In their instrument, the current, which passes through a body of moderately conducting capacity, acts on an electro-magnet provided with an induction coil, and this electro-magnet reacts on the diaphragm, in order to increase the range of its vibrations, and to create at the same moment two electric actions in the same direction: the only difference lies in the arrangement of the contact of this indifferent conductor with the vibrating plate. Instead of a simple contact effected by pressure between this plate and a carbon pencil, a fragment of the same substance with a sharpened point is fixed on the vibrating plate, and it dips into a drop of mercury which has been poured into the receptacle made for it at the upper end of the electro-magnet. In other respects, the arrangement of the instrument is that of an ordinary telephone, and the iron rod of the electro-magnet represents the magnetised bar of the Bell telephone. The inventors assert that this instrument can be used both as a sender and receiver, and it is in the following manner that it is worked in each case. When the instrument is transmitting, the morsel of carbon dips more or less into the mercury, and consequently differences are produced in the surfaces of contact, according to the range of vibrations made by the plate; the current varies in intensity in proportion to this range, and induced currents in the induction coil result from these variations; the induced currents react on the receiving telephone, as in Bell’s instrument, and are further strengthened by those which are produced electrically by the movement of the diaphragm before the induction coil, and the iron of the electro-magnet. When the instrument is used as a receiver, the usual effects are displayed, for since the iron of the electro-magnet is magnetised by the current, its conditions are precisely those of the ordinary Bell telephone, and the induced currents reach it in the same manner, only with greater intensity. Messrs. Thomson and Houston assert that their system has produced excellent results, and that by it the sound of the voice is much less altered than in other telephones. _Telephones with batteries and liquid senders._--We have seen that in 1867 Mr. Gray conceived the idea of a telephonic system based on the differences of resistance effected in a circuit completed by a liquid, when the layer of liquid interposed between the electrodes varies in thickness under the influence of the vibrations of the telephonic plate which is in communication with one of these electrodes. This system has since been the subject of study by several inventors, among others by MM. Richemond and Salet; and I give some of the accounts which have been published respecting their researches.