offence was committed it was solemnly
forgiven. When Herschel had become the famous astronomer, and as
such visited King George at Windsor, the King at their first meeting
handed to him his pardon for deserting from the army, written out in
due form by his Majesty himself.

It seems that the young musician must have had some difficulty in
providing for his maintenance during the first few years of his abode
in England. It was not until he had reached the age of twenty-two
that he succeeded in obtaining any regular appointment. He was then
made Instructor of Music to the Durham Militia. Shortly afterwards,
his talents being more widely recognised, he was appointed as
organist at the parish church at Halifax, and his prospects in life
now being fairly favourable, and the Seven Years' War being over, he
ventured to pay a visit to Hanover to see his father. We can imagine
the delight with which old Isaac Herschel welcomed his promising son,
as well as his parental pride when a concert was given at which some
of William's compositions were performed. If the father was so
intensely gratified on this occasion, what would his feelings have
been could he have lived to witness his son's future career? But
this pleasure was not to be his, for he died many years before
William became an astronomer.

In 1766, about a couple of years after his return to England from
This visit to his old home, we find that Herschel had received a
further promotion to be organist in the Octagon Chapel, at Bath.
Bath was then, as now, a highly fashionable resort, and many notable
personages patronised the rising musician. Herschel had other points
in his favour besides his professional skill; his appearance was
good, his address was prepossessing, and even his nationality was a
distinct advantage, inasmuch as he was a Hanoverian in the reign of
King George the Third. On Sundays he played the organ, to the great
delight of the congregation, and on week-days he was occupied by
giving lessons to private pupils, and in preparation for public
performances. He thus came to be busily employed, and seems to have
been in the enjoyment of comfortable means.

[PLATE: 7, NEW KING STREET, BATH, WHERE HERSCHEL LIVED.]

From his earliest youth Herschel had been endowed with that
invaluable characteristic, an eager curiosity for knowledge. He was
naturally desirous of perfecting himself in the theory of music, and
thus he was led to study mathematics. When he had once tasted the
charms of mathematics, he saw vast regions of knowledge unfolded
before him, and in this way he was induced to direct his attention to
astronomy. More and more this pursuit seems to have engrossed his
attention, until at last it had become an absorbing passion. Herschel
was, however, still obliged, by the exigency of procuring a
livelihood, to give up the best part of his time to his profession as
a musician; but his heart was eagerly fixed on another science, and
every spare moment was steadily devoted to astronomy. For many
years, however, he continued to labour at his original calling, nor
was it until he had attained middle age and become the most
celebrated astronomer of the time, that he was enabled to concentrate
his attention exclusively on his favourite pursuit.

It was with quite a small telescope which had been lent him by a
friend that Herschel commenced his career as an observer. However,
he speedily discovered that to see all he wanted to see, a telescope
of far greater power would be necessary, and he determined to obtain
this more powerful instrument by actually making it with his own
hands. At first it may seem scarcely likely that one whose
occupation had previously been the study and practice of music should
meet with success in so technical an operation as the construction of
a telescope. It may, however, be mentioned that the kind of
instrument which Herschel designed to construct was formed on a very
different principle from the refracting telescopes with which we are
ordinarily familiar. His telescope was to be what is termed a
reflector. In this type of instrument the optical power is obtained
by the use of a mirror at the bottom of the tube, and the astronomer
looks down through the tube TOWARDS HIS MIRROR and views the
reflection of the stars with its aid. Its efficiency as a telescope
depends entirely on the accuracy with which the requisite form has
been imparted to the mirror. The surface has to be hollowed out a
little, and this has to be done so truly that the slightest deviation
from good workmanship in this essential particular would be fatal to
efficient performance of the telescope.

[PLATE: WILLIAM HERSCHEL.]

The mirror that Herschel employed was composed of a mixture of two
parts of copper to one of tin; the alloy thus obtained is an
intensely hard material, very difficult to cast into the proper
shape, and very difficult to work afterwards. It possesses, however,
when polished, a lustre hardly inferior to that of silver itself.
Herschel has recorded hardly any particulars as to the actual process
by which he cast and figured his reflectors. We are however, told
that in later years, after his telescopes had become famous, he made
a considerable sum of money by the manufacture and sale of great
instruments. Perhaps this may be the reason why he never found it
expedient to publish any very explicit details as to the means by
which his remarkable successes were obtained.

[PLATE: CAROLINE HERSCHEL.]

Since Herschel's time many other astronomers, notably the late Earl
of Rosse, have experimented in the same direction, and succeeded in
making telescopes certainly far greater, and probably more perfect,
than any which Herschel appears to have constructed. The details of
these later methods are now well known, and have been extensively
practised. Many amateurs have thus been able to make telescopes by
following the instructions so clearly laid down by Lord Rosse and the
other authorities. Indeed, it would seem that any one who has a
little mechanical skill and a good deal of patience ought now to
experience no great difficulty in constructing a telescope quite as
powerful as that which first brought Herschel into fame. I should,
however, mention that in these modern days the material generally
used for the mirror is of a more tractable description than the
metallic substance which was employed by Herschel and by Lord Rosse.
A reflecting telescope of the present day would not be fitted with a
mirror composed of that alloy known as speculum metal, whose
composition I have already mentioned. It has been found more
advantageous to employ a glass mirror carefully figured and polished,
just as a metallic mirror would have been, and then to impart to the
polished glass surface a fine coating of silver laid down by a
chemical process. The silver-on-glass mirrors are so much lighter
and so much easier to construct that the more old-fashioned metallic
mirrors may be said to have fallen into almost total disuse. In one
respect however, the metallic mirror may still claim the advantage
that, with reasonable care, its surface will last bright and
untarnished for a much longer period than can the silver film on the
glass. However, the operation of re-silvering a glass has now become
such a simple one that the advantage this indicates is not relatively
so great as might at first be supposed.

[PLATE: STREET VIEW, HERSCHEL HOUSE, SLOUGH.]

Some years elapsed after Herschel's attention had been first directed
to astronomy, before he reaped the reward of his exertions in the
possession of a telescope which would adequately reveal some of the
glories of the heavens. It was in 1774, when the astronomer was
thirty-six years old, that he obtained his first glimpse of the stars
with an instrument of his own construction. Night after night, as
soon as his musical labours were ended, his telescopes were brought
out, sometimes into the small back garden of his house at Bath, and
sometimes into the street in front of his hall-door. It was
characteristic of him that he was always endeavouring to improve his
apparatus. He was incessantly making fresh mirrors, or trying new
lenses, or combinations of lenses to act as eye-pieces, or projecting
alterations in the mounting by which the telescope was supported.
Such was his enthusiasm that his house, we are told, was incessantly
littered with the usual indications of the workman's presence,
greatly to the distress of his sister, who, at this time, had come to
take up her abode with him and look after his housekeeping. Indeed,
she complained that in his astronomical ardour he sometimes omitted
to take off, before going into his workshop, the beautiful lace
ruffles which he wore while conducting a concert, and that
consequently they became soiled with the pitch employed in the
polishing of his mirrors.

This sister, who occupies such a distinct place in scientific history
is the same little girl to whom we have already referred. From her
earliest days she seems to have cherished a passionate admiration for
her brilliant brother William. It was the proudest delight of her
childhood as well as of her mature years to render him whatever
service she could; no man of science was ever provided with a more
capable or energetic helper than William Herschel found in this
remarkable woman. Whatever work had to be done she was willing to
bear her share in it, or even to toil at it unassisted if she could
be allowed to do so. She not only managed all his domestic affairs,
but in the grinding of the lenses and in the polishing of the mirrors
she rendered every assistance that was possible. At one stage of the
very delicate operation of fashioning a reflector, it is necessary
for the workman to remain with his hand on the mirror for many hours
in succession. When such labours were in progress, Caroline used to
sit by her brother, and enliven the time by reading stories aloud,
sometimes pausing to feed him with a spoon while his hands were
engaged on the task from which he could not desist for a moment.

When mathematical work had to be done Caroline was ready for it; she
had taught herself sufficient to enable her to perform the kind of
calculations, not, perhaps, very difficult ones, that Herschel's work
required; indeed, it is not too much to say that the mighty life-work
which this man was enabled to perform could never have been accomplished
had it not been for the self-sacrifice of this ever-loving and faithful
sister. When Herschel was at the telescope at night, Caroline sat by
him at her desk, pen in hand, ready to write down the notes of the
observations as they fell from her brother's lips. This was no
insignificant toil. The telescope was, of course, in the open air,
and as Herschel not unfrequently continued his observations throughout
the whole of a long winter's night, there were but few women who could
have accomplished the task which Caroline so cheerfully executed.
From dusk till dawn, when the sky was clear, were Herschel's observing
hours, and what this sometimes implied we can realise from the fact
that Caroline assures us she had sometimes to desist because the ink
had actually frozen in her pen. The night's work over, a brief rest
was taken, and while William had his labours for the day to attend to,
Caroline carefully transcribed the observations made during the night
before, reduced all the figures and prepared everything in readiness
for the observations that were to follow on the ensuing evening.

But we have here been anticipating a little of the future which lay
before the great astronomer; we must now revert to the history of his
early work, at Bath, in 1774, when Herschel's scrutiny of the skies
first commenced with an instrument of his own manufacture. For some
few years he did not attain any result of importance; no doubt he
made a few interesting observations, but the value of the work during
those years is to be found, not in any actual discoveries which were
accomplished, but in the practice which Herschel obtained in the use
of his instruments. It was not until 1782 that the great achievement
took place by which he at once sprang into fame.

[PLATE: GARDEN VIEW, HERSCHEL HOUSE, SLOUGH.]

It is sometimes said that discoveries are made by accident, and, no
doubt, to a certain extent, but only, I fancy to a very small extent,
this statement may be true. It is, at all events, certain that such
lucky accidents do not often fall to the lot of people unless those
people have done much to deserve them. This was certainly the case
with Herschel. He appears to have formed a project for making a
close examination of all the stars above a certain magnitude. Perhaps
he intended to confine this research to a limited region of the sky,
but, at all events, he seems to have undertaken the work
energetically and systematically. Star after star was brought to the
centre of the field of view of his telescope, and after being
carefully examined was then displaced, while another star was brought
forward to be submitted to the same process. In the great majority
of cases such observations yield really nothing of importance; no
doubt even the smallest star in the heavens would, if we could find
out all about it, reveal far more than all the astronomers that were
ever on the earth have even conjectured. What we actually learn
about the great majority of stars is only information of the most
meagre description. We see that the star is a little point of light,
and we see nothing more.

In the great review which Herschel undertook he doubtless examined
hundreds, or perhaps thousands of stars, allowing them to pass away
without note or comment. But on an ever-memorable night in March,
1782, it happened that he was pursuing his task among the stars in
the Constellation of Gemini. Doubtless, on that night, as on so many
other nights, one star after another was looked at only to be
dismissed, as not requiring further attention. On the evening in
question, however, one star was noticed which, to Herschel's acute
vision seemed different from the stars which in so many thousands are
strewn over the sky. A star properly so called appears merely as a
little point of light, which no increase of magnifying power will
ever exhibit with a true disc. But there was something in the
star-like object which Herschel saw that immediately arrested his
attention and made him apply to it a higher magnifying power. This
at once disclosed the fact that the object possessed a disc, that is,
a definite, measurable size, and that it was thus totally different
from any one of the hundreds and thousands of stars which exist
elsewhere in space. Indeed, we may say at once that this little
object was not a star at all; it was a planet. That such was its
true nature was confirmed, after a little further observation, by
perceiving that the body was shifting its place on the heavens
relatively to the stars. The organist at the Octagon Chapel at Bath
had, therefore, discovered a new planet with his home-made telescope.

I can imagine some one will say, "Oh, there was nothing so wonderful
in that; are not planets always being discovered? Has not M. Palisa,
for instance, discovered about eighty of such objects, and are there
not hundreds of them known nowadays?" This is, to a certain extent,
quite true. I have not the least desire to detract from the credit
of those industrious and sharp-sighted astronomers who have in modern
days brought so many of these little objects within our cognisance. I
think, however, it must be admitted that such discoveries have a
totally different importance in the history of science from that
which belongs to the peerless achievement of Herschel. In the first
place, it must be observed that the minor planets now brought to
light are so minute that if a score of them were rolled to together
into one lump it would not be one-thousandth part of the size of the
grand planet discovered by Herschel. This is, nevertheless, not the
most important point. What marks Herschel's achievement as one of
the great epochs in the history of astronomy is the fact that the
detection of Uranus was the very first recorded occasion of the
discovery of any planet whatever.

For uncounted ages those who watched the skies had been aware of the
existence of the five old planets--Jupiter, Mercury, Saturn, Venus,
and Mars. It never seems to have occurred to any of the ancient
philosophers that there could be other similar objects as yet
undetected over and above the well-known five. Great then was the
astonishment of the scientific world when the Bath organist announced
his discovery that the five planets which had been known from all
antiquity must now admit the company of a sixth. And this sixth
planet was, indeed, worthy on every ground to be received into the
ranks of the five glorious bodies of antiquity. It was, no doubt,
not so large as Saturn, it was certainly very much less than Jupiter;
on the other hand, the new body was very much larger than Mercury,
than Venus, or than Mars, and the earth itself seemed quite an
insignificant object in comparison with this newly added member of
the Solar System. In one respect, too, Herschel's new planet was a
much more imposing object than any one of the older bodies; it swept
around the sun in a majestic orbit, far outside that of Saturn, which
had previously been regarded as the boundary of the Solar System, and
its stately progress required a period of not less than eighty-one
years.

King George the Third, hearing of the achievements of the Hanoverian
musician, felt much interest in his discovery, and accordingly
Herschel was bidden to come to Windsor, and to bring with him the
famous telescope, in order to exhibit the new planet to the King, and
to tell his Majesty all about it. The result of the interview was to
give Herschel the opportunity for which he had so long wished, of
being able to devote himself exclusively to science for the rest of
his life.

[PLATE: VIEW OF THE OBSERVATORY, HERSCHEL HOUSE, SLOUGH.]

The King took so great a fancy to the astronomer that he first, as I
have already mentioned, duly pardoned his desertion from the army,
some twenty-five years previously. As a further mark of his favour
the King proposed to confer on Herschel the title of his Majesty's
own astronomer, to assign to him a residence near Windsor, to provide
him with a salary, and to furnish such funds as might be required for
the erection of great telescopes, and for the conduct of that mighty
scheme of celestial observation on which Herschel was so eager to
enter. Herschel's capacity for work would have been much impaired if
he had been deprived of the aid of his admirable sister, and to her,
therefore, the King also assigned a salary, and she was installed as
Herschel's assistant in his new post.

With his usually impulsive determination, Herschel immediately cut
himself free from all his musical avocations at Bath, and at once
entered on the task of making and erecting the great telescopes at
Windsor. There, for more than thirty years, he and his faithful
sister prosecuted with unremitting ardour their nightly scrutiny of
the sky. Paper after paper was sent to the Royal Society, describing
the hundreds, indeed the thousands, of objects such as double stars;
nebulae and clusters, which were first revealed to human gaze during
those midnight vigils. To the end of his life he still continued at
every possible opportunity to devote himself to that beloved pursuit
in which he had such unparalleled success. No single discovery of
Herschel's later years was, however, of the same momentous
description as that which first brought him to fame.

[PLATE: THE 40-FOOT TELESCOPE AS IT WAS IN THE YEAR 1863, HERSCHEL
HOUSE, SLOUGH.]

Herschel married when considerably advanced in life and he lived to
enjoy the indescribable pleasure of finding that his only son,
afterwards Sir John Herschel, was treading worthily in his footsteps,
and attaining renown as an astronomical observer, second only to that
of his father. The elder Herschel died in 1822, and his illustrious
sister Caroline then returned to Hanover, where she lived for many
years to receive the respect and attention which were so justly
hers. She died at a very advanced age in 1848.




LAPLACE.


The author of the "Mecanique Celeste" was born at Beaumont-en-Auge,
near Honfleur, in 1749, just thirteen years later than his renowned
friend Lagrange. His father was a farmer, but appears to have been
in a position to provide a good education for a son who seemed
promising. Considering the unorthodoxy in religious matters which is
generally said to have characterized Laplace in later years, it is
interesting to note that when he was a boy the subject which first
claimed his attention was theology. He was, however, soon introduced
to the study of mathematics, in which he presently became so
proficient, that while he was still no more than eighteen years old,
he obtained employment as a mathematical teacher in his native town.

Desiring wider opportunities for study and for the acquisition of
fame than could be obtained in the narrow associations of provincial
life, young Laplace started for Paris, being provided with letters of
introduction to D'Alembert, who then occupied the most prominent
position as a mathematician in France, if not in the whole of
Europe. D'Alembert's fame was indeed so brilliant that Catherine the
Great wrote to ask him to undertake the education of her Son, and
promised the splendid income of a hundred thousand francs. He
preferred, however, a quiet life of research in Paris, although there
was but a modest salary attached to his office. The philosopher
accordingly declined the alluring offer to go to Russia, even though
Catherine wrote again to say: "I know that your refusal arises from
your desire to cultivate your studies and your friendships in quiet.
But this is of no consequence: bring all your friends with you, and I
promise you that both you and they shall have every accommodation in
my power." With equal firmness the illustrious mathematician
resisted the manifold attractions with which Frederick the Great
sought to induce him, to take up his residence at Berlin. In reading
of these invitations we cannot but be struck at the extraordinary
respect which was then paid to scientific distinction. It must be
remembered that the discoveries of such a man as D'Alembert were
utterly incapable of being appreciated except by those who possessed
a high degree of mathematical culture. We nevertheless find the
potentates of Russia and Prussia entreating and, as it happens,
vainly entreating, the most distinguished mathematician in France to
accept the positions that they were proud to offer him.

It was to D'Alembert, the profound mathematician, that young Laplace,
the son of the country farmer, presented his letters of
introduction. But those letters seem to have elicited no reply,
whereupon Laplace wrote to D'Alembert submitting a discussion on some
point in Dynamics. This letter instantly produced the desired
effect. D'Alembert thought that such mathematical talent as the
young man displayed was in itself the best of introductions to his
favour. It could not be overlooked, and accordingly he invited
Laplace to come and see him. Laplace, of course, presented himself,
and ere long D'Alembert obtained for the rising philosopher a
professorship of mathematics in the Military School in Paris. This
gave the brilliant young mathematician the opening for which he
sought, and he quickly availed himself of it.

Laplace was twenty-three years old when his first memoir on a
profound mathematical subject appeared in the Memoirs of the Academy
at Turin. From this time onwards we find him publishing one memoir
after another in which he attacks, and in many cases successfully
vanquishes, profound difficulties in the application of the Newtonian
theory of gravitation to the explanation of the solar system. Like
his great contemporary Lagrange, he loftily attempted problems which
demanded consummate analytical skill for their solution. The
attention of the scientific world thus became riveted on the splendid
discoveries which emanated from these two men, each gifted with
extraordinary genius.

Laplace's most famous work is, of course, the "Mecanique Celeste," in
which he essayed a comprehensive attempt to carry out the principles
which Newton had laid down, into much greater detail than Newton had
found practicable. The fact was that Newton had not only to
construct the theory of gravitation, but he had to invent the
mathematical tools, so to speak, by which his theory could be applied
to the explanation of the movements of the heavenly bodies. In the
course of the century which had elapsed between the time of Newton
and the time of Laplace, mathematics had been extensively developed.
In particular, that potent instrument called the infinitesimal
calculus, which Newton had invented for the investigation of nature,
had become so far perfected that Laplace, when he attempted to
unravel the movements of the heavenly bodies, found himself provided
with a calculus far more efficient than that which had been available
to Newton. The purely geometrical methods which Newton employed,
though they are admirably adapted for demonstrating in a general way
the tendencies of forces and for explaining the more obvious
phenomena by which the movements of the heavenly bodies are
disturbed, are yet quite inadequate for dealing with the more subtle
effects of the Law of Gravitation. The disturbances which one planet
exercises upon the rest can only be fully ascertained by the aid of
long calculation, and for these calculations analytical methods are
required.

With an armament of mathematical methods which had been perfected
since the days of Newton by the labours of two or three generations
of consummate mathematical inventors, Laplace essayed in the
"Mecanique Celeste" to unravel the mysteries of the heavens. It will
hardly be disputed that the book which he has produced is one of the
most difficult books to understand that has ever been written. In
great part, of course, this difficulty arises from the very nature of
the subject, and is so far unavoidable. No one need attempt to read
the "Mecanique Celeste" who has not been naturally endowed with
considerable mathematical aptitude which he has cultivated by years
of assiduous study. The critic will also note that there are grave
defects in Laplace's method of treatment. The style is often
extremely obscure, and the author frequently leaves great gaps in his
argument, to the sad discomfiture of his reader. Nor does it mend
matters to say, as Laplace often does say, that it is "easy to see"
how one step follows from another. Such inferences often present
great difficulties even to excellent mathematicians. Tradition
indeed tells us that when Laplace had occasion to refer to his own
book, it sometimes happened that an argument which he had dismissed
with his usual formula, "Il est facile a voir," cost the illustrious
author himself an hour or two of hard thinking before he could
recover the train of reasoning which had been omitted. But there are
certain parts of this great work which have always received the
enthusiastic admiration of mathematicians. Laplace has, in fact,
created whole tracts of science, some of which have been subsequently
developed with much advantage in the prosecution of the study of
Nature.

Judged by a modern code the gravest defect of Laplace's great work is
rather of a moral than of a mathematical nature. Lagrange and he
advanced together in their study of the mechanics of the heavens, at
one time perhaps along parallel lines, while at other times they
pursued the same problem by almost identical methods. Sometimes the
important result was first reached by Lagrange, sometimes it was
Laplace who had the good fortune to make the discovery. It would
doubtless be a difficult matter to draw the line which should exactly
separate the contributions to astronomy made by one of these
illustrious mathematicians, and the contributions made by the other.
But in his great work Laplace in the loftiest manner disdained to
accord more than the very barest recognition to Lagrange, or to any
of the other mathematicians, Newton alone excepted, who had advanced
our knowledge of the mechanism of the heavens. It would be quite
impossible for a student who confined his reading to the "Mecanique
Celeste" to gather from any indications that it contains whether the
discoveries about which he was reading had been really made by
Laplace himself or whether they had not been made by Lagrange, or by
Euler, or by Clairaut. With our present standard of morality in such
matters, any scientific man who now brought forth a work in which he
presumed to ignore in this wholesale fashion the contributions of
others to the subject on which he was writing, would be justly
censured and bitter controversies would undoubtedly arise. Perhaps
we ought not to judge Laplace by the standard of our own time, and in
any case I do not doubt that Laplace might have made a plausible
defence. It is well known that when two investigators are working at
the same subjects, and constantly publishing their results, it
sometimes becomes difficult for each investigator himself to
distinguish exactly between what he has accomplished and that which
must be credited to his rival. Laplace may probably have said to
himself that he was going to devote his energies to a great work on
the interpretation of Nature, that it would take all his time and all
his faculties, and all the resources of knowledge that he could
command, to deal justly with the mighty problems before him. He
would not allow himself to be distracted by any side issue. He could
not tolerate that pages should be wasted in merely discussing to whom
we owe each formula, and to whom each deduction from such formula is
due. He would rather endeavour to produce as complete a picture as
he possibly could of the celestial mechanics, and whether it were by
means of his mathematics alone, or whether the discoveries of others
may have contributed in any degree to the result, is a matter so
infinitesimally insignificant in comparison with the grandeur of his
subject that he would altogether neglect it. "If Lagrange should
think," Laplace might say, "that his discoveries had been unduly
appropriated, the proper course would be for him to do exactly what I
have done. Let him also write a "Mecanique Celeste," let him employ
those consummate talents which he possesses in developing his noble
subject to the utmost. Let him utilise every result that I or any
other mathematician have arrived at, but not trouble himself unduly
with unimportant historical details as to who discovered this, and
who discovered that; let him produce such a work as he could write,
and I shall heartily welcome it as a splendid contribution to our
science." Certain it is that Laplace and Lagrange continued the best
of friends, and on the death of the latter it was Laplace who was
summoned to deliver the funeral oration at the grave of his great
rival.

