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Title: Microscopes and Accessory Apparatus
       Catalogue No. 40

Author: Ernst Leitz

Release Date: April 12, 2011 [EBook #35842]

Language: English

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CATALOGUE No. 40.

MICROSCOPES

AND

ACCESSORY APPARATUS.

ERNST LEITZ

WETZLAR

GERMANY.

Founded in 1850.

Branch Offices:

NEW-YORK:                    CHICAGO:                        BERLIN NW.

411 West 59^th Str.        32-38 Clark Str.        45 Luisenstrasse.

30 East 18th Street.                                                                       

1903.

„Highest award“ Worlds Columbian Exhibition Chicago 1893.

Contents.

Notice.

All previous editions of this catalogue are superceded by the present one, which should be exclusively used in ordering.

Orders will be filled at once after their receipt.

In ordering care should be taken to give the number of each article desired and to state listprice.

To avoid delay and misunderstandings, we request that name and address be plainly written.

Goods are forwarded at the expense and risk of the purchaser.

Our instruments for use in Universities, Colleges, Schools &c. of the United States are by law free of duty and we shall be pleased to make specially low quotations for such orders.

ERNST LEITZ.

[5]

New Constructions.

Since issueing our last catalogue, a number of new apparatus and accessories have been added. The following are the more important ones:

1. A completely new stand "A" with extra fine micrometerscrew transmitting its movement directly to the tube. The stand is of elegant appearance and large dimensions, making it especially well adapted for work in photo-micrography.

2. Stand I is now fitted out with the new special fine adjustment (each division 1/1000 mm).

3. Stand II with round centering stage.

4. Stand IV is replaced by a model of larger size.

5. Photo-micrographic apparatus for use in horizontal and vertical position, having joint for inclination, large size bellows and plateholder.

6. Large projection-apparatus for electric lamp of 30 Ampère with triple collecting lens of 210 mm aperture.

7. Objective 1 a with adjustable mounting and changeable magnification. It is an excellent objective of low power for general purposes, having a comparatively short working distance.

8. Objective 1 b with changeable magnification of lowest power, as far down as two diameters. It serves for drawing extended sections and specimens.

9. Saccharimeter after Mitcherlich improved form.

10. Trichinoscope, projection-apparatus of strong and simple construction.

Preface.

Our American Branch house in New-York under the management of Mr. Wm. Krafft has now been established for over 10 years. This period has witnessed a gradual development of our business in the United States, making it necessary to establish some years ago a Western Branch in Chicago of which Mr. R. Gibson has charge.

The cordial reception our firm received has been most gratifying and we take this opportunity to thank our many patrons for their kind consideration.

It is our aim to co-operate with the scientists and construct new apparatus to meet their needs or improve others wherever this is possible.

The foregoing list of additions and improvements made since issueing our last catalogue is proof that we spare no time nor labor to hold pace with the increased wants of modern times.

We have now manufactured and sold over 71000 compound microscopes and 31000 oil immersion objectives, a large number of which are used in the laboratories of Universities, Colleges, and other Educational Institutions of the United States.

We are prepared at New-York and Chicago to repair our instruments or make alterations at short notice and at lowest prices. The optical part of a microscope should invariably be sent to the maker, as he is best in a position to repair same and has an added interest to bring a lens back to its original quality or even improve it.

Microscopes, bacteriological apparatus and all other scientific instruments or preparations expressly imported for use in educational institutions are exempt from duty.

Catalogues may be had on application by addressing:

ERNST LEITZ,

NEW-YORK                    CHICAGO
411 West 59th Street        32 Clark, Cor. Lake Street.

Objectives and Eye-pieces.

In the manufacture of our objectives only such glass is employed as has been subjected to the most rigid scientific tests. By these the exact index of refraction and the exact degree of dispersion of the glass are determined, and with these data available it is possible to very perfectly correct both spherical and chromatic aberrations while still making use of wide angular apertures in the objectives.

The precise mathematical calculation, combined with accurate systematical working and testing methods, make it possible for us to guarantee our objectives to be all of equal and excellent quality.

Every objective before leaving our hands, is subjected to the most careful test, and only such lenses as are of the highest grade, are sent out.

