The Telephone of the Future.

A new telephone, invented by Mr Marshall, a New York electrician, is described by the Paper World. In principle it is altogether different from the costly instruments now in use, which it will probably entirely supersede. It has neither magnet nor diaphragm, hence there are no sounds of its own to blur and interfere with the sounds transmitted, and it may be used with the ordinary telephone transmitter. The instrument, which can be manufactured for a few cents, appears like a duodecimo volume of wrapping-paper, interleaved with tinfoil, the whole being perforated in the middle, and pressed together at the outside edge. To this is attached a plain black walnut handle like a newspaper file, and a pair of binding screws connect the tinfoil with the line. The principle of operation is thus described: In electrodynamics, bodies charged with similar electricities attract, and with opposite electricities repel each other. The tinfoil sheets of the condenser, arranged in alternate layers of polarity, form practically a compound electroscope, the leaves of which, excited by the induced currents, attract each other. On the excitement ceasing, the elasticity of the interposing paper causes a divergence. These impulses are exactly synchronous and in unison with the transmitting operators' voice, and hence form acoustic waves in the receiver exactly similar to those affecting the transmitter. In the instruments where a magnet is employed, not more than two diaphragms can be used simultaneously. In the Marshall instrument there are fifty sheets of tinfoil and paper, each practically a diaphragm, and contributing its quota of motive power. The perfection of the instrument's operation is as remarkable as its simplicity. A novel feature in the Marshall system is the employment of a constant battery current upon the line in addition to the interrupted induced currents from the transmitter proper. It is difficult to understand exactly the precise action of this current, but experiments show that its efficacy is unquestionable. On a short line but one or two cells are required, and the ratio of increase as the line lengthens is about the same as that on the line of the common telegraph. By the use of this battery Mr Marshall claims that telephony is practicable on as long lines as telegraphy, the electromotive force of the current being supplied by the battery and not by the instrument.