The investigations of Laplace are, generally speaking, of too
technical a character to make it possible to set forth any account of
them in such a work as the present. He did publish, however, one
treatise, called the "Systeme du Monde," in which, without
introducing mathematical symbols, he was able to give a general
account of the theories of the celestial movements, and of the
discoveries to which he and others had been led. In this work the
great French astronomer sketched for the first time that remarkable
doctrine by which his name is probably most generally known to those
readers of astronomical books who are not specially mathematicians.
It is in the "Systeme du Monde" that Laplace laid down the principles
of the Nebular Theory which, in modern days, has been generally
accepted by those philosophers who are competent to judge, as
substantially a correct expression of a great historical fact.

[PLATE: LAPLACE.]

The Nebular Theory gives a physical account of the origin of the
solar system, consisting of the sun in the centre, with the planets
and their attendant satellites. Laplace perceived the significance
of the fact that all the planets revolved in the same direction
around the sun; he noticed also that the movements of rotation of the
planets on their axes were performed in the same direction as that in
which a planet revolves around the sun; he saw that the orbits of the
satellites, so far at least as he knew them, revolved around their
primaries also in the same direction. Nor did it escape his
attention that the sun itself rotated on its axis in the same sense.
His philosophical mind was led to reflect that such a remarkable
unanimity in the direction of the movements in the solar system
demanded some special explanation. It would have been in the highest
degree improbable that there should have been this unanimity unless
there had been some physical reason to account for it. To appreciate
the argument let us first concentrate our attention on three
particular bodies, namely the earth, the sun, and the moon. First
the earth revolves around the sun in a certain direction, and the
earth also rotates on its axis. The direction in which the earth
turns in accordance with this latter movement might have been that in
which it revolves around the sun, or it might of course have been
opposite thereto. As a matter of fact the two agree. The moon in
its monthly revolution around the earth follows also the same
direction, and our satellite rotates on its axis in the same period
as its monthly revolution, but in doing so is again observing this
same law. We have therefore in the earth and moon four movements,
all taking place in the same direction, and this is also identical
with that in which the sun rotates once every twenty-five days. Such
a coincidence would be very unlikely unless there were some physical
reason for it. Just as unlikely would it be that in tossing a coin
five heads or five tails should follow each other consecutively. If
we toss a coin five times the chances that it will turn up all heads
or all tails is but a small one. The probability of such an event is
only one-sixteenth.

There are, however, in the solar system many other bodies besides the
three just mentioned which are animated by this common movement.
Among them are, of course, the great planets, Jupiter, Saturn, Mars,
Venus, and Mercury, and the satellites which attend on these
planets. All these planets rotate on their axes in the same
direction as they revolve around the sun, and all their satellites
revolve also in the same way. Confining our attention merely to the
earth, the sun, and the five great planets with which Laplace was
acquainted, we have no fewer than six motions of revolution and seven
motions of rotation, for in the latter we include the rotation of the
sun. We have also sixteen satellites of the planets mentioned whose
revolutions round their primaries are in the same direction. The
rotation of the moon on its axis may also be reckoned, but as to the
rotations of the satellites of the other planets we cannot speak with
any confidence, as they are too far off to be observed with the
necessary accuracy. We have thus thirty circular movements in the
solar system connected with the sun and moon and those great planets
than which no others were known in the days of Laplace. The
significant fact is that all these thirty movements take place in the
same direction. That this should be the case without some physical
reason would be just as unlikely as that in tossing a coin thirty
times it should turn up all heads or all tails every time without
exception.

We can express the argument numerically. Calculation proves that
such an event would not generally happen oftener than once out of
five hundred millions of trials. To a philosopher of Laplace's
penetration, who had made a special study of the theory of
probabilities, it seemed well-nigh inconceivable that there should
have been such unanimity in the celestial movements, unless there had
been some adequate reason to account for it. We might, indeed, add
that if we were to include all the objects which are now known to
belong to the solar system, the argument from probability might be
enormously increased in strength. To Laplace the argument appeared
so conclusive that he sought for some physical cause of the
remarkable phenomenon which the solar system presented. Thus it was
that the famous Nebular Hypothesis took its rise. Laplace devised a
scheme for the origin of the sun and the planetary system, in which
it would be a necessary consequence that all the movements should
take place in the same direction as they are actually observed to do.

Let us suppose that in the beginning there was a gigantic mass of
nebulous material, so highly heated that the iron and other
substances which now enter into the composition of the earth and
planets were then suspended in a state of vapour. There is nothing
unreasonable in such a supposition indeed, we know as a matter of
fact that there are thousands of such nebulae to be discerned at
present through our telescopes. It would be extremely unlikely that
any object could exist without possessing some motion of rotation; we
may in fact assert that for rotation to be entirety absent from the
great primeval nebula would be almost infinitely improbable. As ages
rolled on, the nebula gradually dispersed away by radiation its
original stores of heat, and, in accordance with well-known physical
principles, the materials of which it was formed would tend to
coalesce. The greater part of those materials would become
concentrated in a mighty mass surrounded by outlying uncondensed
vapours. There would, however, also be regions throughout the extent
of the nebula, in which subsidiary centres of condensation would be
found. In its long course of cooling, the nebula would, therefore,
tend ultimately to form a mighty central body with a number of
smaller bodies disposed around it. As the nebula was initially
endowed with a movement of rotation, the central mass into which it
had chiefly condensed would also revolve, and the subsidiary bodies
would be animated by movements of revolution around the central
body. These movements would be all pursued in one common direction,
and it follows, from well-known mechanical principles, that each of
the subsidiary masses, besides participating in the general
revolution around the central body, would also possess a rotation
around its axis, which must likewise be performed in the same
direction. Around the subsidiary bodies other objects still smaller
would be formed, just as they themselves were formed relatively to
the great central mass.

As the ages sped by, and the heat of these bodies became gradually
dissipated, the various objects would coalesce, first into molten
liquid masses, and thence, at a further stage of cooling, they would
assume the appearance of solid masses, thus producing the planetary
bodies such as we now know them. The great central mass, on account
of its preponderating dimensions, would still retain, for further
uncounted ages, a large quantity of its primeval heat, and would thus
display the splendours of a glowing sun. In this way Laplace was
able to account for the remarkable phenomena presented in the
movements of the bodies of the solar system. There are many other
points also in which the nebular theory is known to tally with the
facts of observation. In fact, each advance in science only seems to
make it more certain that the Nebular Hypothesis substantially
represents the way in which our solar system has grown to its present
form.

Not satisfied with a career which should be merely scientific,
Laplace sought to connect himself with public affairs. Napoleon
appreciated his genius, and desired to enlist him in the service of
the State. Accordingly he appointed Laplace to be Minister of the
Interior. The experiment was not successful, for he was not by
nature a statesman. Napoleon was much disappointed at the ineptitude
which the great mathematician showed for official life, and, in
despair of Laplace's capacity as an administrator, declared that he
carried the spirit of his infinitesimal calculus into the management
of business. Indeed, Laplace's political conduct hardly admits of
much defence. While he accepted the honours which Napoleon showered
on him in the time of his prosperity, he seems to have forgotten all
this when Napoleon could no longer render him service. Laplace was
made a Marquis by Louis XVIII., a rank which he transmitted to his
son, who was born in 1789. During the latter part of his life the
philosopher lived in a retired country place at Arcueile. Here he
pursued his studies, and by strict abstemiousness, preserved himself
from many of the infirmities of old age. He died on March the 5th,
1827, in his seventy-eighth year, his last words being, "What we know
is but little, what we do not know is immense."




BRINKLEY.


Provost Baldwin held absolute sway in the University of Dublin for
forty-one years. His memory is well preserved there. The Bursar
still dispenses the satisfactory revenues which Baldwin left to the
College. None of us ever can forget the marble angels round the
figure of the dying Provost on which we used to gaze during the pangs
of the Examination Hall.

Baldwin died in 1785, and was succeeded by Francis Andrews, a Fellow
of seventeen years' standing. As to the scholastic acquirements of
Andrews, all I can find is a statement that he was complimented by
the polite Professors of Padua on the elegance and purity with which
he discoursed to them in Latin. Andrews was also reputed to be a
skilful lawyer. He was certainly a Privy Councillor and a prominent
member of the Irish House of Commons, and his social qualities were
excellent. Perhaps it was Baldwin's example that stimulated a desire
in Andrews to become a benefactor to his college. He accordingly
bequeathed a sum of 3,000 pounds and an annual income of 250 pounds
wherewith to build and endow an astronomical Observatory in the
University. The figures just stated ought to be qualified by the
words of cautious Ussher (afterwards the first Professor of
Astronomy), that "this money was to arise from an accumulation of a
part of his property, to commence upon a particular contingency
happening to his family." The astronomical endowment was soon in
jeopardy by litigation. Andrews thought he had provided for his
relations by leaving to them certain leasehold interests connected
with the Provost's estate. The law courts, however, held that these
interests were not at the disposal of the testator, and handed them
over to Hely Hutchinson, the next Provost. The disappointed
relations then petitioned the Irish Parliament to redress this
grievance by transferring to them the moneys designed by Andrews for
the Observatory. It would not be right, they contended, that the
kindly intentions of the late Provost towards his kindred should be
frustrated for the sake of maintaining what they described as "a
purely ornamental institution." The authorities of the College
protested against this claim. Counsel were heard, and a Committee of
the House made a report declaring the situation of the relations to
be a hard one. Accordingly, a compromise was made, and the dispute
terminated.

The selection of a site for the new astronomical Observatory was made
by the Board of Trinity College. The beautiful neighbourhood of
Dublin offered a choice of excellent localities. On the north side
of the Liffey an Observatory could have been admirably placed, either
on the remarkable promontory of Howth or on the elevation of which
Dunsink is the summit. On the south side of Dublin there are several
eminences that would have been suitable: the breezy heaths at
Foxrock combine all necessary conditions; the obelisk hill at
Killiney would have given one of the most picturesque sites for an
Observatory in the world; while near Delgany two or three other good
situations could be mentioned. But the Board of those pre-railway
days was naturally guided by the question of proximity. Dunsink was
accordingly chosen as the most suitable site within the distance of a
reasonable walk from Trinity College.

The northern boundary of the Phoenix Park approaches the little river
Tolka, which winds through a succession of delightful bits of sylvan
scenery, such as may be found in the wide demesne of Abbotstown and
the classic shades of Glasnevin. From the banks of the Tolka, on the
opposite side of the park, the pastures ascend in a gentle slope to
culminate at Dunsink, where at a distance of half a mile from the
stream, of four miles from Dublin, and at a height of 300 feet above
the sea, now stands the Observatory. From the commanding position of
Dunsink a magnificent view is obtained. To the east the sea is
visible, while the southern prospect over the valley of the Liffey is
bounded by a range of hills and mountains extending from Killiney to
Bray Head, thence to the little Sugar Loaf, the Two Rock and the
Three Rock Mountains, over the flank of which the summit of the Great
Sugar Loaf is just perceptible. Directly in front opens the fine
valley of Glenasmole, with Kippure Mountain, while the range can be
followed to its western extremity at Lyons. The climate of Dunsink
is well suited for astronomical observation. No doubt here, as
elsewhere in Ireland, clouds are abundant, but mists or haze are
comparatively unusual, and fogs are almost unknown.

The legal formalities to be observed in assuming occupation exacted a
delay of many months; accordingly, it was not until the 10th
December, 1782, that a contract could be made with Mr. Graham Moyers
for the erection of a meridian-room and a dome for an equatorial, in
conjunction with a becoming residence for the astronomer. Before the
work was commenced at Dunsink, the Board thought it expedient to
appoint the first Professor of Astronomy. They met for this purpose
on the 22nd January, 1783, and chose the Rev. Henry Ussher, a Senior
Fellow of Trinity College, Dublin. The wisdom of the appointment was
immediately shown by the assiduity with which Ussher engaged in
founding the observatory. In three years he had erected the
buildings and equipped them with instruments, several of which were
of his own invention. On the 19th of February, 1785, a special grant
of 200 pounds was made by the Board to Dr. Ussher as some recompense
for his labours. It happened that the observatory was not the only
scientific institution which came into being in Ireland at this
period; the newly-kindled ardour for the pursuit of knowledge led, at
the same time, to the foundation of the Royal Irish Academy. By a
fitting coincidence, the first memoir published in the "Transactions
Of The Royal Irish Academy," was by the first Andrews, Professor of
Astronomy. It was read on the 13th of June, 1785, and bore the
title, "Account of the Observatory belonging to Trinity College," by
the Rev. H. Ussher, D.D., M.R.I.A., F.R.S. This communication shows
the extensive design that had been originally intended for Dunsink,
only a part of which was, however, carried out. For instance, two
long corridors, running north and south from the central edifice,
which are figured in the paper, never developed into bricks and
mortar. We are not told why the original scheme had to be
contracted; but perhaps the reason may be not unconnected with a
remark of Ussher's, that the College had already advanced from its
own funds a sum considerably exceeding the original bequest. The
picture of the building shows also the dome for the South equatorial,
which was erected many years later.

Ussher died in 1790. During his brief career at the observatory, he
observed eclipses, and is stated to have done other scientific work.
The minutes of the Board declare that the infant institution had
already obtained celebrity by his labours, and they urge the claims
of his widow to a pension, on the ground that the disease from which
he died had been contracted by his nightly vigils. The Board also
promised a grant of fifty guineas as a help to bring out Dr. Ussher's
sermons. They advanced twenty guineas to his widow towards the
publication of his astronomical papers. They ordered his bust to be
executed for the observatory, and offered "The Death of Ussher" as
the subject of a prize essay; but, so far as I can find, neither the
sermons nor the papers, neither the bust nor the prize essay, ever
came into being.

There was keen competition for the chair of Astronomy which the death
of Ussher vacated. The two candidates were Rev. John Brinkley, of
Caius College, Cambridge, a Senior Wrangler (born at Woodbridge,
Suffolk, in 1763), and Mr. Stack, Fellow of Trinity College, Dublin,
and author of a book on Optics. A majority of the Board at first
supported Stack, while Provost Hely Hutchinson and one or two others
supported Brinkley. In those days the Provost had a veto at
elections, so that ultimately Stack was withdrawn and Brinkley was
elected. This took place on the 11th December, 1790. The national
press of the day commented on the preference shown to the young
Englishman, Brinkley, over his Irish rival. An animated controversy
ensued. The Provost himself condescended to enter the lists and to
vindicate his policy by a long letter in the "Public Register" or
"Freeman's Journal," of 21st December, 1790. This letter was
anonymous, but its authorship is obvious. It gives the
correspondence with Maskelyne and other eminent astronomers, whose
advice and guidance had been sought by the Provost. It also contends
that "the transactions of the Board ought not to be canvassed in the
newspapers." For this reference, as well as for much other
information, I am indebted to my friend, the Rev. John Stubbs, D.D.

[PLATE: THE OBSERVATORY, DUNSINK. From a Photograph by W. Lawrence,
Upper Sackville Street, Dublin.]

The next event in the history of the Observatory was the issue of
Letters Patent (32 Geo. III., A.D. 1792), in which it is recited that
"We grant and ordain that there shall be forever hereafter a
Professor of Astronomy, on the foundation of Dr. Andrews, to be
called and known by the name of the Royal Astronomer of Ireland." The
letters prescribe the various duties of the astronomer and the mode
of his election. They lay down regulations as to the conduct of the
astronomical work, and as to the choice of an assistant. They direct
that the Provost and the Senior Fellows shall make a thorough
inspection of the observatory once every year in June or July; and
this duty was first undertaken on the 5th of July, 1792. It may be
noted that the date on which the celebration of the tercentenary of
the University was held happens to coincide with the centenary of the
first visitation of the observatory. The visitors on the first
occasion were A. Murray, Matthew Young, George Hall, and John
Barrett. They record that they find the buildings, books and
instruments in good condition; but the chief feature in this report,
as well as in many which followed it, related to a circumstance to
which we have not yet referred.

In the original equipment of the observatory, Ussher, with the
natural ambition of a founder, desired to place in it a telescope of
more magnificent proportions than could be found anywhere else. The
Board gave a spirited support to this enterprise, and negotiations
were entered into with the most eminent instrument-maker of those
days. This was Jesse Ramsden (1735-1800), famous as the improver of
the sextant, as the constructor of the great theodolite used by
General Roy in the English Survey, and as the inventor of the
dividing engine for graduating astronomical instruments. Ramsden had
built for Sir George Schuckburgh the largest and most perfect
equatorial ever attempted. He had constructed mural quadrants for
Padua and Verona, which elicited the wonder of astronomers when Dr.
Maskelyne declared he could detect no error in their graduation so
large as two seconds and a half. But Ramsden maintained that even
better results would be obtained by superseding the entire quadrant
by the circle. He obtained the means of testing this prediction when
he completed a superb circle for Palermo of five feet diameter.
Finding his anticipations were realised, he desired to apply the same
principles on a still grander scale. Ramsden was in this mood when
he met with Dr. Ussher. The enthusiasm of the astronomer and the
instrument-maker communicated itself to the Board, and a tremendous
circle, to be ten feet in diameter, was forthwith projected.

Projected, but never carried out. After Ramsden had to some extent
completed a 10-foot circle, he found such difficulties that he tried
a 9-foot, and this again he discarded for an 8-foot, which was
ultimately accomplished, though not entirely by himself.
Notwithstanding the contraction from the vast proportions originally
designed, the completed instrument must still be regarded as a
colossal piece of astronomical workmanship. Even at this day I do
not know that any other observatory can show a circle eight feet in
diameter graduated all round.

I think it is Professor Piazzi Smith who tells us how grateful he was
to find a large telescope he had ordered finished by the opticians on
the very day they had promised it. The day was perfectly correct; it
was only the year that was wrong. A somewhat remarkable experience
in this direction is chronicled by the early reports of the visitors
to Dunsink Observatory. I cannot find the date on which the great
circle was ordered from Ramsden, but it is fixed with sufficient
precision by an allusion in Ussher's paper to the Royal Irish
Academy, which shows that by the 13th June, 1785, the order had been
given, but that the abandonment of the 10-foot scale had not then
been contemplated. It was reasonable that the board should allow
Ramsden ample time for the completion of a work at once so elaborate
and so novel. It could not have been finished in a year, nor would
there have been much reason for complaint if the maker had found he
required two or even three years more.

Seven years gone, and still no telescope, was the condition in which
the Board found matters at their first visitation in 1792. They had,
however, assurances from Ramsden that the instrument would be
completed within the year; but, alas for such promises, another seven
years rolled on, and in 1799 the place for the great circle was still
vacant at Dunsink. Ramsden had fallen into bad health, and the Board
considerately directed that "inquiries should be made." Next year
there was still no progress, so the Board were roused to threaten
Ramsden with a suit at law; but the menace was never executed, for
the malady of the great optician grew worse, and he died that year.

Affairs had now assumed a critical aspect, for the college had
advanced much money to Ramsden during these fifteen years, and the
instrument was still unfinished. An appeal was made by the Provost
to Dr. Maskelyne, the Astronomer Royal of England, for his advice and
kindly offices in this emergency. Maskelyne responds--in terms
calculated to allay the anxiety of the Bursar--"Mr. Ramsden has left
property behind him, and the College can be in no danger of losing
both their money and the instrument." The business of Ramsden was
then undertaken by Berge, who proceeded to finish the circle quite as
deliberately as his predecessor. After four years Berge promised the
instrument in the following August, but it did not come. Two years
later (1806) the professor complains that he can get no answer from
Berge. In 1807, it is stated that Berge will send the telescope in a
month. He did not; but in the next year (1808), about twenty-three
years after the great circle was ordered, it was erected at Dunsink,
where it is still to be seen.

The following circumstances have been authenticated by the signatures
of Provosts, Proctors, Bursars, and other College dignitaries:--In
1793 the Board ordered two of the clocks at the observatory to be
sent to Mr. Crosthwaite for repairs. Seven years later, in 1800, Mr.
Crosthwaite was asked if the clocks were ready. This impatience was
clearly unreasonable, for even in four more years, 1804, we find the
two clocks were still in hand. Two years later, in 1806, the Board
determined to take vigorous action by asking the Bursar to call upon
Crosthwaite. This evidently produced some effect, for in the
following year, 1807, the Professor had no doubt that the clocks
would be speedily returned. After eight years more, in 1815, one of
the clocks was still being repaired, and so it was in 1816, which is
the last record we have of these interesting time-pieces. Astronomers
are, however, accustomed to deal with such stupendous periods in
their calculations, that even the time taken to repair a clock seems
but small in comparison.

The long tenure of the chair of Astronomy by Brinkley is divided into
two nearly equal periods by the year in which the great circle was
erected. Brinkley was eighteen years waiting for his telescope, and
he had eighteen years more in which to use it. During the first of
these periods Brinkley devoted himself to mathematical research;
during the latter he became a celebrated astronomer. Brinkley's
mathematical labours procured for their author some reputation as a
mathematician. They appear to be works of considerable mathematical
elegance, but not indicating any great power of original thought.
Perhaps it has been prejudicial to Brinkley's fame in this direction,
that he was immediately followed in his chair by so mighty a genius
as William Rowan Hamilton.

After the great circle had been at last erected, Brinkley was able to
begin his astronomical work in earnest. Nor was there much time to
lose. He was already forty-five years old, a year older than was
Herschel when he commenced his immortal career at Slough. Stimulated
by the consciousness of having the command of an instrument of unique
perfection, Brinkley loftily attempted the very highest class of
astronomical research. He resolved to measure anew with his own eye
and with his own hand the constants of aberration and of nutation. He
also strove to solve that great problem of the universe, the
discovery of the distance of a fixed star.

These were noble problems, and they were nobly attacked. But to
appraise with justice this work of Brinkley, done seventy years ago,
we must not apply to it the same criterion as we would think right to
apply to similar work were it done now. We do not any longer use
Brinkley's constant of aberration, nor do we now think that
Brinkley's determinations of the star distances were reliable. But,
nevertheless, his investigations exercised a marked influence on the
progress of science; they stimulated the study of the principles on
which exact measurements were to be conducted.

Brinkley had another profession in addition to that of an
astronomer. He was a divine. When a man endeavours to pursue two
distinct occupations concurrently, it will be equally easy to explain
why his career should be successful, or why it should be the
reverse. If he succeeds, he will, of course, exemplify the wisdom of
having two strings to his bow. Should he fail, it is, of course,
because he has attempted to sit on two stools at once. In Brinkley's
case, his two professions must be likened to the two strings rather
than to the two stools. It is true that his practical experience of
his clerical life was very slender. He had made no attempt to
combine the routine of a parish with his labours in the observatory.
Nor do we associate a special eminence in any department of religious
work with his name. If, however, we are to measure Brinkley's merits
as a divine by the ecclesiastical preferment which he received, his
services to theology must have rivalled his services to astronomy.
Having been raised step by step in the Church, he was at last
appointed to the See of Cloyne, in 1826, as the successor of Bishop
Berkeley.

Now, though it was permissible for the Archdeacon to be also the
Andrews Professor, yet when the Archdeacon became a Bishop, it was
understood that he should transfer his residence from the observatory
to the palace. The chair of Astronomy accordingly became vacant.
Brinkley's subsequent career seems to have been devoted entirely to
ecclesiastical matters, and for the last ten years of his life he did
not contribute a paper to any scientific society. Arago, after a
characteristic lament that Brinkley should have forsaken the pursuit
of science for the temporal and spiritual attractions of a bishopric,
pays a tribute to the conscientiousness of the quondam astronomer,
who would not even allow a telescope to be brought into the palace
lest his mind should be distracted from his sacred duties.

The good bishop died on the 13th September, 1835. He was buried in
the chapel of Trinity College, and a fine monument to his memory is a
familiar object at the foot of the noble old staircase of the library.
The best memorial of Brinkley is his admirable book on the "Elements
of Plane Astronomy." It passed through many editions in his lifetime,
and even at the present day the same work, revised first by Dr. Luby,
and more recently by the Rev. Dr. Stubbs and Dr. Brunnow, has a large
and well-merited circulation.




JOHN HERSCHEL.


This illustrious son of an illustrious father was born at Slough,
near Windsor, on the 7th March, 1792. He was the only child of Sir
William Herschel, who had married somewhat late in life, as we have
already mentioned.