For the past seventeen years we have used glasses manufactured by Schott & Co. of Jena. This glass has many points to recommend it for the construction of optical instruments, and only such kinds are employed by us, which have for many years been thoroughly tested as to their durability.

Our lenses are therefore absolutely permanent. Objectives of the earlier type which have become cloudy, we shall gladly repair.

The three illustrations given above afford an idea of the plan of construction of our achromatic objectives.

The first figure represents the plan of our low power objectives, and it will be noted that they consist of two doublets, or triplets each carefully corrected.[8]

The central figure shows the construction of our high power dry objectives. A hemispherical front lens is combined with two doublets or sometimes triplets. The front lens is the chief magnifier of the combination, while the other lenses serve to correct the various aberrations.

The Oil-immersion, represented by the last illustration consists of a front lens, hemispherical, behind which is a meniscus, which is in turn followed by a doublet and a triplet, these latter acting as the correcting lenses of the combination.

We manufacture both Achromatic and Apochromatic objectives. They differ in that the glasses made use of in the apochromatics and the manner in which they are combined permit a more perfect correction of chromatic aberration. This advantage is not gained without a certain sacrifice of simplicity in construction; by avoiding the use of flint glass having a high refractive index and substituting materials to take the place of crownglass. The apochromatics as a matter of fact do resolve the fine markings of test objects (butterfly scales and diatomes) somewhat more clearly than the achromatics, but the difference is slight and in ordinary stained microscope preparations is hardly detectable.

The correction of both achromatics and apochromatics is complete. The ordinary Huyghenian eye-pieces are consequently well adapted for use with the objectives of either construction. Only with the highest powers is it desirable to make use of the so-called "compensation" eye-pieces.

The achromatics and Huyghenian eye-pieces are also well adapted to the requirements of photomicrography, special objectives being unnecessary for this purpose. This statement is substantiated by the excellent results obtained with our achromatic objectives, as shown in the photomicrographs accompanying our brochure on Photomicrography:—"Anleitung zur Mikrophotographie".

In making use of the higher power objectives—from No. 5 on—it should be remembered, that the lenses are corrected for cover glasses of 0,17 mm in thickness and for a microscope tube-length of 170 mm. When using the oil-immersion objectives it is particularly desirable, that this exact tube length should be employed. With a view to facilitate the adjustment of the tube-length the draw tubes of all our larger stands are graduated in millimeters, the scale[9] indicating the exact length of the microscope tube in any given position of the draw tube. In this connection it should be remembered, that the width of the collar of the nose-pieces is 15 millimeters, and that consequently, when a nose-piece is attached to the tube the reading of the draw tube scale should be 155 mm instead of 170 when the adjustment is proper.

Figure comparative merits of the dry and immersion systems.

The above sketch may serve to make clear the advantages of the immersion objectives over those of the dry series. It is intended to represent diagrammatically a section through a cover-glass and the front lens of an objective, one half of the figure representing the conditions present in the case of the Oil-immersion, the other those which are present in the dry objectives. It will be noticed that by the interposition of a drop of oil of the same index of refraction as the glass between the cover-glass and the objective the refraction which occurs in the dry system when the light leaves the upper surface of the cover-glass is done away with. Since this second refraction is attended with much loss of light it must be evident, that in the immersion system a much greater quantity of light enters the objective than is possible, other things being equal, in objectives of the dry system.[10]

If we let u represent one half the angular aperture of an objective, represented in the diagram by D'BN in the case of the immersion, and n the index of refraction of the medium interposed between the cover-glass and the objective we have in the formula n sin. u a mathematical expression of the optic power of the various systems of lenses, or in other words for what is designated the numerical aperture.

The following table gives the numerical apertures of objectives of the various systems and of various angular apertures. In the dry system n., representing the index of refraction of air is taken as 1.00; in the immersion systems n equals 1.33 for water, 1.52 for cedar oil and 1.66 for monobromnaphthalin. A glance at the table will suffice to show the great advantage which the immersion objectives have over those of the dry series.

Numerical apertures.

Photographic objectives with iris diaphragms, f/3.5

Objective 1b.

