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Marvels of Modern Science

<h5 id="id00094">WIRELESS TELEGRAPHY</h5> Primitive Signalling—Principles of Wireless Telegraphy—Ether Vibrations—Wireless Apparatus—The Marconi System. At a very early stage in the world's history, man found it necessary to be able to communicate with places at a distance by means of signals. Fire was the first agent employed for the purpose. On hill-tops or other eminences, what were known as beacon fires were kindled and owing to their elevation these could be seen for a considerable distance throughout the surrounding country. These primitive signals could be passed on from one point to another, until a large region could be covered and many people brought into communication with one another. These fires expressed a language of their own, which the observers could readily interpret. For a long time they were the only method used for signalling. Indeed in many backward localities and in some of the outlying islands and among savage tribes the custom still prevails. The bushmen of Australia at night time build fires outside their huts or kraals to attract the attention of their followers. Even in enlightened Ireland the kindling of beacon fires is still observed among the people of backward districts especially on May Eve and the festival of mid-summer. On these occasions bonfires are lit on almost every hillside throughout that country. This custom has been handed down from the days of the Druids. For a long time fires continued to be the mode of signalling, but as this way could only be used in the night, it was found necessary to adopt some method that would answer the purpose in daytime; hence signal towers were erected from which flags were waved and various devices displayed. Flags answered the purposes so very well that they came into general use. In course of time they were adopted by the army, navy and merchant marine and a regular code established, as at the present time. The railroad introduced the semaphore as a signal, and field tactics the heliograph or reflecting mirror which, however, is only of service when there is a strong sunlight. Then came the electric telegraph which not only revolutionized all forms of signalling but almost annihilated distance. Messages and all sorts of communications could be flashed over the wires in a few minutes and when a cable was laid under the ocean, continent could converse with continent as if they were next door neighbors. The men who first enabled us to talk over a wire certainly deserve our gratitude, all succeeding generations are their debtors. To the man who enabled us to talk to long distances without a wire at all it would seem we owe a still greater debt. But who is this man around whose brow we should twine the laurel wreath, to the altar of whose genius we should carry frankincense and myrrh? This is a question which does not admit of an answer, for to no one man alone do we owe wireless telegraphy, though Hertz was the first to discover the waves which make it possible. However, it is to the men whose indefatigable labors and genius made the electric telegraph a reality, that we also owe wireless telegraphy as we have it at present, for the latter may be considered in many respects the resultant of the former, though both are different in medium. Radio or wireless telegraphy in principle is as old as mankind. Adam delivered the first wireless when on awakening in the Garden of Eden he discovered Eve and addressed her in the vernacular of Paradise in that famous sentence which translated in English reads both ways the same,—"Madam, I'm Adam." The oral words issuing from his lips created a sound wave which the medium of the air conveyed to the tympanum of the partner of his joys and the cause of his sorrows. When one person speaks to another the speaker causes certain vibrations in the air and these so stimulate the hearing apparatus that a series of nerve impulses are conveyed to the sensorium where the meaning of these signals is unconsciously interpreted. In wireless telegraphy the sender causes vibrations not in the air but in that all-pervading impalpable substance which fills all space and which we call the ether. These vibrations can reach out to a great distance and are capable of so affecting a receiving apparatus that signals are made, the movements of which can be interpreted into a distinct meaning and consequently into the messages of language. Let us briefly consider the underlying principles at work. When we cast a stone into a pool of water we observe that it produces a series of ripples which grow fainter and fainter the farther they recede from the centre, the initial point of the disturbance, until they fade altogether in the surrounding expanse of water. The succession of these ripples is what is known as wave motion. When the clapper strikes the lip of a bell it produces a sound and sends a tremor out upon the air. The vibrations thus made are air waves. In the first of these cases the medium communicating the ripple or wavelet is the water. In the second case the medium which sustains the tremor and communicates the vibrations is the air. Let us now take the case of a third medium, the substance of which puzzled the philosophers of ancient time and still continues to puzzle the scientists of the present. This is the ether, that attenuated fluid which fills all inter-stellar space and all space in masses and between molecules and atoms not otherwise occupied by gross matter. When a lamp is lit the light radiates from it in all directions in a wave motion. That which transmits the light, the medium, is ether. By this means energy is conveyed from the sun to the earth, and scientists have calculated the speed of the ether vibrations called light at 186,400 miles per second. Thus a beam of