Harper's Electricity Book for Boys

The wiring is comparatively simple, and may be easily followed if the description and plan are constantly consulted when setting up the line. R and R 2 are the receivers, T and T 2 the transmitters, C 1 and C 2 the batteries, E B and E B 2 the buzzers or bells, P B and P B 2 the push-buttons, and L S and L S 2 the lever-switches. For convenience of illustration the induction-coils are separated. The primary coil (P C) is indicated by the heavy spring line and the secondary coil (S C) by the fine spring line. When the line is “dead” both receivers are hanging from the hooks of the lever-switches. If the boy at the left wishes to call the boy at the right he lifts the receiver (R) from the hook (L S) and presses the button (P B). This throws the battery (C 1 C 1 C 1) in circuit with lines Nos. 1 and 2, and operates the buzzer (E B 2). When the boy at the right lifts his receiver (R 2) from the hook (L S 2), the bell circuit is cut out and the ’phone circuit is cut in. When the lever-switches are drawn up against the contact-springs (A, B, and C and A A, B B, and C C), both batteries are thrown into circuit with the transmitters at their respective ends through the primary coils (P C and P C 2). By inductance through the secondary coils (S C and S C 2), lines Nos. 1 and 2 are electrified, and when the voice strikes the disks in the transmitters the same tone and vibration is heard through the receivers at the other end of the line. While conversation is going on the batteries at either end are being drawn upon or depleted; but as soon as the receivers are hung on the hooks and the lever-switches are drawn away from the contact-springs, the flow of current is stopped. The buzzers or bells consume but a small amount of current when operated, and in dry cells the active parts recuperate quickly and depolarize. The greatest drain on a battery, therefore, is when the line is closed for conversation.

An Installation Plan

A simple manner in which to install this apparatus in boxes is shown in Fig. 22. The box is depicted with the front opened and with the receiver hanging on the hook. When the lever-switch (L S) is down it rests on the contact-spring (A), thus throwing in the bell circuit. When the boy at the other end of the line pushes the button on his box it operates the buzzer (E B). This can be understood by following with a pointer the wires from the buzzer to the outlet-posts (Nos. 1 and 3) at the bottom of the wall-plate.

When the receiver (R) is lifted from the hook (L S), it cuts out the bell circuit and cuts in the telephone circuit, through the spring-contacts (B and C). This circuit may easily be followed through the wires connecting transmitter, receiver, induction-coil, and batteries. The heavy lines leading out from the induction-coil are the primary coil wires, and the fine hair lines are those forming the secondary coil. The medium lines are those that connect the binding-posts, batteries, and lines.

When the bell circuit is connected the impulse coming from the other end of the line enters through wire No. 10 to post No. 3, thence to strip E and plate G, and so on to E B, which it operates. The current then passes from E B to contact A, through L S to post No. 1, and out on wire No. 11.

To operate the buzzer at other end of the line the button (P B) is pushed in. This moves the spring (E) away from the plate (G), and brings it into contact with F. This connects the circuit through the battery wire (No. 8) to post No. 1 to line No. 11 without going into the box, and from wire No. 9 to post No. 2; thence to hinge No. 7 to plate F, through E, down to post No. 3, and out through wire No. 10. In this manner the current is taken from the batteries at the foot of wires Nos. 8 and 9, and used to ring the buzzer at the other end of the line.

When the hook (L S) is up the circuit is closed through T, I C, and battery. The current runs from the battery through wire No. 8 to post No. 1, to L S, through C and primary coil out to hinge No. 6, through transmitter to hinge No. 7, to post No. 2, and back to battery through wire No. 9.

By inductance the sound is carried over the line, in at wire No. 10, to post No. 3, through secondary coil to post No. 4, through receiver R to post No. 5, through B and L S to post No. 1, and out through wire No. 11. At the other end of the line it goes through the same parts of the apparatus.

A Portable Apparatus

For convenience it is often desirable to have a portable transmitter, and so avoid the inconvenience of having to stand while speaking. A neat portable apparatus that will stand on a ledge or table, and which may be moved about within the radius of the connecting lines, is shown in Fig. 23.