[PLATE: ASTRONOMETER MADE BY SIR J. HERSCHEL to compare the light
of certain stars by the intervention of the moon.]

The surroundings among which the young astronomer was reared afforded
him an excellent training for that career on which he was to enter,
and in which he was destined to attain a fame only less brilliant
than that of his father. The circumstances of his youth permitted
him to enjoy one great advantage which was denied to the elder
Herschel. He was able, from his childhood, to devote himself almost
exclusively to intellectual pursuits. William Herschel, in the early
part of his career, had only been able to snatch occasional hours for
study from his busy life as a professional musician. But the son,
having been born with a taste for the student's life, was fortunate
enough to have been endowed with the leisure and the means to enjoy
it from the commencement. His early years have been so well
described by the late Professor Pritchard in the "Report of the
Council of the Royal Astronomical Society for 1872," that I venture
to make an extract here:--

"A few traits of John Herschel's boyhood, mentioned by himself in his
maturer life, have been treasured up by those who were dear to him,
and the record of some of them may satisfy a curiosity as pardonable
as inevitable, which craves to learn through what early steps great
men or great nations become illustrious. His home was singular, and
singularly calculated to nurture into greatness any child born as
John Herschel was with natural gifts, capable of wide development. At
the head of the house there was the aged, observant, reticent
philosopher, and rarely far away his devoted sister, Caroline
Herschel, whose labours and whose fame are still cognisable as a
beneficent satellite to the brighter light of her illustrious
brother. It was in the companionship of these remarkable persons,
and under the shadow of his father's wonderful telescope, that John
Herschel passed his boyish years. He saw them, in silent but
ceaseless industry, busied about things which had no apparent concern
with the world outside the walls of that well-known house, but which,
at a later period of his life, he, with an unrivalled eloquence,
taught his countrymen to appreciate as foremost among those living
influences which but satisfy and elevate the noblest instincts of our
nature. What sort of intercourse passed between the father and the
boy may be gathered from an incident or two which he narrated as
having impressed themselves permanently on the memory of his youth.
He once asked his father what he thought was the oldest of all
things. The father replied, after the Socratic method, by putting
another question: 'And what do you yourself suppose is the oldest of
all things?' The boy was not successful in his answers, thereon the
old astronomer took up a small stone from the garden walk: 'There, my
child, there is the oldest of all the things that I certainly know.'
On another occasion his father is said to have asked the boy, 'What
sort of things, do you think, are most alike?' The delicate,
blue-eyed boy, after a short pause, replied, 'The leaves of the same
tree are most like each other.' 'Gather, then, a handful of leaves of
that tree,' rejoined the philosopher, 'and choose two that are
alike.' The boy failed; but he hid the lesson in his heart, and his
thoughts were revealed after many days. These incidents may be
trifles; nor should we record them here had not John Herschel
himself, though singularly reticent about his personal emotions,
recorded them as having made a strong impression on his mind. Beyond
all doubt we can trace therein, first, that grasp and grouping of
many things in one, implied in the stone as the oldest of things;
and, secondly, that fine and subtle discrimination of each thing out
of many like things as forming the main features which characterized
the habit of our venerated friend's philosophy."

John Herschel entered St. John's College, Cambridge, when he was
seventeen years of age. His university career abundantly fulfilled
his father's eager desire, that his only son should develop a
capacity for the pursuit of science. After obtaining many lesser
distinctions, he finally came out as Senior Wrangler in 1813. It
was, indeed, a notable year in the mathematical annals of the
University. Second on that list, in which Herschel's name was first,
appeared that of the illustrious Peacock, afterwards Dean of Ely, who
remained throughout life one of Herschel's most intimate friends.

Almost immediately after taking his degree, Herschel gave evidence of
possessing a special aptitude for original scientific investigation.
He sent to the Royal Society a mathematical paper which was published
in the PHILOSOPHICAL TRANSACTIONS. Doubtless the splendour that
attached to the name he bore assisted him in procuring early
recognition of his own great powers. Certain it is that he was made
a Fellow of the Royal Society at the unprecedentedly early age of
twenty-one. Even after this remarkable encouragement to adopt a
scientific career as the business of his life, it does not seem that
John Herschel at first contemplated devoting himself exclusively to
science. He commenced to prepare for the profession of the Law by
entering as a student at the Middle Temple, and reading with a
practising barrister.

But a lawyer John Herschel was not destined to become. Circumstances
brought him into association with some leading scientific men. He
presently discovered that his inclinations tended more and more in
the direction of purely scientific pursuits. Thus it came to pass
that the original intention as to the calling which he should follow
was gradually abandoned. Fortunately for science Herschel found its
pursuit so attractive that he was led, as his father had been before
him, to give up his whole life to the advancement of knowledge. Nor
was it unnatural that a Senior Wrangler, who had once tasted the
delights of mathematical research, should have been tempted to devote
much time to this fascinating pursuit. By the time John Herschel was
twenty-nine he had published so much mathematical work, and his
researches were considered to possess so much merit, that the Royal
Society awarded him the Copley Medal, which was the highest
distinction it was capable of conferring.

At the death of his father in 1822, John Herschel, with his tastes
already formed for a scientific career, found himself in the
possession of ample means. To him also passed all his father's great
telescopes and apparatus. These material aids, together with a
dutiful sense of filial obligation, decided him to make practical
astronomy the main work of his life. He decided to continue to its
completion that great survey of the heavens which had already been
inaugurated, and, indeed, to a large extent accomplished, by his
father.

The first systematic piece of practical astronomical work which John
Herschel undertook was connected with the measurement of what are
known as "Double Stars." It should be observed, that there are in
the heavens a number of instances in which two stars are seen in very
close association. In the case of those objects to which the
expression "Double Stars" is generally applied, the two luminous
points are so close together that even though they might each be
quite bright enough to be visible to the unaided eye, yet their
proximity is such that they cannot be distinguished as two separate
objects without optical aid. The two stars seem fused together into
one. In the telescope, however, the bodies may be discerned
separately, though they are frequently so close together that it
taxes the utmost power of the instrument to indicate the division
between them.

The appearance presented by a double star might arise from the
circumstance that the two stars, though really separated from each
other by prodigious distances, happened to lie nearly in the same
line of vision, as seen from our point of view. No doubt, many of
the so-called double stars could be accounted for on this
supposition. Indeed, in the early days when but few double stars
were known, and when telescopes were not powerful enough to exhibit
the numerous close doubles which have since been brought to light,
there seems to have been a tendency to regard all double stars as
merely such perspective effects. It was not at first suggested that
there could be any physical connection between the components of each
pair. The appearance presented was regarded as merely due to the
circumstance that the line joining the two bodies happened to pass
near the earth.

[PLATE: SIR JOHN HERSCHEL.]

In the early part of his career, Sir William Herschel seems to have
entertained the view then generally held by other astronomers with
regard to the nature of these stellar pairs. The great observer
thought that the double stars could therefore be made to afford a
means of solving that problem in which so many of the observers of
the skies had been engaged, namely, the determination of the
distances of the stars from the earth. Herschel saw that the
displacement of the earth in its annual movement round the sun would
produce an apparent shift in the place of the nearer of the two stars
relatively to the other, supposed to be much more remote. If this
shift could be measured, then the distance of the nearer of the stars
could be estimated with some degree of precision.

As has not unfrequently happened in the history of science, an effect
was perceived of a very different nature from that which had been
anticipated. If the relative places of the two stars had been
apparently deranged merely in consequence of the motion of the earth,
then the phenomenon would be an annual one. After the lapse of a
year the two stars would have regained their original relative
positions. This was the effect for which William Herschel was
looking. In certain of the so called double stars, he, no doubt, did
find a movement. He detected the remarkable fact that both the
apparent distance and the relative positions of the two bodies were
changing. But what was his surprise to observe that these
alterations were not of an annually periodic character. It became
evident then that in some cases one of the component stars was
actually revolving around the other, in an orbit which required many
years for its completion. Here was indeed a remarkable discovery. It
was clearly impossible to suppose that movements of this kind could
be mere apparent displacements, arising from the annual shift in our
point of view, in consequence of the revolution of the earth.
Herschel's discovery established the interesting fact that, in
certain of these double stars, or binary stars, as these particular
objects are more expressively designated, there is an actual orbital
revolution of a character similar to that which the earth performs
around the sun. Thus it was demonstrated that in these particular
double stars the nearness of the two components was not merely
apparent. The objects must actually lie close together at a distance
which is small in comparison with the distance at which either of
them is separated from the earth. The fact that the heavens contain
pairs of twin suns in mutual revolution was thus brought to light.

In consequence of this beautiful discovery, the attention of
astronomers was directed to the subject of double stars with a degree
of interest which these objects had never before excited. It was
therefore not unnatural that John Herschel should have been attracted
to this branch of astronomical work. Admiration for his father's
discovery alone might have suggested that the son should strive to
develop this territory newly opened up to research. But it also
happened that the mathematical talents of the younger Herschel
inclined his inquiries in the same direction. He saw clearly that,
when sufficient observations of any particular binary star had been
accumulated, it would then be within the power of the mathematician
to elicit from those observations the shape and the position in space
of the path which each of the revolving stars described around the
other. Indeed, in some cases he would be able to perform the
astonishing feat of determining from his calculations the weight of
these distant suns, and thus be enabled to compare them with the mass
of our own sun.

[PLATE: NEBULA IN SOUTHERN HEMISPHERE, drawn by Sir John Herschel.]

But this work must follow the observations, it could not precede
them. The first step was therefore to observe and to measure with
the utmost care the positions and distances of those particular
double stars which appear to offer the greatest promise in this
particular research. In 1821, Herschel and a friend of his, Mr.
James South, agreed to work together with this object. South was a
medical man with an ardent devotion to science, and possessed of
considerable wealth. He procured the best astronomical instruments
that money could obtain, and became a most enthusiastic astronomer
and a practical observer of tremendous energy.

South and John Herschel worked together for two years in the
observation and measurement of the double stars discovered by Sir
William Herschel. In the course of this time their assiduity was
rewarded by the accumulation of so great a mass of careful
measurements that when published, they formed quite a volume in the
"Philosophical Transactions." The value and accuracy of the work,
when estimated by standards which form proper criteria for that
period, is universally recognised. It greatly promoted the progress
of sidereal astronomy, and the authors were in consequence awarded
medals from the Royal Society, and the Royal Astronomical Society,
as well as similar testimonials from various foreign institutions.

This work must, however, be regarded as merely introductory to the
main labours of John Herschel's life. His father devoted the greater
part of his years as an observer to what he called his "sweeps" of
the heavens. The great reflecting telescope, twenty feet long, was
moved slowly up and down through an arc of about two degrees towards
and from the pole, while the celestial panorama passed slowly in the
course of the diurnal motion before the keenly watching eye of the
astronomer. Whenever a double star traversed the field Herschel
described it to his sister Caroline, who, as we have already
mentioned, was his invariable assistant in his midnight watches. When
a nebula appeared, then he estimated its size and its brightness, he
noticed whether it had a nucleus, or whether it had stars disposed in
any significant manner with regard to it. He also dictated any other
circumstance which he deemed worthy of record. These observations
were duly committed to writing by the same faithful and indefatigable
scribe, whose business it also was to take a memorandum of the exact
position of the object as indicated by a dial placed in front of her
desk, and connected with the telescope.

John Herschel undertook the important task of re-observing the
various double stars and nebulae which had been discovered during
these memorable vigils. The son, however, lacked one inestimable
advantage which had been possessed by the father. John Herschel had
no assistant to discharge all those duties which Caroline had so
efficiently accomplished. He had, therefore, to modify the system of
sweeping previously adopted in order to enable all the work both of
observing and of recording to be done by himself. This, in many
ways, was a great drawback to the work of the younger astronomer. The
division of labour between the observer and the scribe enables a
greatly increased quantity of work to be got through. It is also
distinctly disadvantageous to an observer to have to use his eye at
the telescope directly after he has been employing it for reading the
graduations on a circle, by the light of a lamp, or for entering
memoranda in a note book. Nebulae, especially, are often so
excessively faint that they can only be properly observed by an eye
which is in that highly sensitive condition which is obtained by long
continuance in darkness. The frequent withdrawal of the eye from the
dark field of the telescope, and the application of it to reading by
artificial light, is very prejudicial to its use for the more
delicate purpose. John Herschel, no doubt, availed himself of every
precaution to mitigate the ill effects of this inconvenience as much
as possible, but it must have told upon his labours as compared with
those of his father.

But nevertheless John Herschel did great work during his "sweeps." He
was specially particular to note all the double stars which presented
themselves to his observation. Of course some little discretion must
be allowed in deciding as to what degree of proximity in adjacent
stars does actually bring them within the category of "double
stars." Sir John set down all such objects as seemed to him likely
to be of interest, and the results of his discoveries in this branch
of astronomy amount to some thousands. Six or seven great memoirs in
the TRANSACTIONS of the Royal Astronomical Society have been devoted
to giving an account of his labours in this department of astronomy.

[PLATE: THE CLUSTER IN THE CENTAUR, drawn by Sir John Herschel.]

One of the achievements by which Sir John Herschel is best known is
his invention of a method by which the orbits of binary stars could
be determined. It will be observed that when one star revolves
around another in consequence of the law of gravitation, the orbit
described must be an ellipse. This ellipse, however, generally
speaking, appears to us more or less foreshortened, for it is easily
seen that only under highly exceptional circumstances would the plane
in which the stars move happen to be directly square to the line of
view. It therefore follows that what we observe is not exactly the
track of one star around the other; it is rather the projection of
that track as seen on the surface of the sky. Now it is remarkable
that this apparent path is still an ellipse. Herschel contrived a
very ingenious and simple method by which he could discover from the
observations the size and position of the ellipse in which the
revolution actually takes place. He showed how, from the study of
the apparent orbit of the star, and from certain measurements which
could easily be effected upon it, the determination of the true
ellipse in which the movement is performed could be arrived at. In
other words, Herschel solved in a beautiful manner the problem of
finding the true orbits of double stars. The importance of this work
may be inferred from the fact that it has served as the basis on
which scores of other investigators have studied the fascinating
subject of the movement of binary stars.

The labours, both in the discovery and measurement of the double
stars, and in the discussion of the observations with the object of
finding the orbits of such stars as are in actual revolution,
received due recognition in yet another gold medal awarded by the
Royal Society. An address was delivered on the occasion by the Duke
of Sussex (30th November, 1833), in the course of which, after
stating that the medal had been conferred on Sir John Herschel, he
remarks:--

"It has been said that distance of place confers the same privilege
as distance of time, and I should gladly avail myself of the
privilege which is thus afforded me by Sir John Herschel's separation
from his country and friends, to express my admiration of his
character in stronger terms than I should otherwise venture to use;
for the language of panegyric, however sincerely it may flow from the
heart, might be mistaken for that of flattery, if it could not thus
claim somewhat of an historical character; but his great attainments
in almost every department of human knowledge, his fine powers as a
philosophical writer, his great services and his distinguished
devotion to science, the high principles which have regulated his
conduct in every relation of life, and, above all, his engaging
modesty, which is the crown of all his other virtues, presenting such
a model of an accomplished philosopher as can rarely be found beyond
the regions of fiction, demand abler pens than mine to describe them
in adequate terms, however much inclined I might feel to undertake
the task."

The first few lines of the eulogium just quoted allude to Herschel's
absence from England. This was not merely an episode of interest in
the career of Herschel, it was the occasion of one of the greatest
scientific expeditions in the whole history of astronomy.

Herschel had, as we have seen, undertaken a revision of his father's
"sweeps" for new objects, in those skies which are visible from our
latitudes in the northern hemisphere. He had well-nigh completed
this task. Zone by zone the whole of the heavens which could be
observed from Windsor had passed under his review. He had added
hundreds to the list of nebulae discovered by his father. He had
announced thousands of double stars. At last, however, the great
survey was accomplished. The contents of the northern hemisphere, so
far at least as they could be disclosed by his telescope of twenty
feet focal length, had been revealed.

[PLATE: SIR JOHN HERSCHEL'S OBSERVATORY AT FELDHAUSEN,
Cape of Good Hope.]

But Herschel felt that this mighty task had to be supplemented by
another of almost equal proportions, before it could be said that the
twenty-foot telescope had done its work. It was only the northern
half of the celestial sphere which had been fully explored. The
southern half was almost virgin territory, for no other astronomer
was possessed of a telescope of such power as those which the
Herschels had used. It is true, of course, that as a certain margin
of the southern hemisphere was visible from these latitudes, it had
been more or less scrutinized by observers in northern skies. And
the glimpses which had thus been obtained of the celestial objects in
the southern sky, were such as to make an eager astronomer long for a
closer acquaintance with the celestial wonders of the south. The
most glorious object in the sidereal heavens, the Great Nebula in
Orion, lies indeed in that southern hemisphere to which the younger
Herschel's attention now became directed. It fortunately happens,
however, for votaries of astronomy all the world over, that Nature
has kindly placed her most astounding object, the great Nebula in
Orion, in such a favoured position, near the equator, that from a
considerable range of latitudes, both north and south, the wonders of
the Nebula can be explored. There are grounds for thinking that the
southern heavens contain noteworthy objects which, on the whole, are
nearer to the solar system than are the noteworthy objects in the
northern skies. The nearest star whose distance is known, Alpha
Centauri, lies in the southern hemisphere, and so also does the most
splendid cluster of stars.

Influenced by the desire to examine these objects, Sir John Herschel
determined to take his great telescope to a station in the southern
hemisphere, and thus complete his survey of the sidereal heavens. The
latitude of the Cape of Good Hope is such that a suitable site could
be there found for his purpose. The purity of the skies in South
Africa promised to provide for the astronomer those clear nights
which his delicate task of surveying the nebulae would require.

On November 13, 1833, Sir John Herschel, who had by this time
received the honour of knighthood from William IV., sailed from
Portsmouth for the Cape of Good Hope, taking with him his gigantic
instruments. After a voyage of two months, which was considered to
be a fair passage in those days, he landed in Table Bay, and having
duly reconnoitred various localities, he decided to place his
observatory at a place called Feldhausen, about six miles from Cape
Town, near the base of the Table Mountain. A commodious residence
was there available, and in it he settled with his family. A
temporary building was erected to contain the equatorial, but the
great twenty-foot telescope was accommodated with no more shelter
than is provided by the open canopy of heaven.

As in his earlier researches at home, the attention of the great
astronomer at the Cape of Good Hope was chiefly directed to the
measurement of the relative positions and distances apart of the
double stars, and to the close examination of the nebulae. In the
delineation of the form of these latter objects Herschel found ample
employment for his skilful pencil. Many of the drawings he has made
of the celestial wonders in the southern sky are admirable examples
of celestial portraiture.

The number of the nebulae and of those kindred objects, the star
clusters, which Herschel studied in the southern heavens, during four
years of delightful labour, amount in all to one thousand seven
hundred and seven. His notes on their appearance, and the
determinations of their positions, as well as his measurements of
double stars, and much other valuable astronomical research, were
published in a splendid volume, brought out at the cost of the Duke
of Northumberland. This is, indeed, a monumental work, full of
interesting and instructive reading for any one who has a taste for
astronomy.

Herschel had the good fortune to be at the Cape on the occasion of
the periodical return of Halley's great comet in 1833. To the study
of this body he gave assiduous attention, and the records of his
observations form one of the most interesting chapters in that
remarkable volume to which we have just referred.

[PLATE: COLUMN AT FELDHAUSEN, CAPE TOWN, to commemorate Sir John
Herschel's survey of the Southern Heavens.]

Early in 1838 Sir John Herschel returned to England. He had made
many friends at the Cape, who deeply sympathised with his self-
imposed labours while he was resident among them. They desired to
preserve the recollection of this visit, which would always, they
considered, be a source of gratification in the colony. Accordingly,
a number of scientific friends in that part of the world raised a
monument with a suitable inscription, on the spot which had been
occupied by the great twenty-foot reflector at Feldhausen.

His return to England after five years of absence was naturally an
occasion for much rejoicing among the lovers of astronomy. He was
entertained at a memorable banquet, and the Queen, at her coronation,
made him a baronet. His famous aunt Caroline, at that time aged
eighty, was still in the enjoyment of her faculties, and was able to
estimate at its true value the further lustre which was added to the
name she bore. But there is reason to believe that her satisfaction
was not quite unmixed with other feelings. With whatever favour she
might regard her nephew, he was still not the brother to whom her
life had been devoted. So jealous was this vigorous old lady of the
fame of the great brother William, that she could hardly hear with
patience of the achievements of any other astronomer, and this
failing existed in some degree even when that other astronomer
happened to be her illustrious nephew.

With Sir John Herschel's survey of the Southern Hemisphere it may be
said that his career as an observing astronomer came to a close. He
did not again engage in any systematic telescopic research. But it
must not be inferred from this statement that he desisted from active
astronomical work. It has been well observed that Sir John Herschel
was perhaps the only astronomer who has studied with success, and
advanced by original research, every department of the great science
with which his name is associated. It was to some other branches of
astronomy besides those concerned with looking through telescopes,
that the rest of the astronomer's life was to be devoted.

To the general student Sir John Herschel is best known by the volume
which he published under the title of "Outlines of Astronomy." This
is, indeed, a masterly work, in which the characteristic difficulties
of the subject are resolutely faced and expounded with as much
simplicity as their nature will admit. As a literary effort this
work is admirable, both on account of its picturesque language and
the ennobling conceptions of the universe which it unfolds. The
student who desires to become acquainted with those recondite
departments of astronomy, in which the effects of the disturbing
action of one planet upon the motions of another planet are
considered, will turn to the chapters in Herschel's famous work on
the subject. There he will find this complex matter elucidated,
without resort to difficult mathematics. Edition after edition of
this valuable work has appeared, and though the advances of modern
astronomy have left it somewhat out of date in certain departments,
yet the expositions it contains of the fundamental parts of the
science still remain unrivalled.

Another great work which Sir John undertook after his return from the
Cape, was a natural climax to those labours on which his father and
he had been occupied for so many years. We have already explained
how the work of both these observers had been mainly devoted to the
study of the nebulae and the star clusters. The results of their
discoveries had been announced to the world in numerous isolated
memoirs. The disjointed nature of these publications made their use
very inconvenient. But still it was necessary for those who desired
to study the marvellous objects discovered by the Herschels, to have
frequent recourse to the original works. To incorporate all the
several observations of nebular into one great systematic catalogue,
seemed, therefore, to be an indispensable condition of progress in
this branch of knowledge. No one could have been so fitted for this
task as Sir John Herschel. He, therefore, attacked and carried
through the great undertaking. Thus at last a grand catalogue of
nebulae and clusters was produced. Never before was there so
majestic an inventory. If we remember that each of the nebulae is an
object so vast, that the whole of the solar system would form an
inconsiderable speck by comparison, what are we to think of a
collection in which these objects are enumerated in thousands? In
this great catalogue we find arranged in systematic order all the
nebulae and all the clusters which had been revealed by the diligence
of the Herschels, father and son, in the Northern Hemisphere, and of
the son alone in the Southern Hemisphere. Nor should we omit to
mention that the labours of other astronomers were likewise
incorporated. It was unavoidable that the descriptions given to each
of the objects should be very slight. Abbreviations are used, which
indicate that a nebula is bright, or very bright, or extremely
bright, or faint, or very faint, or extremely faint. Such phrases
have certainly but a relative and technical meaning in such a
catalogue. The nebulae entered as extremely bright by the
experienced astronomer are only so described by way of contrast to
the great majority of these delicate telescopic objects. Most of the
nebulae, indeed, are so difficult to see, that they admit of but very
slight description. It should be observed that Herschel's catalogue
augmented the number of known nebulous objects to more than ten times
that collected into any catalogue which had ever been compiled before
the days of William Herschel's observing began. But the study of
these objects still advances, and the great telescopes now in use
could probably show at least twice as many of these objects as are
contained in the list of Herschel, of which a new and enlarged
edition has since been brought out by Dr. Dreyer.

