Wireless Telegraph Construction For Amateurs

The Transmission and Reception of Electric Waves.

Wireless telegraphy by means of electromagnetic waves may be divided into four distinct operations, namely:

1. The generation of electrical oscillations.

2. The transformation of electrical oscillations into electrical waves.

3. The transformation of electrical waves into electrical oscillations.

4. The detection of the electrical oscillations.

The first two operations comprise those taking place at the transmitter, while the last two, which are the converse of the first, are in evidence only when receiving.

Fig. 1 illustrates the original Hertz oscillator and resonator, which is the simplest form a wireless installation may take. T represents the transmitting apparatus and R the receptor. At the transmitting station a telegraph key is placed in series with a battery and an induction coil. Two large metal plates, t and t', are connected to the opposite sides of the spark gap, which in turn is connected to the secondary of the induction coil. When the key is pressed the electrical circuit is completed and the voltage of the battery is raised sufficiently by the induction coil to charge the metal plates t and t'.

The key serves to break the current into periods corresponding to the dots and dashes of the telegraph code. When the high voltage of the induction coil is impressed upon the plates they become charged, and being of opposite polarity, when at a maximum the energy rushes across the gap and produces a disruptive spark. Each discharge, although appearing like a single spark passing in one direction, is in reality made up of a large number of rapid oscillations or surgings. The first passage of current serves to more than discharge the plates and they become charged in the opposite direction. A reverse discharge then occurs which also oversteps itself, and thus the oscillations go on, but gradually become weaker and weaker until they die completely or are damped out. The heated air of the spark gap becomes a conductor during the passage of the spark, and the oscillations are enabled to surge back and forth at the rate of 15,000 to 1,000,000 per second, although the actual discharge may take only a fraction of a second.

The generation of electrical oscillations may perhaps be made more clear by reference to the hydraulic apparatus illustrated in Fig. 2. T and T' are communicating tubes divided by an elastic membrane M. The tubes may be likened to the metal plates t and t' or the arms of the oscillator. The membrane may be likened to the layer of air between the knobs which separates the opposite arms of the oscillator. P is a pump connected to the two tubes T and T', and the broken lines in the apparatus represent water. The pump corresponds to the induction coil in Fig. 1, and the water to the secondary currents of the induction coil. When the pump is set in operation, the water is drawn from the tube T and injected into T'. The pump valves prevent it from flowing back. When the level becomes very high in T', the great pressure distends the membrane in the direction shown by the dotted line until finally it bursts and the water is allowed to flow with a rush into the tube T. But the inertia of the water causes it to rise higher in the tube than its final position of equilibrium, while in returning and endeavoring to seek its level its inertia carries it below this position. Thus the water oscillates back and forth until finally it comes to rest.

Similarly the difference of potential of the oscillator arms is not immediately equalized upon the breaking down of the air gap, and the apparatus becomes the seat of extremely rapid electrical oscillations, as explained above.

All space is supposed to be filled with a highly attenuated, invisible and weightless medium called ether. When the electrical oscillations surge back and forth through the arms of the oscillator, portions of the energy are thrown off from the apparatus and travel in enlarging circles like the ripples on a pond. These consist of lines of dielectric stress or electrostatic flux which pass through the ether and constitute electromagnetic waves.

The receptor or resonator R, Fig. 1, consists of a circle of wire having in it a small spark gap capable of minute adjustment. Two metal plates r and r' are sometimes attached to the opposite sides of the spark gap. When the key is pressed at the transmitting station and waves are sent out through the ether, they strike the resonator and set up therein electrical oscillations which pass across the gap in the shape of sparks.

To make the explanation clearer, let us consider Fig. 3 in which two floats or blocks of wood are represented as resting on the surface of a tank or pool of water. One float, A, is connected by a rope and pulley so that by jerking the rope the float may be made to oscillate and cause little ripples or waves to pass outwards in a gradually enlarging circle. When the waves reach the float, B, they cause it to rise and fall with each wave or to oscillate and reproduce the movements of the float, A. Likewise the oscillations set up by a wireless transmitter are sent out into space to be caught and duplicated at the receiving station. Of course this analogy to the propagation and reception of electric waves is not the same as the true electrical actions, but is merely a graphical, representation.

The wireless telegraph outfit illustrated in Fig. 1 would not serve for more than short distances of a few feet, and so a somewhat similar but more efficient apparatus is employed in practice. Fig. 4 shows such a system in its simplest form. In this case the secondary or high potential leads of the induction coil are connected, one to an earth and the other to an aerial or antenna composed of a number of bare copper wires insulated and suspended from a mast.

All electrically charged bodies are surrounded by an electrostatic field of force, the nature of which in theory is a state of strain.

The action of an induction coil connected as in Fig. 4 is to charge the upper part of the aerial above the spark gap, say with negative electricity and establish a field of force in its vicinity varying in area from a few feet to several miles. When the charge reaches a certain potential it is sufficient to puncture the layer of air in the gap and a spark takes place, setting up electrical oscillations.

Previous to the rupture of the spark gap, lines of electric strain or force stretch from the aerial to the earth on all sides as in the center of Fig. 5. A line of force may be defined as a curve drawn in the electric field so that the direction of the curve is the same as that of the electric intensity at that point.

The aerial and the earth act like the two metal plates in Fig. 1 or like the opposite plates of a condenser. As soon as the air gap is punctured it becomes conductive and the aerial charge rushes down into the earth. With the discharge, the strain in the electrostatic field is released and the aerial charge rushes down into the earth, but in so relaxing produces a new current and builds up a strain around the antenna opposite in direction to the first. This process repeats itself very rapidly and electrical oscillations are thus set up in the antenna. Every oscillation changes the direction of the magnetic flux or dielectric strain and causes the imaginary lines which originally stretched from the aerial to the earth to be displaced and the ends terminating at the aerial to run down it and form semi-loops or inverted "U's" standing with their ends on the earth in a circular ripple around the aerial and moving away from it with the speed of light. In Fig. 5 three oscillations are supposed to have taken place. The shortest distance between two adjacent points at which the electric strain is at a maximum in the same direction and period of time is the wave length emitted by the aerial. The separate standing groups of dielectric strain moving away from the antenna are electromagnetic waves. In the figure, the adjacent groups are separated by half a wave length. These waves are emitted at right angles to the transmitting aerial, whence they pass through the ether to the other station. When they reach the receiving aerial they set up electrical oscillations therein which are too weak to be perceptible in the shape of sparks as in the original Hertz oscillator and resonator because of the great distance separating the stations, so they are made to flow through a detector, which in Fig. 4 is represented as being a crystal of a mineral called silicon. When the high frequency currents strike the silicon, they set up a weak pulsating direct current. This action is due to a peculiar rectifying property of the mineral. The direct current flows through the telephone receiver and produces an audible sound. If the aerial and ground were connected directly to the terminals of the telephone receiver, without the silicon, the oscillations would not pass because of the impeding or choking action of the electro-magnets in the telephone receivers.

Tuning.—It is sometimes desirable that messages should be made selective or secretive. It is obvious that if there were several large stations in the same neighborhood they could not all operate at the same time unless some means of preventing the stations from receiving more than one message at a time were possible. This is the object in view of the so-called "tuning" of wireless telegraphy. It also accomplishes a second purpose which is perhaps considered more important than the first. The length of the aerial may be too great or too short for the amount of energy and the length of the waves which it emits or receives. When this is the case, the oscillations are quickly damped out and do not generate very powerful waves or produce strong signals at the receiving station and thus by properly adjusting the circuit all undesirable messages may be cut out as well as the signaling range greatly increased. Every electrical circuit has a definite period or electrical length, determined by its inductance and capacity. A circuit emits waves of only one length for given values of inductance and capacity, and must also be of a certain length before it will respond to waves sent out by another transmitter. The careful adjustment of a circuit to emit or receive a given wave constitutes tuning.

This may be made more clear by the comparison of an electrical circuit with a column of air. Fig. 6 represents a cross section of a glass tube, T, lying in a horizontal position and containing a cork, C, which can be slid to various positions. By adjusting the cork we are able to obtain various depths of air in the tube from its open end, M, to the cork, C.

When a vibrating tuning fork, F, is held opposite the open mouth and the cork slid back and forth it is found that the sound of the tuning fork is greatly increased in volume at a certain position of the cork. If the cork is then removed from this position the sound decreases in intensity. When the cork is in such a position that the sound of the fork is reenforced, we have secured resonance. When in this condition and the prong of the vibrating fork is moving toward the open mouth of the tube a "condensed" pulse of air travels down the tube and back again, having been reflected at the cork and reaching M just as the prong of the fork begins its excursion away from the open mouth of the tube. When the prong of the fork is moving away from M a "rarefied" pulse of air moves from M to C and back again by the time the prong is ready to begin its next vibration. When the tube is not in resonance, the successive condensations and rarefactions passing up and down the air column interfere with one another and decrease instead of increase the sound of the tuning fork.

If we substitute the sound waves emitted by the tuning fork for high frequency oscillations and the air column for the electrical circuit we may readily see that by adjusting its length, resonance can be produced. If the length of the air column is measured it will be found that the reenforcing of the sound of the fork reaches a maximum when the depth of the air column is one-fourth of the sound wave length given by the fork. Likewise resonance is produced in wireless telegraphy when the length of the circuit is approximately one-fourth the length of the waves. Vice versa, the wave emitted from an ordinary closed circuit transmitter is approximately four times the length of the aerial wire. For example, an aerial 25 meters long will emit waves having a length in the neighborhood of 100 meters.

As stated above, tuning is accomplished and resonance or syntony established by varying the inductance and capacity of the circuit. The capacity of a circuit may be defined as its relative ability to retain an electrical charge, while inductance is the property of an electric circuit by virtue of which lines of force are developed around it.

Capacity and inductance are opposite or reactive in their effects upon a circuit. If the value of one is decreased the influence of the other in increased. Fig. 7 and the following explanation will serve to illustrate this.

Alternating currents do not always keep step with the voltage impulses of a circuit. If there is inductance in the circuit, the current will lag behind the voltage, and if there is capacity, the impulses of the current will lead. Fig. 7 A illustrates the lag produced by inductance and B the lead produced by capacity. In A the impulses of the current, represented by the full line, occur a little later than those of the volts as represented by the dotted line. In B the effect is just the opposite and the current leads. These reactive effects of inductance and capacity are very pronounced with the high frequency currents of wireless telegraphy, and, as stated before, are the factors which determine the period of the circuit.