The wooden base is four inches square and the upright one inch and a half square. The stand is twelve inches high over all, and on the bottom a plate of iron or lead must be screwed fast to make it bottom-heavy, so that it will not topple over.

The lever-switch may be arranged at the back of the upright and the push-button at the front near the base, as shown at A. The wall-box contains the buzzer and induction-coil, and within it the wiring is arranged from the portable stand to the batteries and line as shown at C. This illustration is too small, however, to show the complete wiring, and the young electrician is therefore referred to Fig. 22. The battery (B) is composed of as many dry or wet cells as may be required to operate the line. These must be connected in series at both ends. At D a rear view of the upright and transmitter is shown to illustrate the manner in which the wiring can be done. If a hollow upright is made of four thin pieces of wood a much neater appearance may be secured by enclosing the wires.

In all of these telephone systems one wire must lead to the ground, or be connected with a water-pipe, taking care, however, to solder the wire to a galvanized pipe so that perfect contact will be the result. If the wire is carried directly to the ground it must be attached to a plate, which in turn is buried deep enough to reach moist earth, as described in the chapter on Line and Wireless Telegraphs, page 215.

Care and accuracy will lead to success in telephony, but one slip or error will throw the best system out of order and render it useless. This, indeed, applies to all electrical apparatus; there can be no half-way; it will either work or it won’t.

Chapter IX
LINE AND WIRELESS TELEGRAPHS

A Ground Telegraph

Nearly every boy is interested in telegraphy, and it is a fascinating field for study and experimental work, to say nothing of the amusement to be gotten out of it. The instruments are not difficult to make, and two boys can easily have a line between their houses.

The key is a modified form of the push-button, and is simply a contact maker and breaker for opening and closing an electrical circuit. A practical telegraph-key is shown in Fig. 1, and in Fig. 2 is given the side elevation.

The base-board is four inches wide, six inches long, and half an inch in thickness. At the front end a small metal connector-plate is screwed fast, and through a hole in the middle of it a brass-headed upholsterer’s tack is driven for the underside of the key to strike against. Two L pieces of metal are bent and attached to the middle of the board to support the key-bar, and at the rear of the board another upholsterer’s tack is driven in the wood for the end of the bar to strike on and make a click. The bar is of brass or iron, measuring three-eighths by half an inch, and is provided with a hole bored at an equal distance from each end for a small bolt to pass through, in order to pivot it between the L plates. A hole made at the forward end will admit a brass screw that in turn will hold a spool-end to act as a finger-piece. The screw should be cut off and riveted at the underside. A short, strong spring is to be attached to the back of the base-block and to the end of the key-bar by means of a hook, which may be made from a steel-wire nail flattened. It is bound to the top of the bar with wire, as shown in Figs. 2 and 3.

The incoming and outgoing wires are made fast to one end of the connector-plate and to one of the L pieces that support the key. When the key is at rest the circuit is open, but when pressed down against the brass tack it is closed, and whether pressed down or released it clicks at both movements. A simple switch may be connected with the L-plate and the connection-post at the opposite side of the key-base, so that, if necessary, the circuit may be closed. Or an arm may be caught under the screw at the L-plate, and brought forward so that it can be thrown in against a screw-head on the connector-plate, as shown in Fig. 3. The screw-head may be flattened with a file, and the underside of the switch bevelled at the edges, so that it will mount easily on the screw.

In Fig. 4 (page 191) a simple telegraph-sounder is shown. A base-board, four inches wide, six inches long, and seven-eighths of an inch in thickness, is made of hard-wood, and two holes are bored, with the centres two inches from one end, so that the lower nuts of the horseshoe magnet will fit in them, as shown in Fig. 5. This allows the yoke to rest flat on the top of the base, and with a stout screw passed down through a hole in the middle of the yoke and into the wood the magnets are held in an upright position.