One of the best illustrations of Sir John Herschel's literary powers
is to be found in the address which he delivered at the Royal
Astronomical Society, on the occasion of presenting a medal to Mr.
Francis Baily, in recognition of his catalogue of stars. The passage
I shall here cite places in its proper aspect the true merit of the
laborious duty involved in such a task as that which Mr. Baily had
carried through with such success:--

"If we ask to what end magnificent establishments are maintained by
states and sovereigns, furnished with masterpieces of art, and placed
under the direction of men of first-rate talent and high-minded
enthusiasm, sought out for those qualities among the foremost in the
ranks of science, if we demand QUI BONO? for what good a Bradley has
toiled, or a Maskelyne or a Piazzi has worn out his venerable age in
watching, the answer is--not to settle mere speculative points in the
doctrine of the universe; not to cater for the pride of man by
refined inquiries into the remoter mysteries of nature; not to trace
the path of our system through space, or its history through past and
future eternities. These, indeed, are noble ends and which I am far
from any thought of depreciating; the mind swells in their
contemplation, and attains in their pursuit an expansion and a
hardihood which fit it for the boldest enterprise. But the direct
practical utility of such labours is fully worthy of their
speculative grandeur. The stars are the landmarks of the universe;
and, amidst the endless and complicated fluctuations of our system,
seem placed by its Creator as guides and records, not merely to
elevate our minds by the contemplation of what is vast, but to teach
us to direct our actions by reference to what is immutable in His
works. It is, indeed, hardly possible to over-appreciate their value
in this point of view. Every well-determined star, from the moment
its place is registered, becomes to the astronomer, the geographer,
the navigator, the surveyor, a point of departure which can never
deceive or fail him, the same for ever and in all places, of a
delicacy so extreme as to be a test for every instrument yet invented
by man, yet equally adapted for the most ordinary purposes; as
available for regulating a town clock as for conducting a navy to the
Indies; as effective for mapping down the intricacies of a petty
barony as for adjusting the boundaries of Transatlantic empires. When
once its place has been thoroughly ascertained and carefully
recorded, the brazen circle with which that useful work was done may
moulder, the marble pillar may totter on its base, and the astronomer
himself survive only in the gratitude of posterity; but the record
remains, and transfuses all its own exactness into every
determination which takes it for a groundwork, giving to inferior
instruments--nay, even to temporary contrivances, and to the
observations of a few weeks or days--all the precision attained
originally at the cost of so much time, labour, and expense."

Sir John Herschel wrote many other works besides those we have
mentioned. His "Treatise on Meteorology" is, indeed, a standard work
on this subject, and numerous articles from the same pen on
miscellaneous subjects, which have been collected and reprinted,
seemed as a relaxation from his severe scientific studies. Like
certain other great mathematicians Herschel was also a poet, and he
published a translation of the Iliad into blank verse.

In his later years Sir John Herschel lived a retired life. For a
brief period he had, indeed, been induced to accept the office of
Master of the Mint. It was, however, evident that the routine of
such an occupation was not in accordance with his tastes, and he
gladly resigned it, to return to the seclusion of his study in his
beautiful home at Collingwood, in Kent.

His health having gradually failed, he died on the 11th May, 1871, in
the seventy-ninth year of his age.




THE EARL OF ROSSE.


The subject of our present sketch occupies quite a distinct position
in scientific history. Unlike many others who have risen by their
scientific discoveries from obscurity to fame, the great Earl of
Rosse was himself born in the purple. His father, who, under the
title of Sir Lawrence Parsons, had occupied a distinguished position
in the Irish Parliament, succeeded on the death of his father to the
Earldom which had been recently created. The subject of our present
memoir was, therefore, the third of the Earls of Rosse, and he was
born in York on June 17, 1800. Prior to his father's death in 1841,
he was known as Lord Oxmantown.

The University education of the illustrious astronomer was begun in
Dublin and completed at Oxford. We do not hear in his case of any
very remarkable University career. Lord Rosse was, however, a
diligent student, and obtained a first-class in mathematics. He
always took a great deal of interest in social questions, and was a
profound student of political economy. He had a seat in the House of
Commons, as member for King's County, from 1821 to 1834, his
ancestral estate being situated in this part of Ireland.

[PLATE: THE EARL OF ROSSE.]

Lord Rosse was endowed by nature with a special taste for mechanical
pursuits. Not only had he the qualifications of a scientific
engineer, but he had the manual dexterity which qualified him
personally to carry out many practical arts. Lord Rosse was, in
fact, a skilful mechanic, an experienced founder, and an ingenious
optician. His acquaintances were largely among those who were
interested in mechanical pursuits, and it was his delight to visit
the works or engineering establishments where refined processes in
the arts were being carried on. It has often been stated--and as I
have been told by members of his family, truly stated--that on one
occasion, after he had been shown over some large works in the north
of England, the proprietor bluntly said that he was greatly in want
of a foreman, and would indeed be pleased if his visitor, who had
evinced such extraordinary capacity for mechanical operations, would
accept the post. Lord Rosse produced his card, and gently explained
that he was not exactly the right man, but he appreciated the
compliment, and this led to a pleasant dinner, and was the basis of a
long friendship.

I remember on one occasion hearing Lord Rosse explain how it was that
he came to devote his attention to astronomy. It appears that when
he found himself in the possession of leisure and of means, he
deliberately cast around to think how that means and that leisure
could be most usefully employed. Nor was it surprising that he
should search for a direction which would offer special scope for his
mechanical tastes. He came to the conclusion that the building of
great telescopes was an art which had received no substantial advance
since the great days of William Herschel. He saw that to construct
mighty instruments for studying the heavens required at once the
command of time and the command of wealth, while he also felt that
this was a subject the inherent difficulties of which would tax to
the uttermost whatever mechanical skill he might possess. Thus it
was he decided that the construction of great telescopes should
become the business of his life.

[PLATE: BIRR CASTLE.

PLATE: THE MALL, PARSONSTOWN.]

In the centre of Ireland, seventy miles from Dublin, on the border
between King's County and Tipperary, is a little town whereof we must
be cautious before writing the name. The inhabitants of that town
frequently insist that its name is Birr, * while the official
designation is Parsonstown, and to this day for every six people who
apply one name to the town, there will be half a dozen who use the
other. But whichever it may be, Birr or Parsonstown--and I shall
generally call it by the latter name--it is a favourable specimen of
an Irish county town. The widest street is called the Oxmantown
Mall. It is bordered by the dwelling-houses of the chief residents,
and adorned with rows of stately trees. At one end of this
distinctly good feature in the town is the Parish Church, while at
the opposite end are the gates leading into Birr Castle, the
ancestral home of the house of Parsons. Passing through the gates
the visitor enters a spacious demesne, possessing much beauty of wood
and water, one of the most pleasing features being the junction of
the two rivers, which unite at a spot ornamented by beautiful
timber. At various points illustrations of the engineering skill of
the great Earl will be observed. The beauty of the park has been
greatly enhanced by the construction of an ample lake, designed with
the consummate art by which art is concealed. Even in mid-summer it
is enlivened by troops of wild ducks preening themselves in that
confidence which they enjoy in those happy localities where the sound
of a gun is seldom heard. The water is led into the lake by a tube
which passes under one of the two rivers just mentioned, while the
overflow from the lake turns a water-wheel, which works a pair of
elevators ingeniously constructed for draining the low-lying parts of
the estate.

 * Considering the fame acquired by Parsonstown from Lord Rosse's
   mirrors, it may be interesting to note the following extract from
   "The Natural History of Ireland," by Dr. Gerard Boate, Thomas
   Molyneux M.D., F.R.S., and others, which shows that 150 years ago
   Parsonstown was famous for its glass:--

   "We shall conclude this chapter with the glass, there having been
   several glasshouses set up by the English in Ireland, none in Dublin
   or other cities, but all of them in the country; amongst which the
   principal was that of Birre, a market town, otherwise called
   Parsonstown, after one Sir Lawrence Parsons, who, having purchased
   that lordship, built a goodly house upon it; his son William Parsons
   having succeeded him in the possession of it; which town is situate
   in Queen's County, about fifty miles (Irish) to the southwest of
   Dublin, upon the borders of the two provinces of Leinster and Munster;
   from this place Dublin was furnished with all sorts of window and
   drinking glasses, and such other as commonly are in use. One part of
   the materials, viz., the sand, they had out of England; the other,
   to wit the ashes, they made in the place of ash-tree, and used no
   other. The chiefest difficulty was to get the clay for the pots to
   melt the materials in; this they had out of the north."--Chap. XXI.,
   Sect. VIII. "Of the Glass made in Ireland."

Birr Castle itself is a noble mansion with reminiscences from the
time of Cromwell. It is surrounded by a moat and a drawbridge of
modern construction, and from its windows beautiful views can be had
over the varied features of the park. But while the visitors to
Parsonstown will look with great interest on this residence of an
Irish landlord, whose delight it was to dwell in his own country, and
among his own people, yet the feature which they have specially come
to observe is not to be found in the castle itself. On an extensive
lawn, sweeping down from the moat towards the lake, stand two noble
masonry walls. They are turreted and clad with ivy, and considerably
loftier than any ordinary house. As the visitor approaches, he will
see between those walls what may at first sight appear to him to be
the funnel of a steamer lying down horizontally. On closer approach
he will find that it is an immense wooden tube, sixty feet long, and
upwards of six feet in diameter. It is in fact large enough to admit
of a tall man entering into it and walking erect right through from
one end to the other. This is indeed the most gigantic instrument
which has ever been constructed for the purpose of exploring the
heavens. Closely adjoining the walls between which the great tube
swings, is a little building called "The Observatory." In this the
smaller instruments are contained, and there are kept the books which
are necessary for reference. The observatory also offers shelter to
the observers, and provides the bright fire and the cup of warm tea,
which are so acceptable in the occasional intervals of a night's
observation passed on the top of the walls with no canopy but the
winter sky.

Almost the first point which would strike the visitor to Lord Rosse's
telescope is that the instrument at which he is looking is not only
enormously greater than anything of the kind that he has ever seen
before, but also that it is something of a totally different nature.
In an ordinary telescope he is accustomed to find a tube with lenses
of glass at either end, while the large telescopes that we see in our
observatories are also in general constructed on the same principle.
At one end there is the object-glass, and at the other end the
eye-piece, and of course it is obvious that with an instrument of
this construction it is to the lower end of the tube that the eye of
the observer must be placed when the telescope is pointed to the
skies. But in Lord Rosse's telescope you would look in vain for
these glasses, and it is not at the lower end of the instrument that
you are to take your station when you are going to make your
observations. The astronomer at Parsonstown has rather to avail
himself of the ingenious system of staircases and galleries, by which
he is enabled to obtain access to the mouth of the great tube. The
colossal telescope which swings between the great walls, like
Herschel's great telescope already mentioned, is a reflector, the
original invention of which is due of course to Newton. The optical
work which is accomplished by the lenses in the ordinary telescope is
effected in the type of instrument constructed by Lord Rosse by a
reflecting mirror which is placed at the lower end of the vast tube.
The mirror in this instrument is made of a metal consisting of two
parts of copper to one of tin. As we have already seen, this mixture
forms an alloy of a very peculiar nature. The copper and the tin
both surrender their distinctive qualities, and unite to form a
material of a very different physical character. The copper is tough
and brown, the tin is no doubt silvery in hue, but soft and almost
fibrous in texture. When the two metals are mixed together in the
proportions I have stated, the alloy obtained is intensely hard and
quite brittle being in both these respects utterly unlike either of
the two ingredients of which it is composed. It does, however,
resemble the tin in its whiteness, but it acquires a lustre far
brighter than tin; in fact, this alloy hardly falls short of silver
itself in its brilliance when polished.

[PLATE: LORD ROSSE'S TELESCOPE. From a photograph by W. Lawrence,
Upper Sackville Street, Dublin.]

The first duty that Lord Rosse had to undertake was the construction
of this tremendous mirror, six feet across, and about four or five
inches thick. The dimensions were far in excess of those which had
been contemplated in any previous attempt of the same kind. Herschel
had no doubt fashioned one mirror of four feet in diameter, and many
others of smaller dimensions, but the processes which he employed had
never been fully published, and it was obvious that, with a large
increase in dimensions, great additional difficulties had to be
encountered. Difficulties began at the very commencement of the
process, and were experienced in one form or another at every
subsequent stage. In the first place, the mere casting of a great
disc of this mixture of tin and copper, weighing something like three
or four tons, involved very troublesome problems. No doubt a casting
of this size, if the material had been, for example, iron, would have
offered no difficulties beyond those with which every practical
founder is well acquainted, and which he has to encounter daily in
the course of his ordinary work. But speculum metal is a material of
a very intractable description. There is, of course, no practical
difficulty in melting the copper, nor in adding the proper proportion
of tin when the copper has been melted. There may be no great
difficulty in arranging an organization by which several crucibles,
filled with the molten material, shall be poured simultaneously so as
to obtain the requisite mass of metal, but from this point the
difficulties begin. For speculum metal when cold is excessively
brittle, and were the casting permitted to cool like an ordinary
copper or iron casting, the mirror would inevitably fly into pieces.
Lord Rosse, therefore, found it necessary to anneal the casting with
extreme care by allowing it to cool very slowly. This was
accomplished by drawing the disc of metal as soon as it had entered
into the solid state, though still glowing red, into an annealing
oven. There the temperature was allowed to subside so gradually,
that six weeks elapsed before the mirror had reached the temperature
of the external air. The necessity for extreme precaution in the
operation of annealing will be manifest if we reflect on one of the
accidents which happened. On a certain occasion, after the cooling
of a great casting had been completed, it was found, on withdrawing
the speculum, that it was cracked into two pieces. This mishap was
eventually traced to the fact that one of the walls of the oven had
only a single brick in its thickness, and that therefore the heat had
escaped more easily through that side than through the other sides
which were built of double thickness. The speculum had,
consequently, not cooled uniformly, and hence the fracture had
resulted. Undeterred, however, by this failure, as well as by not a
few other difficulties, into a description of which we cannot now
enter, Lord Rosse steadily adhered to his self-imposed task, and at
last succeeded in casting two perfect discs on which to commence the
tedious processes of grinding and polishing. The magnitude of the
operations involved may perhaps be appreciated if I mention that the
value of the mere copper and tin entering into the composition of
each of the mirrors was about 500 pounds.

In no part of his undertaking was Lord Rosse's mechanical ingenuity
more taxed than in the devising of the mechanism for carrying out the
delicate operations of grinding and polishing the mirrors, whose
casting we have just mentioned. In the ordinary operations of the
telescope-maker, such processes had hitherto been generally effected
by hand, but, of course, such methods became impossible when dealing
with mirrors which were as large as a good-sized dinner table, and
whose weight was measured by tons. The rough grinding was effected
by means of a tool of cast iron about the same size as the mirror,
which was moved by suitable machinery both backwards and forwards,
and round and round, plenty of sand and water being supplied between
the mirror and the tool to produce the necessary attrition. As the
process proceeded and as the surface became smooth, emery was used
instead of sand; and when this stage was complete, the grinding tool
was removed and the polishing tool was substituted. The essential
part of this was a surface of pitch, which, having been temporarily
softened by heat, was then placed on the mirror, and accepted from
the mirror the proper form. Rouge was then introduced as the
polishing powder, and the operation was continued about nine hours,
by which time the great mirror had acquired the appearance of highly
polished silver. When completed, the disc of speculum metal was
about six feet across and four inches thick. The depression in the
centre was about half an inch. Mounted on a little truck, the great
speculum was then conveyed to the instrument, to be placed in its
receptacle at the bottom of the tube, the length of which was sixty
feet, this being the focal distance of the mirror. Another small
reflector was inserted in the great tube sideways, so as to direct
the gaze of the observer down upon the great reflector. Thus was
completed the most colossal instrument for the exploration of the
heavens which the art of man has ever constructed.

[PLATE: ROMAN CATHOLIC CHURCH AT PARSONSTOWN.]

It was once my privilege to be one of those to whom the illustrious
builder of the great telescope entrusted its use. For two seasons in
1865 and 1866 I had the honour of being Lord Rosse's astronomer.
During that time I passed many a fine night in the observer's
gallery, examining different objects in the heavens with the aid of
this remarkable instrument. At the time I was there, the objects
principally studied were the nebulae, those faint stains of light
which lie on the background of the sky. Lord Rosse's telescope was
specially suited for the scrutiny of these objects, inasmuch as their
delicacy required all the light-grasping power which could be
provided.

One of the greatest discoveries made by Lord Rosse, when his huge
instrument was first turned towards the heavens, consisted in the
detection of the spiral character of some of the nebulous forms.
When the extraordinary structure of these objects was first
announced, the discovery was received with some degree of
incredulity. Other astronomers looked at the same objects, and when
they failed to discern--and they frequently did fail to discern--the
spiral structure which Lord Rosse had indicated, they drew the
conclusion that this spiral structure did not exist. They thought it
must be due possibly to some instrumental defect or to the
imagination of the observer. It was, however, hardly possible for
any one who was both willing and competent to examine into the
evidence, to doubt the reality of Lord Rosse's discoveries. It
happens, however, that they have been recently placed beyond all
doubt by testimony which it is impossible to gainsay. A witness
never influenced by imagination has now come forward, and the
infallible photographic plate has justified Lord Rosse. Among the
remarkable discoveries which Dr. Isaac Roberts has recently made in
the application of his photographic apparatus to the heavens, there
is none more striking than that which declares, not only that the
nebulae which Lord Rosse described as spirals, actually do possess
the character so indicated, but that there are many others of the
same description. He has even brought to light the astonishingly
interesting fact that there are invisible objects of this class which
have never been seen by human eye, but whose spiral character is
visible to the peculiar delicacy of the photographic telescope.

In his earlier years, Lord Rosse himself used to be a diligent
observer of the heavenly bodies with the great telescope which was
completed in the year 1845. But I think that those who knew Lord
Rosse well, will agree that it was more the mechanical processes
incidental to the making of the telescope which engaged his interest
than the actual observations with the telescope when it was
completed. Indeed one who was well acquainted with him believed Lord
Rosse's special interest in the great telescope ceased when the last
nail had been driven into it. But the telescope was never allowed to
lie idle, for Lord Rosse always had associated with him some ardent
young astronomer, whose delight it was to employ to the uttermost the
advantages of his position in exploring the wonders of the sky. Among
those who were in this capacity in the early days of the great
telescope, I may mention my esteemed friend Dr. Johnston Stoney.

Such was the renown of Lord Rosse himself, brought about by his
consummate mechanical genius and his astronomical discoveries, and
such the interest which gathered around the marvellous workshops at
Birr castle, wherein his monumental exhibitions of optical skill were
constructed, that visitors thronged to see him from all parts of the
world. His home at Parsonstown became one of the most remarkable
scientific centres in Great Britain; thither assembled from time to
time all the leading men of science in the country, as well as many
illustrious foreigners. For many years Lord Rosse filled with marked
distinction the exalted position of President of the Royal Society,
and his advice and experience in practical mechanical matters were
always at the disposal of those who sought his assistance. Personally
and socially Lord Rosse endeared himself to all with whom he came in
contact. I remember one of the attendants telling me that on one
occasion he had the misfortune to let fall and break one of the small
mirrors on which Lord Rosse had himself expended many hours of hard
personal labour. The only remark of his lordship was that "accidents
will happen."

The latter years of his life Lord Rosse passed in comparative
seclusion; he occasionally went to London for a brief sojourn during
the season, and he occasionally went for a cruise in his yacht; but
the greater part of the year he spent at Birr Castle, devoting
himself largely to the study of political and social questions, and
rarely going outside the walls of his demesne, except to church on
Sunday mornings. He died on October 31, 1867.

He was succeeded by his eldest son, the present Earl of Rosse, who
has inherited his father's scientific abilities, and done much
notable work with the great telescope.




AIRY.


In our sketch of the life of Flamsteed, we have referred to the
circumstances under which the famous Observatory that crowns
Greenwich Hill was founded. We have also had occasion to mention
that among the illustrious successors of Flamsteed both Halley and
Bradley are to be included. But a remarkable development of
Greenwich Observatory from the modest establishment of early days
took place under the direction of the distinguished astronomer whose
name is at the head of this chapter. By his labours this temple of
science was organised to such a degree of perfection that it has
served in many respects as a model for other astronomical
establishments in various parts of the world. An excellent account
of Airy's career has been given by Professor H. H. Turner, in the
obituary notice published by the Royal Astronomical Society. To this
I am indebted for many of the particulars here to be set down
concerning the life of the illustrious Astronomer Royal.

The family from which Airy took his origin came from Kentmere, in
Westmoreland. His father, William Airy, belonged to a Lincolnshire
branch of the same stock. His mother's maiden name was Ann Biddell,
and her family resided at Playford, near Ipswich. William Airy held
some small government post which necessitated an occasional change of
residence to different parts of the country, and thus it was that his
son, George Biddell, came to be born at Alnwick, on 27th July, 1801.
The boy's education, so far as his school life was concerned was
partly conducted at Hereford and partly at Colchester. He does not,
however, seem to have derived much benefit from the hours which he
passed in the schoolroom. But it was delightful to him to spend his
holidays on the farm at Playford, where his uncle, Arthur Biddell,
showed him much kindness. The scenes of his early youth remained
dear to Airy throughout his life, and in subsequent years he himself
owned a house at Playford, to which it was his special delight to
resort for relaxation during the course of his arduous career. In
spite of the defects of his school training he seems to have
manifested such remarkable abilities that his uncle decided to enter
him in Cambridge University. He accordingly joined Trinity College
as a sizar in 1819, and after a brilliant career in mathematical and
physical science he graduated as Senior Wrangler in 1823. It may be
noted as an exceptional circumstance that, notwithstanding the
demands on his time in studying for his tripos, he was able, after
his second term of residence, to support himself entirely by taking
private pupils. In the year after he had taken his degree he was
elected to a Fellowship at Trinity College.

Having thus gained an independent position, Airy immediately entered
upon that career of scientific work which he prosecuted without
intermission almost to the very close of his life. One of his most
interesting researches in these early days is on the subject of
Astigmatism, which defect he had discovered in his own eyes. His
investigations led him to suggest a means of correcting this defect
by using a pair of spectacles with lenses so shaped as to counteract
the derangement which the astigmatic eye impressed upon the rays of
light. His researches on this subject were of a very complete
character, and the principles he laid down are to the present day
practically employed by oculists in the treatment of this
malformation.

On the 7th of December, 1826, Airy was elected to the Lucasian
Professorship of Mathematics in the University of Cambridge, the
chair which Newton's occupancy had rendered so illustrious. His
tenure of this office only lasted for two years, when he exchanged it
for the Plumian Professorship. The attraction which led him to
desire this change is doubtless to be found in the circumstance that
the Plumian Professorship of Astronomy carried with it at that time
the appointment of director of the new astronomical observatory, the
origin of which must now be described.

Those most interested in the scientific side of University life
decided in 1820 that it would be proper to found an astronomical
observatory at Cambridge. Donations were accordingly sought for this
purpose, and upwards of 6,000 pounds were contributed by members of
the University and the public. To this sum 5,000 pounds were added
by a grant from the University chest, and in 1824 further sums
amounting altogether to 7,115 pounds were given by the University for
the same object. The regulations as to the administration of the new
observatory placed it under the management of the Plumian Professor,
who was to be provided with two assistants. Their duties were to
consist in making meridian observations of the sun, moon, and the
stars, and the observations made each year were to be printed and
published. The observatory was also to be used in the educational
work of the University, for it was arranged that smaller instruments
were to be provided by which students could be instructed in the
practical art of making astronomical observations.

The building of the Cambridge Astronomical Observatory was completed
in 1824, but in 1828, when Airy entered on the discharge of his
duties as Director, the establishment was still far from completion,
in so far as its organisation was concerned. Airy commenced his work
so energetically that in the next year after his appointment he was
able to publish the first volume of "Cambridge Astronomical
Observations," notwithstanding that every part of the work, from the
making of observations to the revising of the proof-sheets, had to be
done by himself.

It may here be remarked that these early volumes of the publications
of the Cambridge Observatory contained the first exposition of those
systematic methods of astronomical work which Airy afterwards
developed to such a great extent at Greenwich, and which have been
subsequently adopted in many other places. No more profitable
instruction for the astronomical beginner can be found than that
which can be had by the study of these volumes, in which the Plumian
Professor has laid down with admirable clearness the true principles
on which meridian work should be conducted.