Tuning is represented graphically in Fig. 8. The two floats A and B are not only resting on the surface of a pool of water as in Fig. 3 but are also suspended from the springs S and S'. The springs will have, like a pendulum, a definite time of rising and falling, or period of oscillation, depending upon their length. If we strike the float A the spring will cause the float to rise and fall at a definite rate and send out a little wave or ripple with every oscillation. If the springs S and S' are of the same length, the float B will be caused to oscillate with every wave sent out by A, for, the periods of the springs being equal, B will be permitted to rise with a wave and fall again just in time to be raised by the next oncoming ripple. On the other hand, if the springs are of different lengths, B may only rise slightly and in falling meet an oncoming wave which will cause it to rise before it has reached its lowest point and so dampen or weaken its oscillations that they either do not become very strong or are entirely obliterated. Thus several floats having different periods of oscillation might be sending out ripples in the same pool, and the float B could be made to respond to any of them by adjusting the length of the spring.

We may also see in this illustration the part that tuning plays in causing the apparatus to emit or receive more powerful impulses. When the rope in the untuned apparatus illustrated in Fig. 3 is jerked, the block A oscillates only once or twice before a new jerk is required to keep it in motion. In Fig. 8 it is quite the contrary, for when an impulse has been given to the float A it will oscillate much longer than the untuned float before it requires to be set in motion again. Likewise the float B in Fig. 8 will oscillate longer and more powerfully than the float B in Fig. 3, when once it has been set in motion.

Fig. 9 shows a diagram of a simple wireless telegraph system employing an inductance and capacity for tuning the circuits. When the induction coil is in operation it charges a condenser. The condenser discharges through the sending helix and across the spark gap. The sending helix is merely a spiral coil of wire of large diameter, and constitutes the greater part of the inductance in the circuit. Two movable contacts, A and B, make connections with the helix. The spark gap, condenser and lower portion of the helix up to the movable contact A are known as the closed circuit. By shifting A, more or less inductance may be included in the closed circuit until resonance is secured. The aerial, the inductance from the contact B down, the condenser and the ground compose the open circuit. By varying the contact B more or less inductance may be included in the open circuit and its period altered until the oscillatory currents of both circuits flow in the same period of time. The closed and open portions of the transmitting helix form an auto transformer, and the voltages of the open circuit are raised above those of the closed circuit.

The tuned receptor shown in Fig. 9 is the simplest form possible and is known as the single slide system. The tuning coil or helix is much longer in proportion to its diameter than the sending helix, and is made of finer wire, since it does not carry such heavy currents. When the contact is slid up or down on the tuning coil, the inductance of the circuit is varied. Since the oscillating currents in the receiving aerial have the same frequency as those in the radiating aerial, the receptor must have the same relative values of inductance and capacity. This condition is obtained by varying the slider until the signals in the telephone receivers are the loudest.

In practice more than one sliding contact is used, and these together with adjustable condensers make the circuit more complicated. These devices are necessary because oscillations may be forced on a receptor by a near-by transmitter unless other precautions than the "single slider" are taken. Such circuits are illustrated in Plates IV and V. With them it is possible to obtain a considerable degree of selectivity and "tune out" an undesirable message.

Construction of a 2-K.W. Transformer.

Core.—Strips 2 1/2 inches wide are cut from soft sheet iron. One half of them should be 11 1/2 inches long and the other half 6 1/2 inches. Enough are cut to make two piles of each size 2 1/2 inches high. Both sides (the longest strips) of the core are built up with the ends overlapping as in Fig. 41.

The ends (the short pieces) are then slipped between the overlapping ends of the long strips and the whole core squared up. The completed core should have a cross section of 2 1/2 inches square and form a hollow rectangle 8 x 14 inches. The strips of iron must be dipped in P. & B. insulating varnish and dried before they are assembled.

Primary.—Four fiber heads 6 inches square, 1/2 inch thick and having a hole 2 1/2 inches square are made. One of these is placed on the core legs as shown by Fig. 48. Two or three layers of well varnished linen are wound over the core preparatory to winding the primary. Room must be left for the other head to be placed on the opposite end after the windings are all in place. The primary consists of 100 double turns of No. 12 B. S. gauge double cotton covered magnet wire. Fifty of the double turns are wound on each leg. The four terminals of the primary are led out through the fiber heads. Care should be taken to distinguish them from each other so that they may be identified when the transformer is completed. The primary is then wound with a strip of micanite or empire cloth 8 inches wide until it measures 4 inches square over all.

Secondary.—The secondary coils, which are eight in number, are wound on a form 4 inches square and 1 1/2 inches between the flanges. The construction of the form is similar to that shown in Fig. 46 but is larger. The slots are also necessary here so that the completed section may be tied up.

About ten pounds of No. 30 B. S. gauge single silk covered wire are required to wind the secondary. The sections are wound in smooth even layers until they are six inches in outside diameter. They are then tied up and removed from the winder. The sections are separated by sheets of fiber 6 1/2 inches square on the outside, 1/2 inch thick, having a hole 4 inches square cut in the center. The sections are all connected in series and the terminals soldered to strips of copper.

After the secondary coils are all in place and connected, the fiber head is slipped on the end of the leg. Then the short lengths of the core, which had been pulled out again after squaring the core up, are slipped into place. The core is squared up again and fastened together by boring a 3/8-inch hole completely through the core at each corner. Two strips of fiber 12 x 2 1/2 x 1/2 inches are bored with corresponding holes in their ends. These strips are placed at the end of the transformer, on top of the core, and 1/4-inch bolts passed through the holes in the fiber and the core. The bolts are wrapped with micanite cloth where they pass through the core, and an insulating washer is placed under the nuts, so that the iron core laminations are not electrically connected. The nuts are tightened until the core is held firmly together.

The fiber strips also serve as insulated supports for the binding posts. The copper terminals of the secondary lead to two binding posts mounted on two fiber or hard rubber pillars 1 inch diameter and 4 inches high. The rods are arranged as explained in the section under the heading of a 1/4-K.W. transformer.

The transformer is designed for use on a 60-cycle 110-volt current. It may be used on 220 volts if the two primary coils are connected in series. When the primaries are in series, and the transformer is used on the 110-volt current, it will deliver a voltage of about 12,000 at the secondary. With either primary alone the voltage will be about 12,000, and with both in parallel about 25,000. It will then deliver a very heavy current at the secondary and draw from the line about 20 amperes in the primary. If used with a proper tuning helix, condenser and aerial, the transformer is capable of sending about 300 miles under favorable conditions.

If the transformer is to be used for long periods at a time, it is best to place it in a tight wooden box 18 inches square and 12 inches deep. The box is then filled with boiled linseed oil or amber petroleum.

A rheostat or impedance and reactance coil should be placed in series with the transformer to regulate the current and also to prevent arcing across the spark gap.

Reactance.—In Chapter I, the lag and lead of a circuit were explained in connection with tuning. This is a property of every alternating circuit and is brought to our notice again in the transformer which charges the condenser. The current developed by a transformer is a leading current, since the instantaneous values of the current do not correspond to the proportionate values of the voltage supplying the current. In order to force the current values of the charging current to correspond with the voltage it is necessary to produce a "lag." This is accomplished by means of an adjustable reactance in series with the primary of the transformer.

A reactance or inductance suitable for the 2-K.W. transformer may be made by building up a coil in the same manner as described under the heading of the J-K.W. transformer. The reactance will have to be somewhat larger on account of the heavier currents. The core is built up of sheet iron to measure 2 1/2 x 2 1/2 x 10 inches when completed. The coil is wound around a wooden form and is composed of about 100 turns of No. 8 B. S. gauge double cotton covered magnet wire. By varying the amount of core inserted in the hollow coil the energy may be adjusted as desired.

Fig. 51 illustrates the 1/4-K.W. transformer manufactured by the Clapp-Eastham Company. The core is so constructed that a small metal tongue of soft iron projects from one side of the core towards the opposite side between the windings, but is separated from the opposite side by a small air gap. Several objects are accomplished by this tongue, which gives rise to magnetic leakage; the inductance of the primary is increased thereby to such an extent that the transformer is self-controlling, so that it may be connected directly to the source of alternating current supply of ordinary commercial frequencies and potential, and the current flowing in this circuit be regulated by varying the number of turns in the primary coil. As this magnetic leakage gives rise to a loose coupling effect, the primary and secondary circuits may be brought into resonance by placing a suitable capacity across the secondary terminals. This condition of resonance brings the power factor to a materially higher percentage. While the power factor of the open or closed core transformer is seldom above 50%, this type of transformer has a power factor of 80 to 90% when used with a suitable condenser.

Another point of considerable advantage is the almost entire freedom from arcing at the spark gap when this type of transformer is used. The spark gap is connected directly across the secondary terminals of the transformer and the condenser. The primary turns of the helix and the spark gap are connected in series. When the transformer is in operation, this condenser being across the secondary, the transformer is in resonance and the condenser is charged to such a point that it will jump the spark gap. At the instant that the spark passes, the secondary of the transformer is practically short circuited through the spark gap. As this circuit is now closed and the condenser out of circuit, the secondary circuit of the transformer is no longer in resonance and the energy immediately drops off, destroying at once the tendency for an arc to form. As soon as the spark has passed, the condenser of course comes in to play and the condition of resonance being reestablished the same process is repeated. The Clapp-Eastham Company have made application for a patent on any transformer employing this or any similar construction for use in charging a condenser.

"UNIVERSAL" DETECTOR.

The purpose and position of the detector in a wireless telegraph system has already received some notice in the first chapter, but its operation and adjustment are so important that this chapter deserves the most careful consideration. The receiving range of a station is not as much dependent upon the aerial system as it is upon the adjustment of the tuning circuits and the detector itself.

It is suggested that the amateur experimenter not confine his work to receiving only with a single type of detector but rather accustom himself to the different instruments.

During the past few years many wireless telegraph detectors have been invented which lend themselves readily to amateur construction. It is somewhat of a convenience to have a "universal" detector which with a little manipulation may be used as more than one type and thus save unnecessary expense and much labor.

The "universal" detector shown in Fig. 88 has been so designed as to present a good appearance and at the same time be successfully operated as an electrolytic, tantalum, peroxide of lead, silicon, carborundum or any of the crystal type detectors.