It is designed principally for drawing extended sections and large specimens, and consists of two adjustable doublets. By varying their distance, a changeable magnification down to two diameters may be obtained.

Price $8.—

Huyghenian Eye-pieces.

Price of each eyepiece $ 2.00.

The objectives designed for the Edinger apparatus of 64, 42, 35, and 24 mm focal distance have been found to be very useful for a number of purposes and have come into great favor.

(see. Dr. Kaiserling: Praktikum der wissenschaftlichen Photographie p. 263).

Achromatic Objectives.

Magnification

of the Achromatic and Apochromatic Objectives in combination with the Huyghenian Eye-pieces.

Tube-length 170 mm.    Distance of image 250 mm.

Apochromatic Objectives.

Compensation Eye-pieces.

for Apochromatic Objectives.

Compensation Eye-piece 6 with micrometer $8.50

Magnification

of the Apochromatic Objectives in combination with the Compensation Eye-pieces.

Double revolving Eye-piece.

Until very recently we have manufactured no arrangement for changing oculars on the microscope. This was due in part to the fact that there was no great demand for such an accessory and in part to the clumsiness of all those revolving eye-pieces which changed the entire ocular. The latter of these difficulties has been overcome in our present revolving eye-piece by such an adjustment of the collecting or lower lens of the eye-piece that it may remain permanently in position, the eye lens of the combination alone moving in the revolver. So accurate is the construction of the revolver and so carefully are the lenses adjusted that the eye-pieces may be changed while a specimen is in focus on the microscope stage without a readjustment of the focus.

The revolving eye-piece is also particularly well adapted to use as a micrometer ocular, for when the eye lens is turned aside a micrometer scale may be inserted and rests upon the diaphragm of the eye-piece. Once adjusted in this way the micrometer values are the same for all the eye lenses of the combination.

Stands.

For the past thirty years division of labor has been employed to the utmost possible extent in the manufacture of our microscopes. This principle has been applied to our machinery as well as to our workmen, with the result that we have gradually accumulated a large plant of special machinery of the most accurate construction, each machine especially adapted to the manufacture of some particular part of our microscopes. By this development of mechanical appliances for microscope manufacture two ends have been attained:—The greatest accuracy and uniformity of construction of our microscopes has been made possible, while at the same time it has been possible to cheapen the cost of manufacture. Instruments which are the product of delicate machinery must always be more uniform, more accurate and should be less costly than those manufactured by hand.

In the following remarks we refer more particularly to the larger microscope stands of our manufacture and draw attention to those parts which should be present in every well equipped microscope.

The elements of these microscopes are:

1. The foot and upright support are solid and are of such weight and shape as to permit inclination of the body of the microscope to a horizontal position. The foot is horse-shoe shaped and is made to touch the table at three points, thus insuring stability even on a surface which is not entirely level. Inclination of the body of the microscope is permitted by a joint in the upright, which joint[17] may be fastened in the larger stands by a set-screw operated by a lever. Stands Ia and IIb are also made with the English foot. Abundant space is left under the stage for the various attachments of the sub-stage.

2. The stage of Stands A, I, Ia and II is round, revolving and centering. The centering arrangement consists of two small thumb-screws so situated at the sides of the stage as to control motion of the stage in all directions, thus to a limited extent serving the purpose of a mechanical stage.

The other microscope stands have square immovable stages, sufficiently large for general microscopic work. For the examination of very large sections two instruments are manufactured: the Nebelthau sliding microscope (p. 50) and the stand after Dölken (p. 52). The former is for magnifications up to 120 diam, whereas the latter can be used with any magnification.

3. The sub-stage carries a plane and concave mirror, the condenser and the diaphragm for regulating the illumination of the object.

The Condenser is so adjusted as to concentrate the rays of light about 2 mm above its surface, which is the average thickness of the microscopic slides, under an angle equal to the angular aperture of the highest power objective, which is about 120°.

In the lower power objectives the angular aperture is to be reduced by the iris diaphragm.

To focus the Condenser properly it is adjustable by rack and pinion movement on Stands A, I, Ia, Ib, and by side screw on Stands II and IIa.