[PLATE: SIR GEORGE AIRY.
From a Photograph by Mr. E.P. Adams, Greenwich.]

Airy gradually added to the instruments with which the observatory
was originally equipped. A mural circle was mounted in 1832, and in
the same year a small equatorial was erected by Jones. This was made
use of by Airy in a well-known series of observations of Jupiter's
fourth satellite for the determination of the mass of the great
planet. His memoir on this subject fully expounds the method of
finding the weight of a planet from observations of the movements of
a satellite by which the planet is attended. This is, indeed, a
valuable investigation which no student of astronomy can afford to
neglect. The ardour with which Airy devoted himself to astronomical
studies may be gathered from a remarkable report on the progress of
astronomy during the present century, which he communicated to the
British Association at its second meeting in 1832. In the early
years of his life at Cambridge his most famous achievement was
connected with a research in theoretical astronomy for which
consummate mathematical power was required. We can only give a brief
account of the Subject, for to enter into any full detail with regard
to it would be quite out of the question.

Venus is a planet of about the same size and the same weight as the
earth, revolving in an orbit which lies within that described by our
globe. Venus, consequently, takes less time than the earth to
accomplish one revolution round the sun, and it happens that the
relative movements of Venus and the earth are so proportioned that in
the time in which our earth accomplishes eight of her revolutions the
other planet will have accomplished almost exactly thirteen. It,
therefore, follows that if the earth and Venus are in line with the
sun at one date, then in eight years later both planets will again be
found at the same points in their orbits. In those eight years the
earth has gone round eight times, and has, therefore, regained its
original position, while in the same period Venus has accomplished
thirteen complete revolutions, and, therefore, this planet also has
reached the same spot where it was at first. Venus and the earth, of
course, attract each other, and in consequence of these mutual
attractions the earth is swayed from the elliptic track which it
would otherwise pursue. In like manner Venus is also forced by the
attraction of the earth to revolve in a track which deviates from
that which it would otherwise follow. Owing to the fact that the sun
is of such preponderating magnitude (being, in fact, upwards of
300,000 times as heavy as either Venus or the earth), the
disturbances induced in the motion of either planet, in consequence
of the attraction of the other, are relatively insignificant to the
main controlling agency by which each of the movements is governed.
It is, however, possible under certain circumstances that the
disturbing effects produced upon one planet by the other can become
so multiplied as to produce peculiar effects which attain measurable
dimensions. Suppose that the periodic times in which the earth and
Venus revolved had no simple relation to each other, then the points
of their tracks in which the two planets came into line with the sun
would be found at different parts of the orbits, and consequently the
disturbances would to a great extent neutralise each other, and
produce but little appreciable effect. As, however, Venus and the
earth come back every eight years to nearly the same positions at the
same points of their track, an accumulative effect is produced. For
the disturbance of one planet upon the other will, of course, be
greatest when those two planets are nearest, that is, when they lie
in line with the sun and on the same side of it. Every eight years a
certain part of the orbit of the earth is, therefore, disturbed by
the attraction of Venus with peculiar vigour. The consequence is
that, owing to the numerical relation between the movements of the
planets to which I have referred, disturbing effects become
appreciable which would otherwise be too small to permit of
recognition. Airy proposed to himself to compute the effects which
Venus would have on the movement of the earth in consequence of the
circumstance that eight revolutions of the one planet required almost
the same time as thirteen revolutions of the other. This is a
mathematical inquiry of the most arduous description, but the Plumian
Professor succeeded in working it out, and he had, accordingly, the
gratification of announcing to the Royal Society that he had detected
the influence which Venus was thus able to assert on the movement of
our earth around the sun. This remarkable investigation gained for
its author the gold medal of the Royal Astronomical Society in the
year 1832.

In consequence of his numerous discoveries, Airy's scientific fame
had become so well recognised that the Government awarded him a
special pension, and in 1835, when Pond, who was then Astronomer
Royal, resigned, Airy was offered the post at Greenwich. There was
in truth, no scientific inducement to the Plumian Professor to leave
the comparatively easy post he held at Cambridge, in which he had
ample leisure to devote himself to those researches which specially
interested him, and accept that of the much more arduous observatory
at Greenwich. There were not even pecuniary inducements to make the
change; however, he felt it to be his duty to accede to the request
which the Government had made that he would take up the position
which Pond had vacated, and accordingly Airy went to Greenwich as
Astronomer Royal on October 1st, 1835.

He immediately began with his usual energy to organise the systematic
conduct of the business of the National Observatory. To realise one
of the main characteristics of Airy's great work at Greenwich, it is
necessary to explain a point that might not perhaps be understood
without a little explanation by those who have no practical
experience in an observatory. In the work of an establishment such
as Greenwich, an observation almost always consists of a measurement
of some kind. The observer may, for instance, be making a
measurement of the time at which a star passes across a spider line
stretched through the field of view; on another occasion his object
may be the measurement of an angle which is read off by examining
through a microscope the lines of division on a graduated circle when
the telescope is so pointed that the star is placed on a certain mark
in the field of view. In either case the immediate result of the
astronomical observation is a purely numerical one, but it rarely
happens, indeed we may say it never happens, that the immediate
numerical result which the observation gives expresses directly the
quantity which we are really seeking for. No doubt the observation
has been so designed that the quantity we want to find can be
obtained from the figures which the measurement gives, but the object
sought is not those figures, for there are always a multitude of
other influences by which those figures are affected. For example,
if an observation were to be perfect, then the telescope with which
the observation is made should be perfectly placed in the exact
position which it ought to occupy; this is, however, never the case,
for no mechanic can ever construct or adjust a telescope so perfectly
as the wants of the astronomer demand. The clock also by which we
determine the time of the observation should be correct, but this is
rarely if ever the case. We have to correct our observations for
such errors, that is to say, we have to determine the errors in the
positions of our telescopes and the errors in the going of our
clocks, and then we have to determine what the observations would
have been had our telescopes been absolutely perfect, and had our
clocks been absolutely correct. There are also many other matters
which have to be attended to in order to reduce our observations so
as to obtain from the figures as yielded to the observer at the
telescope the actual quantities which it is his object to determine.

The work of effecting these reductions is generally a very intricate
and laborious matter, so that it has not unfrequently happened that
while observations have accumulated in an observatory, yet the
tedious duty of reducing these observations has been allowed to fall
into arrear. When Airy entered on his duties at Greenwich he found
there an enormous mass of observations which, though implicitly
containing materials of the greatest value to astronomers, were, in
their unreduced form, entirely unavailable for any useful purpose.
He, therefore, devoted himself to coping with the reduction of the
observations of his predecessors. He framed systematic methods by
which the reductions were to be effected, and he so arranged the work
that little more than careful attention to numerical accuracy would
be required for the conduct of the operations. Encouraged by the
Admiralty, for it is under this department that Greenwich Observatory
is placed, the Astronomer Royal employed a large force of computers
to deal with the work. BY his energy and admirable organisation he
managed to reduce an extremely valuable series of planetary
observations, and to publish the results, which have been of the
greatest importance to astronomical investigation.

The Astronomer Royal was a capable, practical engineer as well as an
optician, and he presently occupied himself by designing astronomical
instruments of improved pattern, which should replace the antiquated
instruments he found in the observatory. In the course of years the
entire equipment underwent a total transformation. He ordered a
great meridian circle, every part of which may be said to have been
formed from his own designs. He also designed the mounting for a
fine equatorial telescope worked by a driving clock, which he had
himself invented. Gradually the establishment at Greenwich waxed
great under his incessant care. It was the custom for the
observatory to be inspected every year by a board of visitors, whose
chairman was the President of the Royal Society. At each annual
visitation, held on the first Saturday in June, the visitors received
a report from the Astronomer Royal, in which he set forth the
business which had been accomplished during the past year. It was on
these occasions that applications were made to the Admiralty, either
for new instruments or for developing the work of the observatory in
some other way. After the more official business of the inspection
was over, the observatory was thrown open to visitors, and hundreds
of people enjoyed on that day the privilege of seeing the national
observatory. These annual gatherings are happily still continued,
and the first Saturday in June is known to be the occasion of one of
the most interesting reunions of scientific men which takes place in
the course of the year.

Airy's scientific work was, however, by no means confined to the
observatory. He interested himself largely in expeditions for the
observation of eclipses and in projects for the measurement of arcs
on the earth. He devoted much attention to the collection of magnetic
observations from various parts of the world. Especially will it be
remembered that the circumstances of the transits of Venus, which
occurred in 1874 and in 1882, were investigated by him, and under his
guidance expeditions were sent forth to observe the transits from
those localities in remote parts of the earth where observations most
suitable for the determination of the sun's distance from the earth
could be obtained. The Astronomer Royal also studied tidal
phenomena, and he rendered great service to the country in the
restoration of the standards of length and weight which had been
destroyed in the great fire at the House of Parliament in October,
1834. In the most practical scientific matters his advice was often
sought, and was as cheerfully rendered. Now we find him engaged in
an investigation of the irregularities of the compass in iron ships,
with a view to remedying its defects; now we find him reporting on
the best gauge for railways. Among the most generally useful
developments of the observatory must be mentioned the telegraphic
method for the distribution of exact time. By arrangement with the
Post Office, the astronomers at Greenwich despatch each morning a
signal from the observatory to London at ten o'clock precisely. By
special apparatus, this signal is thence distributed automatically
over the country, so as to enable the time to be known everywhere
accurately to a single second. It was part of the same system that a
time ball should be dropped daily at one o'clock at Deal, as well as
at other places, for the purpose of enabling ship's chronometers to
be regulated.

Airy's writings were most voluminous, and no fewer than forty-eight
memoirs by him are mentioned in the "Catalogue of Scientific
Memoirs," published by the Royal Society up to the year 1873, and
this only included ten years out of an entire life of most
extraordinary activity. Many other subjects besides those of a
purely scientific character from time to time engaged his attention.
He wrote, for instance, a very interesting treatise on the Roman
invasion of Britain, especially with a view of determining the port
from which Caesar set forth from Gaul, and the point at which he
landed on the British coast. Airy was doubtless led to this
investigation by his study of the tidal phenomena in the Straits of
Dover. Perhaps the Astronomer Royal is best known to the general
reading public by his excellent lectures on astronomy, delivered at
the Ipswich Museum in 1848. This book has passed through many
editions, and it gives a most admirable account of the manner in
which the fundamental problems in astronomy have to be attacked.

As years rolled by almost every honour and distinction that could be
conferred upon a scientific man was awarded to Sir George Airy. He
was, indeed, the recipient of other honours not often awarded for
scientific distinction. Among these we may mention that in 1875 he
received the freedom of the City of London, "as a recognition of his
indefatigable labours in astronomy, and of his eminent services in
the advancement of practical science, whereby he has so materially
benefited the cause of commerce and civilisation."

Until his eightieth year Airy continued to discharge his labours at
Greenwich with unflagging energy. At last, on August 15th, 1881, he
resigned the office which he had held so long with such distinction
to himself and such benefit to his country. He had married in 1830
the daughter of the Rev. Richard Smith, of Edensor. Lady Airy died
in 1875, and three sons and three daughters survived him. One
daughter is the wife of Dr. Routh, of Cambridge, and his other
daughters were the constant companions of their father during the
declining years of his life. Up to the age of ninety he enjoyed
perfect physical health, but an accidental fall which then occurred
was attended with serious results. He died on Saturday, January 2nd,
1892, and was buried in the churchyard at Playford.




HAMILTON.


William Rowan Hamilton was born at midnight between the 3rd and 4th
of August, 1805, at Dublin, in the house which was then 29, but
subsequently 36, Dominick Street. His father, Archibald Hamilton,
was a solicitor, and William was the fourth of a family of nine. With
reference to his descent, it may be sufficient to notice that his
ancestors appear to have been chiefly of gentle Irish families, but
that his maternal grandmother was of Scottish birth. When he was
about a year old, his father and mother decided to hand over the
education of the child to his uncle, James Hamilton, a clergyman of
Trim, in County Meath. James Hamilton's sister, Sydney, resided with
him, and it was in their home that the days of William's childhood
were passed.

In Mr. Graves' "Life of Sir William Rowan Hamilton" a series of
letters will be found, in which Aunt Sydney details the progress of
the boy to his mother in Dublin. Probably there is no record of an
infant prodigy more extraordinary than that which these letters
contain. At three years old his aunt assured the mother that William
is "a hopeful blade," but at that time it was his physical vigour to
which she apparently referred; for the proofs of his capacity, which
she adduces, related to his prowess in making boys older than himself
fly before him. In the second letter, a month later, we hear that
William is brought in to read the Bible for the purpose of putting to
shame other boys double his age who could not read nearly so well.
Uncle James appears to have taken much pains with William's
schooling, but his aunt said that "how he picks up everything is
astonishing, for he never stops playing and jumping about." When he
was four years and three months old, we hear that he went out to dine
at the vicar's, and amused the company by reading for them equally
well whether the book was turned upside down or held in any other
fashion. His aunt assures the mother that "Willie is a most sensible
little creature, but at the same time has a great deal of roguery."
At four years and five months old he came up to pay his mother a
visit in town, and she writes to her sister a description of the
boy;--

"His reciting is astonishing, and his clear and accurate knowledge of
geography is beyond belief; he even draws the countries with a pencil
on paper, and will cut them out, though not perfectly accurate, yet
so well that a anybody knowing the countries could not mistake them;
but, you will think this nothing when I tell you that he reads Latin,
Greek, and Hebrew."

Aunt Sydney recorded that the moment Willie got back to Trim he was
desirous of at once resuming his former pursuits. He would not eat
his breakfast till his uncle had heard him his Hebrew, and he
comments on the importance of proper pronunciation. At five he was
taken to see a friend, to whom he repeated long passages from
Dryden. A gentleman present, who was not unnaturally sceptical about
Willie's attainments, desired to test him in Greek, and took down a
copy of Homer which happened to have the contracted type, and to his
amazement Willie went on with the greatest ease. At six years and
nine months he was translating Homer and Virgil; a year later his
uncle tells us that William finds so little difficulty in learning
French and Italian, that he wishes to read Homer in French. He is
enraptured with the Iliad, and carries it about with him, repeating
from it whatever particularly pleases him. At eight years and one
month the boy was one of a party who visited the Scalp in the Dublin
mountains, and he was so delighted with the scenery that he forthwith
delivered an oration in Latin. At nine years and six months he is
not satisfied until he learns Sanscrit; three months later his thirst
for the Oriental languages is unabated, and at ten years and four
months he is studying Arabic and Persian. When nearly twelve he
prepared a manuscript ready for publication. It was a "Syriac
Grammar," in Syriac letters and characters compiled from that of
Buxtorf, by William Hamilton, Esq., of Dublin and Trim. When he was
fourteen, the Persian ambassador, Mirza Abul Hassan Khan, paid a
visit to Dublin, and, as a practical exercise in his Oriental
languages, the young scholar addressed to his Excellency a letter in
Persian; a translation of which production is given by Mr. Graves.
When William was fourteen he had the misfortune to lose his father;
and he had lost his mother two years previously. The boy and his
three sisters were kindly provided for by different members of the
family on both sides.

It was when William was about fifteen that his attention began to be
turned towards scientific subjects. These were at first regarded
rather as a relaxation from the linguistic studies with which he had
been so largely occupied. On November 22nd, 1820, he notes in his
journal that he had begun Newton's "Principia": he commenced also the
study of astronomy by observing eclipses, occultations, and similar
phenomena. When he was sixteen we learn that he had read conic
sections, and that he was engaged in the study of pendulums. After
an attack of illness, he was moved for change to Dublin, and in May,
1822, we find him reading the differential calculus and Laplace's
"Mecanique Celeste." He criticises an important part of Laplace's
work relative to the demonstration of the parallelogram of forces. In
this same year appeared the first gushes of those poems which
afterwards flowed in torrents.

His somewhat discursive studies had, however, now to give place to a
more definite course of reading in preparation for entrance to the
University of Dublin. The tutor under whom he entered, Charles
Boyton, was himself a distinguished man, but he frankly told the
young William that he could be of little use to him as a tutor, for
his pupil was quite as fit to be his tutor. Eliza Hamilton, by whom
this is recorded, adds, "But there is one thing which Boyton would
promise to be to him, and that was a FRIEND; and that one proof he
would give of this should be that, if ever he saw William beginning
to be UPSET by the sensation he would excite, and the notice he would
attract, he would tell him of it." At the beginning of his college
career he distanced all his competitors in every intellectual
pursuit. At his first term examination in the University he was
first in Classics and first in Mathematics, while he received the
Chancellor's prize for a poem on the Ionian Islands, and another for
his poem on Eustace de St. Pierre.

There is abundant testimony that Hamilton had "a heart for friendship
formed." Among the warmest of the friends whom he made in these
early days was the gifted Maria Edgeworth, who writes to her sister
about "young Mr. Hamilton, an admirable Crichton of eighteen, a real
prodigy of talents, who Dr. Brinkley says may be a second Newton,
quiet, gentle, and simple." His sister Eliza, to whom he was
affectionately attached, writes to him in 1824:--

"I had been drawing pictures of you in my mind in your study at
Cumberland Street with 'Xenophon,' &c., on the table, and you, with
your most awfully sublime face of thought, now sitting down, and now
walking about, at times rubbing your hands with an air of
satisfaction, and at times bursting forth into some very heroical
strain of poetry in an unknown language, and in your own internal
solemn ventriloquist-like voice, when you address yourself to the
silence and solitude of your own room, and indeed, at times, even
when your mysterious poetical addresses are not quite unheard."

This letter is quoted because it refers to a circumstance which all
who ever met with Hamilton, even in his latest years, will remember.
He was endowed with two distinct voices, one a high treble, the other
a deep bass, and he alternately employed these voices not only in
ordinary conversation, but when he was delivering an address on the
profundities of Quaternions to the Royal Irish Academy, or on
similar occasions. His friends had long grown so familiar with this
peculiarity that they were sometimes rather surprised to find how
ludicrous it appeared to strangers.

Hamilton was fortunate in finding, while still at a very early age, a
career open before him which was worthy of his talents. He had not
ceased to be an undergraduate before he was called to fill an
illustrious chair in his university. The circumstances are briefly
as follows.

We have already mentioned that, in 1826, Brinkley was appointed
Bishop of Cloyne, and the professorship of astronomy thereupon became
vacant. Such was Hamilton's conspicuous eminence that,
notwithstanding he was still an undergraduate, and had only just
completed his twenty-first year, he was immediately thought of as a
suitable successor to the chair. Indeed, so remarkable were his
talents in almost every direction that had the vacancy been in the
professorship of classics or of mathematics, of English literature or
of metaphysics, of modern or of Oriental languages, it seems
difficult to suppose that he would not have occurred to every one as
a possible successor. The chief ground, however, on which the
friends of Hamilton urged his appointment was the earnest of original
power which he had already shown in a research on the theory of
Systems of Rays. This profound work created a new branch of optics,
and led a few years later to a superb discovery, by which the fame of
its author became world-wide.

At first Hamilton thought it would be presumption for him to apply
for so exalted a position; he accordingly retired to the country, and
resumed his studies for his degree. Other eminent candidates came
forward, among them some from Cambridge, and a few of the Fellows
from Trinity College, Dublin, also sent in their claims. It was not
until Hamilton received an urgent letter from his tutor Boyton, in
which he was assured of the favourable disposition of the Board
towards his candidature, that he consented to come forward, and on
June 16th, 1827, he was unanimously chosen to succeed the Bishop of
Cloyne as Professor of Astronomy in the University. The appointment
met with almost universal approval. It should, however, be noted
that Brinkley, whom Hamilton succeeded, did not concur in the general
sentiment. No one could have formed a higher opinion than he had
done of Hamilton's transcendent powers; indeed, it was on that very
ground that he seemed to view the appointment with disapprobation.
He considered that it would have been wiser for Hamilton to have
obtained a Fellowship, in which capacity he would have been able to
exercise a greater freedom in his choice of intellectual pursuits.
The bishop seems to have thought, and not without reason, that
Hamilton's genius would rather recoil from much of the routine work
of an astronomical establishment. Now that Hamilton's whole life is
before us, it is easy to see that the bishop was entirely wrong. It
is quite true that Hamilton never became a skilled astronomical
observer; but the seclusion of the observatory was eminently
favourable to those gigantic labours to which his life was devoted,
and which have shed so much lustre, not only on Hamilton himself, but
also on his University and his country.

In his early years at Dunsink, Hamilton did make some attempts at a
practical use of the telescopes, but he possessed no natural aptitude
for such work, while exposure which it involved seems to have acted
injuriously on his health. He, therefore, gradually allowed his
attention to be devoted to those mathematical researches in which he
had already given such promise of distinction. Although it was in
pure mathematics that he ultimately won his greatest fame, yet he
always maintained and maintained with justice, that he had ample
claims to the title of an astronomer. In his later years he set
forth this position himself in a rather striking manner. De Morgan
had written commending to Hamilton's notice Grant's "History of
Physical Astronomy." After becoming acquainted with the book,
Hamilton writes to his friend as follows:--

"The book is very valuable, and very creditable to its composer. But
your humble servant may be pardoned if he finds himself somewhat
amused at the title, 'History of Physical Astronomy from the Earliest
Ages to the Middle of the Nineteenth Century,' when he fails to
observe any notice of the discoveries of Sir W. R. Hamilton in the
theory of the 'Dynamics of the Heavens.'"

The intimacy between the two correspondents will account for the tone
of this letter; and, indeed, Hamilton supplies in the lines which
follow ample grounds for his complaint. He tells how Jacobi spoke of
him in Manchester in 1842 as "le Lagrange de votre pays," and how
Donkin had said that, "The Analytical Theory of Dynamics as it exists
at present is due mainly to the labours of La Grange Poisson,
Sir W. R. Hamilton, and Jacobi, whose researches on this subject
present a series of discoveries hardly paralleled for their elegance
and importance in any other branch of mathematics." In the same
letter Hamilton also alludes to the success which had attended the
applications of his methods in other hands than his own to the
elucidation of the difficult subject of Planetary Perturbations.
Even had his contributions to science amounted to no more than these
discoveries, his tenure of the chair would have been an illustrious
one. It happens, however, that in the gigantic mass of his
intellectual work these researches, though intrinsically of such
importance, assume what might almost be described as a relative
insignificance.

The most famous achievement of Hamilton's earlier years at the
observatory was the discovery of conical refraction. This was one of
those rare events in the history of science, in which a sagacious
calculation has predicted a result of an almost startling character,
subsequently confirmed by observation. At once this conferred on the
young professor a world-wide renown. Indeed, though he was still
only twenty-seven, he had already lived through an amount of
intellectual activity which would have been remarkable for a man of
threescore and ten.

Simultaneously with his growth in fame came the growth of his several
friendships. There were, in the first place, his scientific
friendships with Herschel, Robinson, and many others with whom he had
copious correspondence. In the excellent biography to which I have
referred, Hamilton's correspondence with Coleridge may be read, as
can also the letters to his lady correspondents, among them being
Maria Edgeworth, Lady Dunraven, and Lady Campbell. Many of these
sheets relate to literary matters, but they are largely intermingled
With genial pleasantry, and serve at all events to show the affection
and esteem with which he was regarded by all who had the privilege of
knowing him. There are also the letters to the sisters whom he
adored, letters brimming over with such exalted sentiment, that most
ordinary sisters would be tempted to receive them with a smile in the
excessively improbable event of their still more ordinary brothers
attempting to pen such effusions. There are also indications of
letters to and from other young ladies who from time to time were the
objects of Hamilton's tender admiration. We use the plural
advisedly, for, as Mr. Graves has set forth, Hamilton's love affairs
pursued a rather troubled course. The attention which he lavished on
one or two fair ones was not reciprocated, and even the intense
charms of mathematical discovery could not assuage the pangs which
the disappointed lover experienced. At last he reached the haven of
matrimony in 1833, when he was married to Miss Bayly. Of his married
life Hamilton said, many years later to De Morgan, that it was as
happy as he expected, and happier than he deserved. He had two sons,
William and Archibald, and one daughter, Helen, who became the wife
of Archdeacon O'Regan.

[PLATE: SIR W. ROWAN HAMILTON.]