The standard, R, is a 3/4-inch hard rubber rod, 1 1/4 inches long, with a 3/16 inch hole bored through its axis. A spring, S, is made after the plan shown in Fig. 86. It is 2 inches long and 1/16 inch thick. A brass collar 1/8 inch thick and 3/8 inch diameter is soldered on the smaller end of the spring in order to so reenforce it that it may be bored and threaded with an 8-32 tap to receive a thumbscrew. The brass standard, D, is a small cylinder 3/8 inch high and 1/2 inch in diameter. A 3/16 inch hole is bored through its axis. The arm, A, is brass and measures 1 1/2 x 1/2 x 1/4 inches. The ends are rounded by filing or grinding so that they coincide with the semi-circumference of a circle having a diameter of 1/2 inch. Two holes are bored on the center line 1/4 inch from each end.

One is a 1/8-inch hole and the other is threaded with a 10-32 tap to fit the large adjusting screw. The adjusting screw, H, is 1 1/4 inches long and has a 10-32 thread. A hard rubber head 1 inch thick and 1 1/4 inches in diameter is clamped to the upper end by means of two hexagonal brass nuts. A small brass washer should be placed between the head and each of the nuts to give it a more finished appearance and prevent the nuts from marring the rubber.

The brass bed plate, B, is 1/8 inch thick, 3 inches long and 2 inches wide. Two holes are drilled on the center line 9/16 inch and 7/8 inch from either end. One is 3/8 inch in diameter and the other is threaded with an 8-32 tap. An insulating bushing in the shape of a hard rubber washer on the lower end of R, 1/8 inch thick and 3/8 inch in diameter, has a 3/16-inch hole bored in its center and is fitted in the larger hole in the bedplate. The whole detector is assembled and mounted on a hard rubber base 4 x 5 x 4 inches. A brass binding rod, M, 3 1/4 inches long and having an 8-32 thread, is passed successively through the arm, the brass standard, the spring, the hard rubber standard and the bedplate. A hexagonal brass nut on the under side of the base and a thumb nut on the brass arm serves to bind the whole tightly together. Four binding posts are mounted on the four corners of the base. Two are connected to the brass binding rod and two to the bedplate. This completes the universal part of the detector. The remaining parts are each described under the headings of the respective detectors to which they belong.

ELECTROLYTIC DETECTORS.

"Bare Point" Type.—Although the electrolytic is the oldest of a long line of very sensitive detectors,³ it still holds first rank when in the hands of an experienced and skillful operator. It exists in two different forms, but the more favored is that known as the Fessenden "bare point" type, which consists of a very fine Woolaston platinum wire (.001-.00002 of an inch in diameter) dipping in a small cup of dilute acid. The acid is either 20 per cent chemically pure nitric or sulphuric.

A large electrode of platinum wire or foil dips into or is sealed in the bottom of the cup so as to make an electrical connection with the liquid. The fine Woolaston wire is clamped over the cup in a holder which permits of vertical adjustment, by means of a thumbscrew, so that the depth of immersion in the acid may be regulated.

Woolaston wire is covered with a comparatively thick coating of silver, which before using must be removed from the end for about 1/32 inch by dipping it in strong nitric acid, which will dissolve the silver and expose the almost invisible platinum core. Too much of the fine platinum core must not be exposed or else the surface tension of the acid will cause the wire to curl over and present a large flat surface instead of a fine point. This is a very necessary and important precaution, for the detector is more sensitive as the area of contact between the fine wire and the liquid is smaller.

Whenever this condition is reached the end of the wire should be cut off with a pair of sharp scissors and a new point exposed.

The detector circuit is shown in Fig. 93. The fine "bare point" is always made the positive or anode of the battery circuit. Otherwise the detector will not operate. A potentiometer must be shunted across the terminals of the battery to reduce the voltage to a value just below that which is required to break down the thin film of oxygen gas which collects on the "bare point" and polarizes it or insulates it from the liquid so that little or no battery current can flow. This film of gas is caused by the electrolysis of the acid solution and the decomposition of the water into hydrogen and oxygen gas.

When oscillations are set up in the receiving aerial and they surge through the detector, a sufficient e.m.f. is generated to break down the film of gas and permit the battery current to flow again. The passage of current causes the signals in the telephone receivers.

The electrolytic cup for the universal detector is illustrated in Fig. 90. It is made of a piece of hard rubber rod 3/4 inch in diameter and 3/4 inch high. A recess 1/2 inch in diameter and 3/8 inch deep is cut in the top to contain the acid. A small hole 1/4 inch deep is bored in the under side and threaded with an 8-32 tap. A brass pin 1/2 inch long, having a corresponding thread, is fitted in the hole. The pin may then be screwed into the small hole in the bedplate. A piece of No. 30 B. S. gauge platinum wire or a strip of platinum foil is clamped between the bottom of the cup and the bedplate and then bent over the top of the cup into the liquid.

A 1/16-inch hole 1/4 inch deep is bored in the lower end of a thumbscrew having an 8-32 thread. A piece of Woolaston wire 1/2 inch long is placed in the center of the hole and tinfoil packed into the surrounding space with the head of a sewing needle until the wire is held firmly in position. The free end of the wire must then be dipped in some strong nitric acid to remove the silver. The thumbscrew is placed in the collar on the end of the spring of the universal detector and lowered until the "bare point" almost touches the surface of the electrolyte in the cup beneath. Pressure must then be applied to the spring by turning the large adjusting screw until the "bare point" touches the liquid and a click is heard in the telephone receivers and a faint bubbling sound is also audible. The adjusting screw must then be slowly and carefully turned in the opposite direction so as to raise the point until the bubbling changes to a hissing sound. The point is then above the level of the electrolyte in the cup but is still in contact with it because of the capillary action of the fine wire and the liquid.

By using the large adjusting screw as much as possible, instead of the small thumbscrew, the point is raised or lowered without giving it a circular motion and much finer adjustment is made possible. The potentiometer is adjusted until the hissing noise caused by excessive battery voltage just disappears. The detector is then in its most sensitive condition for receiving signals.

When the detector is in use for long periods, the potentiometer must be frequently readjusted to compensate the gradual loss in voltage of the battery. It is well to provide a small switch which will disconnect the battery from the potentiometer when the detector is not in use. In the same case the acid should be removed and placed in a tightly stoppered bottle. A pipette or fountain pen filler furnishes the most convenient means for filling or emptying the cup. The acid must be kept perfectly pure and out of contact with all metals other than platinum. Great care should be exercised in filling the cup, for the acid, if spilled, will not only badly corrode the metal fittings, but will also provide a current leak and seriously weaken the signals.

Shoemaker and Stone Detectors.—These two types of detectors make use of "glass points," so called because the fine platinum wire is sealed in a glass tube and the end of the tube is then ground down on a fine oilstone until the platinum wire is exposed. This results in a very fine contact area and insures constant immersion of the point without readjustment.

The fine platinum wire for a glass point may be secured from one of the flaming pocket cigar lighters making use of spongy platinum. The center of a thick walled glass tube is softened by heat and contracted as shown at A-B in Fig. 95. After cooling, the tube is cut in half at the point indicated by the dotted line. The platinum wire is placed in the contracted end of the tube and carefully fused in so that about one-half of the wire, which is about 1/2 inch long, is embedded in the glass. The contracted end of the tube containing the wire should be closed. Connection is established to the upper end of the fine platinum wire by filling the tube with mercury and dipping a piece of flexible conductor in the mercury. The upper end of the tube is closed and the mercury prevented from escaping by a small dab of sealing wax.

The "point" is slowly and carefully rubbed on a fine oilstone kept well wet with water. The tube must be held in a vertical position so that the glass will be ground away at right angles. When it is thought that the platinum wire has been exposed by the grinding, connect the flexible conductor to one pole of a battery. The other pole of the battery is connected to a pair of sensitive telephone receivers and the telephone receivers to a vessel containing dilute acid. If the platinum wire is exposed, a sharp click will be heard in the telephone receivers when the "point" is dipped in the acid. Do not confuse the sharp click with the sound which may be occasioned because the outside of the glass tube is damp or wet.

After the point has been sufficiently ground, disconnect the testing apparatus and connect the free end of the flexible conductor to a binding post placed on the end of the detector spring, S. The detector circuit is similar to that of the "bare point" type.

The illustration shows what is sometimes called a "primary cell" detector because it furnishes its own current and does not require a battery. A Stone detector may be very easily changed to one of the Shoemaker type by substituting an amalgamated zinc rod for the platinum wire anode which makes connection with the liquid in the cup. This combination of platinum and zinc results in an electromotive force of about 0.7 volt, and the telephone receivers are connected directly to the terminals of the detector without any local battery or potentiometer. The electrolyte in the cup must be a 20 per cent solution of pure sulphuric acid, as nitric acid would dissolve the zinc in a very few minutes. The zinc must be kept well amalgamated with mercury.

The Shoemaker system makes use of a loop aerial, and the circuits with a single and double coil tuner are illustrated in Fig. 97. It is not necessary to use these, and the detector will operate just exactly as well on a "straightaway" aerial.

Lamp Detector.—All electrolytic detectors, more especially those of the "glass point" type, are subject to the annoyance of "burn-outs." That is, the fine platinum wire melts when receiving strong signals from a near-by station.

In such case, the "bare point" must be lowered until it again makes contact with the liquid, and the "glass point" reground until the wire is again exposed.

When this trouble comes often it is very convenient to have at hand a simple detector which will not burn out and which may be substituted for the usual one when great sensitiveness is not required.

Such an instrument is made by snipping off the tip of a small incandescent electric lamp and removing the filament with a wire. One of the leading-in wires is broken off as close as possible to the glass stub and the globe half filled with a 20 per cent acid solution. The broken wire must be made the negative or cathode and connected like a Fessenden or Stone detector. This lamp detector though crude will give good service without burning out when used to receive from near-by stations.

In place of a lamp detector, a glass point having a larger wire than that of the cigar lighter may be used instead of the usual point, but it will not be so sensitive.

Fig. 99 illustrates a simple form of electrolytic detector which is not so sensitive as that shown in Fig. 100 but is still very serviceable.

The cup is made from the carbon of an old dry cell, the brass connecting cap serving very well to make the connections to. It has a recess about 1/2 inch in diameter and 1/4 inch deep cut in the top to contain the electrolyte. The cup should be about one inch high. A file will smooth up any rough edges and give it a good appearance.

The yoke is made of a piece of 1/8-inch sheet brass about 3/4 inch wide, bent in the shape shown in the illustration. Two small holes are drilled in the feet, to serve to fasten the yoke firmly to the base and also to make connection to.

The adjusting screw may be made from the screw taken from the carbon of an old dry cell. To permit of accurate adjustment, it should be fitted with a large head made from a piece of 1/4-inch hard rubber or fiber cut in a circle about 1 1/4 inches in diameter. Bore a small hole about 1/8 inch in diameter through the center of the head and force it on the screw. A nut screwed on the under side will then clamp it tightly against the brass head. A hole is bored in the center of the yoke and a battery nut which will fit the adjusting screw soldered directly under it.