light can travel from the sun to the earth, a distance of between 92,000,000 and 95,000,000 miles (according to season), in a little over eight minutes. The fire messages sent by the ancients from hill to hill were ether vibrations. The greater the fires, the greater were the vibrations and consequently they carried farther to the receiver, which was the eye. If a signal is to be sent a great distance by light the source of that light must be correspondingly powerful in order to disturb the ether sufficiently. The same principle holds good in wireless telegraphy. If we wish to communicate to a great distance the ether must be disturbed in proportion to the distance. The vibrations that produce light are not sufficient in intensity to affect the ether in such a way that signals can be carried to a distance. Other disturbances, however, can be made in the ether, stronger than those which create light. If we charge a wire with an electric current and place a magnetic needle near it we find it moves the needle from one position to another. This effect is called an electro-magnetic disturbance in the ether. Again when we charge an insulated body with electricity we find that it attracts any light substance indicating a material disturbance in the ether. This is described as an electro-static disturbance or effect and it is upon this that wireless telegraphy depends for its operations. The late German physicist, Dr. Heinrich Hertz, Ph.D., was the first to detect electrical waves in the ether. He set up the waves in the ether by means of an electrical discharge from an induction coil. To do this he employed a very simple means. He procured a short length of wire with a brass knob at either end and bent around so as to form an almost complete circle leaving only a small air gap between the knobs. Each time there was a spark discharge from the induction coil, the experimenter found that a small electric spark also generated between the knobs of the wire loop, thus showing that electric waves were projected through the ether. This discovery suggested to scientists that such electric waves might be used as a means of transmitting signals to a distance through the medium of the ether without connecting wires. When Hertz discovered that electric waves crossed space he unconsciously became the father of the modern system of radio-telegraphy, and though he did not live to put or see any practical results from his wonderful discovery, to him in a large measure should be accorded the honor of blazoning the way for many of the intellectual giants who came after him. Of course those who went before him, who discovered the principles of the electric telegraph made it possible for the Hertzian waves to be utilized in wireless. It is easy to understand the wonders of wireless telegraphy when we consider that electric waves transverse space in exactly the same manner as light waves. When energy is transmitted with finite velocity we can think of its transference only in two ways: first by the actual transference of matter as when a stone is hurled from one place to another; second, by the propagation of energy from point to point through a medium which fills the space between two bodies. The body sending out energy disturbs the medium contiguous to it, which disturbance is communicated to adjacent parts of the medium and so the movement is propagated outward from the sending body through the medium until some other body is affected. A vibrating body sets up vibrations in another body, as for instance, when one tuning fork responds to the vibrations of another when both have the same note or are in tune. The transmission of messages by wireless telegraphy is effected in a similar way. The apparatus at the sending station sends out waves of a certain period through the ether and these waves are detected at the receiving station, by apparatus attuned to this wave length or period. The term electric radiation was first employed by Hertz to designate waves emitted by a Leyden jar or oscillator system of an induction coil, but since that time these radiations have been known as Hertzian waves. These waves are the underlying principles in wireless telegraphy. It was found that certain metal filings offered great resistance to the passage of an electric current through them but that this resistance was very materially reduced when electric waves fell upon the filings and remained so until the filings were shaken, thus giving time for the fact to be observed in an ordinary telegraphic instrument. The tube of filings through which the electric current is made to pass in wireless telegraphy is called a coherer signifying that the filings cohere or cling together under the influence of the electric waves. Almost any metal will do for the filings but it is found that a combination of ninety per cent. nickel and ten per cent. silver answers the purpose best. The tube of the coherer is generally of glass but any insulating substance will do; a wire enters at each end and is attached to little blocks of metal which are separated by a very small space. It is into this space the filings are loosely filled. Another form of coherer consists of a glass tube with small carbon blocks or plugs attached to the ends of the wires and instead of the metal filings there is a globule of mercury between the plugs. When electric waves fall upon this coherer, the mercury coheres to the carbon blocks, and thus forms a bridge for the battery current. Marconi and several others have from time to time invented many other kinds of detectors for the electrical waves. Nearly all have to serve the same purpose, viz., to close a local battery circuit when the electric waves fall upon the detector. There are other inventions on which the action is the reverse. These are called anti-coherers. One of the best known of