Of more recent invention than any of the classes of instruments already mentioned for electrical communication at a distance is the telephone, which differs widely from the rest in many notable particulars. Though the telephone completely realized what had for years before been the dream of physicists, the first announcement of its capabilities was received, even by the scientific world, with some pause of incredulity; but when its powers were demonstrated, it created no small sensation. It has now, within a few years afterwards, become so familiar as an appliance of ordinary life and business, that people in general are less impressed by the wonder of it than were their fathers half a century ago by the electric telegraphs of Wheatstone and of Morse. Like all other inventions, it was led up to by preceding discoveries and tentative efforts. It will be unnecessary here to trace those successive steps with minuteness, or to attempt to adjust the claims of merit or priority that have been put forward for different inventors, but a notice of some of the stages in the evolution of this wonderful contrivance may be of interest. If the reader has no previous knowledge of the physical nature of sounds in relation to music, and especially to articulate speech, he should now refer to the brief explanation given in a subsequent chapter, at the commencement of the section on the Phonograph. He should, however, bear in mind that in that explanation are included some acoustical discoveries of a later date than some of the inventions we are here to speak of, or, at least, the real causes of which give other qualities than pitch to sound, had not been fully demonstrated when the notion of the electric telephone was conceived.
When the electric telegraph came into use and it was found possible to use it for communication of intelligence to great distances, it is not surprising that the further problem of transmitting by electricity, not signals merely, but audible speech, should be suggested. Perhaps the first scientific person who avowed a belief in the possibility of doing this, and even indicated the direction in which the solution of the problem was to be sought, was a Frenchman of science, M. Charles Bourseul. In 1854, he pointed out that sounds are caused by vibrations, and reach the ear by like vibrations of the intervening medium, and, although he could not say what took place in the modifications of the organs of speech by which syllables are produced, he inferred that these syllables could reach the ear only by vibrations of the medium, and that if these vibrations could be reproduced the syllables would be reproduced. He suggests that a man might speak near a flexible disc, which the vibrations of his voice would throw into oscillatory movements that could be caused to make and break a battery circuit, and that, at a distance, the currents might be arranged to produce the like vibrations in another disc. The weak point of this scheme was the want of any suggestion as to the mode in which this last effect was to be produced. Even when this part of the problem was solved in a few years afterwards, as we shall presently see, it was musical—and not articulate—sound that could be transmitted by an arrangement, using make and break contacts. The reader, who has understood what has been said of electrical currents, and also the account of the compounded vibrations in articulate sounds introduced into our section on the phonograph, should have little difficulty in seeing this must necessarily be the case, for the contacts could only give the succession of the vibrations by currents of equal intensity, and could not, like the yielding wax of the phonograph cylinder, correspond with their relative intensities. M. Bourseul pointed out advantages which would arise from the transmission of speech by electricity, such as simplicity of apparatus and facility in use—for, unlike the telegraph, no skilled operators would be needed—to signal messages, or time spent in spelling out the words letter by letter. He says that he had made some experiments, which promised a favourable result, but demanded time and patience, and that he is certain that, in a more or less distant future, speech will be transmitted by electricity, so that what is spoken in Vienna may be heard in Paris. One cannot help thinking that if M. Bourseul had but pursued his experiments a little longer, he would not improbably have achieved the invention of the speaking telephone, for which the world had to wait twenty years longer. As it is, we cannot but admire his scientific foresight and his confidence in the ultimate realization of his idea.
But before this came to pass, an intermediate stage was reached in the apparatus contrived by M. Reiss, a schoolmaster of Friedrichsdorf, who, in 1860, solved the problem of electrically transmitting musical tones. So far as concerned the reproduction of the sounds, this telephone was founded upon a discovery, made in 1837, by an American physicist, named Page, which was this: At the moment a bar of iron is magnetized, by sending a current through a coil surrounding it, as shown in Fig. [265], a slight but sharp click is heard. The transmitting apparatus was, in principle, Mr. Scott’s phono-autograph (described in the section on the phonograph), which had been invented in 1855. The tracing style of this was replaced in Reiss’ apparatus by a small disc of platinum, connected by a very light spring of the same metal with a binding-screw for the battery connection. Nearly in contact with the little disc was a platinum point, so arranged that the slightest oscillation of the membrane would bring them into actual contact and thus close the circuit. Worthy of remark is the very primitive nature of the materials with which Reiss made his first experimental apparatus. The receptacle for the voice was simply a large bung hollowed out into a conical cavity, and the membrane was supplied by the skin of a German sausage, while the clicking bar of the receiver was a stout knitting needle, surrounded by a coil of covered copper wire and stuck into the bridge of a violin, which, by acting as a sounding board, made the clicks produced in the needle distinctly audible. M. Reiss finally produced his telephone in the form shown in Fig. [302a], where I is the receiver; B, the voltaic battery; I I, the receiver; c c is a coil of insulated wire, surrounding a slender iron rod, mounted on the supports, f f, which rest on the sounding board, g g. The transmitter consists of the hollow box, A, provided with a trumpet-mouthed opening in one side and having at the top a circular piece cut out, across which is stretched a membrane with the little disc of platinum, n, fixed in its centre. When a person applying his mouth to A sings into the box, the membrane is thrown into vibrations corresponding with the notes, and at each vibration a contact is made and a click is emitted from the distant sounding box. The tones are concentrated by covering this box with the perforated lid. It was afterwards found that a trumpet mouth fitted into the receiver was still more effective. Reiss tried to use his arrangement for transmitting speech, but without success, although occasionally a syllable could be very indistinctly heard. An instrument, with springs so nicely adjusted that slight vibrations did not separate the platinum from actual contact, but merely caused change of pressure, has indeed been made to convey articulate sounds, although the arrangement was not essentially different from that of M. Reiss. This mode of action is, however, a different thing, and we shall presently see that very effective speech transmitters have been constructed by applying it in a more refined way. This musical telephone could give the pitch of the sounds in the song but not their quality (timbre), and the receiver added to the main system of vibration other sets that belonged to itself, the result being a shrill and by no means pleasing tone, recalling that of a penny trumpet. Messrs. C. and L. Wray afterwards effected some considerable improvements in M. Reiss’s telephone, with the object of intensifying the effects and producing better tones.
