The slightest shock which affects the microphone has the effect of sending currents, more or less broken, through the telephones, which transform them into sound vibrations, and since these are mechanically transmitted by the board to the microphone, they maintain and even amplify its action, and produce fresh vibrations on the telephones. Thus a fresh action is exerted on the microphone, and so on indefinitely. Again, if a second microphone, in connection with another telephonic circuit, be placed upon the same board, we have an instrument which acts as a telephonic relay, that is, it transmits to a distance the sounds communicated to the board, and these sounds may serve either as a call, or as the elements of a message in the Morse code, if a Morse manipulator is placed in the circuit of the first microphone. Mr. Hughes adds that he has made several very successful experiments with this system of instruments, although he only employed a Daniell battery of six cells without any induction coil. By fastening a pasteboard tube, 40 centimètres in length, to the receiving telephone, he was able to hear in all parts of a large room the continuous sound of the relay, the ticking of a watch, and the scratching of a pen upon paper. He did not try to transmit speech, since it would not have been reproduced with sufficient distinctness under such conditions. Since this first attempt, Mr. Hughes has arranged another and still more curious system of microphonic relays, for which two microphones with vertical carbons are required. He places two microphones of this description on a board, and connects one of them with a third microphone, which acts as a sender, while the second is in communication with a telephone and a second battery: in this way the words uttered before the sender are heard in the telephone, without employing any electro-magnetic organ for the telephonic relay. In August 1878, Messrs. Houston and Thomson likewise arranged a system of telephonic relays which only differs from that of Mr. Hughes in the particular of having the microphone fixed on the diaphragm of the telephone, and not on the board beside it. The system consists of three vertical microphones, which can be combined for tension or quantity, according to the conditions for which they are required. The model of this instrument was represented in the ‘Telegraphic Journal’ of August 15, 1878, to which we must refer our readers, if they wish for further information on the subject.