these is a tube arranged in a somewhat similar manner to the filings tube but with two small blocks of tin, between which is placed a paste made up of alcohol, tin filings and lead oxide. In its normal state the paste allows the battery current to get across from one block to another, but when electric waves touch it a chemical action is produced which immediately breaks down the bridge and stops the electric waves, the paste resumes its normal condition and allows the battery current to pass again. Therefore by this arrangement the signals are made by a sudden breaking and making of the battery circuit. Then there is the magnetic detector. This is not so easy of explanation. When we take a piece of soft iron and continuously revolve it in front of a permanent magnet, the magnetic poles of the soft iron piece will keep changing their position at each half revolution. It requires a little time to effect this magnetic change which makes it appear as if a certain amount of resistance was being made against it. (If electric waves are allowed to fall upon the iron, resistance is completely eliminated, and the magnetic poles can change places instantly as it revolves.) From this we see that if we have a quickly changing magnetic field it will induce or set up an electric current in a neighboring coil of wire. In this way we can detect the changes in the magnetic field, for we can place a telephone receiver in connection with the coil of wire. In a modern wireless receiver of this kind it is found more convenient to replace the revolving iron piece by an endless band of soft iron wire. This band is kept passing in front of a permanent magnet, the magnetism of the wire tending to change as it passes from one pole to the other. This change takes place suddenly when the electric waves form the transmitting station, fall upon the receiving aerial conductor and are conducted round the moving wire, and as the band is passing through a coil of insulated wire attached to a telephone receiver, this sudden change in the magnetic field induces an electric current in the surrounding coil and the operator hears a sound in the telephone at his ear. The Morse code may thus be signalled from the distant transmitter. There are various systems of wireless telegraphy for the most part called after the scientists who developed or perfected them. Probably the foremost as well as the best known is that which bears the name of Marconi. A popular fallacy makes Marconi the discoverer of the wireless method. Marconi was the first to put the system on a commercial footing or business basis and to lead the way for its coming to the front as a mighty factor in modern progress. Of course, also, the honor of several useful inventions and additions to wireless apparatus must be given him. He started experimenting as far back as 1895 when but a mere boy. In the beginning he employed the induction coil, Morse telegraph key, batteries, and vertical wire for the transmission of signals, and for their reception the usual filings coherer of nickel with a very small percentage of silver, a telegraph relay, batteries and a vertical wire. In the Marconi system of the present time there are many forms of coherers, also the magnetic detector and other variations of the original apparatus. Other systems more or less prominent are the Lodge-Muirhead of England, Braun-Siemens of Germany and those of DeForest and Fessenden of America. The electrolytic detector with the paste between the tin blocks belongs to the system of DeForest. Besides these the names of Popoff, Jackson, Armstrong, Orling, Lepel, and Poulsen stand high in the wireless world. A serious drawback to the operations of wireless lies in the fact that the stations are liable to get mixed up and some one intercept the messages intended for another, but this is being overcome by the adoption of a special system of wave lengths for the different wireless stations and by the use of improved apparatus. In the early days it was quite a common occurrence for the receivers of one system to reply to the transmitters of a rival system. There was an all-round mix-up and consequently the efficiency of wireless for practical purposes was for a good while looked upon with more or less suspicion. But as knowledge of wave motions developed and the laws of governing them were better understood, the receiver was "tuned" to respond to the transmitter, that is, the transmitter was made to set up a definite rate of vibrations in the ether and the receiver made to respond to this rate, just like two tuning forks sounding the same note. In order to set up as energetic electric waves as possible many methods have been devised at the transmitting stations. In some methods a wire is attached to one of the two metal spheres between which the electric charge takes place and is carried up into the air for a great height, while to the second sphere another wire is connected and which leads into the earth. Another method is to support a regular network of wires from strong steel towers built to a height of two hundred feet or more. Long distance transmission by wireless was only made possible by grounding one of the conductors in the transmitter. The Hertzian waves were provided without any earth connection and radiated into space in all directions, rapidly losing force like the disappearing ripples on a pond, whereas those set up by a grounded transmitter with the receiving instrument similarly connected to earth, keep within the immediate neighborhood of the earth. For instance up to about two hundred miles a storage battery and induction coil are sufficient to produce the necessary ether disturbance, but when a greater distance is to be spanned an engine and a dynamo are necessary to supply energy for the electric waves. In the most recent Marconi transmitter the current