Fig. 302a.—Reiss’ Musical Telephone.
Fig. 302b.—Bell’s Musical Telephone.
A further step towards the speaking telephone may be illustrated by an earlier invention of Mr. Graham Bell, a native of Scotland, who had settled in the United States. Mr. Bell’s inventions, it may be mentioned, were by no means the results of fortunate accidents or of unsought and spontaneous flashes of conception, but rather the outcome of long, patient and systematic studies. His father, Mr. Alexander Melville Bell, of Edinburgh, had assiduously cultivated acoustic science, and had in conjunction with his son, undertaken special researches into the mechanism of the organs of speech, the elements of articulate speech in different languages, and the musical components of vocal sounds. When Graham afterwards pursued these studies in the light of the fuller investigation carried out by Helmholtz, he was naturally led to the application of electricity to acoustic transmission. After some experiments in the production of vowel sounds by combinations of electric tuning forks, he invented a telephone for reproducing musical sounds at a distance, which was a great improvement on that of Reiss, and involved another principle, which indeed is the same as that utilized in his more mature invention of the speaking telephone. As a like explanation of the action would apply in both cases, the reader will find his advantage in following the observations we have to make on the earlier instrument. This consisted of what was virtually two sets of electric tuning forks, each set being acted upon by one electro-magnet. Fig. [302b] will suffice to show the general form of the arrangement. A plate of steel is bent twice at right angles longitudinally, and is magnetized so that any transverse slice of it would constitute an ordinary horse shoe magnet. This is seen endways in Fig. [302b] at M, and N. and S. will indicate the north and south poles respectively. To each limb of this broad magnet is attached a plate of steel, T, cut into teeth, just in the same way as the steel plate in a common musical box or mechanical piano, except that the teeth are not pointed. These are tuned to give severally in pairs the notes of the musical scale when thrown into vibration. Between the prongs of the series of tuning forks thus formed is an electro-magnet, L, made of a bar of soft iron, I, wound longitudinally by a coil, one end of which makes an earth connection at E and the other is connected by the wire, W W´, to complete the circuit through the coil of the distant apparatus. It will be observed that the receiving and transmitting instruments are exactly alike. Now, suppose one of these teeth is struck or otherwise thrown into vibration, the result will be, since the free ends of the teeth are magnetic poles, that alternating electric currents will be generated in the coil of the electro-magnet (see page [509]), and these will flow through the entire circuit, including the coil of the distant instrument, where the magnetism generated will alternately attract and repel the polar extremities of the teeth in the steel plate. It will be understood, of course, that the fellow prong of the fork will vibrate also, and will simultaneously approach to and recede from the soft iron core, so that being of opposite polarity, the effect on the electro-magnet will be doubled. The action on the distant electro-magnet will be a rapid series of reversals of the polarities of the core, and hundreds of times in every second the ends of the steel teeth will be alternately attracted and repelled. But not all of these will thereby be thrown into vibration—only the one pair which were tuned into unison with the former can and will respond to that particular series of impulses, and the consequence will be that the same note will be emitted by the receiving instrument. If two or more notes of the transmitter be simultaneously thrown into vibration, the same notes will be heard from the receiver, for each series of currents will flow along the wire independently, just as if the other did not exist, and each will produce its particular effect on the transmitter. In this way an air played on the one instrument is heard also from the other, with all its accents and combinations. But more than this, if a tune be played on a musical instrument near the sender, or if a song be sung, the air will be reproduced by the distant receiver. The reason of this is that the steel tongues take up, or are thrown into movement by, the vibrations that have the same periodicity. The manner in which a vibratory body responds to impulses of its own periodicity may be easily shown by exposing the wires of a piano and raising the dampers, when, if a note be sung near the instrument, it will be found that a number of the wires respond, namely, those that are capable of vibrating synchronously with the constituent vibrations of the voice, for neither a voice nor a sounding wire gives forth one simple system of vibrations, the audible effect being due to the superposition or composition of several diverse elementary systems. With the same arrangement another experiment may be made, as an illustration of a matter important for our subject. Let the different vowels be sung to the piano-wire on the same note or pitch, and in the responses to each a difference of the quality of the sound will be noticed, although the piano will not distinctly give back the vowel itself. It would, however, do so if a number of its wires were strung with certain definite relations in pitch to that of the fundamental note and in unison with the voice components of the vowel sound.
Fig. 302c.—Superposition of Currents.