The apparatus thus acted as both a transmitter and a receiver; indeed it is essentially the magneto-receiver which has come into universal use in practical telephony, though for transmission it was soon superseded by forms of microphonic transmitters.
The microphonic arrangement consisted of a spring S, about the hundredth of an inch thick and the eighth of an inch broad, fixed at one end to a lever L, and carrying at its free extremity a brass block W.
In this several microphonic joints were employed.
The vast number of microphonic contacts present give rise to very strong electrical undulations, and hence to a loud sound.
The microphonic portion of the transmitter is contained in a thin cylindrical box or case of brass A, the inner curved surface of which is covered with an insulating layer of paper.