In order to put an end to the sputtering usual in microphones, it occurred to M. de Courtois to prevent any cessation of contact between the carbons by keeping them close together, and to effect the variations of resistance necessary for articulate sounds by making them slide over each other, so as to insert a shorter or longer portion of the carbon in the circuit. For this purpose a vibrating disk is placed in a vertical position in a rigid frame, and a small conducting rod, terminated by a pointed carbon, is applied to it, with this carbon point resting on another flat piece of carbon placed below it. Influenced by the vibrations of the disk, the carbon point moves to and fro, effecting more or less extensive contacts with the lower carbon, and thus producing variations of resistance which almost correspond to the range of vibrations on the disk. _Experiments made with the Microphone._--I must now mention the interesting experiments which led Mr. Hughes to the invention of the remarkable instrument of which we have spoken, as well as those undertaken by other scientific men, either from a scientific or a practical point of view. Believing that light and heat can modify the conductivity of bodies, Mr. Hughes went on to consider whether sound vibrations, transmitted to a conductor traversed by a current, would not also modify this conductivity by provoking the contraction and expansion of the conducting molecules, which would be equivalent to the shortening or lengthening of the conductor thus affected. If such a property existed, it would make it possible to transmit sounds to a distance, since variations in the conductivity would result from variations corresponding to the intensity of the current acting on the telephone. The experiment which he made on a stretched metal wire did not, however, fulfil his expectation, and it was only when the wire vibrated so strongly as to break, that he heard a sound at the moment of its fracture. When he again joined the two ends of the wire, another sound was produced, and he soon perceived that imperfect contact between the two broken ends of wire would enable him to obtain a sound. Mr. Hughes was then convinced that the effects he wished to produce could only be obtained with a divided conductor, and by means of imperfect contacts.