From the base-block to the top of the bolt the magnets are two inches and a quarter high. The bar of brass or iron to which the armature (A in Fig. 5) is attached is four inches and a half in length and three-eighths by half an inch thick. At the middle of the bar and through the side a hole is bored, through which a small bolt may be passed to hold it between the upright blocks of wood. At the front end two small holes are to be bored, so that its armature may be riveted to it with brass escutcheon-pins or slim round-headed screws. The heads are at the top and the riveting is underneath. A small block of wood is cut, as shown in Fig. 6, against which the two upright pieces of wood are made fast. This block is two inches and a half long, one inch and a quarter high, and seven-eighths of an inch wide. The laps cut from each side are an inch wide and a quarter of an inch deep, to receive the uprights of the same dimensions.

At the top of this block a brass-headed nail is driven for the underside of the bar to strike on. A hook and spring are to be attached to the rear of the sounder-bar, as described for the key, and at the front of the base two binding-posts are arranged, to which the loose ends of the coil-wires are attached.

Just behind the yoke, and directly under the armature-bar, a long screw is driven into the base-block, as shown at B in Fig. 5. It must not touch the yoke, and the head should be less than one-eighth of an inch below the bar when at rest. On this the armature-bar strikes and clicks when drawn to the magnets. The armature must not touch the magnets; otherwise the residual magnetism would hold it down. The screw must be nicely adjusted, so that a loud, clear click will result.

In the plan of the telegraph-line connections (Fig. 7, page 196) a clear idea is given for the wiring; and if the line and return wires are to be very long, it would be best to have them of No. 14 galvanized telegraph-wire, copper being too expensive, although much better. These wires must not touch each other, and when attached to a house, barn, or trees, porcelain or glass insulators should be used. If nothing better can be had, the necks of some stout glass bottles may be held with wooden pins or large nails, and the wire twisted to them, as shown in Fig. 8. When the line is not in use the switches on both keys should be closed; otherwise it would be impossible for the boy having the closed switch to call up the boy with the open one. Take great care in wiring your apparatus to study the plan, for a misconnected wire will throw the whole system out of order.

To operate the line see that all switches are closed and that the connections are in good condition. When the boy in house No. 2 wants to call up his friend in house No. 1 he throws open the switchon key, as shown in the plan, and by pressing down on the finger-key his sounder and that in house No. 1 click simultaneously. As soon as he raises or releases the key the armatures rise, making the up-click. If he presses his key and releases it quickly the two clicks on the sounder in house No. 1 are close together; this makes what is called a dot. If the key is held down longer it makes a long time between clicks, and this is called a dash. The dot and dash are the two elements of the telegraphic code. You will understand that the boy in house No. 2 hears just what the one in No. 1 is hearing, since the electric current passing through both coils causes the magnets to act in unison. So soon as the operator in house No. 2 has finished he closes his switch, and the other in house No. 1 opens his switch on the key and begins his reply. This is the simple principle of the telegraph, and all the improved apparatus is based on it, no matter how complicated. The complete Morse alphabet is appended:

Any persevering boy can soon learn the dot-and-dash letters of the Morse code, and very quickly become a fairly good operator. Telegraphic messages are sent and received in this way, and are read by the sound of the clicks. Various kinds of recording instruments are also employed, so that when an operator is away from his table the automatic recorder takes down the message on a paper tape. In the stock-ticker, employed in brokerage offices, the recording is done by letters and numerals, and the paper tape drops into a basket beside the machine, so that any one picking up the strip of paper can see the quotations from the opening of business up to the time of reading them. These quotations are sent out directly from the floor of the exchanges, and by the action of one man’s hand thousands of machines are set in operation all over the city.

Perhaps the most unique and wonderful telegraphic signal-apparatus is that located on the floor of the New York Produce Exchange and the Chicago Exchange. The dials, side by side, are operated by direct wire from Chicago. When the New York operator flashes a quotation it appears simultaneously on the New York dial and simultaneously on the Chicago dial, and vice versa.

Electrical instruments are not the only means by which the Morse alphabet may be transmitted, for in some instances instruments would be in the way, while in others the wires might be down and communication cut off.