The platinum wire may be either soldered to the adjusting screw or fastened with tinfoil in the method which has been described.

The cup and yoke are best mounted on a piece of hard rubber 1/2 inch thick, 3 inches wide and 4 inches long. A binding post is placed near each of the four corners.

It is possible to do extremely fine and long distance work with the detector illustrated in Fig. 100. It is so arranged that the "bare point" need not necessarily be revolved when making an adjustment, and so it is possible to place it in a very sensitive condition.

A brass standard, U, 1 1/4 inches long is cut from a piece of 1/2-inch rod. A hole bored in the top and bottom of the standard is threaded with an 8-32 tap. A brass rod, R, 2 inches long is threaded with an 8-32 die throughout its entire length. One end is screwed in the top of U.

A piece of brass tubing, P, 1 1/4 inches long and having an internal bore of 1/2 inch is slipped over U. A slot cut in P fits over a small pin set in U and permits P to be slid up and down but not to turn around.

A head in the form of a circular brass washer, E, 1/8 inch thick, 1/2 inch in diameter and having a 5/32-inch hole bored in the center is soldered in the top of the tube, P.

A circular piece of hard rubber, H, 2 inches in diameter and 1/2 inch thick is fitted with a brass bushing having a hole in the center with an 8-32 thread to screw on the rod, R.

A spiral spring is placed around R between U and the head E. A small brass washer should be placed between H and E in order to eliminate friction. When H is turned in one direction, the spring will cause P to rise, and when turned in the other direction it will be lowered.

A brass arm, A, 1/4 x 1/4 x 1 1/2 inches carries a small thumbscrew, r, at one end, while the other end is soldered to P as shown in Fig. 96. The Woolaston wire is soldered to T.

A small carbon cup 3/4 x 3/4 inch serves to hold the electrolyte. A 3/8-inch hole is bored 1/4 inch deep in the bottom of the cup and poured full of melted lead. The lead is then bored and tapped to fit a machine screw which fastens the cup to the base. Connection is made from a binding post to the machine screw. A second binding post is connected to the screw which fits into the bottom of U and holds it to the base.

If desirable a circular piece of hard wood, F, may be turned out and glued to the base around the cup in order to give it a more finished appearance.

The thumbscrew, T, is used to lower the "bare point" until it almost touches the liquid, and then the large head, H, is brought into play to make the finer adjustment.

Increasing the Sensitiveness of an Electrolytic Detector. The sensitiveness of an electrolytic detector may be increased in three ways, viz., by connecting two detectors in series, by warming the electrolyte and by agitating it.

The first method is clearly apparent.

The second is accomplished by placing the detector over a sand bath and gently warming it. It will then show a marked increase in the strength of the signals at a temperature of about 30 C. This increase will continue to rise with the temperature until it reaches a maximum at about 60 C.

Branly discovered that a fine stream of gas passed through the electrolyte in order to agitate it increases the strength of the signals in the phones. He devised a detector provided with two extra platinum terminals sealed in the cup. When connected in series with a battery and an adjustable resistance, these terminals cause electrolysis of the water, and a fine stream of oxygen and hydrogen gas flows through the acid electrolyte. The stream of gas agitates the liquid just sufficiently so that when oscillations strike the detector they augment the breaking down of the film of gas which collects on the fine platinum point. This results in an increase in the battery current flowing through the telephone receivers of from two to four times and a corresponding increase in the volume of sound. The adjustable resistance is used to regulate the decomposition of the electrolyte and formation of gas, for if this proceeds too rapidly an undesirable rumbling noise will be produced in the telephone receivers.

TANTALUM DETECTOR.

The tantalum detector is especially suitable for the amateur experimenter because its change in resistance when struck by oscillations is so great that high resistance telephone receivers are not necessary. Its normal resistance is about 1000-2000 ohms, and this sometimes drops as low as 125-100 ohms when struck by oscillations of ordinary strength. It is not nearly so sensitive as the electrolytic or crystal detectors, but gives very much louder tones in the telephone receivers when used for short distance work.

The detector is easily made by substituting a piece of tantalum wire for the Woolaston wire of an ordinary electrolytic detector. The dilute acid solution is removed from the cup and replaced by some pure mercury. The connections remain the same as for the "bare point." The potentiometer is adjusted until the potential of the battery is in the neighborhood of 0.2-0.4 volt.

The tantalum wire may be easily secured by breaking the globe of a tantalum lamp and using a piece of the filament. It is best to snip off the lamp tip before breaking the globe. This precaution admits the air and prevents an explosion which would shatter the glass and scatter the filament in fragments.

If the universal detector is used with a tantalum point, turn the small thumbscrew until the wire almost touches the surface of the mercury. Then lower it with the large adjusting screw until the tantalum touches the surface and a sharp click is heard in the telephone receivers. Adjust the potentiometer until the signals are the loudest.

CRYSTAL DETECTORS.

Certain minerals and crystals, principally members of the carbon and sulphur groups, possess the peculiar property of rectifying electrical oscillations and converting them into a pulsating direct current. These crystals conduct the current better in one direction than in the other. In the case of a current having a potential of ten volts and applied to the ends of a carborundum crystal, the current may be one hundred times greater when flowing in one direction than when flowing in the other. This ratio decreases as the voltage is raised, for with 25 volts it may be only about forty times greater. The crystals when properly inserted in the aerial circuit are enabled to rectify the oscillations and produce sounds in the telephone receivers without the aid of a battery.

The following is a partial list of the minerals and crystals exhibiting these properties to a sufficient extent that they are of value as oscillation detectors in wireless telegraphy.

In the case of iron pyrites the writer has found that a specimen of this mineral containing very little or no copper as an impurity does not exhibit these properties to an appreciable extent.

In order to use the universal detector for minerals, a special contact similar to that shown in Fig. 90 must be made. The contact is bored and threaded on its under side to fit a brass pin 3/4 inch long and having an 8-32 thread. The other end of the pin screws into the hole in the bedplate. The large knurled portion of the contact permits it to be raised or lowered without the fingers coming in contact with the crystal. The crystal is clamped between the contact and the spring, S. The position is varied until a sensitive spot is found and then the pressure is carefully regulated by means of the large adjusting screw until the signals in the telephone receivers are the loudest. If possible avoid touching the crystals with the fingers, as the oil and dirt, even though it cannot always be seen, spoils their value for long distance work. Use instead a pair of steel forceps.

The United Wireless Telegraph Co. makes use of carborundum in the detectors shown in Figs. 104 and 105. The principal advantage of carborundum over such substances as silicon, etc., is that it is not affected by the heavy discharge of the transmitting apparatus and does not require a new adjustment after each period of sending. All the crystals will not work, and so a large cake should be purchased and the desired crystals selected. The dark blue portions of the mass, which are the hardest, will give the clearest tones in the telephone receivers, and are preferable to the lighter colored crystals. Since the crystals conduct better in one direction than in the other, as explained above, the adjustment must be made with the view of determining in which position the particular crystal will work the best.

Carborundum will produce sounds in the telephone receivers without the aid of any battery, but for careful work a battery and a potentiometer are necessary.

The other crystals given in the column merely require that the telephone receivers be connected to the detector terminals as in the wiring diagram in Fig. 108.

The Clapp-Eastham detector makes use of a crystal of iron pyrites held in a brass retaining cup beneath the metal contact point. It is not affected by strong signals and requires no battery or potentiometer. When adjusted it will remain in a sensitive condition for a long time without further attention.

Silicon Detector.—While the silicon and "perikon" detectors are classed as mineral or crystal detectors they deserve special attention.

Silicon gives fair results if a crystal is placed between two metal electrodes as, for instance, between the contact and spring of the "universal" detector, but is much more sensitive when properly mounted. A brass cup such as that shown in Fig. 90 is made and the interior brightened by scraping with a file. The cup is then poured full of a molten fusible alloy and the silicon pressed in it until it cools and becomes set. It should then present an appearance similar to that shown by A in Fig. 107. The silicon is ground down by rubbing on the surface of a clean oilstone kept well wet with water, until the surface is flat and shows a polish.

The cup containing the silicon is placed over the hole in the bedplate of the universal detector. A knurled brass thumbscrew having a point on its lower end is screwed into the collar on the spring, S, and brought to bear on the polished surface of the silicon. The pressure may be easily regulated by means of the large adjusting screw until the signals in the telephone receivers are the loudest. It is not advisable to fasten the cup to the bedplate but merely to brighten the bottom so as to insure a good contact. The cup may then be moved around so that different portions of the polished surface of the silicon may be brought into play when desirable.

If the knurled brass thumbscrew is fitted with a platinum point which can be brought to bear on the surface of the silicon, the efficiency of the detector will be materially increased.

When mounting silicon or other crystals some careless experimenters use lead or a metal having a high melting point instead of a fusible alloy. This is poor policy because the high temperature coats the surface of the crystals and the interior of the cup with a non-conducting layer which destroys the sensitiveness and makes it unfit for long distance work. A fusible alloy melting at about the boiling point of water or even lower should be used. Such alloys are usually composed of tin, lead and bismuth. The addition of a little cadmium serves to make the fusing point considerably lower in each case. The alloys may be prepared by the experimenter from the following formulae, or are obtainable from a firm manufacturing fire plugs for automatic fire extinguishers.

The lead should be melted first and then the bismuth, tin and cadmium added in the order named.

Perikon Detector.—The Perikon detector is one of the latest types to come into extensive use. It consists of two crystals, zincite and chalcopyrites,⁴ set in cups in the manner just described and placed in contact with each other. The minerals are mounted similar to those in Fig. 105. The zincite should present a rather flat surface with the grain of the crystal parallel to the sides of the cup so that the top surface corresponds to the end of a stick of wood sawed at right angles to the grain. More than one crystal of zincite is usually set in the same cup. The chalcopyrites should present a rather blunt point. The cup containing the chalcopyrites is the smaller and is bored and threaded to fit a thumbscrew which passes through the collar in the spring, S, of the "universal" detector. The bottom of the cup containing the zincite is brightened so as to insure a good contact and then placed on the bed plated under the cup containing the chalcopyrites which is fastened to the thumbscrew. The zincite may then be moved around until the most sensitive portion is found. The chalcopyrites is lowered until it comes into contact with the zincite and then the pressure regulated by means of the large adjusting screw.

The Perikon detector gives excellent results without a battery and is preferably used in that manner. If a battery is used, a potentiometer to lower the voltage is necessary.