4. The body of the microscope carries the tube and is fitted with two adjustments for focussing; a coarse adjustment and a fine adjustment. The smooth working of these adjustments is one of the chief requirements of a good microscope.

The coarse adjustment consists of rack and pinion and moves the tube of the microscope in a vertical groove with the least possible friction. The teeth of the rack and pinion are set obliquely to the axis of the tube and are so adjusted that two teeth of each are always interlocked, thus avoiding all possibility of slipping or loss of motion in the movement.[18]

Figure of the Micrometer-screw of the fine adjustment.

The fine adjustment consists of a micrometer screw which moves the tube and arm of the microscope supporting the coarse adjustment vertically upon a triangular column. This column is virtually a continuation upward of the upright support of the base of the microscope. Around the column is a broad collar so accurately fitted that it moves smoothly upon it with a minimum of friction and still without lateral motion, the movement being controlled by means of a micrometer screw at the top of the column. The head of this micrometer screw, a section of which is shown in the accompanying figure, is milled and is graduated in such a way as to indicate the exact degree of motion of the microscope tube which is accomplished by turning the micrometer screw, each division of the graduation corresponding to a motion of the tube through 1/100 millimeter, and a complete revolution of the screw corresponding to a motion of the tube through ½ millimeter. The accuracy of this adjustment and the smoothness of its motion must be conceded to be a triumph of mechanical skill.

Stands A. and I. are fitted with a new fine adjustment device (one division on the micrometer screw corresponding to 1/1000 mm.) which is fully described on pages 25-26.

5. The tube of the microscope encloses a second tube, or draw-tube, which latter carries the eye-piece, and is so graduated as to indicate the exact length of tube in use at any time. The lower end of the tube has a thread into which the various objectives or a nose-piece screw. Tube and objectives are provided with the so-called "Society screw".

The nose-piece has now become an almost indispensable part of a working microscope. It can, however, be used to best advantage only on such stands as are provided with a coarse adjustment by rack and pinion. Aside from the advantage derived from the[19] rapid changing of objectives, which it permits, it is so accurately made and centered as to materially facilitate the focussing of the various objectives. It is only necessary to focus with the fine adjustment to obtain a view of the same microscope field which had been under observation before the change was made.

As it is necessary for this purpose that the objectives should be accurately adjusted to the nose-piece, it is very desirable that in ordering an instrument its nose-piece should be ordered at the same time if one is to be used, as subsequent ordering may necessitate the return of the stand and objectives to us.

Stands A, I, Ia, Ib, II, IIa, IIb and III are those which are best suited to fine microscopical investigations. Among them the physician and bacteriologist will find an instrument entirely suited to his particular needs.

Stand III is now provided with rack and pinion adjustment.

Stands IV and V are small instruments, which serve nevertheless many purposes where the more elaborate outfits are unnecessary. They make excellent laboratory stands for elementary courses in microscopy.

In Stands IV and V the coarse adjustment is by means of sliding tube. They are all provided with fine adjustment by micrometer screw.

Stand VI is provided with rack and pinion adjustment only. It has a large stage, and is particularly intended for searching for trichinae and for similar examinations where a very strong durable stand is desired and where the use of high power objectives is unnecessary. It may also be useful as an auxiliary stand for purposes of demonstration in laboratories.

Stands III, IV, V, VI have no joint for inclining the body.

Stands A, I, Ia, Ib, II, IIa, IIb, III, IV have mahogany cases (provided with a nickelled handle), in which the microscopes stand.

Stands V and VI are laid in mahogany boxes.

These cases are furnished with the microscopes without extra charge, when a complete outfit, including oculars and objectives is purchased.

Object clamps and test objects accompany every microscope.

The objectives to Stands A, I, Ia, Ib, II, IIa, IIb are in brass boxes; those for Stands III, IV, V and VI are in morocco cases.

Illuminating Apparatus.

a. Illuminating Apparatus of Stands A and I.

$30.—

Abbe's Illuminating Apparatus for Stand A and I.
Swing-out Condenser.
Cylinder Iris Diaphragm.

b. Illuminating Apparatus of Stands Ia and Ib (p. 30, 32, 34).