This is interestingly illustrated by an event in Thomas A. Edison’s life. When he was a boy and an apprentice telegraph operator on the Grand Trunk Line, an ice-jam had broken the cable between Port Huron, in Michigan, and Sarnia, in Canada, so that communication by electricity was cut off. The river at that point is a mile and a half wide, the ice made the passage impossible, and there was no way of repairing the cable. Edison impulsively jumped on a locomotive standing near the river-bank and seized the whistle-cord.

He had an idea that blasts of the whistle might be broken into long and short sounds corresponding to the dots and dashes of the Morse code. In a moment the whistle sounded over the river: “Toot, toot, toot, toot,—toot, tooooot,—tooooot—tooooot—toot, toot—toot, toot.” “Halloo, Sarnia! Do you get me? Do you hear what I say?”

No answer.

“Do you hear what I say, Sarnia?”

A third, fourth, and fifth time the message went across, to receive no response. Then suddenly the operator at Sarnia heard familiar sounds, and, opening the station door, he clearly caught the toot, toot of the far-away whistle. He found a locomotive, and, mounting to the cab, responded to Edison, and soon messages were tooted back and forth as freely as though the parted cable were again in operation.

Some years ago the police of New York were mystified over a murder case. The man they suspected had not fled, but was still in his usual place, and attending to his business quite as though nothing had happened to connect him with the tragedy.

Detectives in plain clothes had been following him and watching closely his every move in and out of restaurants and shops and at social affairs; but not the slightest proof could be secured against him.

One noon-time they followed him into a café, where he had gone with a friend. The detectives took seats near him, but each of them sat at different tables in the room full of people.

When in the café the suspect sat next the wall, a habit the detectives had noticed. Consequently, only those persons who sat at one side of him or directly in front could see his face. During the time they were in the restaurant the detectives communicated with each other by tapping on the table tops with a lead-pencil; and something the man said, which the nearest detective heard, led to the climax. One detective rose, paid his check, and loitered near the door; another got up a little later and sauntered out, but returned with a cardboard sign. Going over to the table where the suspected criminal and his friend sat, he deliberately tacked it on the wall above them, then went out again, leaving the third detective to watch the face of the man as he read:

$1000 REWARD
for information leading to the arrest of the murderer of ————————
on March ————, 1876

The man cast a glance about the restaurant, then said to his companion: “Did I show any signs of agitation?” The third detective rose, stepped over to the man, tapped him on the shoulder, and said, “I want you.” There would have been a scene of violence had not the other two detectives closed in on the man, and within six months he paid the penalty of his crime.

If it had not been for the dot-and-dash alphabet, tapped out with lead-pencils, the detectives could not have communicated; but like Edison, they used the means at hand to open up and carry on a silent conversation.

Wireless Telegraphy

Everybody nowadays understands that wireless telegraphy means the transmission of electrical vibrations through the ether and earth without the aid of wires or any visible means of conductivity. The feat of sending an electrical communication over thousands of miles of wire, or through submarine cables, is wonderful enough, for all that custom has made it an every-day miracle. To accomplish this same end by sending our messages through the apparently empty air is indeed awe-inspiring and almost beyond belief. And yet we know that wireless telegraphy is to-day a real scientific fact.

At first sight it would seem that the instruments must be complicated and necessarily beyond the ability of the average boy to make, and far too expensive as well. As a matter of fact, the young electrician may construct his wireless apparatus at a very moderate cost, it being understood that the sending and receiving poles may be mounted on a housetop or barn.

But first let us consider the theory upon which we are to work. There is no doubt but that electricity is the highest known form of vibration—so high, indeed, that as yet man has been unable to invent any instrument to record the number of pulsations per second. This vibration will occur in, and can be sent through, the ordinary form of conductor, such as metals, water, fluids and liquids, wet earth, air and ice. Also through what we call the ether.

Now the ether of the atmosphere, estimated to be fifteen trillion times lighter than air, is the medium through which the electrical vibrations pass in travelling in their radial direction from a central point, corresponding to the ripples or wavelets formed when a pond or surface of still water is disturbed. Ether is so fine a substance that the organs of sense are not delicate enough to detect it, and it is of such a volatile and uneasy nature that it is continually in motion. It vibrates under certain conditions, and when disturbed (as by a dynamo) it undoubtedly forms the active principle of electricity and magnetism.