When adjusting this or the carborundum detector where a battery is used, the pressure must be very carefully regulated until it is found to be the best. When the pressure is light the signals in the phones are due to an imperfect contact, and when it is slightly increased the rectifying properties of the crystal are brought into play.

The Perikon detector illustrated in Fig. 110 is somewhat similar to that used for commercial work.

The standards or posts supporting the cups which contain the elements are brass rods 1/2 inch square and 1 1/2 inches high. A hole is bored in the bottom of each and threaded with an 8-32 tap to receive a machine screw which passes through the base and holds them in an upright position. A hole is bored 1 1/8 inches from the bottom, in the face of one standard and threaded with an 8-32 tap. A brass rod 1 1/4 inches long, carrying at one end a cup 1 inch in diameter and 3/8 inch deep, is threaded to fit in the hole in the standard. The zincite is mounted in this cup.

The other standard is cut in half with a hack saw and a 1/8-inch hole bored 1/4 inch deep in the axis of each piece. A pin, 1/2 inch long, is set in the lower half by soldering it in the hole. The upper half of the standard is placed over the pin and left free to move when twisted. A 1/8-inch brass tube, 1 inch long, passes through the upper part of the standard. A 1/8-inch brass rod, 1 3/4 inches long, passes through the tube.

The small cup containing the zincite is mounted on one end of the rod and a hard rubber handle on the other.

A brass spring is placed between the cup and the standard in order to press the chalcopyrites against the zincite. The cup is mounted out of center so that by revolving it and twisting the standard at the same time the chalcopyrites may be brought into contact with any portion of the zincite. By screwing the rod supporting the zincite cup in or out of the standard the pressure with which the two elements are pressed together may be regulated.

The base of the detector is hard rubber of the dimensions indicated in the illustration. Four binding posts on each corner of the base are necessary. The detector is connected in a similar manner to the silicon detector shown in Fig. 108. If a battery is used the circuit should be like that of the "bare point" electrolytic, and the current must flow from the zincite to the chalcopyrites.

LEAD PEROXIDE DETECTOR.

The peroxide of lead detector makes use of no liquids, but still may be classed as an electrolytic since its action is of that nature.

It consists of a pellet of lead peroxide held between an electrode of lead and one of platinum. Contrary to most other detectors, the resistance is increased upon the passage of electrical oscillations. The oscillations stimulate chemical action and increase a counter-electromotive force sufficiently so that a decrease in the current sent through the phones by the local battery takes place. The action may be outlined more in detail as follows. The current of the local battery decomposes part of the lead peroxide into its components, lead and oxygen. The lead ions are positively electrified and so they tend to pass upward toward the lead electrode which is negative. The negative ions of oxygen gas tend to pass downwards towards the platinum. But the lead and platinum electrodes with the intervening lead peroxide constitute a small cell acting independently of the local battery and sending a current in the opposite direction. This counter-electromotive force tends to send the ions in an opposite direction to that in which they are sent by the battery current. Upon the passage of electrical oscillations this counter electromotive force is increased and sufficient ions sent out in opposition to those of the battery current so that an appreciable drop in the current flowing through the telephone receivers takes place. The sudden current drop produces a sound in the receivers.

The lead pellets may be secured from a druggist who can mold them in his tablet press. They should be subjected to as great a pressure as possible in order to reduce resistance and prevent crumbling.

A piece of platinum foil about 1/2 inch square is placed beneath the pellet on the crystal electrode. A piece of clean, bright sheet lead 3/8 inch in diameter and 1/8 inch thick is laid on the pellet and the whole clamped together by tightening the thumbscrew passing through the collar on the spring, S. The detector is connected up similar to the "bare point," The platinum is made the positive of the local battery. Adjustment is secured by regulating the pressure.

It is very necessary that the pellets be kept dry, as otherwise a loud singing and hissing noise, due to the decomposition of the water, will render the reception of signals very difficult.

THE MARCONI MAGNETIC DETECTOR.

When an oscillatory discharge takes place through a coil of wire surrounding a needle, it magnetizes the needle in a totally different manner from a voltaic current. The needle will have several poles throughout its length, many of them reversed. Rutherford applied this phenomenon to the detection of electrical oscillations, but it remained for Marconi to improve it and give the magnetic detector its existing form. This type of detector is very sensitive, free from all adjustment and is not made inoperative by the heavier discharge of the transmitter during each period of sending.

A small transformer is provided with a core composed of a band or cord of iron wires in the form of an endless belt which passes around two pulleys kept in motion by a clockwork motor. The band revolves in the field of a strong horseshoe magnet and passes directly over the poles after issuing from the transformer bobbin, so that the portion approaching the bobbin are constantly in a state of increasing magnetism. The actual operation is based upon the property of iron called hysteresis, for the magnetism of the core lags behind that of the permanent magnet and is of a different degree from what it ought to be, in view of its position in the vicinity of the permanent magnet. The moment the oscillations pass through the primary coil of the transformer, this lag is set free and the magnetism assumes its full value. The change in magnetism induces a current in the secondary, which registers as a sound in the telephone receivers.

The primary coil is made up of a single layer of No. 36 B. S. gauge silk covered wire wound on a thin walled glass or hard rubber tube. The ends of the tube, which is 2 inches long and 1/4 inch external diameter, are slightly flared so as not to chafe the band. The primary is thoroughly shellacked and covered with a single layer of paper.

The secondary is also of No. 36 B. S. silk covered wire and is wound between two disks of hard rubber, 1/4 inch thick and 1 1/2 inches in diameter, placed 3/8 inch apart in the center of the secondary and the intervening space wound full of wire.

The terminals of both the primary and secondary are extended to binding posts mounted on the case of the instrument.

The core or revolving band is made by winding 100 strands of No. 36 silk covered soft iron wire between two small pegs, placed a distance apart, equal to twice the circumference of the oval formed by the two pulleys. The wire is all wound in the same direction. It should be carefully removed from the pegs and kept taut while it is slightly twisted, doubled, and then further twisted into a rope or cord. The ends are threaded together with a separate piece of insulated wire, into a link which will pass easily through the primary tube.

The pulleys around which the band revolves are made of hard wood. They are 4 inches in diameter and 3/8 inch thick and have a V-shaped groove cut in the edge. In order to minimize friction and wear, it is advisable to fit them with a bearing which may be made out of brass tubing and a couple of washers. One of the pulleys is geared to a clockwork motor so that the band makes a complete revolution about once every two minutes. An old eight day clock may be adapted for this purpose, or, what is much better, the motor from an old phonograph.

The horseshoe magnet is mounted with its north pole pointing towards and nearly touching the middle of the outside of the secondary. The south pole is placed opposite the end of the primary tube which is on the side towards which the band is revolving, that is, the band in revolving passes first over the north pole and then over the south. Two magnets are sometimes used with their north poles together in the center of the secondary, and a south pole opposite each end of the primary tube.

The commercial instrument is placed in a glass covered case which protects it from dust and injury. The clockwork motor is concealed in the lower part of the case. This is a good plan but an experimental detector may be merely mounted on a flat wooden base as illustrated in Fig. 112.

The secondary terminals are connected directly to the telephone receivers while the primary leads to the aerial and the ground. When the detector is started up it should make a very slight hissing sound in the telephone receivers as the band passes slowly through the coils. This shows the instrument to be in good working order and ready for the reception of signals.

The Audion.—Dr. Lee DeForest was led by the flickering of a sensitive gas flame to investigate whether or not it would respond to Hertzian vibrations as well as to those of heat and sound. His experiments led to the invention of the audion, a peculiar instrument making use of ionized gas for its operation.

The audion consists of an incandescent lamp having a metallic filament, on either side of which are a grid and a plate made of nickel. When the filament is lighted it throws off ions which act as a relay to high frequency oscillations passing between the plate and the grid. A properly constructed audion is exceedingly sensitive and produces very loud tones in the telephone receivers. It has the further advantages of entire absence of adjustment except the governing of the battery voltage, and is capable of extremely fine tuning.

Fleming originated the oscillation valve illustrated in Fig. 118. It consists of an ordinary incandescent lamp with a carbon filament, having a metal cylinder, C, placed around the filament, but attached to an independently insulated platinum wire sealed in the glass. When the lamp is lighted by passing a current through the filament, the incandescent carbon liberates negative ions. If oscillations are then set up in a circuit which includes a pair of sensitive telephone receivers and is formed by connecting the negative terminal of the filament with the platinum cylinder, negative electricity will be enabled to pass from the filament to the cylinder but not in the opposite direction, and so sounds will be produced in the telephone receivers. High frequency oscillations themselves could not be made to pass through the telephone receivers because of the choking action of the iron cores of the electromagnets.

The simple but sensitive form of detector illustrated in Fig. 119 is not of practical value for commercial work, but is very interesting as the progenitor of the audion, and provides a good field for amateur investigation. Its only drawback is that the gas flame is very difficult to keep steady and every flicker registers as a sound in the telephone receivers.

A Bunsen burner using coal gas furnishes the flame, and a salt of an alkaline metal heated in the flame, the ions. The hydroxides of caesium, potassium and sodium give the best results in the order named.

The salt is contained in a piece of trough-shaped platinum foil, about 3/8 inch long and 1/16 inch wide. This trough is made the cathode or negative of the telephone circuit and placed in the outer oxidizing flame just above its juncture with the interior reducing flame and must be kept incandescent. The upper electrode or anode is a piece of platinum wire about 1/16 inch above the trough.

The arrangement and construction of the detector is clearly indicated by the drawing so that it is unnecessary to go into details. The block, E, which fits on the tube of the Bunsen burner, is made of fiber. Two double binding posts, D, are fastened to E to support the rods, R, which are fitted at the tops with binding posts, B, into which the electrodes may be clamped.

Twelve dry cells are connected with a multiple point switch so that an electromotive force of 6-18 volts, varying in steps of one cell at a time, may be secured. The flame is best provided with a mica chimney to protect it from drafts. By keeping plenty of salt in the trough and carefully adjusting the voltage, this detector may be made marvelously sensitive.

[3]	The different detectors in order of their sensitiveness are electrolytic, perikon, magnetic, silicon, carborundum.

[4]	Peacock ore or bornite, which consists of about 60 parts of copper, 14 parts of iron and 26 parts of sulphur, may be substituted for the chalcopyrites with excellent results.

ELECTRICAL TERMS AND DEFINITIONS.

Accumulator:

A cell whose positive and negative electrodes are formed or deposited by a current flowing from a separate source.

