To understand the principle of this telephone, we must give some account of Mr. Edison’s electro-motograph, discovered in 1872. This instrument is based upon the principle that if a sheet of paper, prepared with a solution of hydrate of potash, is fastened on a metallic plate which is united to the positive pole of a battery, and if a point of lead or platinum connected with the negative pole is moved about the paper, the friction which this point encounters ceases after the passage of the current, and it is then able to slide as if upon a mirror until the current is interrupted. Now, as this reaction may be effected instantaneously under the influence of extremely weak currents, the mechanical effects produced by these alternations of arrest and motion may, by a suitable arrangement of the instrument, determine vibrations in correspondence with the interruptions of current produced by the transmitter. In this system the telephonic receiver consists of a resonator and a drum mounted on an axis and turned by a winch. A paper band, wound upon a reel, passes over the drum, of which the surface is rough, and a point tipped with platinum, and fitted to the end of a spring which is fixed in the centre of the resonator, presses strongly on the paper. The current from the battery, first directed on the spring, passes by the platinum point through the chemical paper, and returns by the drum to the battery. On turning the winch, the paper moves forward, and the normal friction which is produced between the paper and the platinum point pushes the point forward, while producing by means of the spring a tension on one side of the resonator; but since the friction ceases at each passage of the current through the paper, the spring is no longer drawn out, and the resonator returns to its normal position. Since this double effect is produced by each vibration made in the sender, a series of vibrations takes place in the resonator, repeating those of the sender, and consequently the musical sounds which affected the sender are reproduced to a certain extent. According to the American journals, the results produced by this instrument are astonishing: the weakest currents, which would have no effect on an electro-magnet, become perfectly efficacious in this way. The instrument can even reproduce with great intensity the highest notes of the human voice, notes which can hardly be distinguished by the use of electro-magnets.