$24.—

c. Illuminating Apparatus for Stand II and IIa (p. 36 & 38).

$12.—

d. Illuminating apparatus for Stand IIb (p. 40).

$10.—

e. Small Illuminating Apparatus.

Small Illuminating Apparatus.

$8.—

Cylinder iris diaphragm.

$6.—

Iris diaphragm fitted to stage of stand III.

$6.—

Complete Microscope Outfits.

The outfits comprised in the following pages are made up with achromatic objectives, which suffice for all ordinary needs.

We are glad to supply any other combination of eye-pieces and objectives which may be preferred. The price of each outfit may be readily computed by adding together the cost of its various items.

Microscope stands, without objectives, will not be sold separately.

Stand A.—Universal Microscope.

Stand "A".

Universal Microscope.

In the construction of our new stand "A" we have taken special care to enlarge all the parts proportionately in order to secure strength and stability, at the same time adding to the beauty of the instrument.

The upper pillar of the microscope is shaped in such a way as to form a convenient handle; and to increase the free working space over the stage, thereby allowing the examination of very large specimen and culture plates. A specially constructed mechanical stage larger than No. 98 may be attached, which is adapted for slides up to 2×4 inches (50×100 mm).

The extra large dimensions of all the main parts of this microscope such as the base and stage etc., allow that freedom of movement so desired in a stand for photo-micrography.

Both the body tube and graduated draw tube are very wide and permit the use of low power objectives to cover specimen of large extent; for the same reason the opening in the stage is very wide but can be narrowed down by a stop.

The most important innovation on the microscope is the new fine adjustment device, which is unexcelled both in solidity of construction and accuracy of movement, representing the highest attainment of the designers and mechanics skill.

Sectional cuts of this unique arrangement are shown in illustration (p. 26-27).

All that can be seen on the exterior are two small milled heads mounted below and somewhat back of the two larger knobs controlling the rack and pinion (coarse) adjustment of the microscope. The knob on the right side is provided with a graduated drum r, indicating the movement of the fine adjustment.

The two knobs with drum are mounted on an axle a, which in its central portion is enlarged and provided with a worm gear. The latter in its turn drives the gear wheel, d. A spiral spring pressing against one of the journals into which the axle is mounted prevents any lost motion in the worm gear. Mounted on the same shaft with the gear-wheel d, is a heartshaped cam f. On this cam rests the steel roller g, fitted on the support k, which in its turn carries[26] the microscope tube. By its weight and a spiral spring the latter presses on the cam f, and effects a direct vertical movement.

The periphery of the heart shaped cam f, is exactly symmetrical and mathematically correct. The distance traversed by its curved sides from the lowest to the highest point and vice versa is 3 mm. There are cut 60 teeth in the entire periphery of the gear-wheel d; the number corresponding to one side of the heart-shaped cam or 3 mm elevation, are 30 teeth, therefore 1 tooth means a movement of 3/30 mm or 0,1 mm.

This in turn requires one complete revolution of the axle a, the drum of which is graduated into 100 parts. The value of each division on the drum is therefore 0,1/100=0,001 mm.

This micrometer fine adjustment is exceedingly accurate and reliable, and besides it has the following advantages;

By virtue of its unique construction the movement is continuous, there is absolutely no limit to the motion of the micrometer screw, which may be turned forward or backward as the work requires.

This movement extends in exact ratio to the revolution of the cam for a distance of 3 mm. As another advantage we may mention, that it is almost impossible to break the coverglass of the specimen with this fine adjustment.

Should the objective come in contact with the coverglass and assuming the knob is turned still further then the tube, which is of aluminium and very light would simply rest on the specimen, without breaking the coverglass, as the latter will easily stand the small pressure of the tube and the fine spiral spring.

[28]

Stand I.

Stand I.

[30]

Stand Ia.

Stand Ia.

[32]

Stand Ia
with English foot.

Stand Ia
with English foot.

[34]

Stand Ib.

Stand Ib.

[36]

Stand II.

Stand II.

Stand IIa.

Stand IIa.

Stand IIb.