Aerial:

A network or a number of wires insulated from surrounding objects and suspended in the air to emit or intercept electromagnetic waves.

Alternating Current:

An electric current, of which the direction of flow reverses a number of times per second.

Ampere:

The quantity of current which will flow through a resistance of one ohm under a potential of one volt. The unit of current.

Ampere Hour:

The quantity of electricity passed when flowing at the rate of one ampere for one hour.

Anode:

The positive terminal of a broken circuit or a source of electricity. It is the carbon of a cell or the pole at which a current enters a solution.

Capacity:

The relative ability of a conductor to receive and retain an electric charge.

Circuit:

An unbroken conducting path for an electric current.

Condenser:

A device for receiving and storing up electrostatic energy.

Cycle:

The full period of reversal of an alternating current. A 60-cycle current is one making 60 complete reversals per second.

Detector, Wireless:

An instrument for detecting oscillations in the aerial of a receiving station. It either varies its own internal resistance or generates a weak intermittent direct current similar in time and duration with the signals emitted by the transmitting station.

Dielectric:

A non-conductor or insulator. It usually refers to the material interposed between the oppositely charged coatings of a condenser.

Direct Current:

A current flowing in one direction only.

Electrode:

The terminal of an open electric circuit or a conductor carrying a current and immersed in an electrolyte.

Electrolysis:

The separation of a chemical compound into its elements by the action of an electric current.

Electrolyte:

A solution which will conduct a current of electricity.

Electromagnet:

A mass of iron which is magnetized by the passage of a current of electricity through a coil of wire wound around the mass and insulated therefrom.

Farad:

The unit of electrical capacity. A condenser having a capacity of one farad would be raised to a potential of one volt by one ampere flowing for one second.

Field of Force:

The space which is under magnetic stress in the neighborhood of a magnet or a wire carrying a current.

Helix, Transmitting:

A coil of heavy wire which furnishes the inductance for the closed oscillation circuit of a wireless transmitter and acts as an auto-transformer to raise the voltage of the high frequency currents.

Henry:

The unit of induction. It is the induction in a circuit when the electromotive force induced in this circuit is one volt, while the inducing current varies at the rate of one ampere per second.

Inductance:

The property of an electric circuit whereby lines of force are developed around it.

Induction Coil:

An instrument or device consisting of two independent coils of wire wound around an iron core, and which by magnetic induction steps up an intermittent direct current from a low to a high voltage.

Insulator:

A non-conductor or a substance impervious to the passage of electricity.

Key:

A device for making and breaking a current into periods corresponding to the dots and dashes of the telegraph code.

Kilowatt:

1,000 watts. See watt.

Leyden Jar:

A static condenser which will store up static electricity and is cylindrical in form. So-called because it was originated in Leyden, Holland.

Multiple:

The term expressing the connection of several pieces of electrical apparatus in parallel with each other so that the current is divided between them.

Ohm:

The unit of resistance. It is arbitrarily taken as the resistance of a column of mercury, one square millimeter in cross sectional area and 106 centimeters in height.

Parallel:

The same meaning as multiple. Parallel circuits are those which start at a common point and end at a common point.

Polarization:

The collection of hydrogen upon the positive electrode of a primary cell with a consequent loss of voltage.

Potential:

Voltage or electrical force.

Resistance:

The quality of an electrical conductor whereby it opposes the passage of an electric current. The unit of resistance is the ohm.

Rheostat:

A variable resistance to regulate the strength of an electric current.

Series:

Opposed to parallel or multiple. Instruments in series are so connected that the current passes from one to the other and does not divide.

Spark Gap:

An air gap or open space between two electrodes for the passage of a high voltage discharge.

Storage Battery:

See accumulator.

Transformer:

A device for stepping up or stepping down the voltage of an alternating current by means of magnetic induction.

Tuning Coil:

A variable inductance for changing the period of the receptor circuit.

Volt:

The unit of electrical force or potential. The electromotive force which, if steadily applied to a conductor whose resistance is one ohm, will produce a current of one ampere.

Voltmeter:

An instrument for measuring voltage.

Watt:

Unit of work. It is the rate of work of one ampere flowing under a potential of one volt. Seven hundred and forty-six watts represent one electrical horsepower.

APPARATUS REQUIRED IN MANY INSTANCES IN ORDER TO COMPLY WITH THE WIRELESS LAW.

OSCILLATION HELIX

The oscillation helix has almost become a necessity in order to comply with the regulations of the Wireless Law regarding wave form, except in those stations where a quenched gap is used.

The wave emitted by many stations is not pure. It is composed usually of two or three separate waves of different lengths instead of all the energy being confined to oscillations of one period. It is possible to tune such a wave in two or more places or "humps," as they are called, on the tuning coil. It is obvious that a wave possessing such humps cannot be closely tuned and is liable to interfere with the signals of another station. This is one of the principal causes of interference.

The reason for this phenomenon is simple. The action of a transmitter is to first charge a condenser. When the potential of the condenser rises to sufficient value it discharges across the spark gap and sets up oscillations in the closed circuit. These oscillations immediately induce oscillations in the open circuit or aerial system and part of the energy passes off into the ether as electro-magnetic waves. However, the oscillations in the aerial system do not immediately die away after the oscillations in the closed circuit cease during the interim until the next condenser discharge, but continue to surge and react upon the dosed circuit to sufficient extent to induce therein currents which surge back and forth long after the current from the condenser discharge has died away.

We might call the oscillations due to the condenser discharge primary oscillations and those induced in the aerial thereby secondary oscillations. Those which are then set up in the closed circuit by the reaction of the secondary currents are tertiary. This third train of oscillations persist after the secondary currents have died away, and induce another set of oscillations in the aerial which send out a second set of electromagnetic waves differing in length from the first.

The oscillations which take place after the initial surge in the closed and open circuits are naturally somewhat weak. By using an oscillation helix in which the primary and secondary are separated from each other it is possible to eliminate the third and fourth trains of oscillations and all others having a tendency to follow, by placing the circuits apart so that the weak oscillations are not strong enough* to react across the intervening space. The immediate oscillations set up by the condenser discharge are strong enough to act across the space and set up powerful oscillations in the aerial.

A hot wire ammeter placed in the aerial circuit of a transmitter employing an oscillation transformer will not indicate as much current as if placed in the same position in a circuit using an ordinary helix; but in spite of the fact, a transmitter using an oscillation helix will send farther because the energy is concentrated in waves of one length.

The construction of one type of oscillation helix has already been outlined on page 92. The form shown in Fig. 152 has no special advantages over the other but is preferred by many experimenters.

It is of the "pancake" type, so-called because of the flat form of the windings which are made in the shape of a spiral of brass ribbon set in a slotted frame.

The dimensions of the helix are clearly apparent from the drawing. The primary is composed of seven turns of brass ribbon 1/2 inch wide and 1/16 inch thick. The secondary should have from 10 to 15 turns of ribbon 3/8 x 1/16. The coils may be slid back and forth on the brass rod so that the distance between them is variable. Connection is made to the coils by means of suitable clips. A clip similar to that shown on page 92, but made to snap on a flat ribbon instead of a round wire, will serve the purpose.

QUENCHED SPARK GAP.

A "quenched" gap is made up of a number of brass or copper disks accurately turned to a true surface and separated by mica or rubber rings about .01 inch thick. The spark discharge takes place in the air-tight space at the center of the disks, inside of the mica rings.

The quenched gap has several advantages over other forms. It is practically noiseless and the nuisance of a crashing discharge may be avoided by its use.

The large surface offered to the spark by the disks cools the spark and quickly stops the oscillations in the closed circuit, and thereby leaves the open circuit and aerial system free to vibrate in its own period and therefore radiates pure waves. By pure wave a wave of one length is meant.

A quenched gap cannot be used on a set of over 1 K.W. power without artificial cooling by an air blast.

Fig. 154 shows an efficient form of quenched gap for use in stations up to 1 K.W. in power.

The disks are shown in detail in Fig. 155. They are cast out of copper and then turned perfectly true and smooth in a lathe. After surfacing, the discharge surface should be heavily silver plated and buffed smooth.

The disks are piled on a marble base with a mica ring between each. They are clamped down by a strong set screw mounted on a heavy brass yoke. Enough pressure should be brought to bear to force the plates tightly together and make them air tight.

The number of disks required is governed by the voltage of the charging condenser. Generally speaking it is one section of .01-inch gap for each thousand volts delivered by the secondary of the transformer. It is very important to secure just the proper number of disks. If properly adjusted, the quenched gap will give one discharge for each alternation of the current and produce a musical tone.

The quenched gap is placed in the same position in the transmitting circuit as any other form of gap.

ROTARY GAPS.

Rotary gaps are divided into two general classes, the synchronous gap and the non-synchronous gap.

The former usually consists of one or more stationary electrodes and a rotating member made like a star wheel with projecting spokes. This rotary member is attached directly to the shaft of the alternator or motor generator and arranged so that a spoke always comes opposite a stationary member at the exact moment that the maximum of potential is obtained in the condenser. Such an arrangement permits one discharge for each alternation of the current and produces a pure musical note easily distinguished in the telephone receivers at a distant station.

In the non-synchronous rotary gap the wheel is driven at a high rate of speed without any regard to synchronism with the alternations of the current.

The rotary gap shown in Fig. 157 is of the non-synchronous type.

The rotating member is cast from an alloy of equal parts of zinc and aluminum. It is necessary to first make a wooden pattern from which the casting may be made. The details of the wheel are shown in Fig. 158. The casting must be placed in a lathe chuck and turned true. It is mounted on a hard rubber disk 2 7/8 inches in diameter and 1/4 of an inch thick. The disk serves to insulate the revolving electrodes from the motor shaft. The "rotor" is mounted upon the shaft by means of a small brass bushing which passes through the center of the disk.

The motor must be well built and capable of running at high speed. A "Juno" motor will be found very satisfactory. When running free its speed is about 4500 r.p.m. With the rotor in place the speed is about 3600 r.p.m.

The motor should be mounted on a heavy marble base capable of absorbing any little vibration that the gap may be subject to when running at high speed.

The stationary electrodes are made in the same manner as those for an ordinary gap and consists of two flanged zinc electrodes mounted upon threaded brass rods supported by two hexagonal standards. The axis of the electrodes should be the same height above the base as that of the motor shaft.

The rotor should be carefully balanced so that it is practically free from vibration by boring small holes in the back face so as to make the weight on opposite sides equal.

