shown in Fig, 25. It is like the ordinary magneto-telephone, except that the circular diaphragm is replaced by a strip of thin iron, the edges having been bent so as to render it stiff. We mention it, simply because it demonstrates the fact that it is not essential that the diaphragm be circular.
A novel and purely mechanical telephone is illustrated by Fig. 26. In place of a line-wire, the illuminating gas, contained in gas-pipes, is used. It is calculated for short distances only, as it is essential that
the gas used in communicating offices should be drawn from the same main pipe. In the figure, P is the main pipe. The telephones are represented at T and T'. The instrument is merely a cone fastened by its apex to the gas-pipe in place of the burner. The larger end is closed by a thin circular diaphragm. The vibrations are conveyed from one diaphragm to another through the medium of the gas.
The phonograph and telephone, when combined, form an instrument known as the telephonograph, of which Fig. 27 is a representation. The drum of the phonograph is shown in section. The diaphragm, instead of being vibrated by the voice, is vibrated by the currents which traverse the helix, H, and which originate at a distant station. The object of the instrument is to obtain a record of what is said at the distant office, which can be converted into sound when desired.
The Motograph.—The motograph-receiver, from which we have been accustomed to hear sounds almost destitute of quality, has, by a little modification, become an articulating telephone. It works quite well in conjunction with the Edison carbon-transmitter. In Fig. 28 the back of the motograph-receiver has been removed, showing its construction. Within the drum D is contained the decomposing solution,
