Wireless Telegraphy (Apr. 8, 1899)

Recent Success of the Marconi System — How It Does Its Marvelous Work — Its Record on Land and Sea — Varied Usefulness in Warfare — The Preece and Tesla Inventions.

The recent success of Marconi in telegraphing with facility from the South Foreland Lighthouse on the English coast to Boulogne-sur-Mer in France without the use of connecting wires, together with the favorable reports of commissions appointed by foreign governments to investigate the matter of wireless telegraphy in general, and the receipt by Mr. Marconi of various government orders for the manufacture of his mechanisms, obviously to be used in warfare, has attracted the attention of the world. To those unversed in the physical conceptions of science, it appears little short of miraculous that by touching a lever in one place a sounder may be affected in another, thirty-two miles away, without the use of any material medium.

Wireless telegraphy, which is today acknowledged a success for moderate distances, with the practical certainty of its application to ever-increasing distances in the future, is due, not so much to the inventor, Marconi, as to careful experimentation at the hands of the patient investigators who preceded him. Marconi has discovered no new law and no new fact. His work has been merely that of the ingenious mechanician in the careful application of facts and laws already well known. The Marconi system of telegraphy through space depends primarily on the work of Hertz, who proved, some ten years ago, in a series of researches which are now classic, the existence of electrical waves in free space, the identity of electricity with light, and who made it a tenet of modern science that the universe is not a universe of emptiness, but of "plenum." His work, as well as the wireless telegraphy based on it, is explicable only on the assumption that, between the particles of all material bodies, and throughout all space to the farthest star to be seen with the mightiest telescope, there exists a medium whose most marked characteristics are tenuity and almost infinite elasticity. This medium is the ether of the physicist. Wave motions may be set up in this medium with ease, their affect depending solely upon their length. The X-rays of Röntgen form probably the shortest of the series; and, in their order of length, come the actinic waves, which affect the camera, light waves, which affect the eye, and waves of radiant heat, then a vast unexplored space, and, finally, the long, electrical waves, which affect the Marconi receiver.

Dr. Hertz succeeded in setting up these electrical waves by means of a rapidly oscillating electric spark from an induction coil. They vary in length from a few inches to many feet, travel at the rate of 186,000 miles a second, and vary in intensity inversely as the square of the distance. That is, at twice the distance they are one-fourth as intense, at five times the distance one-twenty-fifth as intense, and so on, rapidly decreasing as the distance increases.

The Marconi transmitter is simply a Hertzian oscillator for the propagation of these waves, consisting of a medium-sized induction coil with the spark passing between two perfect spheres of polished brass, half immersed in oil.

The electrical waves in ether, caused by this rapidly intermittent spark, start out with a frequency of some two billion a second in a series of concentric, ever-widening spheres of undulation, travelling with the speed of light in all directions and straight through the ordinary forms of matter with but little opposition. Into the primary circuit of the induction coil is introduced a common telegraphic circuit breaker, by which the sparks may be made to come in the order of telegraphic signals.

The Marconi receiver depends for its efficiency on the discovery of Branly, that when these electrical waves strike a pinch of metallic filings, such filings become a conductor. The coherer, the essential part of the Marconi receiver, consists simply of a small glass vacuum tube, into each end of which runs a brass rod tipped with silver. The ends of these rods are separated by a distance of about one-sixteenth of an inch, and into this tiny space is placed a pinch of metallic filings, preferably nickel, with a trace of silver. The coherer is in circuit with one battery-cell and a sensitive relay; the current of the cell being interrupted by the filings. This relay is, in turn, in circuit with a larger local battery and a telegraphic sounder. From each end of the coherer there runs a copper wire, one into the earth to intercept the waves travelling through the ground, and the other high up in the air to catch the waves that travel through the air. These waves run along the wires and across the pinch of filings, which then become a conductor. When the filings become in this way a conductor, the current from the single cell is allowed to travel through the relay and the relay in turn lets loose the local circuit, which makes the sounder click.

The matter is somewhat complicated, however, by the fact that when the electrical waves strike the filings they become permanently a conductor, at least until they are tumbled about or disturbed. In order to obviate this difficulty an electrical tapper is introduced into the same circuit with the sounder; a little hammer continually strikes the glass tube and thus disturbs the filings so that they become an insulator the instant the waves from the transmitter cease to come.

Such is the Marconi telegraph, so simple that it has been found quite practicable for a schoolboy to make one which will answer through a few hundred yards, at least, and through any number of walls.

Objection has frequently been made that there is no secrecy in such a method of telegraphy, that receivers all over the country would answer to the same impulses of the transmitter. This is, however, a profound error. By Prof. Oliver Lodge of England, it has been found quite feasible to tune the wings of the receiver so accurately that they will answer only one transmitter. This is done by sending out from the transmitter a series of waves of one wave-length only, and by making the wings of just such a length that they will respond only to such waves, much as two tuning-forks, when accurately in tune, will respond to each other by the principle of sympathetic vibration. Secrecy, in fact, if needed, is assured. On the other hand, if it is desired to make all receivers free of the one message, all that is necessary is that a series of mixed and Irregular waves should be sent from the transmitter.