The motor may be driven by a battery or from the same source that supplies the transformer, in series with two or three suitable lamps. A motor wound to run directly from the 110-volt line or a higher potential must have its fields wound with very fine wire and is apt to give trouble through "burn-outs," due to "kick back." When the motor is operated on batteries or is wound for running in series with a lamp the danger is lessened.

A rotary gap is placed in the transmitting circuit in the same position as any other gap. Its use will result in a wonderful increase in the transmitting range of almost any station, for not only will the amount of energy passing through the aerial be raised, but the clear musical tone given off is more plainly distinguishable at a greater distance in the receiving station than a spark of the ordinary sort.

"KICK BACK."

The oscillations taking place in the closed circuit and aerial system of a wireless transmitter continue to surge after the current in the condenser has dropped below a certain value, and react upon the primary winding of the coil or transformer by induction and produce high voltage, high frequency currents termed "kick back," in wireless telegraph parlance.

"Kick back," wherever it exists to an appreciable extent, is liable to damage insulation and cause possible "burn-outs." The "kick-back" preventers illustrated in the accompanying diagrams will be found an efficient method of avoiding this danger.

The first method shows an ordinary pressed telephone condenser of about two microfarads capacity connected directly across the A. C. mains near the transformer terminals, in series with two 6-ampere fuses. The condenser is shunted by a small spark gap made of needle points with a very small space, about .005 of an inch, between them.

The second method is an elaboration of the first and shows two sets of condensers in series with fuses and bridged by spark gaps with a "ground" through a third condenser connected between. This second method is the best and is often used to prevent delicate instruments, such as a voltmeter, from the effects of "kick back."

A proper "kick-back" preventer is part of the Fire Insurance Underwriters requirements for a wireless telegraph station.

Receiving Apparatus.

THE VARIOMETER.

A variometer is a tuning device in which two coils of wire are placed in series and connected so that the turns can be made to oppose one another. One coil is movable and by turning it the currents flowing through the adjacent coils oppose each other and decrease the self-induction of the whole and consequently the period of the circuit.

The accompanying illustration shows the constructive details of an efficient form of variometer.

The coils are wound around two cardboard cylinders. One cylinder is 6 inches in diameter and the other 5 inches. Both are 2 inches long. The large cylinder is wound with twenty-five turns of No. 22 B. S. gauge single silk covered wire wound in two sections so as to leave a space 3/8 inch wide in the center. The small cylinder is wound in the same manner with the same size of wire but contains thirty turns so as to make the length of wire in each of the coils practically equal.

The space in the center of each of the coils allows a supporting rod to pass through without interfering with the wire. The shaft is a piece of 5/16 brass rod about 7 1/2 inches long. The upper end is provided with a knob and a pointer. The large coil is mounted on the under side of a wooden cover made to fit a containing case of the proper size to receive the variometer and of a style similar to that ordinarily used to enclose a variable condenser.

The shaft passes through the larger coil, at two points diametrically opposite, but should not fit tightly. It also passes through the smaller coil but is fastened to the latter by means of a cross bar so that when the knob is turned the coil will revolve also. The coils are connected by means of a piece of braided wire or flexible conductor, long enough so as not to interfere with the movement of the inner coil.

The outside terminals of the coils terminate in binding posts mounted on the top of the case. When making a variometer be careful not to employ any iron or steel in its construction, not even iron screws.

The variometer is placed in the receiving circuit by connecting it in series with the aerial before it reaches the tuning coil or loose coupler.

NEW CRYSTAL DETECTORS.

Silicon Detector.—The silicon detector is always interesting because it was one of the first mineral rectifiers to come into extended use. The photograph shown below illustrates one of the latest forms of the silicon detector.

The large cup supported by the left-hand standard contacts several pieces of fused silicon embedded in fusible alloy. The right-hand standard supports a movable "offset" cup the same as that used on the Perikon type of Detector. A small piece of arsenic is mounted in this cup and may be brought to bear against any portion of any of the silicon crystals.

Pyron Detector.—The Pyron detector is not new, but the photograph shows a very simple and efficient form in which a fine wire is brought to bear against a crystal of iron pyrites mounted in a small cup.

Galena Detector.—Although galena is named in the list of sensitive minerals on page 132 it has come into such extensive use as a detector since the first edition of this book to be worthy of special attention. Galena detectors are often spoken of as "cat-whisker" detectors because of the long fine wire used to secure a delicate contact with the mineral.

The mineral is usually placed in a cup and held in position by imbedding in fusible alloy or clamped with a set screw. The best surface of the mineral should be selected by testing previous to imbedding it in the cup. Contact is made with the surface of the mineral by means of a piece of No. 30 phosphor bronze wire mounted on the end of a short brass rod fitted with an adjusting screw so that by turning or twisting the surface of the mineral may be "searched" and the tension varied.

Such an arrangement is illustrated in Fig. 164. The base is a hard rubber block 3 3/4 x 1 3/4 x 1/2. The binding posts are of the type commonly used on electrical instruments. One of the posts is pivoted by placing a spring washer under the head of the screw which holds the post to the base. A short piece of brass rod fitted with a hard rubber knob passes through the wire hole in the post. A piece of No. 30 phosphor bronze wire is soldered to the end of the rod. By twisting the post and sliding the rod any portion of the mineral surface may be selected. Twisting the rod varies the tension of the contact.

The galena detector is connected in the receiving circuit in the same manner as other detectors of the mineral type.

THE AUDION.

The Audion—is finding favor in many amateur wireless stations, because of its almost entire lack of adjustment and of the loud clear signals which it gives even when used for long distance work.

The illustration shows the latest form of audion, the plate and the grid both being on the same side of the filament.

The filament of an audion is usually lighted by means of a six-volt storage battery. A small battery rheostat placed in series with the battery serves to regulate the amount of current flowing through the filament. Only one filament is used at a time, the other being saved as a reserve in case the first burns out.

The higher voltage necessary to operate an audion is supplied by a battery consisting of fifteen flashlight batteries, each flashlight battery being composed of three separate cells. The batteries are connected to an eight-point switch so that throwing the switch on the first point will connect five sets of batteries. The second point places five more in circuit and each additional point one set only. It is also a good plan to connect a four-point switch and three separate cells of battery in series with the eight-point switch so that they may be added to the circuit one at a time and the potential varied more closely than the steps on the eight-point switch permit. The maximum voltage of such a battery is approximately 56 volts.

The diagram in Fig. 166 shows exactly how an audion is connected. The wires A and B are the terminals leading to the tuning coil or loose coupler. It is not necessary that the telephone receivers used with an audion be wound to a high resistance in order to secure good results.

The audion is placed in operation by turning the rheostat until the filament lights brightly. Then adjust the voltage of the high potential battery until the signals are clearest. If the voltage is too high the audion will become filled with a bluish light and the voltage should be immediately reduced. The signals will be loudest when the filament is brilliantly lighted. No more current should be passed through the filament than is necessary to render the signals plain, for if "forced" its life will be limited to only a few hours.

Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled. That a person, company, or corporation within the jurisdiction of the United States shall not use or operate any apparatus for radio communication as a means of commercial intercourse among the several States, or with foreign nations, or upon any vessel of the United States engaged in interstate or foreign commerce, or for the transmission of radiograms or signals the effect of which extends beyond the jurisdiction of the State or Territory in which the same are made, or where interference would be caused thereby with the receipt of messages or signals from beyond the jurisdiction of the said State or Territory, except under and in accordance with a license, revocable for cause, in that behalf granted by the Secretary of Commerce and Labor upon application therefor; but nothing in this Act shall be construed to apply to the transmission and exchange of radiograms or signals between points situated in the same State: Provided, That the effect thereof shall not extend beyond the jurisdiction of the said State or interfere with the reception of radiograms or signals from beyond said jurisdiction; and a license shall not be required for the transmission or exchange of radiograms or signals by or on behalf of the Government of the United States, but every Government station on land or sea shall have special call letters designated and published in the list of radio stations of the United States by the Department of Commerce and Labor. Any person, company, or corporation that shall use or operate any apparatus for radio communication in violation of this section, or knowingly aid or abet another person, company, or corporation in so doing, shall be deemed guilty of a misdemeanor, and on conviction thereof shall be punished by a fine not exceeding five hundred dollars, and the apparatus or device so unlawfully used and operated may be adjudged forfeited to the United States.

SEC. 2. That every such license shall be in such form as the Secretary of Commerce and Labor shall determine and shall contain the restrictions, pursuant to this Act, on and subject to which the license is granted; that every such license shall be issued only to citizens of the United States or Porto Rico or to a company incorporated under the laws of some State or Territory or of the United States or Porto Rico, and shall specify the ownership and location of the station in which said apparatus shall be used and other particulars for its identification and to enable its range to be estimated; shall state the purpose of the station, and, in case of a station in actual operation at the date of passage of this Act, shall contain the statement that satisfactory proof has been furnished that it was actually operating on the above-mentioned date; shall state the wave length or the wave lengths authorized for use by the station for the prevention of interference and the hours for which the station is licensed for work; and shall not be construed to authorize the use of any apparatus for radio communication in any other station than that specified. Every such license shall be subject to the regulations contained herein, and such regulations as may be established from time to time by authority of this Act or subsequent Acts and treaties of the United States. Every such license shall provide that the President of the United States in time of war or public peril or disaster may cause the closing of any station for radio communication and the removal therefrom of all radio apparatus, or may authorize the use or control of any such station or apparatus by any department of the Government, upon just compensation to the owners.

SEC. 3. That every such apparatus shall at all times while in use and operation as aforesaid be in charge or under the supervision of a person or persons licensed for that purpose by the Secretary of Commerce and Labor. Every person so licensed who in the operation of any radio apparatus shall fail to observe and obey regulations contained in or made pursuant to this Act or subsequent Acts or treaties of the United States, or any one of them, or who shall fail to enforce obedience thereto by an unlicensed person while serving under his supervision, in addition to the punishments and penalties herein prescribed, may suffer the suspension of the said license for a period to be fixed by the Secretary of Commerce and Labor not exceeding one year. It shall be unlawful to employ any unlicensed person or for any unlicensed person to serve in charge or in supervision of the use and operation of such apparatus, and any person violating this provision shall be guilty of a misdemeanor, and on conviction thereof shall be punished by a fine of not more than one hundred dollars or imprisonment for not more than two months, or both, in the discretion of the court, for each and every such offense: Provided, That in case of emergency the Secretary of Commerce and Labor may authorize a collector of customs to issue a temporary permit, in lieu of a license, to the operator on a vessel subject to the radio ship Act of June twenty-fourth, nineteen hundred and ten.

