_Telephones with several diaphragms._--When we remember that the induced currents caused in a magnet result from the vibratory movements of the diaphragm, and that these are produced by the vibrations of the stratum of air interposed between this diaphragm and the vocal organ, it necessarily follows that if these vibrations of the air react on several diaphragms, each attached to its electro-magnetic organ, several induced currents might be caused simultaneously, and if these were properly connected, their effects on the receiver would be so much the more intense, since the sounds produced would result from the combination of several sources of sound. Several inventors, starting from this argument, have planned instruments of varying ingenuity, which we will now describe, but without being able to declare who was the first to realise this idea. It is in fact so simple, that it probably suggested itself to the minds of several inventors at the same time, and we see that while M. Trouvé proposed this improvement in France in November 1877, it was tried in America and discussed in England, where indeed it was not expected to produce very favourable results. Mr. Preece wrote on the subject in a paper entitled ‘On some Physical Points connected with the Telephone,’ which was published in April 1878. He observes that all the attempts to improve the telephone have ended in disappointment and failure. One of the first attempts of the kind was made by Mr. Wilmot, who expected to obtain favourable results by augmenting the number of diaphragms, helices, and magnets, connecting the helices in a series, and causing them to act simultaneously, so as to increase the energy of the currents developed by the influence of the voice; but experience showed that when the instrument acted directly, the vibratory effect of each of the diaphragms decreased in proportion to their number, and the general effect remained the same as with a single diaphragm. Mr. Wilmot’s instrument was made in the beginning of October 1877, and that of M. Trouvé was only an imitation of it.