James Clark Maxwell believed that magnetism, electricity, and light are all transmitted by vibrations in one common ether, and he finally demonstrated his theory by proving that pulsations of light, electricity, and magnetism differed only in their wave lengths. In 1887 Professor Hertz succeeded in establishing proof positive that Maxwell’s theories were correct, and, after elaborate experiments, he proved that all these forces used ether as a common medium. Therefore, if it were not for the ether, wireless telegraphy, with all its wonders, would not be possible. We understand, then, that the waves of ether are set in motion from a central disturbing point, and this can be accomplished only by means of electrical impulse.

Suppose that we strike a bell held high in the air. The sound is the result of the vibrations of its mass sending its pulsating energy through the air. The length of the sound-waves is measured in the direction in which the waves are travelling, and if the air is quiet and not disturbed by wind the sound will travel equally in all directions. The sound of a bell will not travel so well against a wind as it will with it, just as the ripples on a pond would be checked by an adverse set of wavelets.

Now the ether can be made to vibrate in a similar manner to the air by a charge of electricity oscillating or surging to and fro on a wire several hundred thousand times in a second. These oscillations strike out and affect the surrounding ether, so that, according to the intensity of the disruptive charge at the starting-point, the ether waves may be made to reach near or distant points.

This is, perhaps, more clearly shown by the action of a pendulum. In Fig. 9 the rod and ball are at rest, but if drawn to one side and released it swings over to the other side nearly as far away from its central position of rest as from the starting-point. If allowed to swing to and fro it will oscillate until at last it will come to rest in a vertical position. This same oscillation (oscillation being a form of vibration) takes place in the water when a stone has been flung into it, and in the ether when affected by the electrical discharge. In Fig. 10 are shown the principal varieties of vibration—the oscillating, pulsating, and alternating.

It is known that if these oscillations are damped, so that the over-intense agitation of the central disturbance is lessened, a new series of vibrations, such as the pulsating or alternating, is set up, and these secondary vibrations possess the power to travel around the world—yes, and perhaps to other worlds in the planetary cosmos.

The study of ether disturbances, wave currents, oscillating currents, and the other phenomena dependant upon this invisible force is most interesting and fascinating, and were it possible to devote more space to this topic several chapters could be written on the scientific theory of wireless telegraphy.[2]

The principle difference between wire, or line, and wireless telegraphy is that the overhead wire, or underground or submarine cable, is omitted. In its stead the ether of the air is set in vibratory motion by properly constructed instruments, and the communication is recorded at a distance by instruments especially designed to receive the transmitted waves.

It seems to be the popular impression that a wireless message sent from one point to another travels in a straight line, as indicated by Fig. 11, B representing Boston, which receives the message from N. Y., or New York. As a matter of fact, if several sets of wireless receiving instruments were located on the circumference of a circle the same distance from New York in all directions, or even at nearer or farther points, they would all receive the same message. Instead of travelling in one direction, the ether waves are set in motion by the electrical disturbance, just as water is agitated by the stone thrown into it. The ripples, or wavelets, are started from the central point of disturbance and radiate out, so that instead of reaching Boston only the waves travel over every inch of ground, or air space, in all directions, and would be recorded in every town and village within the sphere of energy set up by the original force that put the ether waves in motion. The stronger this initial force the wider its field of action. This is shown at Fig. 12, which is an area comprising Philadelphia, Pittsburg, Buffalo, Washington, and other cities. Moreover, the waves of electrical disturbance would carry far beyond in all directions, taking in the cities of the north, south, and west, and at the east, going far out to sea, beyond Boston harbor and below Cape Hatteras, where ships carrying receiving instruments could pick up the messages. Like the ripples on the water, the radiating waves, or rings, become larger as they reach out farther and farther from the centre of disturbance, until at last they are imperceptible, and lose their shape and force.