The most remarkable of Hamilton's friendships in his early years was
unquestionably that with Wordsworth. It commenced with Hamilton's
visit to Keswick; and on the first evening, when the poet met the
young mathematician, an incident occurred which showed the mutual
interest that was aroused. Hamilton thus describes it in a letter to
his sister Eliza:--

"He (Wordsworth) walked back with our party as far as their lodge,
and then, on our bidding Mrs. Harrison good-night, I offered to walk
back with him while my party proceeded to the hotel. This offer he
accepted, and our conversation had become so interesting that when we
had arrived at his home, a distance of about a mile, he proposed to
walk back with me on my way to Ambleside, a proposal which you may be
sure I did not reject; so far from it that when he came to turn once
more towards his home I also turned once more along with him. It was
very late when I reached the hotel after all this walking."

Hamilton also submitted to Wordsworth an original poem, entitled
"It Haunts me Yet." The reply of Wordsworth is worth repeating:--

"With a safe conscience I can assure you that, in my judgment, your
verses are animated with the poetic spirit, as they are evidently the
product of strong feeling. The sixth and seventh stanzas affected me
much, even to the dimming of my eyes and faltering of my voice while
I was reading them aloud. Having said this, I have said enough. Now
for the per contra. You will not, I am sure, be hurt when I tell you
that the workmanship (what else could be expected from so young a
writer?) is not what it ought to be. . .

"My household desire to be remembered to you in no formal way.
Seldom have I parted--never, I was going to say--with one whom after
so short an acquaintance I lost sight of with more regret. I trust
we shall meet again."

The further affectionate intercourse between Hamilton and Wordsworth
is fully set forth, and to Hamilton's latest years a recollection of
his "Rydal hours" was carefully treasured and frequently referred
to. Wordsworth visited Hamilton at the observatory, where a
beautiful shady path in the garden is to the present day spoken of as
"Wordsworth's Walk."

It was the practice of Hamilton to produce a sonnet on almost every
occasion which admitted of poetical treatment, and it was his delight
to communicate his verses to his friends all round. When Whewell was
producing his "Bridgewater Treatises," he writes to Hamilton in
1833:--

"Your sonnet which you showed me expressed much better than I could
express it the feeling with which I tried to write this book, and I
once intended to ask your permission to prefix the sonnet to my book,
but my friends persuaded me that I ought to tell my story in my own
prose, however much better your verse might be."

The first epoch-marking contribution to Theoretical Dynamics after
the time of Newton was undoubtedly made by Lagrange, in his discovery
of the general equations of Motion. The next great step in the same
direction was that taken by Hamilton in his discovery of a still more
comprehensive method. Of this contribution Hamilton writes to
Whewell, March 31st, 1834:--

"As to my late paper, a day or two ago sent off to London, it is
merely mathematical and deductive. I ventured, indeed, to call it
the 'Mecanique Analytique' of Lagrange, 'a scientific poem'; and
spoke of Dynamics, or the Science of Force, as treating of 'Power
acting by Law in Space and Time.' In other respects it is as
unpoetical and unmetaphysical as my gravest friends could desire."

It may well be doubted whether there is a more beautiful chapter in
the whole of mathematical philosophy than that which contains
Hamilton's dynamical theory. It is disfigured by no tedious
complexity of symbols; it condescends not to any particular problems;
it is an all embracing theory, which gives an intellectual grasp of
the most appropriate method for discovering the result of the
application of force to matter. It is the very generality of this
doctrine which has somewhat impeded the applications of which it is
susceptible. The exigencies of examinations are partly responsible
for the fact that the method has not become more familiar to students
of the higher mathematics. An eminent professor has complained that
Hamilton's essay on dynamics was of such an extremely abstract
character, that he found himself unable to extract from it problems
suitable for his examination papers.

The following extract is from a letter of Professor Sylvester to
Hamilton, dated 20th of September, 1841. It will show how his works
were appreciated by so consummate a mathematician as the writer:--

"Believe me, sir, it is not the least of my regrets in quitting this
empire to feel that I forego the casual occasion of meeting those
masters of my art, yourself chief amongst the number, whose
acquaintance, whose conversation, or even notice, have in themselves
the power to inspire, and almost to impart fresh vigour to the
understanding, and the courage and faith without which the efforts of
invention are in vain. The golden moments I enjoyed under your
hospitable roof at Dunsink, or moments such as they were, may
probably never again fall to my lot.

"At a vast distance, and in an humble eminence, I still promise myself
the calm satisfaction of observing your blazing course in the
elevated regions of discovery. Such national honour as you are able
to confer on your country is, perhaps, the only species of that
luxury for the rich (I mean what is termed one's glory) which is not
bought at the expense of the comforts of the million."

The study of metaphysics was always a favourite recreation when
Hamilton sought for a change from the pursuit of mathematics. In the
year 1834 we find him a diligent student of Kant; and, to show the
views of the author of Quaternions and of Algebra as the Science of
Pure Time on the "Critique of the Pure Reason," we quote the
following letter, dated 18th of July, 1834, from Hamilton to Viscount
Adare:--

"I have read a large part of the 'Critique of the Pure Reason,' and
find it wonderfully clear, and generally quite convincing.
Notwithstanding some previous preparation from Berkeley, and from my
own thoughts, I seem to have learned much from Kant's own statement
of his views of 'Space and Time.' Yet, on the whole, a large part of
my pleasure consists in recognising through Kant's works, opinions,
or rather views, which have been long familiar to myself, although
far more clearly and systematically expressed and combined by him.
. . . Kant is, I think, much more indebted than he owns, or, perhaps
knows, to Berkeley, whom he calls by a sneer, 'GUTEM Berkeley'. . .
as it were, 'good soul, well meaning man,' who was able for all that
to shake to its centre the world of human thought, and to effect a
revolution among the early consequences of which was the growth of
Kant himself."

At several meetings of the British Association Hamilton was a very
conspicuous figure. Especially was this the case in 1835, when the
Association met in Dublin, and when Hamilton, though then but thirty
years old, had attained such celebrity that even among a very
brilliant gathering his name was perhaps the most renowned. A
banquet was given at Trinity College in honour of the meeting. The
distinguished visitors assembled in the Library of the University.
The Earl of Mulgrave, then Lord Lieutenant of Ireland, made this the
opportunity of conferring on Hamilton the honour of knighthood,
gracefully adding, as he did so: "I but set the royal, and therefore
the national mark, on a distinction already acquired by your genius
and labours."

The banquet followed, writes Mr. Graves. "It was no little addition
to the honour Hamilton had already received that, when Professor
Whewell returned thanks for the toast of the University of Cambridge,
he thought it appropriate to add the words, 'There was one point
which strongly pressed upon him at that moment: it was now one
hundred and thirty years since a great man in another Trinity College
knelt down before his sovereign, and rose up Sir Isaac Newton.' The
compliment was welcomed by immense applause."

A more substantial recognition of the labours of Hamilton took place
subsequently. He thus describes it in a letter to Mr. Graves of 14th
of November, 1843:--

"The Queen has been pleased--and you will not doubt that it was
entirely unsolicited, and even unexpected, on my part--'to express
her entire approbation of the grant of a pension of two hundred
pounds per annum from the Civil List' to me for scientific services.
The letters from Sir Robert Peel and from the Lord Lieutenant of
Ireland in which this grant has been communicated or referred to have
been really more gratifying to my feelings than the addition to my
income, however useful, and almost necessary, that may have been."

The circumstances we have mentioned might lead to the supposition
that Hamilton was then at the zenith of his fame but this was not
so. It might more truly be said, that his achievements up to this
point were rather the preliminary exercises which fitted him for the
gigantic task of his life. The name of Hamilton is now chiefly
associated with his memorable invention of the calculus of
Quaternions. It was to the creation of this branch of mathematics
that the maturer powers of his life were devoted; in fact he gives us
himself an illustration of how completely habituated he became to the
new modes of thought which Quaternions originated. In one of his
later years he happened to take up a copy of his famous paper on
Dynamics, a paper which at the time created such a sensation among
mathematicians, and which is at this moment regarded as one of the
classics of dynamical literature. He read, he tells us, his paper
with considerable interest, and expressed his feelings of
gratification that he found himself still able to follow its
reasoning without undue effort. But it seemed to him all the time as
a work belonging to an age of analysis now entirely superseded.

In order to realise the magnitude of the revolution which Hamilton
has wrought in the application of symbols to mathematical
investigation, it is necessary to think of what Hamilton did beside
the mighty advance made by Descartes. To describe the character of
the quaternion calculus would be unsuited to the pages of this work,
but we may quote an interesting letter, written by Hamilton from his
death-bed, twenty-two years later, to his son Archibald, in which he
has recorded the circumstances of the discovery:--

"Indeed, I happen to be able to put the finger of memory upon the year
and month--October, 1843--when having recently returned from visits
to Cork and Parsonstown, connected with a meeting of the British
Association, the desire to discover the laws of multiplication
referred to, regained with me a certain strength and earnestness
which had for years been dormant, but was then on the point of being
gratified, and was occasionally talked of with you. Every morning in
the early part of the above-cited month, on my coming down to
breakfast, your (then) little brother William Edwin, and yourself,
used to ask me, 'Well papa, can you multiply triplets?' Whereto I
was always obliged to reply, with a sad shake of the head: 'No, I
can only ADD and subtract them,'

"But on the 16th day of the same month--which happened to be Monday,
and a Council day of the Royal Irish Academy--I was walking in to
attend and preside, and your mother was walking with me along the
Royal Canal, to which she had perhaps driven; and although she talked
with me now and then, yet an UNDERCURRENT of thought was going on in
my mind which gave at last a RESULT, whereof it is not too much to
say that I felt AT ONCE the importance. An ELECTRIC circuit seemed
to CLOSE; and a spark flashed forth the herald (as I FORESAW
IMMEDIATELY) of many long years to come of definitely directed
thought and work by MYSELF, if spared, and, at all events, on the
part of OTHERS if I should even be allowed to live long enough
distinctly to communicate the discovery. Nor could I resist the
impulse--unphilosophical as it may have been--to cut with a knife on
a stone of Brougham Bridge as we passed it, the fundamental formula
which contains the SOLUTION of the PROBLEM, but, of course, the
inscription has long since mouldered away. A more durable notice
remains, however, on the Council Books of the Academy for that day
(October 16, 1843), which records the fact that I then asked for and
obtained leave to read a Paper on 'Quaternions,' at the First General
Meeting of the Session; which reading took place accordingly, on
Monday, the 13th of November following."

Writing to Professor Tait, Hamilton gives further particulars of the
same event. And again in a letter to the Rev. J. W. Stubbs:--

"To-morrow will be the fifteenth birthday of the Quaternions. They
started into life full-grown on the 16th October, 1843, as I was
walking with Lady Hamilton to Dublin, and came up to Brougham
Bridge--which my boys have since called Quaternion Bridge. I pulled
out a pocketbook which still exists, and made entry, on which at the
very moment I felt that it might be worth my while to expend the
labour of at least ten or fifteen years to come. But then it is fair
to say that this was because I felt a problem to have been at that
moment solved, an intellectual want relieved which had haunted me for
at least fifteen years before.

"But did the thought of establishing such a system, in which
geometrically opposite facts--namely, two lines (or areas) which are
opposite IN SPACE give ALWAYS a positive product--ever come into
anybody's head till I was led to it in October, 1843, by trying to
extend my old theory of algebraic couples, and of algebra as the
science of pure time? As to my regarding geometrical addition of
lines as equivalent to composition of motions (and as performed by
the same rules), that is indeed essential in my theory but not
peculiar to it; on the contrary, I am only one of many who have been
led to this view of addition."

Pilgrims in future ages will doubtless visit the spot commemorated by
the invention of Quaternions. Perhaps as they look at that by no
means graceful structure Quaternion Bridge, they will regret that the
hand of some Old Mortality had not been occasionally employed in
cutting the memorable inscription afresh. It is now irrecoverably
lost.

It was ten years after the discovery that the great volume appeared
under the title of "Lectures on Quaternions," Dublin, 1853. The
reception of this work by the scientific world was such as might have
been expected from the extraordinary reputation of its author, and
the novelty and importance of the new calculus. His valued friend,
Sir John Herschel, writes to him in that style of which he was a
master:--

"Now, most heartily let me congratulate you on getting out your
book--on having found utterance, ore rotundo, for all that labouring
and seething mass of thought which has been from time to time sending
out sparks, and gleams, and smokes, and shaking the soil about you;
but now breaks into a good honest eruption, with a lava stream and a
shower of fertilizing ashes.

"Metaphor and simile apart, there is work for a twelve-month to any
man to read such a book, and for half a lifetime to digest it, and I
am glad to see it brought to a conclusion."

We may also record Hamilton's own opinion expressed to Humphrey
Lloyd:--

"In general, although in one sense I hope that I am actually growing
modest about the quaternions, from my seeing so many peeps and vistas
into future expansions of their principles, I still must assert that
this discovery appears to me to be as important for the middle of the
nineteenth century as the discovery of fluxions was for the close of
the seventeenth."

Bartholomew Lloyd died in 1837. He had been the Provost of Trinity
College, and the President of the Royal Irish Academy. Three
candidates were put forward by their respective friends for the
vacant Presidency. One was Humphrey Lloyd, the son of the late
Provost, and the two others were Hamilton and Archbishop Whately.
Lloyd from the first urged strongly the claims of Hamilton, and
deprecated the putting forward of his own name. Hamilton in like
manner desired to withdraw in favour of Lloyd. The wish was strongly
felt by many of the Fellows of the College that Lloyd should be
elected, in consequence of his having a more intimate association
with collegiate life than Hamilton; while his scientific eminence was
world-wide. The election ultimately gave Hamilton a considerable
majority over Lloyd, behind whom the Archbishop followed at a
considerable distance. All concluded happily, for both Lloyd and the
Archbishop expressed, and no doubt felt, the pre-eminent claims of
Hamilton, and both of them cordially accepted the office of a
Vice-President, to which, according to the constitution of the
Academy, it is the privilege of the incoming President to nominate.

In another chapter I have mentioned as a memorable episode in
astronomical history, that Sir J. Herschel went for a prolonged
sojourn to the Cape of Good Hope, for the purpose of submitting the
southern skies to the same scrutiny with the great telescope that his
father had given to the northern skies. The occasion of Herschel's
return after the brilliant success of his enterprise, was celebrated
by a banquet. On June 15th, 1838, Hamilton was assigned the high
honour of proposing the health of Herschel. This banquet is
otherwise memorable in Hamilton's career as being one of the two
occasions in which he was in the company of his intimate friend De
Morgan.

In the year 1838 a scheme was adopted by the Royal Irish Academy for
the award of medals to the authors of papers which appeared to
possess exceptionally high merit. At the institution of the medal
two papers were named in competition for the prize. One was
Hamilton's "Memoir on Algebra, as the Science of Pure Time." The
other was Macullagh's paper on the "Laws of Crystalline Reflection
and Refraction." Hamilton expresses his gratification that, mainly
in consequence of his own exertions, he succeeded in having the medal
awarded to Macullagh rather than to himself. Indeed, it would almost
appear as if Hamilton had procured a letter from Sir J. Herschel,
which indicated the importance of Macullagh's memoir in such a way as
to decide the issue. It then became Hamilton's duty to award the
medal from the chair, and to deliver an address in which he expressed
his own sense of the excellence of Macullagh's scientific work. It
is the more necessary to allude to these points, because in the whole
of his scientific career it would seem that Macullagh was the only
man with whom Hamilton had ever even an approach to a dispute about
priority. The incident referred to took place in connection with the
discovery of conical refraction, the fame of which Macullagh made a
preposterous attempt to wrest from Hamilton. This is evidently
alluded to in Hamilton's letter to the Marquis of Northampton, dated
June 28th, 1838, in which we read:--

"And though some former circumstances prevented me from applying to
the person thus distinguished the sacred name of FRIEND, I had the
pleasure of doing justice...to his high intellectual merits... I
believe he was not only gratified but touched, and may, perhaps,
regard me in future with feelings more like those which I long to
entertain towards him."

Hamilton was in the habit, from time to time, of commencing the
keeping of a journal, but it does not appear to have been
systematically conducted. Whatever difficulties the biographer may
have experienced from its imperfections and irregularities, seem to
be amply compensated for by the practice which Hamilton had of
preserving copies of his letters, and even of comparatively
insignificant memoranda. In fact, the minuteness with which
apparently trivial matters were often noted down appears almost
whimsical. He frequently made a memorandum of the name of the person
who carried a letter to the post, and of the hour in which it was
despatched. On the other hand, the letters which he received were
also carefully preserved in a mighty mass of manuscripts, with which
his study was encumbered, and with which many other parts of the
house were not unfrequently invaded. If a letter was laid aside for
a few hours, it would become lost to view amid the seething mass of
papers, though occasionally, to use his own expression, it might be
seen "eddying" to the surface in some later disturbance.

The great volume of "Lectures on Quaternions" had been issued, and
the author had received the honours which the completion of such a
task would rightfully bring him. The publication of an immortal work
does not, however, necessarily provide the means for paying the
printer's bill. The printing of so robust a volume was necessarily
costly; and even if all the copies could be sold, which at the time
did not seem very likely, they would hardly have met the inevitable
expenses. The provision of the necessary funds was, therefore, a
matter for consideration. The Board of Trinity College had already
contributed 200 pounds to the printing, but yet another hundred was
required. Even the discoverer of Quaternions found this a source of
much anxiety. However, the board, urged by the representation of
Humphrey Lloyd, now one of its members, and, as we have already seen,
one of Hamilton's staunchest friends, relieved him of all liability.
We may here note that, notwithstanding the pension which Hamilton
enjoyed in addition to the salary of his chair, he seems always to
have been in some what straitened circumstances, or, to use his own
words in one of his letters to De Morgan, "Though not an embarrassed
man, I am anything rather than a rich one." It appears that,
notwithstanding the world-wide fame of Hamilton's discoveries, the
only profit in a pecuniary sense that he ever obtained from any of
his works was by the sale of what he called his Icosian Game. Some
enterprising publisher, on the urgent representations of one of
Hamilton's friends in London, bought the copyright of the Icosian
Game for 25 pounds. Even this little speculation proved unfortunate
for the purchaser, as the public could not be induced to take the
necessary interest in the matter.

After the completion of his great book, Hamilton appeared for awhile
to permit himself a greater indulgence than usual in literary
relaxations. He had copious correspondence with his intimate friend,
Aubrey de Vere, and there were multitudes of letters from those
troops of friends whom it was Hamilton's privilege to possess. He
had been greatly affected by the death of his beloved sister Eliza, a
poetess of much taste and feeling. She left to him her many papers
to preserve or to destroy, but he said it was only after the
expiration of four years of mourning that he took courage to open her
pet box of letters.

The religious side of Hamilton's character is frequently illustrated
in these letters; especially is this brought out in the
correspondence with De Vere, who had seceded to the Church of Rome.
Hamilton writes, August 4, 1855:--

"If, then, it be painfully evident to both, that under such
circumstances there CANNOT (whatever we may both DESIRE) be NOW in
the nature of things, or of minds, the same degree of INTIMACY
between us as of old; since we could no longer TALK with the same
degree of unreserve on every subject which happened to present
itself, but MUST, from the simplest instincts of courtesy, be each on
his guard not to say what might be offensive, or, at least, painful
to the other; yet WE were ONCE so intimate, and retain still, and, as
I trust, shall always retain, so much of regard and esteem and
appreciation for each other, made tender by so many associations of
my early youth and your boyhood, which can never be forgotten by
either of us, that (as times go) TWO OR THREE VERY RESPECTABLE
FRIENDSHIPS might easily be carved out from the fragments of our
former and ever-to-be-remembered INTIMACY. It would be no
exaggeration to quote the words: 'Heu! quanto minus est cum reliquis
versari, quam tui meminisse!'"

In 1858 a correspondence on the subject of Quaternions commenced
between Professor Tait and Sir William Hamilton. It was particularly
gratifying to the discoverer that so competent a mathematician as
Professor Tait should have made himself acquainted with the new
calculus. It is, of course, well known that Professor Tait
subsequently brought out a most valuable elementary treatise on
Quaternions, to which those who are anxious to become acquainted with
the subject will often turn in preference to the tremendous work of
Hamilton.

In the year 1861 gratifying information came to hand of the progress
which the study of Quaternions was making abroad. Especially did the
subject attract the attention of that accomplished mathematician,
Moebius, who had already in his "Barycentrische Calculus" been led to
conceptions which bore more affinity to Quaternions than could be
found in the writings of any other mathematician. Such notices of
his work were always pleasing to Hamilton, and they served, perhaps,
as incentives to that still closer and more engrossing labour by
which he became more and more absorbed. During the last few years of
his life he was observed to be even more of a recluse than he had
hitherto been. His powers of long and continuous study seemed to
grow with advancing years, and his intervals of relaxation, such as
they were, became more brief and more infrequent.

It was not unusual for him to work for twelve hours at a stretch.
The dawn would frequently surprise him as he looked up to snuff his
candles after a night of fascinating labour at original research.
Regularity in habits was impossible to a student who had prolonged
fits of what he called his mathematical trances. Hours for rest and
hours for meals could only be snatched in the occasional the lucid
intervals between one attack of Quaternions and the next. When
hungry, he would go to see whether anything could be found on the
sideboard; when thirsty, he would visit the locker, and the one
blemish in the man's personal character is that these latter visits
were sometimes paid too often.

As an example of one of Hamilton's rare diversions from the all-
absorbing pursuit of Quaternions, we find that he was seized with
curiosity to calculate back to the date of the Hegira, which he found
on the 15th July, 622. He speaks of the satisfaction with which he
ascertained subsequently that Herschel had assigned precisely the
same date. Metaphysics remained also, as it had ever been, a
favourite subject of Hamilton's readings and meditations and of
correspondence with his friends. He wrote a very long letter to Dr.
Ingleby on the subject of his "Introduction to Metaphysics." In it
Hamilton alludes, as he has done also in other places, to a
peculiarity of his own vision. It was habitual to him, by some
defect in the correlation of his eyes, to see always a distinct image
with each; in fact, he speaks of the remarkable effect which the use
of a good stereoscope had on his sensations of vision. It was then,
for the first time, that he realised how the two images which he had
always seen hitherto would, under normal circumstances, be blended
into one. He cites this fact as bearing on the phenomena of
binocular vision, and he draws from it the inference that the
necessity of binocular vision for the correct appreciation of
distance is unfounded. "I am quite sure," he says, "that I SEE
DISTANCE with EACH EYE SEPARATELY."

The commencement of 1865, the last year of his life saw Hamilton as
diligent as ever, and corresponding with Salmon and Cayley. On April
26th he writes to a friend to say, that his health has not been good
for years past, and that so much work has injured his constitution;
and he adds, that it is not conducive to good spirits to find that he
is accumulating another heavy bill with the printer for the
publication of the "Elements." This was, indeed, up to the day of
his death, a cause for serious anxiety. It may, however, be
mentioned that the whole cost, which amounted to nearly 500 pounds,
was, like that of the previous volume, ultimately borne by the
College. Contrary to anticipation, the enterprise, even in a
pecuniary sense, cannot have been a very unprofitable one. The whole
edition has long been out of print, and as much as 5 pounds has since
been paid for a single copy.

It was on the 9th of May, 1865, that Hamilton was in Dublin for the
last time. A few days later he had a violent attack of gout, and on
the 4th of June he became alarmingly ill, and on the next day had an
attack of epileptic convulsions. However, he slightly rallied, so
that before the end of the month he was again at work at the
"Elements." A gratifying incident brightened some of the last days
of his life. The National Academy of Science in America had then
been just formed. A list of foreign Associates had to be chosen from
the whole world, and a discussion took place as to what name should
be placed first on the list. Hamilton was informed by private
communication that this great distinction was awarded to him by a
majority of two-thirds.

In August he was still at work on the table of contents of the
"Elements," and one of his very latest efforts was his letter to Mr.
Gould, in America, communicating his acknowledgements of the honour
which had been just conferred upon him by the National Academy. On
the 2nd of September Mr. Graves went to the observatory, in response
to a summons, and the great mathematician at once admitted to his
friend that he felt the end was approaching. He mentioned that he
had found in the 145th Psalm a wonderfully suitable expression of his
thoughts and feelings, and he wished to testify his faith and
thankfulness as a Christian by partaking of the Lord's Supper. He
died at half-past two on the afternoon of the 2nd of September, 1865,
aged sixty years and one month. He was buried in Mount Jerome
Cemetery on the 7th of September.