SEC. 4. That for the purpose of preventing or minimizing interference with communication between stations in which such apparatus is operated, to facilitate radio communication, and to further the prompt receipt of distress signals, said private and commercial stations shall be subject to the regulations of this section. These regulations shall be enforced by the Secretary of Commerce and Labor through the collectors of customs and other officers of the Government as other regulations herein provided for.

The Secretary of Commerce and Labor may, in his discretion, waive the provisions of any or all of these regulations when no interference of the character above mentioned can ensue.

The Secretary of Commerce and Labor may grant special temporary licenses to stations actually engaged in conducting experiments for the development of the science of radio communication, or the apparatus pertaining thereto, to carry on special tests, using any amount of power or any wave lengths, at such hours and under such conditions as will insure the least interference with the sending or receipt of commercial or Government radiograms, of distress signals and radiograms, or with the work of other stations.

In these regulations the naval and military stations shall be understood to be stations on land.

First. Every station shall be required to designate certain definite wave length as the normal sending and receiving wave length of the station. This wave length shall not exceed six hundred meters or it shall exceed one thousand six hundred meters. Every coastal station open to general public service shall at all times be ready to receive messages of such wave lengths as are required by the Berlin convention. Every ship station, except as hereinafter provided, and every coast station open to general public service shall be prepared to use two sending wave lengths, one of three hundred meters and one of six hundred meters, as required by the international convention in force: Provided, That the Secretary of Commerce and Labor may, in his discretion, change the limit of wave length reservation made by regulations first and second to accord with any international agreement to which the United States is a party.

Second. In addition to the normal sending wave length all stations, except as provided hereinafter in these regulations, may use other sending wave lengths: Provided, That they do not exceed six hundred meters or that they do exceed one thousand six hundred meters: Provided further, That the character of the waves emitted conforms to the requirements of regulations third and fourth following.

Third. At all stations if the sending apparatus, to be referred to hereinafter as the "transmitter," is of such a character that the energy is radiated in two or more wave lengths, more or less sharply defined, as indicated by a sensitive wave meter, the energy in no one of the lesser waves shall exceed ten per centum of that in the greatest.

Fourth. At all stations the logarithmic decrement per complete oscillation in the wave trains emitted by the transmitter shall not exceed two-tenths, except when sending distress signals or signals and messages relating thereto.

Fifth. Every station on shipboard shall be prepared to send distress calls on the normal wave length designated by the international convention in force, except on vessels of small tonnage unable to have plants insuring that wave length.

Sixth. The distress call used shall be the international signal of distress: dot dot dot, dash dash dash, dot dot dot.

Seventh. When sending distress signals, the transmitter of a station on shipboard may be tuned in such a manner as to create a maximum of interference with a maximum of radiation.

Eighth. Every station on shipboard, wherever practicable, shall be prepared to send distress signals of the character specified in regulations fifth and sixth with sufficient power to enable them to be received by day over sea a distance of one hundred nautical miles by a shipboard station equipped with apparatus for both sending and receiving equal in all essential particulars to that of the station first mentioned.

Ninth. All stations are required to give absolute priority to signals and radiograms relating to ships in distress; to cease all sending on hearing a distress signal; and, except when engaged in answering or aiding the ship in distress, to refrain from sending until all signals and radiograms relating thereto are completed.

Tenth. No station on shipboard, when within fifteen nautical miles of a naval or military station, shall use a transformer input exceeding one kilowatt, nor, when within five nautical miles of such a station, a transformer input exceeding one-half kilowatt, except for sending signals of distress, or signals or radiograms relating thereto.

Eleventh. Each shore station open to general public service between the cost and vessels at sea shall be bound to exchange radiograms with any similar shore station and with any ship station without distinction of the radio systems adopted by such stations, respectively, and each station on shipboard shall be bound to exchange radiograms with any other station on shipboard without distinction of the radio systems adopted by each station respectively.

It shall be the duty of each such shore station, during the hours it is in operation, to listen in at intervals of not less than fifteen minutes and for a period not less than two minutes, with the receiver tuned to receive messages of three hundred meter wave lengths.

Twelfth. At important seaports and at all other places where naval or military and private or commercial shore stations operate in such close proximity that interference with the work of naval and military stations can not be avoided by the enforcement of the regulations contained in the foregoing regulations concerning wave lengths and character of signals emitted, such private or commercial shore stations as do interfere with the reception of signals by the naval and military stations concerned shall not use their transmitters during the first fifteen minutes of each hour, local standard time. The Secretary of Commerce and Labor may, on the recommendation of the department concerned, designate the station or stations which may be required to observe this division of time.

Thirteenth. The naval or military stations for which the above mentioned division of time may be established shall transmit signals or radiograms only during the first fifteen minutes of each hour, local standard time, except in case of signals or radiograms relating to vessels in distress, as hereinbefore provided.

Fourteenth. In all circumstances, except in case of signals or radiograms relating to vessels in distress, all stations shall use the minimum amount of energy necessary to carry out any communication desired.

Fifteenth. No private or commercial station not engaged in the transaction of bona fide commercial business by radio communication or in experimentation in connection with the development and manufacture of radio apparatus for commercial purposes shall use a transmitting wave length exceeding two hundred meters, or a transformer input exceeding one kilowatt, except by special authority of the Secretary of Commerce and Labor contained in the license of the station: Provided, That the owner or operator of a station of the character mentioned in this regulation shall not be liable for a violation of the requirements of the third or fourth regulations to the penalties of one hundred dollars or twenty-five dollars, respectively, provided in this section unless the person maintaining or operating such station shall have been notified in writing that the said transmitter has been found, upon tests conducted by the Government, to be so adjusted as to violate the said third and fourth regulations, and opportunity has been given to said owner or operator to adjust said transmitter in conformity with said regulations.

Sixteenth. No station of the character mentioned in regulation fifteenth situated within five nautical miles of a naval or military station shall use a transmitting wave length exceeding two hundred meters or a transformer input exceeding one-half kilowatt.

Seventeenth. In general, the shipboard stations shall transmit their radiograms to the nearest shore station. A sender on board a vessel shall, however, have the right to designate the shore station through which he desires to have his radiograms transmitted. If this can not be done, the wishes of the sender are to be complied with only if the transmission can be effected without interfering with the service of other stations.

Eighteenth. No station on shore not in actual operation at the date of the passage of this Act shall be licensed for the transaction of commercial business by radio communication within fifteen nautical miles of the following naval or military stations, to wit: Arlington, Virginia; Key West, Florida; San Juan, Porto Rico; North Head and Tatoosh Island, Washington; San Diego, California; and those established or which may be established in Alaska and in the Canal Zone; and the head of the department having control of such Government stations shall, so far as is consistent with the transaction of governmental business, arrange for the transmission and receipt of commercial radiograms under the provisions of the Berlin convention of nineteen hundred and six and future international conventions or treaties to which the United States may be a party, at each of the stations above referred to, and shall fix the rates therefor, subject to control of such rates by Congress. At such stations and wherever and whenever shore stations open for general public business between the coast and vessels at sea under the provisions of the Berlin convention of nineteen hundred and six and future international conventions and treaties to which the United States may be a party shall not be so established as to insure a constant service day and night without interruption, and in all localities wherever or whenever such service shall not be maintained by a commercial shore station within one hundred nautical miles of a naval radio station, the Secretary of the Navy shall, so far as is consistent with the transaction of governmental business, open naval radio stations to the general public business described above, and shall fix rates for such service, subject to control of such rates by Congress. The receipts from such radiograms shall be covered into the Treasury as miscellaneous receipts.

Nineteenth. No person or persons engaged in or having knowledge of the operation of any station or stations shall divulge or publish the contents of any messages transmitted or received by such station, except to the person or persons to whom the same may be directed, or their authorized agent, or to another station employed to forward such message to its destination, unless legally required so to do by the court of competent jurisdiction or other competent authority. Any person guilty of divulging or publishing any message, except as herein provided, shall, on conviction thereof, be punishable by a fine of not more than two hundred and fifty dollars or imprisonment for a period of not exceeding three months, or both fine and imprisonment, in the discretion of the court.

For violation of any of these regulations, subject to which a license under sections one and two of this Act may be issued, the owner of the apparatus shall be liable to a penalty of one hundred dollars, which may be reduced or remitted by the Secretary of Commerce and Labor, and for repeated violations of any of such regulations, the license may be revoked.

For violation of any of these regulations, except as provided in regulation nineteenth, subject to which a license under section three of this Act may be issued, the operator shall be subject to a penalty of twenty-five dollars, which may be reduced or remitted by the Secretary of Commerce and Labor, and for repeated violations of any such regulations, the license shall be suspended or revoked.

SEC. 5. That every license granted under the provisions of this Act for the operation or use of apparatus for radio communication shall prescribe that the operator thereof shall not wilfully or maliciously interfere with any other radio communication. Such interference shall be deemed a misdemeanor, and upon conviction thereof the owner or operator, or both, shall be punishable by a fine of not to exceed five hundred dollars or imprisonment for not to exceed one year, or both.

SEC. 6. That the expression "radio communication" as used in this Act means any system of electrical communication by telegraphy or telephony without the aid of any wire connecting the points from and at which the radiograms, signals, or other communications are sent or received.

SEC. 7. That a person, company, or corporation within the jurisdiction of the United States shall not knowingly utter or transmit, or cause to be uttered or transmitted, any false or fraudulent distress signal or call or false or fraudulent signal, call, or other radiogram of any kind. The penalty for so uttering or transmitting a false or fraudulent distress signal or call shall be a fine of not more than two thousand five hundred dollars or imprisonment for not more than five years, or both, in the discretion of the court, for each and every such offense, and the penalty for so uttering or transmitting, or causing to be uttered or transmitted, any other false or fraudulent signal, call, or other radiogram shall be a fine of not more than one thousand dollars or imprisonment for not more than two years, or both, in the discretion of the court, for each and every such offense.

SEC. 8. That a person, company, or corporation shall not use or operate any apparatus for radio communication on a foreign ship in territorial waters of the United States otherwise than in accordance with the provisions of sections four and seven of this Act and so much of section five as imposes a penalty for interference. Save as aforesaid, nothing in this Act shall apply to apparatus for radio communication on any foreign ship.

SEC. 9. That the trial of any offense under this Act shall be in the district in which it is committed, or if the offense is committed upon the high seas or out of the jurisdiction of any particular State or district the trial shall be in the district where the offender may be found or into which he shall be first brought.

SEC. 10. That this Act shall not apply to the Phillippine Islands.

SEC. 11. That this Act shall take effect and be in force on and after four months from its passage.

Approved, August 13, 1912.

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