HOW WIRELESS TELEPHONES WORK.

Bush Advocate, Volume XXI, Issue 132, 3 December 1908, Page 7

HOW WIRELESS TELEPHONES WORK.

(By T. Thorne- Baker.) This is such an essentially electrical age that one is accustomed to think of Wireless telephony as speaking over great distances byineansof electricity. But shouting is the siir-.ilcot form of wireless telephoning, which, after all, -moans only the transmission of speech or sound without the agency of electrical wires. ... The megaphone, indeed, enables us to be heard at greater distances than many of the early and complicated "wireless telephones" would admit of. The Avhispcring gallery in St. Paul's Cathedral is an excellent example of a wireless telephone. Electricity, however, is the wonderful power which is rendering possible such rapid strides as are just; now being made in the transmission of speech. Had Nelson fought his -great battle a hundred years hence, who knows but what the progress of Trafalgar might have been- discussed with the Admiralty in London; ..to whom even the din and roar of the contest Avould then have been carried. . It is useless to say, "How absurd," for science is year by year giving us such surprises that it is not safe or wise to say that anything is impossible. ■■..'■'.-,.,' Wireless telephony did not follow on as the natural-sequence of. wireless telegraphy. Exactly thirty- years ago wireless telephones were in use-- j of course, in an experimental way— Bell, the inventor of the telephone, and his colleague Tainter, being the first to construct a successful arrangement. EARLY EXPERIMENTS. In many of these earlier, .-experiments rays of light reflected from a looking-glass were used as the medium to convey the sounds from speaker to listener. Light, heat, water and earth have all been tried in turn as media for the transmission of speech. The wireless telephone, in fact, requires some agency to work with. Do not imagine that it is possible to say a few words into a telephone, connected with nothing, and for someone a mile away to hear what you sajf without any intermediary power.. If you send someone a sovereign, and to do so buy a postal order and send it through the post, the recipient cashes the order and gets his gold piece. The postal order was the means by which the gold was transmitted. It is just the same in Avireless telephony. You speak into a telephone, connected by no wires with the receiver, and your words are converted into something else — in. this case merely modified electrical waves. These waves arc sent through the air or the earth, always bearing upon them tho impression made- by the speech, and when they arrive at the receiving post they are .one© again converted into sounds. The electric waves are analogous to the. postal order, the earth or air to the post. The waves possess a subtle and latent value which can bo exchanged for the original words spoken. A SUCCESSFUL WIRELESS TELEPHONE. These waves are more easily transmitted through earth or water than through space, where comparatively short distances are concerned, and one of the most recent and most successful wireless telephones^ — that oi Mr A. W. Sharman — depends on the transmission of electrical waves or impulses through the earth. • This is such a simple method, and is likely to meet with such wide supplication, that it is a very suiintfo one to describe on the present occasion. The speaker talks into a special mouthpiece which contains lightly packed metallic granules. As he speaks, the vibration of the drum of the mouthpiece varies with the pitch of the voice, and causes the granules to cohere more or less in correspondence. An electric current from a battery passes through the microphone into a coil of insulated wire wound round an iron bar. The strength of the current varies always with the amount of cohesion in the granules, and the coil, each end of which is connected to a metal plate buried in the ground, sends out an electrical impulse with each vibration which corresponds in intensity. What is the result ? Impulses are sent out from the metal earth plates in which is latent the character of the speech vibrations. The waves spread outwards like the ripples on a pond when you throw a stone into tho water. They grow ever bigger and bigger, becoming in consequence always weaker and . weaker (in this fact we see tho reason for a limit io possible distance). If now two fresh earth plates or metal rods are put in the ground in such a position as to lie on the wave front, and they are connected by wires to a very sensitive telephone receiver, tho ear placed against this receiver will hear the speech,™ for by its agency electrical impulses are reconverted into sounds. The postal

3) order is ou.ce again converted into the sovereign. THE INSTRUMENT DESCRIBED. Tlio Sharman telephone is a very simple and small piece of apparatus, and can be fixed on an ordinary camera tripod. Speech and music have been easily transmitted over distances of about a quarter of a mile. We now, however, come to- the question of speaking over distances of hundreds of miles. Here a very powerful and peculiar form of arc light is employed. One would hardly think that an electric arc lamp would bo capable of singing, talking, or playing the flute. Yet if- a; telephone transmitter be connected in a certain manner with the current of electricity which supplies the arc iainp with the necessary enorgy, anything said, . or sung, or any music played into the microphone, will be repeated by the electric lamp with wonderful and almost uncanny miini«ry. ...:..... Experiments such as these led Poulsen and others to find that special arc lamps would cause "a continuous "flow of electrical > -■oscillations on which the' : s6unds from a telephone-\y-duld liaye a modifying -effect, which could be again converted into sound by means of suitable receiving apparatus. •"'. * ■ . exact methods of arrangement are far too complicated to admit, of description here,, but the general method may be taken as that of causing the speech vibrations to modify electric waves which are being sent out, by the aid of a special singing arc, from an aerial to another receptive aerial at the receiving station. By means of aji electrolytic detector these waves are reconverted into sound, and the speech is rendered intact owing to the "impress" of the speech vibrations on the wireless waves. Other methods are, needless to say, being investigated. Each expert claims for his own method the most perfect results. Time alone will show which is in reality the most practical of the lot. But the pioneers of this wonderful science seem well agreed on one point, and that is that before many yea.rs speaking across the Atlantic will be a matter of as great ease as handing in a telegram at the present time. Much interest thus attaches to the forthcoming experiments of Mr De Forrest, when the Admiralty offices are to be put into speaking communication with- the Channel Fleet. — Daily Mail?