At great distances, therefore, the ether disturbance becomes so slight that it is impossible to record the vibration or message sent out; and until some improved forms of apparatus and coherer are invented, or the original disturbing force is enormously increased, it will be impossible to send messages at longer distances than four or five thousand miles from a central point. Both Marconi and De Forrest assert that they are perfecting coherers which will make it possible to girdle the earth with a message, and that within the next few years an aerogram may be sent out from a station, and, after instantly encircling the earth and being recorded during its passage at all intermediate stations, it will return and be received at the original sending-point. This, of course, is a matter of future achievement; but now that messages across the Atlantic are a commercial fact, it seems quite possible that the greater feat of overriding space and reaching any point on the earth’s surface will soon be a reality. And now to proceed from theory to the construction of a practical wireless apparatus having a radial area of action over some ten or fifteen miles.

The principal parts of a wireless apparatus include the antennas (or receiving and sending poles with their terminal connections), the induction-coil, strong primary batteries or dynamo, the coherer and de-coherer, the telegraph key and sounder (or a telephone receiver), and the necessary connection wires, binding-posts, and ground-plates.

A large induction-coil with many layers of fine insulated wire will be necessary for the perfect operative outfit. The most practical coil for the amateur is a Ruhmkorff induction-coil. (See the directions and illustrations for constructing this coil, beginning on page 59 of chapter iv.)

The sending apparatus is practically the same in all outfits, and consists of a source of electrical energy, such as a battery, or dynamo, the essential induction-coil and adjustable spark-gap between the brass balls on terminal rods, and the make-and-break switch, or telegraph-key.

It is in the various forms of coherers and receiving apparatus that the different inventors claim superiority and originality. The systems also differ in their theory of harmonic tuning or vibratory sympathy. This is accomplished by means of coils and condensers, so that the messages sent out on one set of instruments will not be picked up or recorded by the receiving apparatus of competitors.

Having made or purchased an induction-coil of proper and adequate size, it will now be necessary to construct the parts so that an adjustable spark-gap may be secured.

Make a hollow wooden base for the induction-coil to rest on. It should be a trifle longer than the length of the coil and about seven inches wide. This may be made from wood half an inch thick. The base should be two inches high, so that it will be easy and convenient to make wire connections under it. Mount the induction-coil on the base and make it fast with screws, arranging it so that the binding-posts are on the side rather than at the top of the coil, as shown in Fig. 13.

Cut a thin board and mount it across the top of the induction-coil on two short blocks, and to this attach two double-pole binding-posts (P P). The fine wires from the induction-coil are made fast to the foot of each post, and from the posts the aerial wire (A W) and ground wire (G W) lead out.

Fasten two binding-posts at the forward corners of the base, and to them make connection-wires fast to the heavy or primary wires of the coil. Wires B and C lead out from these posts to the battery and key, and to complete this part of the sending, or transmitting apparatus it will be necessary to have two terminal rods and balls attached to the top of the binding-posts (P P). This part of the apparatus is generally called the oscillator, and the rods are balanced on the posts, so that they can be moved in order to increase or diminish the space (S G), or spark-gap, between the brass balls.

When, after experiment, the proper space has been determined, the set screw at the top of the posts will hold the terminal rods securely in place.

Obtain a piece of brass, copper, or German-silver rod three-sixteenths of an inch in diameter. Now cut two short rods, each six inches long, and two inches from one end flatten the rods with a hammer, as shown at A in Fig. 14. Flatten the rod in two places at the other end, as shown at B B in Fig. 14; then bore holes through the flattened parts (A), so that the binding-screws at the top of the posts (P P) will pass through them.

Obtain two brass balls from one to one inch and a half in diameter. If they are solid or cast brass they may be attached to the ends of the terminal rods by threading, so that it will be easy to remove them. If the balls are of spun sheet-metal it will be necessary to solder them fast to the ends of the rods, and, when polishing the balls, the rods will have to be removed from the binding-posts. It is imperative that the balls should be kept polished and in bright condition at all times, to facilitate the action of the impulsive sparks.

The overhead part of the apparatus employed to collect the electric waves is called the antennæ, and in the various commercial forms of wireless apparatus this feature differs. The general principle, however, is the same, and in Figs. 15, 16, 17, and 18 some simple forms of construction are shown.