Many were the letters and other more public manifestations of the
feelings awakened by Hamilton's death. Sir John Herschel wrote to
the widow:--

"Permit me only to add that among the many scientific friends whom
time has deprived me of, there has been none whom I more deeply
lament, not only for his splendid talents, but for the excellence of
his disposition and the perfect simplicity of his manners--so great,
and yet devoid of pretensions."

De Morgan, his old mathematical crony, as Hamilton affectionately
styled him, also wrote to Lady Hamilton:--

"I have called him one of my dearest friends, and most truly; for I
know not how much longer than twenty-five years we have been in
intimate correspondence, of most friendly agreement or disagreement,
of most cordial interest in each other. And yet we did not know each
other's faces. I met him about 1830 at Babbage's breakfast table,
and there for the only time in our lives we conversed. I saw him, a
long way off, at the dinner given to Herschel (about 1838) on his
return from the Cape and there we were not near enough, nor on that
crowded day could we get near enough, to exchange a word. And this
is all I ever saw, and, so it has pleased God, all I shall see in
this world of a man whose friendly communications were among my
greatest social enjoyments, and greatest intellectual treats."

There is a very interesting memoir of Hamilton written by De Morgan,
in the "Gentleman's Magazine" for 1866, in which he produces an
excellent sketch of his friend, illustrated by personal reminiscences
and anecdotes. He alludes, among other things, to the picturesque
confusion of the papers in his study. There was some sort of order
in the mass, discernible however, by Hamilton alone, and any invasion
of the domestics, with a view to tidying up, would throw the
mathematician as we are informed, into "a good honest thundering
passion."

Hardly any two men, who were both powerful mathematicians, could have
been more dissimilar in every other respect than were Hamilton and De
Morgan. The highly poetical temperament of Hamilton was remarkably
contrasted with the practical realism of De Morgan. Hamilton sends
sonnets to his friend, who replies by giving the poet advice about
making his will. The metaphysical subtleties, with which Hamilton
often filled his sheets, did not seem to have the same attraction for
De Morgan that he found in battles about the quantification of the
Predicate. De Morgan was exquisitely witty, and though his jokes
were always appreciated by his correspondent, yet Hamilton seldom
ventured on anything of the same kind in reply; indeed his rare
attempts at humour only produced results of the most ponderous
description. But never were two scientific correspondents more
perfectly in sympathy with each other. Hamilton's work on
Quaternions, his labours in Dynamics, his literary tastes, his
metaphysics, and his poetry, were all heartily welcomed by his
friend, whose letters in reply invariably evince the kindliest
interest in all Hamilton's concerns. In a similar way De Morgan's
letters to Hamilton always met with a heartfelt response.

Alike for the memory of Hamilton, for the credit of his University,
and for the benefit of science, let us hope that a collected edition
of his works will ere long appear--a collection which shall show
those early achievements in splendid optical theory, those
achievements of his more mature powers which made him the Lagrange of
his country, and finally those creations of the Quaternion Calculus
by which new capabilities have been bestowed on the human intellect.




LE VERRIER.


The name of Le Verrier is one that goes down to fame on account of
very different discoveries from those which have given renown to
several of the other astronomers whom we have mentioned. We are
sometimes apt to identify the idea of an astronomer with that of a
man who looks through a telescope at the stars; but the word
astronomer has really much wider significance. No man who ever lived
has been more entitled to be designated an astronomer than Le
Verrier, and yet it is certain that he never made a telescopic
discovery of any kind. Indeed, so far as his scientific achievements
have been concerned, he might never have looked through a telescope
at all.

For the full interpretation of the movements of the heavenly bodies,
mathematical knowledge of the most advanced character is demanded.
The mathematician at the outset calls upon the astronomer who uses
the instruments in the observatory, to ascertain for him at various
times the exact positions occupied by the sun, the moon, and the
planets. These observations, obtained with the greatest care, and
purified as far as possible from the errors by which they may be
affected form, as it were, the raw material on which the
mathematician exercises his skill. It is for him to elicit from the
observed places the true laws which govern the movements of the
heavenly bodies. Here is indeed a task in which the highest powers
of the human intellect may be worthily employed.

Among those who have laboured with the greatest success in the
interpretation of the observations made with instruments of
precision, Le Verrier holds a highly honoured place. To him it has
been given to provide a superb illustration of the success with which
the mind of man can penetrate the deep things of Nature.

The illustrious Frenchman, Urban Jean Joseph Le Verrier, was born on
the 11th March, 1811, at St. Lo, in the department of Manche. He
received his education in that famous school for education in the
higher branches of science, the Ecole Polytechnique, and acquired
there considerable fame as a mathematician. On leaving the school Le
Verrier at first purposed to devote himself to the public service, in
the department of civil engineering; and it is worthy of note that
his earliest scientific work was not in those mathematical researches
in which he was ultimately to become so famous. His duties in the
engineering department involved practical chemical research in the
laboratory. In this he seems to have become very expert, and
probably fame as a chemist would have been thus attained, had not
destiny led him into another direction. As it was, he did engage in
some original chemical research. His first contributions to science
were the fruits of his laboratory work; one of his papers was on the
combination of phosphorus and hydrogen, and another on the
combination of phosphorus and oxygen.

His mathematical labours at the Ecole Polytechnique had, however,
revealed to Le Verrier that he was endowed with the powers requisite
for dealing with the subtlest instruments of mathematical analysis.
When he was twenty-eight years old, his first great astronomical
investigation was brought forth. It will be necessary to enter into
some explanation as to the nature of this, inasmuch as it was the
commencement of the life-work which he was to pursue.

If but a single planet revolved around the sun, then the orbit of
that planet would be an ellipse, and the shape and size, as well as
the position of the ellipse, would never alter. One revolution after
another would be traced out, exactly in the same manner, in
compliance with the force continuously exerted by the sun. Suppose,
however, that a second planet be introduced into the system. The sun
will exert its attraction on this second planet also, and it will
likewise describe an orbit round the central globe. We can, however,
no longer assert that the orbit in which either of the planets moves
remains exactly an ellipse. We may, indeed, assume that the mass of
the sun is enormously greater than that of either of the planets. In
this case the attraction of the sun is a force of such preponderating
magnitude, that the actual path of each planet remains nearly the
same as if the other planet were absent. But it is impossible for
the orbit of each planet not to be affected in some degree by the
attraction of the other planet. The general law of nature asserts
that every body in space attracts every other body. So long as there
is only a single planet, it is the single attraction between the sun
and that planet which is the sole controlling principle of the
movement, and in consequence of it the ellipse is described. But
when a second planet is introduced, each of the two bodies is not
only subject to the attraction of the sun, but each one of the
planets attracts the other. It is true that this mutual attraction
is but small, but, nevertheless, it produces some effect. It
"disturbs," as the astronomer says, the elliptic orbit which would
otherwise have been pursued. Hence it follows that in the actual
planetary system where there are several planets disturbing each
other, it is not true to say that the orbits are absolutely elliptic.

At the same time in any single revolution a planet may for most
practical purposes be said to be actually moving in an ellipse. As,
however, time goes on, the ellipse gradually varies. It alters its
shape, it alters its plane, and it alters its position in that
plane. If, therefore, we want to study the movements of the planets,
when great intervals of time are concerned, it is necessary to have
the means of learning the nature of the movement of the orbit in
consequence of the disturbances it has experienced.

We may illustrate the matter by supposing the planet to be running
like a railway engine on a track which has been laid in a long
elliptic path. We may suppose that while the planet is coursing
along, the shape of the track is gradually altering. But this
alteration may be so slow, that it does not appreciably affect the
movement of the engine in a single revolution. We can also suppose
that the plane in which the rails have been laid has a slow
oscillation in level, and that the whole orbit is with more or less
uniformity moved slowly about in the plane.

In short periods of time the changes in the shapes and positions of
the planetary orbits, in consequence of their mutual attractions, are
of no great consequence. When, however, we bring thousands of years
into consideration, then the displacements of the planetary orbits
attain considerable dimensions, and have, in fact, produced a
profound effect on the system.

It is of the utmost interest to investigate the extent to which one
planet can affect another in virtue of their mutual attractions. Such
investigations demand the exercise of the highest mathematical
gifts. But not alone is intellectual ability necessary for success
in such inquiries. It must be united with a patient capacity for
calculations of an arduous type, protracted, as they frequently have
to be, through many years of labour. Le Verrier soon found in these
profound inquiries adequate scope for the exercise of his peculiar
gifts. His first important astronomical publication contained an
investigation of the changes which the orbits of several of the
planets, including the earth, have undergone in times past, and which
they will undergo in times to come.

As an illustration of these researches, we may take the case of the
planet in which we are, of course, especially interested, namely, the
earth, and we can investigate the changes which, in the lapse of
time, the earth's orbit has undergone, in consequence of the
disturbance to which it has been subjected by the other planets. In
a century, or even in a thousand years, there is but little
recognisable difference in the shape of the track pursued by the
earth. Vast periods of time are required for the development of the
large consequences of planetary perturbation. Le Verrier has,
however, given us the particulars of what the earth's journey through
space has been at intervals of 20,000 years back from the present
date. His furthest calculation throws our glance back to the state
of the earth's track 100,000 years ago, while, with a bound forward,
he shows us what the earth's orbit is to be in the future, at
successive intervals of 20,000 years, till a date is reached which is
100,000 years in advance of A.D. 1800.

The talent which these researches displayed brought Le Verrier into
notice. At that time the Paris Observatory was presided over by
Arago, a SAVANT who occupies a distinguished position in French
scientific annals. Arago at once perceived that Le Verrier was just
the man who possessed the qualifications suitable for undertaking a
problem of great importance and difficulty that had begun to force
itself on the attention of astronomers. What this great problem was,
and how astonishing was the solution it received, must now be
considered.

Ever since Herschel brought himself into fame by his superb discovery
of the great planet Uranus, the movements of this new addition to the
solar system were scrutinized with care and attention. The position
of Uranus was thus accurately determined from time to time. At
length, when sufficient observations of this remote planet had been
brought together, the route which the newly-discovered body pursued
through the heavens was ascertained by those calculations with which
astronomers are familiar. It happens, however, that Uranus possesses
a superficial resemblance to a star. Indeed the resemblance is so
often deceptive that long ere its detection as a planet by Herschel,
it had been observed time after time by skilful astronomers, who
little thought that the star-like point at which they looked was
anything but a star. From these early observations it was possible
to determine the track of Uranus, and it was found that the great
planet takes a period of no less than eighty-four years to accomplish
a circuit. Calculations were made of the shape of the orbit in which
it revolved before its discovery by Herschel, and these were compared
with the orbit which observations showed the same body to pursue in
those later years when its planetary character was known. It could
not, of course, be expected that the orbit should remain unaltered;
the fact that the great planets Jupiter and Saturn revolve in the
vicinity of Uranus must necessarily imply that the orbit of the
latter undergoes considerable changes. When, however, due allowance
has been made for whatever influence the attraction of Jupiter and
Saturn, and we may add of the earth and all the other Planets, could
possibly produce, the movements of Uranus were still inexplicable. It
was perfectly obvious that there must be some other influence at work
besides that which could be attributed to the planets already known.

Astronomers could only recognise one solution of such a difficulty.
It was impossible to doubt that there must be some other planet in
addition to the bodies at that time known, and that the perturbations
of Uranus hitherto unaccounted for, were due to the disturbances
caused by the action of this unknown planet. Arago urged Le Verrier
to undertake the great problem of searching for this body, whose
theoretical existence seemed demonstrated. But the conditions of the
search were such that it must needs be conducted on principles wholly
different from any search which had ever before been undertaken for a
celestial object. For this was not a case in which mere survey with
a telescope might be expected to lead to the discovery.

Certain facts might be immediately presumed with reference to the
unknown object. There could be no doubt that the unknown disturber
of Uranus must be a large body with a mass far exceeding that of the
earth. It was certain, however, that it must be so distant that it
could only appear from our point of view as a very small object.
Uranus itself lay beyond the range, or almost beyond the range, of
unassisted vision. It could be shown that the planet by which the
disturbance was produced revolved in an orbit which must lie outside
that of Uranus. It seemed thus certain that the planet could not be
a body visible to the unaided eye. Indeed, had it been at all
conspicuous its planetary character would doubtless have been
detected ages ago. The unknown body must therefore be a planet which
would have to be sought for by telescopic aid.

There is, of course, a profound physical difference between a planet
and a star, for the star is a luminous sun, and the planet is merely
a dark body, rendered visible by the sunlight which falls upon it.
Notwithstanding that a star is a sun thousands of times larger than
the planet and millions of times more remote, yet it is a singular
fact that telescopic planets possess an illusory resemblance to the
stars among which their course happens to lie. So far as actual
appearance goes, there is indeed only one criterion by which a planet
of this kind can be discriminated from a star. If the planet be
large enough the telescope will show that it possesses a disc, and
has a visible and measurable circular outline. This feature a star
does not exhibit. The stars are indeed so remote that no matter how
large they may be intrinsically, they only exhibit radiant points of
light, which the utmost powers of the telescope fail to magnify into
objects with an appreciable diameter. The older and well-known
planets, such as Jupiter and Mars, possess discs, which, though not
visible to the unaided eye, were clearly enough discernible with the
slightest telescopic power. But a very remote planet like Uranus,
though it possessed a disc large enough to be quickly appreciated by
the consummate observing skill of Herschel, was nevertheless so
stellar in its appearance, that it had been observed no fewer than
seventeen times by experienced astronomers prior to Herschel. In
each case the planetary nature of the object had been overlooked, and
it had been taken for granted that it was a star. It presented no
difference which was sufficient to arrest attention.

As the unknown body by which Uranus was disturbed was certainly much
more remote than Uranus, it seemed to be certain that though it might
show a disc perceptible to very close inspection, yet that the disc
must be so minute as not to be detected except with extreme care. In
other words, it seemed probable that the body which was to be sought
for could not readily be discriminated from a small star, to which
class of object it bore a superficial resemblance, though, as a
matter of fact, there was the profoundest difference between the two
bodies.

There are on the heavens many hundreds of thousands of stars, and the
problem of identifying the planet, if indeed it should lie among
these stars, seemed a very complex matter. Of course it is the
abundant presence of the stars which causes the difficulty. If the
stars could have been got rid of, a sweep over the heavens would at
once disclose all the planets which are bright enough to be visible
with the telescopic power employed. It is the fortuitous resemblance
of the planet to the stars which enables it to escape detection. To
discriminate the planet among stars everywhere in the sky would be
almost impossible. If, however, some method could be devised for
localizing that precise region in which the planet's existence might
be presumed, then the search could be undertaken with some prospect
of success.

To a certain extent the problem of localizing the region on the sky
in which the planet might be expected admitted of an immediate
limitation. It is known that all the planets, or perhaps I ought
rather to say, all the great planets, confine their movements to a
certain zone around the heavens. This zone extends some way on
either side of that line called the ecliptic in which the earth
pursues its journey around the sun. It was therefore to be inferred
that the new planet need not be sought for outside this zone. It is
obvious that this consideration at once reduces the area to be
scrutinized to a small fraction of the entire heavens. But even
within the zone thus defined there are many thousands of stars. It
would seem a hopeless task to detect the new planet unless some
further limitation to its position could be assigned.

It was accordingly suggested to Le Verrier that he should endeavour
to discover in what particular part of the strip of the celestial
sphere which we have indicated the search for the unknown planet
should be instituted. The materials available to the mathematician
for the solution of this problem were to be derived solely from the
discrepancies between the calculated places in which Uranus should be
found, taking into account the known causes of disturbance, and the
actual places in which observation had shown the planet to exist.
Here was indeed an unprecedented problem, and one of extraordinary
difficulty. Le Verrier, however, faced it, and, to the astonishment
of the world, succeeded in carrying it through to a brilliant
solution. We cannot here attempt to enter into any account of the
mathematical investigations that were necessary. All that we can do
is to give a general indication of the method which had to be
adopted.

Let us suppose that a planet is revolving outside Uranus, at a
distance which is suggested by the several distances at which the
other planets are dispersed around the sun. Let us assume that this
outer planet has started on its course, in a prescribed path, and
that it has a certain mass. It will, of course, disturb the motion
of Uranus, and in consequence of that disturbance Uranus will follow
a path the nature of which can be determined by calculation. It
will, however, generally be found that the path so ascertained does
not tally with the actual path which observations have indicated for
Uranus. This demonstrates that the assumed circumstances of the
unknown planet must be in some respects erroneous, and the astronomer
commences afresh with an amended orbit. At last after many trials,
Le Verrier ascertained that, by assuming a certain size, shape, and
position for the unknown Planet's orbit, and a certain value for the
mass of the hypothetical body, it would be possible to account for
the observed disturbances of Uranus. Gradually it became clear to
the perception of this consummate mathematician, not only that the
difficulties in the movements of Uranus could be thus explained, but
that no other explanation need be sought for. It accordingly
appeared that a planet possessing the mass which he had assigned, and
moving in the orbit which his calculations had indicated, must indeed
exist, though no eye had ever beheld any such body. Here was,
indeed, an astonishing result. The mathematician sitting at his
desk, by studying the observations which had been supplied to him of
one planet, is able to discover the existence of another planet, and
even to assign the very position which it must occupy, ere ever the
telescope is invoked for its discovery.

Thus it was that the calculations of Le Verrier narrowed greatly the
area to be scrutinised in the telescopic search which was presently
to be instituted. It was already known, as we have just pointed out,
that the planet must lie somewhere on the ecliptic. The French
mathematician had now further indicated the spot on the ecliptic at
which, according to his calculations, the planet must actually be
found. And now for an episode in this history which will be
celebrated so long as science shall endure. It is nothing less than
the telescopic confirmation of the existence of this new planet,
which had previously been indicated only by mathematical
calculation. Le Verrier had not himself the instruments necessary
for studying the heavens, nor did he possess the skill of the
practical astronomer. He, therefore, wrote to Dr. Galle, of the
Observatory at Berlin, requesting him to undertake a telescopic
search for the new planet in the vicinity which the mathematical
calculation had indicated for the whereabouts of the planet at that
particular time. Le Verrier added that he thought the planet ought
to admit of being recognised by the possession of a disc sufficiently
definite to mark the distinction between it and the surrounding
stars.

It was the 23rd September, 1846, when the request from Le Verrier
reached the Berlin Observatory, and the night was clear, so that the
memorable search was made on the same evening. The investigation was
facilitated by the circumstance that a diligent observer had recently
compiled elaborate star maps for certain tracts of the heavens lying
in a sufficiently wide zone on both sides of the equator. These maps
were as yet only partially complete, but it happened that Hora. XXI.,
which included the very spot which Le Verrier's results referred to,
had been just issued. Dr. Galle had thus before his eyes a chart of
all the stars which were visible in that part of the heavens at the
time when the map was made. The advantage of such an assistance to
the search could hardly be over-estimated. It at once gave the
astronomer another method of recognising the planet besides that
afforded by its possible possession of a disc. For as the planet was
a moving body, it would not have been in the same place relatively to
the stars at the time when the map was constructed, as it occupied
some years later when the search was being made. If the body should
be situated in the spot which Le Verrier's calculations indicated in
the autumn of 1846, then it might be regarded as certain that it
would not be found in that same place on a map drawn some years
previously.

The search to be undertaken consisted in a comparison made point by
point between the bodies shown on the map, and those stars in the sky
which Dr. Galle's telescope revealed. In the course of this
comparison it presently appeared that a star-like object of the
eighth magnitude, which was quite a conspicuous body in the
telescope, was not represented in the map. This at once attracted
the earnest attention of the astronomer, and raised his hopes that
here was indeed the planet. Nor were these hopes destined to be
disappointed. It could not be supposed that a star of the eighth
magnitude would have been overlooked in the preparation of a chart
whereon stars of many lower degrees of brightness were set down. One
other supposition was of course conceivable. It might have been that
this suspicious object belonged to the class of variables, for there
are many such stars whose brightness fluctuates, and if it had
happened that the map was constructed at a time when the star in
question had but feeble brilliance, it might have escaped notice. It
is also well known that sometimes new stars suddenly develop, so that
the possibility that what Dr. Galle saw should have been a variable
star or should have been a totally new star had to be provided
against.

Fortunately a test was immediately available to decide whether the
new object was indeed the long sought for planet, or whether it was a
star of one of the two classes to which I have just referred. A star
remains fixed, but a planet is in motion. No doubt when a planet
lies at the distance at which this new planet was believed to be
situated, its apparent motion would be so slow that it would not be
easy to detect any change in the course of a single night's
observation. Dr. Galle, however, addressed himself with much skill
to the examination of the place of the new body. Even in the course
of the night he thought he detected slight movements, and he awaited
with much anxiety the renewal of his observations on the subsequent
evenings. His suspicions as to the movement of the body were then
amply confirmed, and the planetary nature of the new object was thus
unmistakably detected.

Great indeed was the admiration of the scientific world at this
superb triumph. Here was a mighty planet whose very existence was
revealed by the indications afforded by refined mathematical
calculation. At once the name of Le Verrier, already known to those
conversant with the more profound branches of astronomy, became
everywhere celebrated. It soon, however, appeared, that the fame
belonging to this great achievement had to be shared between Le
Verrier and another astronomer, J. C. Adams, of Cambridge. In our
chapter on this great English mathematician we shall describe the
manner in which he was independently led to the same discovery.

Directly the planetary nature of the newly-discovered body had been
established, the great observatories naturally included this
additional member of the solar system in their working lists, so that
day after day its place was carefully determined. When sufficient
time had elapsed the shape and position of the orbit of the body
became known. Of course, it need hardly be said that observations
applied to the planet itself must necessarily provide a far more
accurate method of determining the path which it follows, than would
be possible to Le Verrier, when all he had to base his calculations
upon was the influence of the planet reflected, so to speak, from
Uranus. It may be noted that the true elements of the planet, when
revealed by direct observation, showed that there was a considerable
discrepancy between the track of the planet which Le Verrier had
announced, and that which the planet was actually found to pursue.

The name of the newly-discovered body had next to be considered. As
the older members of the system were already known by the same names
as great heathen divinities, it was obvious that some similar source
should be invoked for a suggestion as to a name for the most recent
planet. The fact that this body was so remote in the depths of
space, not unnaturally suggested the name "Neptune." Such is
accordingly the accepted designation of that mighty globe which
revolves in the track that at present seems to trace out the
frontiers of our system.

Le Verrier attained so much fame by this discovery, that when, in
1854, Arago's place had to be filled at the head of the great Paris
Observatory, it was universally felt that the discoverer of Neptune
was the suitable man to assume the office which corresponds in France
to that of the Astronomer Royal in England. It was true that the
work of the astronomical mathematician had hitherto been of an
abstract character. His discoveries had been made at his desk and
not in the observatory, and he had no practical acquaintance with the
use of astronomical instruments. However, he threw himself into the
technical duties of the observatory with vigour and determination. He
endeavoured to inspire the officers of the establishment with
enthusiasm for that systematic work which is so necessary for the
accomplishment of useful astronomical research. It must, however, be
admitted that Le Verrier was not gifted with those natural qualities
which would make him adapted for the successful administration of
such an establishment. Unfortunately disputes arose between the
Director and his staff. At last the difficulties of the situation
became so great that the only possible solution was to supersede Le
Verrier, and he was accordingly obliged to retire. He was succeeded
in his high office by another eminent mathematician, M. Delaunay,
only less distinguished than Le Verrier himself.

Relieved of his official duties, Le Verrier returned to the
mathematics he loved. In his non-official capacity he continued to
work with the greatest ardour at his researches on the movements of
the planets. After the death of M. Delaunay, who was accidentally
drowned in 1873, Le Verrier was restored to the directorship of the
observatory, and he continued to hold the office until his death.

