LECTURE.

Friday, 21st December, 1877.

Lieut.-General Sir DANIEL LYSONS, K.C.B., QuartermasterGeneral, in the Chair.

THE TELEPHONE AND ITS APPLICATION TO MILITARY AND NAVAL PURPOSES.

By W. H. PREECE, Vice-President Society Telegraph Engineers, and Member Institution Civil Engineers.

No one can deny the enormous value of the electric telegraph for warlike purposes. It has well nigh revolutionized the art of war. It has become a great weapon of offence, as well as a great shield of defence. Operations that were a few years ago impossible are now regarded as essential. The strategist in his office can now grasp a continent in his combinations. The actual manœuvres of armies can be controlled and directed like the toy figures of the game of Kriegs-spiel. The maintenance of the lines of telegraph to an army in the field is as important as that of the more material lines of communication. The telegraph, in fact, has become a necessity of the age. No war could now be undertaken without its aid.

But it is not only in annihilating space, and bringing within the mental view of the master mind a dozen armies and a million men, that telegraphy is so valuable; it is in the rapid communication of intelligence and orders to and from the Commanding Officers of each limb of each army, however small; it is in connecting together, in immediate communication, the different parts of a fortress or an entrenched camp, however much they may be scattered; it is in maintaining an uninterrupted connection between all parts of a besieging force, however extensive may be the lines of circumvallation, that it is so serviceable. It would have been impossible to have kept on the sieges of Paris and Metz without it. Indeed, it has a civilizing influence, for it not only tends to shorten the duration of war, but to diminish the loss of life, by rendering possible those combinations which, in the cases of Sedan as well as of Metz, swallowed up temporaily in prison two great armies. Moreover, it facilitates the supply of food, it

regulates the traffic on railways, it aids the transport home of the sick and wounded, it satisfies the craving for news, and it alleviates anxiety at home. It is well known that the Germans, guided by their experience of 1866, commenced the war of 1870 with a very well organized and extensive system of telegraphs for field service, but that the French had a system wanting in efficient organization and miserably deficient in men and material. We know little of the present Russian system, excepting the fact that by its aid the army around Plevna maintained its bear-like hug on the doomed fortress, aud enabled it to thwart, with overpowering force, the tiger-like rush of Osman Pasha.

So important is efficient telegraphy now considered for the British Army that 6 officers and 160 men are being trained and maintained in efficiency in the British postal telegraph system, so as to be available in time of war. They are, in fact, daily rehearsing that part which they may have some day to perform in earnest in an enemy's country. Moreover, we have our field telegraphs in constant training at Aldershot, Chatham, and elsewhere, though it is very doubtful whether this department has been nearly sufficiently developed, or is anything like being properly equipped, for such an army as ours, However, I am here, not to criticise or describe the equipment of our military telegraphic system, but to describe an apparatus which may prove a most useful and valuable adjunct to the already well matured system of waggons and barrows and cables in actual use. I must draw a distinction between the permanent telegraphic system of the country occupied by an army, the semi-permanent lines of telegraphy which connect head-quarters, as it advances, with this system, and the "flying "line" or temporary system of field telegraphs which follows the movements of the various corps in the field, and maintains their communication with head-quarters. The first two must necessarily be. worked on the ordinary telegraphic system in use, maintained by technical skilled labour, and worked by well trained, experienced telegraphists. The flying line need not necessarily be so manipulated. There is also the visual system, intended for outpost and reconnoitring duties, and which necessarily must be continued under circumstances which render field telegraphs impractical. I do not intend to refer to this admirable system.

At present, the apparatus in use for field telegraphy is the ordinary Morse recording apparatus, which records its messages in the ordinary dot and dash alphabet, understood only by the initiated, supplemented by a sounding instrument, which appeals, by a similar foreign language, to the ear. Thus, to convey intelligence from one point to another, a message has to be written down on paper, it has then to be translated by a telegrapher into the Morse language, which has to be re-translated at the distant end into the ordinary written language, and then read by the recipient. These operations are subject to error, and have not secured faith in their reliability. Is there any Commanding Officer here present who would not wish such an uncertain agent in a very warm place? Those who were present at the Autumn Manoeuvres on Salisbury Plain know how to value its services. It is unquestionable

that the telegraph has not inspired confidence, and this is due as much to its natural uncertainty as to the want of knowledge of the tool that is used. Accuracy in the transmission of orders is the sine qua non of a military telegraph. We know of one great disaster that arose from a mistake. "Some one has blundered." It was the very last thing determined upon in our late Ashantee War, and the rapidly collected materials drawn from the Post Office stores were dispatched at the last moment, by passenger train, and stowed in the officers' baggage room. Yet we have the authority of Sir Lintorn Simmons for saying that the operations in that war could not have been carried on as they were without its assistance, and that it was productive of very great economy to this country by shortening the expedition and enabling the greatest amount of benefit to be derived from the materials and means that were placed at the disposal of the General in command.

Now, the telephone, if it prove a practical instrument, will place in the hand of every officer an instrument which will transfer the actual words and tones of his own voice to his correspondent at any reasonable distance. I have spoken distinctly, at various distances up to ninety miles; last week I spoke from Holyhead with my friends in Dublin, through the cable joining those two places, and I have been able to recognise, with absolute certainty, the voices of different people at sixty-seven miles. It will solve the moot question as to the best form of instrument for military telegraphs, about which there is much diversity of opinion.