About a year ago, the Wireless Telegraph Company of England established communications between three stations on the coast of England, and the Isle of Wight, and messages have been sent and received regularly ever since. Other stations are under process of construction, and the Marconi system is today on a practical and commercial basis. Intelligible signals have also been transmitted to the coast of Ireland, and the permanent intercommunication of the two islands on the basis of this system is an assured success.

In order to accomplish greater distances success must be sought in one of three ways — either by sending out waves of greater intensity, by lengthening the metallic wings, or by the employment of a more sensitive coherer. It is no fantasy to believe that in the comparatively near future the Atlantic will be crossed, and permanent intercommunication established between the countries of America and Europe.

The field of usefulness of the Marconi system is widely extended. It may be used with ease between two places, separated by a body of water of swift current, when cable laying is an expensive and difficult process. It may also be used advantageously by a range of lofty mountains, for Marconi has shown that material obstacles offer somewhat less opposition to the passage of electrical waves than does glass to light.

Another important phase of usefulness is in establishing communication between lighthouses and light-ships and the land. Messages have been interchanged for some months between the South Foreland Lighthouse and the East Goodwin Light-ship, in which work the interesting fact has come to light that the receivers work somewhat better in storm and fog than in clear weather. The wind has no influence whatever. It is quite true today that ships provided with the Marconi apparatus could communicate with harbors when forty miles out to sea. This has been demonstrated by one of Marconi’s assistants, and it was shown in the demonstration that even the near neighborhood of the ship’s dynamos had no effect on the results.

It is, however, in warfare, that the Marconi system has its greatest opportunity. It is of course obvious that the war-ships of a squadron may communicate with each other, and, by employing the system of tuning, this intercommunication may be made secret. It is also just as evident that war-ships may communicate with forts on shore. And furthermore, the garrison of a beleaguered fort may send to and receive intelligence from friends far outside the lines of the encircling enemy, and in defiance of them. It is but a small wonder, then, that the German Emperor is actively interesting himself in the progress of wireless telegraphy.

Another phase of the subject, usually overlooked, is the fact that not only a telegraphic sounder, but a bell, a motor, a torpedo cartridge, or, indeed, any electrical device whatever may be inserted in the receiver of the Marconi system, and may all equally be affected and set into action by the oscillating waves from the transmitter at a distance. Some days ago the writer amused himself by exploding mining cartridges at a distance of several hundred yards from the transmitter, by inserting them into the little local circuit of a Marconi receiver which he had made himself. Submarine mines may be exploded from a distance, and automobile torpedoes may not only be exploded, but even directed in perfect safety. It is may be interesting to note in this connection the scheme of Nikola Tesla, who, during the late war, advised the sending of electrical oscillations against the Spanish war-ships of such a character as to generate sparks in their powder magazines.

In addition to the Marconi system, there is another of totally different character which has possibly an equal chance of success. This second system was devised by W. H. Preece, F. R. S., a man of some prominence in British science. His system is due solely to the influence of magnetic induction. Since the time of Faraday it has been known that intermittent currents in an electrical circuit will set up similar currents in a neighboring circuit, without the aid of any wire between, and in spite of ordinary obstacles. The distance to which this inductive influence extends was unknown until the invention of the Bell telephone in 1877, when it was found quite impossible to string telephone wires in the neighborhood of telegraph wires on account of the disturbance which the intermittent currents in the telegraph circuit induced in the circuit of the telephone.

Mr. Preece has carried induction to an extent of which Faraday never dreamed. He employs for this purpose two parallel electrical circuits. Through one circuit runs an alternating current, and into this circuit is introduced a common circuit-breaker. Into the parallel circuit, miles away, is introduced simply a common telephone-receiver. No battery whatever is used in this circuit.

For every make and break in this circuit-breaker in the first wire a distinct click is heard in the telephone receiver in the other — the sole necessity being that the length of the parallel wires should be equal to the distance through which communication is to be carried. This method is peculiarly valuable to people living on either side of a mountain range, for in order to transmit telegraphic signals it is simply necessary to carry parallel wires along each side of the range.

Two stations, several miles apart, constructed in accordance with Mr. Preece’s system, are in daily operation by the British War Department.

A third system of wireless telegraphy, about which little has been said, is due to the work of Nikola Tesla. He states that he has used it easily through a distance of twenty miles. What little explanation of his system he gives he wraps up in metaphor. He uses, it seems, the static electrification of the earth itself.

In his explanation he compares the earth to an elastic ball filled with water. Into this ball, he imagines, are fitted several pistons. If one piston be moved in the other pistons will be moved out. Similarly, he says, if he alters the electrical potential of the earth at one point, receivers placed over the surface of the earth will register the disturbance.

R. K. DUNCAN.