The nature of the researches to which the life of Le Verrier was
subsequently devoted are not such as admit of description in a
general sketch like this, where the language, and still less the
symbols, of mathematics could not be suitably introduced. It may,
however, be said in general that he was particularly engaged with the
study of the effects produced on the movements of the planets by
their mutual attractions. The importance of this work to astronomy
consists, to a considerable extent, in the fact that by such
calculations we are enabled to prepare tables by which the places of
the different heavenly bodies can be predicted for our almanacs. To
this task Le Verrier devoted himself, and the amount of work he has
accomplished would perhaps have been deemed impossible had it not
been actually done.

The superb success which had attended Le Verrier's efforts to explain
the cause of the perturbations of Uranus, naturally led this
wonderful computer to look for a similar explanation of certain other
irregularities in planetary movements. To a large extent he
succeeded in showing how the movements of each of the great planets
could be satisfactorily accounted for by the influence of the
attractions of the other bodies of the same class. One circumstance
in connection with these investigations is sufficiently noteworthy to
require a few words here. Just as at the opening of his career, Le
Verrier had discovered that Uranus, the outermost planet of the then
known system, exhibited the influence of an unknown external body, so
now it appeared to him that Mercury, the innermost body of our
system, was also subjected to some disturbances, which could not be
satisfactorily accounted for as consequences of any known agents of
attraction. The ellipse in which Mercury revolved was animated by a
slow movement, which caused it to revolve in its plane. It appeared
to Le Verrier that this displacement was incapable of explanation by
the action of any of the known bodies of our system. He was,
therefore, induced to try whether he could not determine from the
disturbances of Mercury the existence of some other planet, at
present unknown, which revolved inside the orbit of the known
planet. Theory seemed to indicate that the observed alteration in
the track of the planet could be thus accounted for. He naturally
desired to obtain telescopic confirmation which might verify the
existence of such a body in the same way as Dr. Galle verified the
existence of Neptune. If there were, indeed, an intramercurial
planet, then it must occasionally cross between the earth and the
sun, and might now and then be expected to be witnessed in the actual
act of transit. So confident did Le Verrier feel in the existence of
such a body that an observation of a dark object in transit, by
Lescarbault on 26th March, 1859, was believed by the mathematician to
be the object which his theory indicated. Le Verrier also thought it
likely that another transit of the same object would be seen in
March, 1877. Nothing of the kind was, however, witnessed,
notwithstanding that an assiduous watch was kept, and the explanation
of the change in Mercury's orbit must, therefore, be regarded as
still to be sought for.

Le Verrier naturally received every honour that could be bestowed
upon a man of science. The latter part of his life was passed during
the most troubled period of modern French history. He was a
supporter of the Imperial Dynasty, and during the Commune he
experienced much anxiety; indeed, at one time grave fears were
entertained for his personal safety.

Early in 1877 his health, which had been gradually failing for some
years, began to give way. He appeared to rally somewhat in the
summer, but in September he sank rapidly, and died on Sunday, the
23rd of that month.

His remains were borne to the cemetery on Mont Parnasse in a public
funeral. Among his pallbearers were leading men of science, from
other countries as well as France, and the memorial discourses
pronounced at the grave expressed their admiration of his talents and
of the greatness of the services he had rendered to science.




ADAMS.


The illustrious mathematician who, among Englishmen, at all events,
was second only to Newton by his discoveries in theoretical
astronomy, was born on June the 5th, 1819, at the farmhouse of
Lidcot, seven miles from Launceston, in Cornwall. His early
education was imparted under the guidance of the Rev. John Couch
Grylls, a first cousin of his mother. He appears to have received an
education of the ordinary school type in classics and mathematics,
but his leisure hours were largely devoted to studying what
astronomical books he could find in the library of the Mechanics'
Institute at Devonport. He was twenty years old when he entered St.
John's College, Cambridge. His career in the University was one of
almost unparalleled distinction, and it is recorded that his
answering at the Wranglership examination, where he came out at the
head of the list in 1843, was so high that he received more than
double the marks awarded to the Second Wrangler.

Among the papers found after his death was the following memorandum,
dated July the 3rd, 1841: "Formed a design at the beginning of this
week of investigating, as soon as possible after taking my degree,
the irregularities in the motion of Uranus, which are as yet
unaccounted for, in order to find whether they may be attributed to
the action of an undiscovered planet beyond it; and, if possible,
thence to determine the elements of its orbit approximately, which
would lead probably to its discovery."

After he had taken his degree, and had thus obtained a little
relaxation from the lines within which his studies had previously
been necessarily confined, Adams devoted himself to the study of the
perturbations of Uranus, in accordance with the resolve which we have
just seen that he formed while he was still an undergraduate. As a
first attempt he made the supposition that there might be a planet
exterior to Uranus, at a distance which was double that of Uranus
from the sun. Having completed his calculation as to the effect
which such a hypothetical planet might exercise upon the movement of
Uranus, he came to the conclusion that it would be quite possible to
account completely for the unexplained difficulties by the action of
an exterior planet, if only that planet were of adequate size and had
its orbit properly placed. It was necessary, however, to follow up
the problem more precisely, and accordingly an application was made
through Professor Challis, the Director of the Cambridge Observatory,
to the Astronomer Royal, with the object of obtaining from the
observations made at Greenwich Observatory more accurate values for
the disturbances suffered by Uranus. Basing his work on the more
precise materials thus available, Adams undertook his calculations
anew, and at last, with his completed results, he called at Greenwich
Observatory on October the 21st, 1845. He there left for the
Astronomer Royal a paper which contained the results at which he had
arrived for the mass and the mean distance of the hypothetical planet
as well as the other elements necessary for calculating its exact
position.

[PLATE: JOHN COUCH ADAMS.]

As we have seen in the preceding chapter, Le Verrier had been also
investigating the same problem. The place which Le Verrier assigned
to the hypothetical disturbing planet for the beginning of the year
1847, was within a degree of that to which Adams's computations
pointed, and which he had communicated to the Astronomer Royal seven
months before Le Verrier's work appeared. On July the 29th, 1846,
Professor Challis commenced to search for the unknown object with the
Northumberland telescope belonging to the Cambridge Observatory. He
confined his attention to a limited region in the heavens, extending
around that point to which Mr. Adams' calculations pointed. The
relative places of all the stars, or rather star-like objects within
this area, were to be carefully measured. When the same observations
were repeated a week or two later, then the distances of the several
pairs of stars from each other would be found unaltered, but any
planet which happened to lie among the objects measured would
disclose its existence by the alterations in distance due to its
motion in the interval. This method of search, though no doubt it
must ultimately have proved successful, was necessarily a very
tedious one, but to Professor Challis, unfortunately, no other method
was available. Thus it happened that, though Challis commenced his
search at Cambridge two months earlier than Galle at Berlin, yet, as
we have already explained, the possession of accurate star-maps by
Dr. Galle enabled him to discover the planet on the very first night
that he looked for it.

The rival claims of Adams and Le Verrier to the discovery of Neptune,
or rather, we should say, the claims put forward by their respective
champions, for neither of the illustrious investigators themselves
condescended to enter into the personal aspect of the question, need
not be further discussed here. The main points of the controversy
have been long since settled, and we cannot do better than quote the
words of Sir John Herschel when he addressed the Royal Astronomical
Society in 1848:--

"As genius and destiny have joined the names of Le Verrier and Adams,
I shall by no means put them asunder; nor will they ever be
pronounced apart so long as language shall celebrate the triumphs of
science in her sublimest walks. On the great discovery of Neptune,
which may be said to have surpassed, by intelligible and legitimate
means, the wildest pretensions of clairvoyance, it Would now be quite
superfluous for me to dilate. That glorious event and the steps
which led to it, and the various lights in which it has been placed,
are already familiar to every one having the least tincture of
science. I will only add that as there is not, nor henceforth ever
can be, the slightest rivalry on the subject between these two
illustrious men--as they have met as brothers, and as such will, I
trust, ever regard each other--we have made, we could make, no
distinction between then, on this occasion. May they both long adorn
and augment our science, and add to their own fame already so high
and pure, by fresh achievements."

Adams was elected a Fellow of St. John's College, Cambridge, in 1843;
but as he did not take holy orders, his Fellowship, in accordance
with the rules then existing came to an end in 1852. In the
following year he was, however, elected to a Fellowship at Pembroke
College, which he retained until the end of his life. In 1858 he was
appointed Professor of Mathematics in the University of St. Andrews,
but his residence in the north was only a brief one, for in the same
year he was recalled to Cambridge as Lowndean Professor of Astronomy
and Geometry, in succession to Peacock. In 1861 Challis retired from
the Directorship of the Cambridge Observatory, and Adams was
appointed to succeed him.

The discovery of Neptune was a brilliant inauguration of the
astronomical career of Adams. He worked at, and wrote upon, the
theory of the motions of Biela's comet; he made important corrections
to the theory of Saturn; he investigated the mass of Uranus, a
subject in which he was naturally interested from its importance in
the theory of Neptune; he also improved the methods of computing the
orbits of double stars. But all these must be regarded as his minor
labours, for next to the discovery of Neptune the fame of Adams
mainly rests on his researches upon certain movements of the moon,
and upon the November meteors.

The periodic time of the moon is the interval required for one
circuit of its orbit. This interval is known with accuracy at the
present day, and by means of the ancient eclipses the period of the
moon's revolution two thousand years ago can be also ascertained. It
had been discovered by Halley that the period which the moon requires
to accomplish each of its revolutions around the earth has been
steadily, though no doubt slowly, diminishing. The change thus
produced is not appreciable when only small intervals of time are
considered, but it becomes appreciable when we have to deal with
intervals of thousands of years. The actual effect which is produced
by the lunar acceleration, for so this phenomenon is called, may be
thus estimated. If we suppose that the moon had, throughout the
ages, revolved around the earth in precisely the same periodic time
which it has at present, and if from this assumption we calculate
back to find where the moon must have been about two thousand years
ago, we obtain a position which the ancient eclipses show to be
different from that in which the moon was actually situated. The
interval between the position in which the moon would have been found
two thousand years ago if there had been no acceleration, and the
position in which the moon was actually placed, amounts to about a
degree, that is to say, to an arc on the heavens which is twice the
moon's apparent diameter.

If no other bodies save the earth and the moon were present in the
universe, it seems certain that the motion of the moon would never
have exhibited this acceleration. In such a simple case as that
which I have supposed the orbit of the moon would have remained for
ever absolutely unchanged. It is, however, well known that the
presence of the sun exerts a disturbing influence upon the movements
of the moon. In each revolution our satellite is continually drawn
aside by the action of the sun from the place which it would
otherwise have occupied. These irregularities are known as the
perturbations of the lunar orbit, they have long been studied, and
the majority of them have been satisfactorily accounted for. It
seems, however, to those who first investigated the question that the
phenomenon of the lunar acceleration could not be explained as a
consequence of solar perturbation, and, as no other agent competent
to produce such effects was recognised by astronomers, the lunar
acceleration presented an unsolved enigma.

At the end of the last century the illustrious French mathematician
Laplace undertook a new investigation of the famous problem, and was
rewarded with a success which for a long time appeared to be quite
complete. Let us suppose that the moon lies directly between the
earth and the sun, then both earth and moon are pulled towards the
sun by the solar attraction; as, however, the moon is the nearer of
the two bodies to the attracting centre it is pulled the more
energetically, and consequently there is an increase in the distance
between the earth and the moon. Similarly when the moon happens to
lie on the other side of the earth, so that the earth is interposed
directly between the moon and the sun, the solar attraction exerted
upon the earth is more powerful than the same influence upon the
moon. Consequently in this case, also, the distance of the moon from
the earth is increased by the solar disturbance. These instances
will illustrate the general truth, that, as one of the consequences
of the disturbing influence exerted by the sun upon the earth-moon
system, there is an increase in the dimensions of the average orbit
which the moon describes around the earth. As the time required by
the moon to accomplish a journey round the earth depends upon its
distance from the earth, it follows that among the influences of the
sun upon the moon there must be an enlargement of the periodic time,
from what it would have been had there been no solar disturbing
action.

This was known long before the time of Laplace, but it did not
directly convey any explanation of the lunar acceleration. It no
doubt amounted to the assertion that the moon's periodic time was
slightly augmented by the disturbance, but it did not give any
grounds for suspecting that there was a continuous change in
progress. It was, however, apparent that the periodic time was
connected with the solar disturbance, so that, if there were any
alteration in the amount of the sun's disturbing effect, there must
be a corresponding alteration in the moon's periodic time. Laplace,
therefore, perceived that, if he could discover any continuous change
in the ability of the sun for disturbing the moon, he would then have
accounted for a continuous change in the moon's periodic time, and
that thus an explanation of the long-vexed question of the lunar
acceleration might be forthcoming.

The capability of the sun for disturbing the earth-moon system is
obviously connected with the distance of the earth from the sun. If
the earth moved in an orbit which underwent no change whatever, then
the efficiency of the sun as a disturbing agent would not undergo any
change of the kind which was sought for. But if there were any
alteration in the shape or size of the earth's orbit, then that might
involve such changes in the distance between the earth and the sun as
would possibly afford the desired agent for producing the observed
lunar effect. It is known that the earth revolves in an orbit which,
though nearly circular, is strictly an ellipse. If the earth were
the only planet revolving around the sun then that ellipse would
remain unaltered from age to age. The earth is, however, only one of
a large number of planets which circulate around the great luminary,
and are guided and controlled by his supreme attracting power. These
planets mutually attract each other, and in consequence of their
mutual attractions the orbits of the planets are disturbed from the
simple elliptic form which they would otherwise possess. The
movement of the earth, for instance, is not, strictly speaking,
performed in an elliptical orbit. We may, however, regard it as
revolving in an ellipse provided we admit that the ellipse is itself
in slow motion.

It is a remarkable characteristic of the disturbing effects of the
planets that the ellipse in which the earth is at any moment moving
always retains the same length; that is to say, its longest diameter
is invariable. In all other respects the ellipse is continually
changing. It alters its position, it changes its plane, and, most
important of all, it changes its eccentricity. Thus, from age to age
the shape of the track which the earth describes may at one time be
growing more nearly a circle, or at another time may be departing
more widely from a circle. These alterations are very small in
amount, and they take place with extreme slowness, but they are in
incessant progress, and their amount admits of being accurately
calculated. At the present time, and for thousands of years past, as
well as for thousands of years to come, the eccentricity of the
earth's orbit is diminishing, and consequently the orbit described by
the earth each year is becoming more nearly circular. We must,
however, remember that under all circumstances the length of the
longest axis of the ellipse is unaltered, and consequently the size
of the track which the earth describes around the sun is gradually
increasing. In other words, it may be said that during the present
ages the average distance between the earth and the sun is waxing
greater in consequence of the perturbations which the earth
experiences from the attraction of the other planets. We have,
however, already seen that the efficiency of the solar attraction for
disturbing the moon's movement depends on the distance between the
earth and the sun. As therefore the average distance between the
earth and the sun is increasing, at all events during the thousands
of years over which our observations extend, it follows that the
ability of the sun for disturbing the moon must be gradually
diminishing.

[PLATE: CAMBRIDGE OBSERVATORY.]

It has been pointed out that, in consequence of the solar
disturbance, the orbit of the moon must be some what enlarged. As it
now appears that the solar disturbance is on the whole declining, it
follows that the orbit of the moon, which has to be adjusted
relatively to the average value of the solar disturbance, must also
be gradually declining. In other words, the moon must be approaching
nearer to the earth in consequence of the alterations in the
eccentricity of the earth's orbit produced by the attraction of the
other planets. It is true that the change in the moon's position
thus arising is an extremely small one, and the consequent effect in
accelerating the moon's motion is but very slight. It is in fact
almost imperceptible, except when great periods of time are
involved. Laplace undertook a calculation on this subject. He knew
what the efficiency of the planets in altering the dimensions of the
earth's orbit amounted to; from this he was able to determine the
changes that would be propagated into the motion of the moon. Thus
he ascertained, or at all events thought he had ascertained, that the
acceleration of the moon's motion, as it had been inferred from the
observations of the ancient eclipses which have been handed down to
us, could be completely accounted for as a consequence of planetary
perturbation. This was regarded as a great scientific triumph. Our
belief in the universality of the law of gravitation would, in fact,
have been seriously challenged unless some explanation of the lunar
acceleration had been forthcoming. For about fifty years no one
questioned the truth of Laplace's investigation. When a
mathematician of his eminence had rendered an explanation of the
remarkable facts of observation which seemed so complete, it is not
surprising that there should have been but little temptation to doubt
it. On undertaking a new calculation of the same question, Professor
Adams found that Laplace had not pursued this approximation
sufficiently far, and that consequently there was a considerable
error in the result of his analysis. Adams, it must be observed, did
not impugn the value of the lunar acceleration which Halley had
deduced from the observations, but what he did show was, that the
calculation by which Laplace thought he had provided an explanation
of this acceleration was erroneous. Adams, in fact, proved that the
planetary influence which Laplace had detected only possessed about
half the efficiency which the great French mathematician had
attributed to it. There were not wanting illustrious mathematicians
who came forward to defend the calculations of Laplace. They
computed the question anew and arrived at results practically
coincident with those he had given. On the other hand certain
distinguished mathematicians at home and abroad verified the results
of Adams. The issue was merely a mathematical one. It had only one
correct solution. Gradually it appeared that those who opposed Adams
presented a number of different solutions, all of them discordant
with his, and, usually, discordant with each other. Adams showed
distinctly where each of these investigators had fallen into error,
and at last it became universally admitted that the Cambridge
Professor had corrected Laplace in a very fundamental point of
astronomical theory.

Though it was desirable to have learned the truth, yet the breach
between observation and calculation which Laplace was believed to
have closed thus became reopened. Laplace's investigation, had it
been correct, would have exactly explained the observed facts. It
was, however, now shown that his solution was not correct, and that
the lunar acceleration, when strictly calculated as a consequence of
solar perturbations, only produced about half the effect which was
wanted to explain the ancient eclipses completely. It now seems
certain that there is no means of accounting for the lunar
acceleration as a direct consequence of the laws of gravitation, if
we suppose, as we have been in the habit of supposing, that the
members of the solar system concerned may be regarded as rigid
particles. It has, however, been suggested that another explanation
of a very interesting kind may be forthcoming, and this we must
endeavour to set forth.

It will be remembered that we have to explain why the period of
revolution of the moon is now shorter than it used to be. If we
imagine the length of the period to be expressed in terms of days and
fractions of a day, that is to say, in terms of the rotations of the
earth around its axis, then the difficulty encountered is, that the
moon now requires for each of its revolutions around the earth rather
a smaller number of rotations of the earth around its axis than used
formerly to be the case. Of course this may be explained by the fact
that the moon is now moving more swiftly than of yore, but it is
obvious that an explanation of quite a different kind might be
conceivable. The moon may be moving just at the same pace as ever,
but the length of the day may be increasing. If the length of the
day is increasing, then, of course, a smaller number of days will be
required for the moon to perform each revolution even though the
moon's period was itself really unchanged. It would, therefore, seem
as if the phenomenon known as the lunar acceleration is the result of
the two causes. The first of these is that discovered by Laplace,
though its value was over-estimated by him, in which the perturbations
of the earth by the planets indirectly affect the motion of the
moon. The remaining part of the acceleration of our satellite is
apparent rather than real, it is not that the moon is moving more
quickly, but that our time-piece, the earth, is revolving more
slowly, and is thus actually losing time. It is interesting to note
that we can detect a physical explanation for the apparent checking
of the earth's motion which is thus manifested. The tides which ebb
and flow on the earth exert a brake-like action on the revolving
globe, and there can be no doubt that they are gradually reducing its
speed, and thus lengthening the day. It has accordingly been
suggested that it is this action of the tides which produces the
supplementary effect necessary to complete the physical explanation
of the lunar acceleration, though it would perhaps be a little
premature to assert that this has been fully demonstrated.

The third of Professor Adams' most notable achievements was connected
with the great shower of November meteors which astonished the world
in 1866. This splendid display concentrated the attention of
astronomers on the theory of the movements of the little objects by
which the display was produced. For the definite discovery of the
track in which these bodies revolve, we are indebted to the labours
of Professor Adams, who, by a brilliant piece of mathematical work,
completed the edifice whose foundations had been laid by Professor
Newton, of Yale, and other astronomers.

Meteors revolve around the sun in a vast swarm, every individual
member of which pursues an orbit in accordance with the well-known
laws of Kepler. In order to understand the movements of these
objects, to account satisfactorily for their periodic recurrence, and
to predict the times of their appearance, it became necessary to
learn the size and the shape of the track which the swarm followed,
as well as the position which it occupied. Certain features of the
track could no doubt be readily assigned. The fact that the shower
recurs on one particular day of the year, viz., November 13th,
defines one point through which the orbit must pass. The position on
the heavens of the radiant point from which the meteors appear to
diverge, gives another element in the track. The sun must of course
be situated at the focus, so that only one further piece of
information, namely, the periodic time, will be necessary to complete
our knowledge of the movements of the system. Professor H. Newton,
of Yale, had shown that the choice of possible orbits for the
meteoric swarm is limited to five. There is, first, the great
ellipse in which we now know the meteors revolve once every thirty
three and one quarter years. There is next an orbit of a nearly
circular kind in which the periodic time would be a little more than
a year. There is a similar track in which the periodic time would be
a few days short of a year, while two other smaller orbits would also
be conceivable. Professor Newton had pointed out a test by which it
would be possible to select the true orbit, which we know must be one
or other of these five. The mathematical difficulties which attended
the application of this test were no doubt great, but they did not
baffle Professor Adams.

There is a continuous advance in the date of this meteoric shower.
The meteors now cross our track at the point occupied by the earth on
November 13th, but this point is gradually altering. The only
influence known to us which could account for the continuous change
in the plane of the meteor's orbit arises from the attraction of the
various planets. The problem to be solved may therefore be attacked
in this manner. A specified amount of change in the plane of the
orbit of the meteors is known to arise, and the changes which ought
to result from the attraction of the planets can be computed for each
of the five possible orbits, in one of which it is certain that the
meteors must revolve. Professor Adams undertook the work. Its
difficulty principally arises from the high eccentricity of the
largest of the orbits, which renders the more ordinary methods of
calculation inapplicable. After some months of arduous labour the
work was completed, and in April, 1867, Adams announced his solution
of the problem. He showed that if the meteors revolved in the
largest of the five orbits, with the periodic time of thirty three
and one quarter years, the perturbations of Jupiter would account for
a change to the extent of twenty minutes of arc in the point in which
the orbit crosses the earth's track. The attraction of Saturn would
augment this by seven minutes, and Uranus would add one minute more,
while the influence of the Earth and of the other planets would be
inappreciable. The accumulated effect is thus twenty-eight minutes,
which is practically coincident with the observed value as determined
by Professor Newton from an examination of all the showers of which
there is any historical record. Having thus showed that the great
orbit was a possible path for the meteors, Adams next proved that no
one of the other four orbits would be disturbed in the same manner.
Indeed, it appeared that not half the observed amount of change could
arise in any orbit except in that one with the long period. Thus was
brought to completion the interesting research which demonstrated the
true relation of the meteor swarm to the solar system.

Besides those memorable scientific labours with which his attention
was so largely engaged, Professor Adams found time for much other
study. He occasionally allowed himself to undertake as a relaxation
some pieces of numerical calculation, so tremendously long that we
can only look on them with astonishment. He has calculated certain
important mathematical constants accurately to more than two hundred
places of decimals. He was a diligent reader of works on history,
geology, and botany, and his arduous labours were often beguiled by
novels, of which, like many other great men, he was very fond. He
had also the taste of a collector, and he brought together about
eight hundred volumes of early printed works, many of considerable
rarity and value. As to his personal character, I may quote the
words of Dr. Glaisher when he says, "Strangers who first met him were
invariably struck by his simple and unaffected manner. He was a
delightful companion, always cheerful and genial, showing in society
but few traces of his really shy and retiring disposition. His
nature was sympathetic and generous, and in few men have the moral
and intellectual qualities been more perfectly balanced."

In 1863 he married the daughter of Haliday Bruce, Esq., of Dublin and
up to the close of his life he lived at the Cambridge Observatory,
pursuing his mathematical work and enjoying the society of his
friends.

He died, after a long illness, on 21st January, 1892, and was
interred in St. Giles's Cemetery, on the Huntingdon Road, Cambridge.


*** END OF THE PROJECT GUTENBERG EBOOK 2298 ***