Stand IIb.

[42]

Stand III.

Stand III.

Stand III is now provided with rack and pinion coarse adjustment instead of sliding tube. In consequence a nose-piece can be used on it to better advantage. It will be found an excellent laboratory stand at low price.

Stand IV.

Stand IV.

The dimensions of this stand are now larger than formerly. The price has not been changed.

[46]

Stand V.

Stand V.

Stand VI.

Demonstration microscope.

Demonstration microscope with condenser.

[50]

Nebelthau's Sliding Microscope.

Nebelthau's Sliding Microscope.

(Cf. Zeitschrift für wissenschaftliche Mikroskopie, XIII, 1896.)

[52]

Dölken's Microscope stand.

Travelling Microscope No. 33.

Large Travelling Microscope No. 34.
(Size of mahogany case 28×19×8 cm.)

This instrument (in size like the Ib.) combines all the essential features of a large laboratory microscope with a folding stand. It will be found invaluable on scientific expeditions, for research work etc.

When lifted out of the case, spread the two parts forming the base, which are then held by a spring-catch. After raising the tube, turn the stage around and tighten it by means of a lever. It is supplied with large Abbe condenser and Iris diaphragm adjustable by side screw. Coarse adjustment by rack and pinion, fine adjustment by micrometer-screw. Graduated draw-tube. The stand has joint for inclination.

Large travelling microscope No. 34 (set up).

[56]

Horizontal-Microscope.

Microscopes for Mineralogical Research.

We construct two Microscopes for mineralogical investigations. Both are adapted for determining the axes of elasticity and for the differentiation of isotropic and anisotropic bodies. Stand I alone is adapted for determining the optical axes and their angles.

Only such objectives, condensers and oculars are available for mineralogical examinations as have been shown after careful examination in polarized light to be free from polarization.

Mineralogical Stand I.

Mineralogical Stand I.

Mineralogical Stand II.

Mineralogical Stand II.

Dissecting Microscopes and Hand Lenses.

Large Dissecting Microscope No. 41.

Simple Dissecting Microscope No. 45.

[64]

Dissecting microscope with erected image after R. Pfeiffer.

The Dissecting microscope with erected image according to Prof. R. Pfeiffer has been constructed in such a way that all parts extending on both sides can be folded or turned, so that the instrument fits in a very small case.

The base consists of two parts which may be folded. The stage can be brought in a position vertical to the optical axis and the metal hand rests laid on top of the stage. They are connected with the latter by joints. The mirror can also be turned and put parallel to the pillar.

A round glassplate is set in the stage, below which is an iris diaphragm to properly regulate the illumination.

The adjustment is by rack and pinion.

Two rightangle prisms are mounted inside the tube in such a manner that the image obtained by the objective is reflected into the eye-piece and appears erected.

The eye-piece is of the Ramsden form. Three objectives of different magnifying power with specially long working-distances have been constructed Nos. 1, 2, 3.[65]

Prices:

No. 52.                        No. 53.                          No. 54.
Lens-holders.

Dissecting Stage No. 57. With Lens No. 71.

Simple Dissecting Microscope No. 58a.

[67]

Demonstration lens-holder No. 59.                                    Focussing-lens No. 60.
Handle No. 61.                                                       

Steinheil lens No. 63.                                                Steinheil lens No. 66.

Doublet No. 70.                        No. 71.                        Pocket lens No. 72.

Binocular Preparation Microscope.

[69]

Greenough's Binocular Microscope.

Apparatus for Blood Examinations.

Micro-Spectroscope.

(A full description accompanies each instrument.)

Thoma's Haemacytometer.

Counting chamber
after Thoma                                                after Türck.

Ehrlich's Eye-piece.

[73]

Micrometers.

Screw Micrometer Eye-piece.

[74]

Drawing Apparatus.

[75]

Drawing eye-piece for drawing with inclined stand.

[76]

Abbe's Drawing Apparatus.

Drawing Board No. 95. Drawing Board after Giesenhagen.

Drawing apparatus after v. Tubeuf.

[78]

Mechanical Stages.

Mechanical stage No. 98.

[79]

Mechanical stage No. 100.