How is it that the human voice itself can be reproduced at such distances? When I strike a bell, blow a whistle, sound a reed, clap my hands, or speak to you, how is it that these different operations are conveyed through your ears so as to produce on the brain that sensation which is called sound? The air itself, in which we breathe and move and have our being, is a highly elastic medium, which readily receives and transmits any motion imparted to it. When I clap my hands, I suddenly throw this air into motion, a wave is formed, just like a stone thrown into water generates a wavn that circles round and round, striking and enveloping everything in its course. This air-wave likewise envelops everything in its course and impinging upon the tympana of your ears, it there affects the nerves in such a way as to convey to the brain that sensation which education has taught us to be that sound due to the clapping of hands. Sound is therefore simply the undulations of the air; but there is sound and sound. I shake this box of nails; it makes a most disagreeable noise. I blow this reed; it makes a soft musical tone. Why have we in the one case noise and in the other music? In the one case the waves follow each other in irregular spasmodic fashion, shivering the drum of the ear with unpleasant shocks; in the other case the waves follow each other regularly, periodically, and rythmically, blending together on the drum of the ear with pleasant sensations. Let us ignore noise, and confine ourselves to this musical instrument. I blow a note. If it were possible to illuminate a tube of air between the mouth of this instrument and any one of your ears, you would see this air chased and moulded into the most beautiful and regular undulations; not

rises and falls, like the vertical waves of the sea, but condensations and rarefactions-close order and open order-more like a field of barley in autumn time responding to the motion of a gentle breeze. If we conceive a line of particles to be arranged along this tube, like a long file of men or a row of marbles, then if each particle takes an excursion to and fro for the same distance (the same amplitude), however small, then if the motion of each particle be successive, and not simultaneous, the line will be excited into waves or sonorous vibrations, as shown in Fig. 1.

FIG. 1.

Now, let us fix our attention upon this musical instrument and this suppositious tube of air. I can produce various notes. One note differs from another note only in the number of waves or sonorous vibrations produced per second. Middle C of the piano makes 264 of these vibrations, E 330, F 352, A 440, and the octave to C 528 per second. The lowest note that can be heard by the human ear is 16 complete vibrations per second; the highest, 38,000. The range of the human voice is between 65 and 1,044 sonorous vibrations per second. Whenever and however we produce air vibrations, pursuing each other regularly between these two limits, we have notes. And one note differs from another note in its pitch, which is the number of its sonorous vibrations per second. But these notes may be soft and gentle or rough and loud. Hence notes differ, not only in their pitch, but they differ in their loudness. Loudness depends upon the energy of the source of sound and upon the amplitude of the consequent vibrations of the particles of air. If I blow gently, the excursion to and fro is small. If I blow fiercely, the excursion to and fro is great. The former undulations strike the ear gently, and the sensation is low; the latter strike it fiercely, and the sensation is loud. Again, I take three or four different instruments and I sound the same note on each with the same force. The pitch is the same, the loudness is the same, but there is no mistaking their difference. This difference is called their quality, clang-tint, or timbre. Now, what causes this clang-tint? I must beg your attention here, for here lies the secret of the new articulating telephone. This clang-tint is due to the form of the wave of air. It is very difficult to conceive a difference in the form of a wave of air. It is simple enough when we regard water. We see this for ourselves upon the surface of a pond or of the mighty deep. But the difference of an air-wave lies, not in its geometrical form so much as in the rate of motion of its different particles. I wave my hand backwards and forwards regularly or irregularly. I can make it move at any given rate, at any given time, and, though the number of excursions and the amplitude of excursion to and fro per unit of time may be the same, I can vary the form or rate of excursion at will. This produces difference of quality, and this is why

middle C, sounded on a piano, on a harp, on a bugle, or by the voice is the same note, but differing so much in clang-tint. It is impossible to picture in the mind the beauty and minuteness of the sound-waves. The ear, though approached by a channel the diameter of only a quill, will receive the vibrations from a hundred voices and instruments and can separate each by attention. Hence we arrive at our first proposition, that sound is due to the undulations of the air, and that, as these undulations vary in number per second, in amplitude, and in form, so we have noise or music, varying in pitch, in loudness, and in clang-tint.

We have now to consider how we can catch up, as it were, these sounds, and convey them into something else. It is said that Lablache could sound a note so deep and loud that he could crack a tumbler. Whenever anyone sings in a room, something can be always heard to rattle. If you open the piano, and sound the vowels on the middle notes, you will hear the piano repeat them. Hence we learn that the air vibrations can be imparted to other grosser matter in their path. I hold before my mouth this disc of parchment-a small drum-head. It responds to the tones of my voice. I can make this evident to you. It is so constructed that it makes and breaks an electric current every time it vibrates. This electric current operates as an electro-magnet. The electro-magnet actuates an armature. If the motions of this armature are of the same number as the disc, we shall have the note repeated. There you are. Every note I direct upon the disc is repeated by the magnet. But I cannot vary this note. Whether I shout or whether I hum; whether I sound the note upon an instrument or upon a tuning-fork, the note given out by the magnet is the same. It varies only in pitch, and not in loudness or in clang-tint. This is the first telephone ever made, that of Riess of Friedericksorff, and it is illustrated in Fig. 2.

FIG. 2.

Now I must make a temporary diversion into the realms of electricity.

There are many ways of producing electricity. We have just used a battery where the electricity was produced by the chemical decomposition or combustion of zinc, just as heat is produced by the chemical decomposition or combustion of coal. We can produce it by friction or by heat, but one very common mode is to produce it by the motion of a coil of wire in the neighbourhood of a permanent magnet, or