Though one or more means of transmitting messages by electricity have been known now for a great many years, the mechanisms by which they are accomplished are understood only by those who take a general interest in physical science, and the few to whom electrical communication is a profession. So far as theory and details of working are concerned, there are a good many people still in the same shadowy frame of mind as the old Aberdeen postmaster, of whom the story is told. When asked to explain the working of a telegraph instrument he said, "Look at that sheepdog. Suppose we hold his hind-quarters here and stretch him out until his head reaches Glasgow. Then if we tread on his tail here he will bark in Glasgow. As it is not convenient to stretch a dog, we stretch a wire, and that serves the purpose."

As the name implies, "stretching a wire" is unnecessary in wireless telegraphy, though in order to understand the finer points of theory one needs to stretch the imagination a little. That, however, is not so much, because there is any inherent obscurity or difficulty in the underlying principles, as because the mechanism of all electrical effects is more or less intangible. Electricity and magnetism operate across apparently empty space, and the links which connect cause and effect have to be guessed at.

Three different methods have been made use of in wireless telegraphy, which may be classed as conduction, induction and wave methods. In the first method currents are sent through the earth from an electrode to another at the sending station. In induction, use is made of the property which alternating currents possess of exciting similar currents in neighboring conductors, the aim being to get as intense a current as possible in the secondary circuit. Mr. W. H. Preece, of England, by combining the two, signaled in this way as far as forty miles. The third and the only method which has proved practically available is by the use of electro-magnetic waves.

Guglielmo Marconi, an Italian, after long experiment, patented in 1897 a method entirely independent of wires, the electric waves being sent, presumably, through the ether, by the aid of a transmitting apparatus, and being detected by a coherer, a glass tube filled with metallic filings, into the end of which the terminals of a relay circuit enter. The wave falls on conducting material and, the spark gap being replaced by a coherer, the metallic filings magnetically cling together, closing the relay circuit, so that a signal is made. On breaking the current, a slight tap on the coherer or other means breaks the cohesion of the filings and the relay circuit is broken. In this way a rapid succession of signals can be sent.

In 1899 Marconi conducted in England an exhaustive series of successful experiments, sending messages across the English Channel from the South Foreland to the French coast near Boulogne, and extending his results until much longer distances were covered. The process of development was continued until, to the world's astonishment, signals were sent across the Atlantic and, finally, commercial messages were transmitted over this distance.

Marconi's system is based on the property supposed to be exerted by the vibrations or waves of electric currents passing through a wire of setting up similar vibrations in the ether of space. These waves extend in every direction from the point of departure, and by ingenious and very delicate receiving instruments their presence in space is indicated and they are taken up in sufficient strength to repeat their pulsations and in this way reproduce the signals sent from the transmitter. One difficulty hitherto has been that a message may be received by hundreds of receiving instruments in all directions, thus preventing secrecy. Many efforts have been made to overcome this defect, but as yet with only partial success.

The distance to which messages can be sent has so far depended largely on the height to which the wires extend above the earth's surface, lofty poles being erected at the stations. The height of these has been gradually increased until the Eiffel Tower at Paris has been utilized as a sending station. The strength of the electric waves has been similarly increased to add to their space-penetrating capacity. The record of wireless telegraphy has been in this way improved until now it has come into daily competition with other means of news sending. Methods of tuning the instruments have been adopted which limit the influence of the currents to properly tuned receivers and in this way some degree of secrecy is attained.

MaRconi Wireless Station.

Though the honor of inventing the art of wireless telegraphy is generally ascribed to Marconi, this is to give him more credit than he deserves. The principles involved were discovered by others and the utmost done by him was to invent a practical method of applying them. There are other systems of wireless telegraphy of later invention than that of Marconi, through a different application of the sameprinciples.

Messages have been sent to enormous distances, far surpassing the width of the Atlantic, as from Nova Scotia and Ireland to Argentina, a distance of 5,600 miles. Under exceptional conditions a distance of 6,500 miles has been attained, but the daily effective range of the best equipped stations is little over 3,000 miles. For overland messages the limit of distance is about 1,000 miles.

There are a number of kinds of interference which arise from electrical disturbances in the earth's atmosphere. A flash of lightning is liable to give rise to a wave of enormous power which will set half the aerials on the earth vibrating in spite of the differences of pitch to which they are tuned. Thunderstorms are at their worst in the summer in temperate latitudes, but they occur to some extent all the year round, and those in the tropics are of extreme violence. As a consequence it is frequently almost impossible to decipher earthly messages owing to the imperious signals from the clouds. Of the various methods adopted for choking off the "atmospherics," as the disturbances are called, one is to use receiving circuits which respond only to a narrow range of oscillations very different from those produced by a lightning flash. The employment of a high-pitched musical note in the telephone is also an advantage because its extreme regularity distinguishes if from the marked irregularity of the stray waves.

On the palatial passenger steamers that plow the Atlantic the Marconi apparatus enables the travelers to keep in touch with their friends, to transact important business on either side of the water, and to secure a continuity of life which was formerly divided by a sea voyage. All the larger vessels now publish a daily paper on board, the news in which has been supplied by the same agencies who feed the newspaper on land. Information is flashed to meet or overtake the vessel and caught up by her aerial, as she pursues her way at twenty-five or thirty miles an hour.

Wireless Station on a Steamship.

In the case of cargo vessels, the owners are able to get into touch with them at any point of their voyage. They can advise the captain where to call for coal or cargp, while he on his part can get into communication with the authorities or his firm's agents at the port of call, and have every necessary or desirable preparation made for his arrival. Should an accident happen, he can call assistance, inform the owners or relieve anxiety and suspense. At no time is he isolated from the world. The fortitude, courage and daring of those "who go down to the sea in ships" has never been called into question, but it has if anything been emphasized by the receipt of messages from an operator at his post, to whom the bonds of duty were as bonds of steel, and who calmly operated the key until the waves entered his cabin and brought him honorable release.

U. S. Battleships "Nevada," "Oklahoma" and "Arizona" The latest type of super-dreadnaught for the United States Navy, with a displacement of 27,500 tons and engines of 28,000 horse-power..

Note The Wireless Equipment At The Top

Relief has been brought in this way to vessels in distress and many lives saved. An important example is that of the sinking of the Titanic in 1912. By means of wireless messages from ship to ship the width of the Pacific has been practically covered, as ships en route from America to Australia or Asia can be kept in touch with Honolulu through almost the entire journey. A law in the United States now requires that all ocean passage-steamers carrying fifty or more passengers on routes of 200 miles or over must be equipped with efficient wireless apparatus and operators. The distance reached must be at least 100 miles. The Canadian law provides that every sea-going and coasting passenger ship of over 400 tons gross, registered in Canada, and every sea-going and coasting freight ship of over 1,200 tons gross, shall be equipped with a wireless apparatus. Wireless messages have been successfully sent from aeroplanes, balloons and submarine vessels, and the naval vessels of all nations are kept in easy communication by this method. Wireless press messages between America and Europe are also matters of daily performances.