Great care must be taken to properly insulate the rod, wire, or fingers of these antennæ, so that the full force of the vibration is carried directly down to the coherer and sounder or receiver. For this purpose, porcelain, glass, or gutta-percha knobs must be employed.

In Fig. 15 the apparatus consists of an upright stick, a cross-stick, and a brace, or bracket, to hold them in proper place.

Porcelain knobs are made fast to the sticks with linen string or stout cotton line. Then an insulated copper wire is run through the holes in the knobs, and from the outer knob a rod of brass, copper, or German-silver, or even a piece of galvanized-iron lightning-rod, is suspended. Care should be taken to see that the joint between rod and wire is soldered so as to make perfect contact. Otherwise rust or corrosion will cause imperfect contact of metals, and interrupted vibrations would be the result. The upright stick should be ten or fifteen feet high, and may be attached to a house-top, a chimney, or on the corner of a barn roof.

Another form of single antenna is shown in Fig. 16. This is a rod held fast in a porcelain insulator with cement. The insulator, in turn, is slipped over the end of a staff, or pole, which is erected on a building top or out in the open, the same as a flag-pole. Near the foot of the rod, and just above the insulator, a conducting-wire is made fast and soldered. This is run down through porcelain insulators to the apparatus.

If the pole is erected on a house-top it may be braced with wires, to stay it, but care must be taken not to have these wires come into contact with the rod, or conducting-wire.

Another form of antennas is shown in Fig. 17, where rods are suspended from a wire which, in turn, is drawn taut between two insulators. The insulators are held in a framework composed of two uprights and a cross-piece of wood.

This frame may be nailed fast to a chimney and to the gable of a roof, as shown in the drawing; and to steady the rods, so that they will not swing in a high wind, the lower ends should be tied together with cotton string, the ends of which should be fastened to the uprights. The leading-in wire is made fast to the top wire, from which the rods are suspended, and all the exposed joints should be soldered to insure perfect contact and conductivity. A modified form of the Marconi antennæ is shown in Fig. 18. This is made of a metal hoop three of four feet in diameter held in shape by cross-sticks of wood, which can be lashed fast to the ring. Leading down from it are numerous copper wires which terminate in a single wire, the whole apparatus resembling a funnel. The upper unions where the wires join the ring need not be soldered, but at the bottom, where they all come together and join the leading-in wire, it is quite necessary that a good soldered joint be made. This funnel may be hung between two upright poles on a house-top, or suspended from the towers or chimneys.

Almost any metal plate will do for the ground, or the ground-wire (G W in Fig. 13) may be bound to a gas or water pipe which goes down deep in the ground, where it is moist. Rust or white lead in the joints of gas-mains sometimes prevent perfect contact, but in water-pipes the current will flow readily through either the metal or the water. To insure the most perfect results, it is best to have an independent ground composed of metal, and connected directly with the oscillator, or coherer, by an insulated copper wire. A simple and easily constructed ground is a sheet of metal, preferably copper, brass, or zinc, to the upper edge of which two wires are soldered, as shown in Fig. 19. This is embedded in the ground three or four feet below the surface. Another ground-plate is a sheet of metal bent in V shape and then inverted. Two wires are soldered to the angle, and the ends brought together and soldered. This ground is buried three or four feet deep, and stands in a vertical position, as shown at Fig. 20. At Fig. 21 a flat ground is shown. This is a sheet of metal cut with pointed ends. The ground-wire is soldered to the middle of it, and it is then buried deep enough to be embedded in moist earth.

One of the best grounds is an old broiler with a copper wire soldered to the ends of the handles, as shown at Fig. 22. This is buried deep in the ground in a vertical position, and the insulated copper wire is carried up to the instruments.

The most important part of the wireless telegraphic apparatus is now to be constructed, and this requires some care and patience. The coherer is the delicate, sensitive part of the apparatus on which hinges success or failure. There are various kinds of coherers designed and used by different inventors, but while the materials differ and the construction takes various forms, the same basic principle applies to all.