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.

When the sounder is at rest the rear end lies on the brass tack in the block, and the armature is about a quarter of an inch above the top of the magnets. The armature is of soft iron, two inches and a half long, seven-eighths of an inch wide, and an eighth of an inch thick. These small scraps of metal may be procured at a blacksmith’s shop, and, for a few cents, he will bore the holes in the required places; or if you have a breast or hand drill the metal may be held in a vise and properly perforated.

By connecting one wire from the key directly with one of the binding-posts of the sounder, and the other with the poles of a battery, and so on to the sounder, the apparatus is ready for use. By pressing on the key the circuit is closed, and the magnetism of the sounder-cores draws the armature down with a click. On releasing the key the bar flies back to rest, having been pulled down by the spring, and it clicks on the brass tack-head. These two instruments may be placed any distance apart, miles if necessary, so long as sufficient current is employed to work the sounder. Two sets of instruments must be made if boys in separate houses are to have a line. Each one must have a key, sounder, and cell, or several cells connected in series to form a battery, according to the current required.

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]

[2] For further information on this subject the student is referred to such well-known books as _Signalling Across Space Without Wires_, by Prof. Oliver J. Lodge, and _Wireless Telegraphy_, by C. H. Sewall.

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