Mechanical stage No. 100a.

Schultze's Warm Stage No. 101.

[81]

Stricker's Warm stage No. 103.

Photo-micrographic Apparatus.

Photo-micrographic Apparatus No. 105.

The method of employing this apparatus and the general technique of photo-micrography are treated of in a separate pamphlet containing also four photo-micrographs taken with this apparatus.

This little work is furnished with each apparatus.

Photo-micrographic Apparatus No. 109.

Edinger's Projection Apparatus.

Edinger's Projection Apparatus with Nieser's Photographic Camera.

The time required for exposure in photographing with this apparatus is from 5 to 20 seconds according to the magnification and character of the specimen.

The following figure shows a further use for the Objective of 64 mm focal distance in connection with the photomicrographic apparatus (page 82).

Photo-micrographic apparatus No. 105 with small stand No. 106.

Large Projection Apparatus.

In this projection apparatus an electric projection lamp is made use of, the lamp being available for electric currents of 20 Ampères and about 48 Volts. To regulate the current a rheostat is necessary. When using constant current the carbons should stand at an angle in order to utilize to best advantage the stronger light of the positive (upper) carbon. For spectroscopic projections the carbons of the lamp have to be in vertical position.

Connected with the lamp is a triple condenser of 150 mm aperture. The latter should be protected from the heat-rays by a large mica-plate which is furnished with the apparatus.

Various devices permit very accurate adjustment of the lamp and condenser. For example, two thumb-screws control the position of the carbons of the lamp so that the luminous point may be readily brought into the exact optical axis of the condenser. Again, the two inner lenses of the condenser are moveable and are controlled by two knobs conveniently situated as shown in the illustration.

By this adjustment of the lenses of the condenser it is possible to do away with disturbing chromatic aberration. The rays of light leave the condenser in moderate convergence.

For direct projection from the preparation the apparatus consists of the optical bench upon which are mounted the various accessories in proper succession (Fig. p. 88):

1. A large cooling cell, which is to be filled with water or alum solution.

2. The bellows with tube. This is connected with the cooling cell by means of a metal ring which slips over the end of the cell and is held in place by a screw. The metal ring is attached to one end of the bellows, while the other end carries a large tube.

3. The microscope condensers and diaphragm holder. A larger tube fits over the tube of the bellows and carries on a revolving arm the cylinder diaphragm and the two condensers. For low power objectives Nos. 1-3, the cylinder diaphragm and the condenser of longer focus have to be used. The latter at the same time serves as the objective for lantern slide projection.[88]

The other condenser is especially needed when high powers are employed (Objectives 4 to 6). A small rack and pinion arrangement serves for the adjustment of condenser and diaphragm.

4. The object stage and small cooler. The stage has connected with it a second cooling cell on which the preparation rests. This arrangement permits prolonged use of the condenser and the greatest intensity of light without burning the most delicate specimens. The adjustment of the object is accomplished by means of an arrangement which permits any particular point to be brought accurately into the field.

5. The objective carrier is provided with a nose-piece for three objectives, with a broad projection tube, having an Iris diaphragm for the purpose of narrowing the aperture, and with a narrow tube which screws into the broad one, in case it is desired to use oculars in making the projection. The adjustments of the objectives are accomplished by rack and pinion and by micrometer screw.

In order to change readily from microscopic to lantern-slide projection, the parts 4 and 5 have been provided with hinges, by means of which they can be thrown to one side after loosening a lever (see illustration below).[89]

6. Wooden cover with cloth curtain which fits over the diaphragm carrier, the stage and the objectives, to shut off any light which may escape at the sides.

For the projection of large preparations of from 8-35 mm diameter our photographic objectives of 24, 35, 42 and 64 mm focal distance are best adapted (p. 86). In connection with these low powers the large tube only should be used.

With this projection apparatus the powers of microscope objectives till number 6 may be well employed.

The picture, even when the highest powers are made use of, and the screen is at a distance of twelve feet from the apparatus, is of sufficient clearness and brightness to be available for demonstration to a large audience.