produced is no longer in the form of intermittent sparks, but is a true alternating current, which in general continues uniformly as long as the key is pressed down. There is no longer any question that wireless telegraphy is here to stay. It has passed the juvenile stage and is fast approaching a lusty adolescence which promises to be a source of great strength to the commerce of the world. Already it has accomplished much for its age. It has saved so many lives at sea that its installation is no longer regarded as a scientific luxury but a practical necessity on every passenger vessel. Practically every steamer in American waters is equipped with a wireless station. Even freight boats and tugs are up-to-date in this respect. Every ship in the American navy, including colliers and revenue cutters, carries wireless operators. So important indeed is it considered in the Navy department that a line of shore stations have been constructed from Maine on the Atlantic to Alaska on the Pacific. In a remarkably short interval wireless has come to exercise an important function in the marine service. Through the shore stations of the commercial companies, press despatches, storm warnings, weather reports and other items of interest are regularly transmitted to ships at sea. Captains keep in touch with one another and with the home office; wrecks, derelicts and storms are reported. Every operator sends out regular reports daily, so that the home office can tell the exact position of the vessel. If she is too far from land on the one side to be reached by wireless she is near enough on the other to come within the sphere of its operations. Weather has no effect on wireless, therefore the question of meteorology does not come into consideration. Fogs, rains, torrents, tempests, snowstorms, winds, thunder, lightning or any aerial disturbance whatsoever cannot militate against the sending or receiving of wireless messages as the ether permeates them all. Submarine and land telegraphy used to look on wireless, the youngest sister, as the Cinderella of their name, but she has surpassed both and captured the honors of the family. It was in 1898 that Marconi made his first remarkable success in sending messages from England to France. The English station was at South Foreland and the French near Boulogne. The distance was thirty-two miles across the British channel. This telegraphic communication without wires was considered a wonderful feat at the time and excited much interest. During the following year Marconi had so much improved his first apparatus that he was able to send out waves detected by receivers up to the one hundred mile limit. In 1900 communication was established between the Isle of Wight and the Lizard in Cornwall, a distance of two hundred miles. Up to this time the only appliances employed were induction coils giving a ten or twenty inch spark. Marconi and others perceived the necessity of employing greater force to penetrate the ether in order to generate stronger electrical waves. Oil and steam engines and other appliances were called into use to create high frequency currents and those necessitated the erection of large power stations. Several were erected at advantageous points and the wireless system was fairly established as a new agent of communication. In December, 1901, at St. John's, Newfoundland, Marconi by means of kites and balloons set up a temporary aerial wire in the hope of being able to receive a signal from the English station in Cornwall. He had made an arrangement with Poldhu station that on a certain date and at a fixed hour they should attempt the signal. The letter S, which in the Morse code consists of three successive dots, was chosen. Marconi feverishly awaited results. True enough on the day and at the time agreed upon the three dots were clicked off, the first signal from Europe to the American continent. Marconi with much difficulty set up other aerial wires and indubitably established the fact that it was possible to send electric waves across the Atlantic. He found, however, that waves in order to traverse three thousand miles and retain sufficient energy on their arrival to affect a telephonic wave-detecting device must be generated by no inordinate power. These experiments proved that if stations were erected of sufficient power transatlantic wireless could be successfully carried on. They gave an impetus to the erection of such stations. On December 21, 1902, from a station at Glace Bay, Nova Scotia, Marconi sent the first message by wireless to England announcing success to his colleagues. The following January from Wellsfleet, Cape Cod, President Roosevelt sent a congratulatory message to King Edward. The electric waves conveying this message traveled 3,000 miles over the Atlantic following round an arc of forty-five degrees of the earth on a great circle, and were received telephonically, by the Marconi magnetic receiver at Poldhu. Most ships are provided with syntonic receivers which are tuned to long distance transmitters, and are capable of receiving messages up to distances of 3,000 miles or more. Wireless communication between Europe and America is no longer a possibility but an accomplishment, though as yet the system has not been put on a general business basis. [Footnote: As we go to press a new record has been established in wireless transmission. Marconi, in the Argentine Republic, near Buenos Ayres, has received messages from the station at Clifden, County Galway, Ireland, a distance of 5,600 miles. The best previous record was made when the United States battleship Tennessee in 1909 picked up a message from San Francisco when 4,580 miles distant.] <h2 id="id00145" style="margin-top: 4em">CHAPTER III</h2> <div style="break-after:column;"></div>

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