In speaking of the Telephone, we must not lose sight of the facts before mentioned, as regards our sense of hearing, and the manner in which the ear acts by the series of bones termed the hammer, the anvil, and stirrup. In the process of reproduction of tone in the magnetic instruments, the mechanism of the human ear was, to a certain extent, imitated, and a diaphragm, by vibrations, generates and controls an electric current.
Professor Wheatstone was the first person to employ the electric wire for the transmission of sounds, but Professor Philip Reiss, of Friedrichsdorf, was the first to make the experiment of producing musical sounds at a distance. His first instrument was of a most primitive nature; subsequently he produced an instrument of which fig. 188 is the Telephone, fig. 189 the “receiver.”
In fig. 188, it will be seen that there is an aperture on the top and one at the side; the latter is the mouthpiece. The top aperture is covered with a membrane which is stretched very tightly. When a person speaks or sings into the mouthpiece his voice is at once concentrated upon the tight membrane, which it causes to vibrate in a manner corresponding with the vibrations of the voice. There are two binding screws, one at each side. To the centre of the tight membrane a piece of platinum is fixed, and this is connected with the binding screw on one side, in which a wire from the battery is fixed. On the membrane is a tripod, the feet of which (two) rest in metal cups, one of them being in a mercury cup connected with the binding screw at the opposite side to that already mentioned. The third “foot”—a platinum point—is on the platinum in the centre of the membrane or top, and moves with it. Every time the membrane is stretched by a vibration the platinum point is touched, and the closed circuit is broken by the return of each vibration.
Fig. 190.—Bell’s first Telephone (Transmitter).
a. Electro-magnet. b. Diaphragm. c. Collar. d. Collar and tube. f. Screw. g. Mouthpiece. h. Battery. i. Wire from battery to coil. k. Telegraph wire. l. Through binding screw. m. Pillar holding magnet.
The receiving instrument (fig. 189) consists of a coil enclosing an iron rod, and fixed upon a hollow sounding box. It is founded upon a fact discovered by Professor Henry, that iron bars when magnetized by an electric current become a little longer, and at the interruption of the current resume their former length. Thus in the receiver the iron will become alternately longer and shorter in accordance with the vibrations of the membrane in the box far away, and so the longitudinal vibrations of the bar of iron will be communicated to the sounding box, and become perfectly audible. This instrument, however, could only produce the “pitch” of sound, “not different degrees of intensity, or other qualities of tones.” It merely sang with its own little trumpet whatever was sung into it; for all the waves were produced by an electric current of a certain and uniform strength, and therefore the sound waves were of the same size.
But in 1874, Mr. Elisha Gray, of Chicago, improved Reiss’ instrument, and discovered a method by which the intensity or loudness of tones, as well as their “pitch,” were transmitted and reproduced. In this method he employed electrical vibrations of varying strength and rapidity, and so was enabled to reproduce a tune. Subsequently he conceived the notion of controlling the vibrations by means of a diaphragm, which responded to every known sound, and by this he managed to transmit speech in an articulate manner.
Fig. 191.—Bell’s Telephone (Receiver).
In 1876, Professor Graham Bell sent a Telephone to the Centennial Exhibition at Philadelphia. Mr. Bell, according to the report, managed to produce a variation of strength of current in exact proportion to the particle of air moved by the sound. A piece of iron attached to a membrane, and moved to and fro in proximity to an electro magnet, proved successful. The battery and wire of the electro magnet are in circuit with the telegraph wire, and the wire of another electro magnet at the receiving station. This second magnet has a solid bar of iron for core, which is connected at one end, by a thick disc of iron, to an iron tube surrounding the coil and bar. The free circular end of the tube constitutes one pole of the electro magnet, and the adjacent free end of the bar core the other. A thin circular iron disc held pressed against the end of the tube by the electro-magnetic attraction, and free to vibrate through a very small space without touching the central pole, constitutes the sounder by which the electric effect is reconverted into sound. The accompanying illustrations (figs. 190, 191) show Mr. Bell’s Telephone as described.