For the projection of lantern slides or of large section of tissue following parts of the apparatus are required: Lamp, condenser, cooler and bellows are the same as in the above described apparatus.[90]

The stage and objective carrier are swung to one side.

The special-projection lens of 300 mm focal distance is to be used.

A slide carrier slips into the frame of the bellows, which is sufficiently large to accommodate lantern slides 9×10 and 9×12 cm in size. The slide carrier has a stop at both ends which facilitates its adjustment in the axis of the instrument, and is arranged for the simultaneous reception of two slides, so that while one is being projected it may be charged with a second which may then without delay be pushed into the optical axis as the first is removed. In this way series of pictures may be thrown on the screen without interruption.

When so arranged the projection can be made upon a screen 30 feet from the apparatus, over the heads of an audience.

Prices:

Trichinoscope No. 121.

Microtomes.

Large Sliding-Microtome.

Our larger microtomes are heavy and all their adjustments are of the most accurate construction, the result being that they are very steady when in use and permit the cutting of very thin and uniform sections.[93]

They are to be had in three different sizes. The larger two are slightly different in construction from the third. The two former microtomes are provided with an automatic feed attachement. A heavy knife-carrier slides smoothly and rapidly on a horizontal track and is so arranged that it may be manipulated by the hand of the operator alone or by a wheel and chain device, which tends to assure a perfectly uniform stroke of the knife.

The objectclamp is raised vertically by a micrometer screw. This motion is accomplished by turning a large disc having teeth cut into its periphery and a turn of one tooth being equal to an elevation of 0.0025 mm.

The automatic feed is arranged as follows: With each return of the knife-carrier to the end of its track pressure is made upon an adjustable lever which regulates the motion of the micrometer wheel. This device may be so adjusted as to move the micrometer disc any number of teeth from one to ten with each sweep of the knife.

Three different forms of clamps may be had for these microtomes, and freezing apparatus as well as paraffin tables can also be fitted.

The Fixed clamp, No. 128, represented in the figure of the large sliding microtome, serves to clamp the specimen in position and does not allow any further adjustment.

The Ball and Socket clamp permits the adjustments of the specimen after it is held in the clamp by means of a ball and socket joint—see figure of No. 129—a set-screw then holds it firmly in position.

The Naples clamp permits the accurate adjustment of the specimen at any level, the clamp being supported on two horizontal axes at right angles to each other, the one controlled by rack and pinion, the other by endless screw.

The knife-carrier is arranged to hold the Thoma form knives, which are fastened by means of a wing-screw. Other knives require a special holder, such as No. 139.[94]

Ball and Socket Clamp No. 129.                                Naples Clamp No. 130.

Support-Microtome No. 131.

[96]

Small Sliding Microtome No. 131a.

Microtome knives.

(Made by W. Walb.)

[97]

Freezing apparatus No. 140.

Hand Microtomes.

No. 141.

[98]

Cylinder Microtome.

[99]

Miscellaneous Accessories.

                Analizer.                        Polarizer.
Polarizing Apparatus No. 144.

Illuminating Lens No. 152.

Turn-table No. 161.

Saccharimeter No. 169.

Microscopical cases.

[104]

1. Catalogue of microscopes etc., which has been issued in three editions, viz. in

2. Anleitung zum Gebrauch des Microscops.

3. Instructions pour l'emploi des microscopes.

4. Directions for using the Microscope.

5. On the method of counting red and white corpuscles with Thoma's Apparatus.

6. Instructions pour l'emploi de l'hématimètre de Thoma.

7. Anleitung zur Mikrophotographie, mit vier Mikrophotogrammen.

8. Anleitung zum Gebrauch des Mikrospectroskops.

9. Anleitung zum Gebrauch des Oculars nach Ehrlich.

10. Description de l'oculaire d'Ehrlich.

11. Direction for using Ehrlich's eye-piece.

12. Anleitung zum Gebrauch des grossen Projectionsapparates.

13. Anleitung zum Gebrauch des Saccharimeters.

Index.

A.

B.

C.

D.

E.

F.

G.

H.

I.

K.

L.

M.

N.

O.

P.

R.

S.

T.

U.

W.

Printed by Fr. Richter, Leipzic.

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