Fig. 6 shows a receiving instrument R, with a vibratory circuit-breaker _v_ attached. The light spring-lever _v_ overlaps the free end of the steel reed A, and normally closes a local circuit, in which may be placed a Morse-sounder or other telegraphic apparatus. When the reed A is thrown into vibration by the passage of a musical signal, the spring arm _v_ is thrown upwards, opening the local circuit at the point 5. When the spring-arm _v_ is so arranged as to have normally a much slower rate of vibration than the reed A_{ 1}, the local circuit is found to remain permanently open during the vibration of A, the spring-arm _v_ coming into contact with the point 5 only upon the cessation of the receiver’s vibration. Thus the signals produced by the vibration of the reed A are reproduced upon an ordinary telegraphic instrument in the local circuit.
Fig. 7 shows the application of electric telephony to autographic telegraphy.
T, T´, &c., represent the reeds of transmitting instruments of different pitch, R, R´, &c., the receivers at the distant station of corresponding pitch, and, _r_, _r´_, &c., the vibratory circuit-breakers attached to the receiving instruments, and connected with metallic bristles, 21, resting upon chemically prepared paper P. The message, or picture, to be copied, is written upon a metallic surface, F__0_, with non-metallic ink, and placed upon a metallic cylinder 7, connected with the main battery B; and the chemically prepared paper P, upon which the message is to be received, is placed upon a metallic cylinder connected with the local battery B´ at the receiving station. When the cylinders at either end of the circuit are rotated in the direction of the arrows—but not necessarily at the same rate of speed—a _fac simile_ of whatever is written or drawn upon the metallic surface F__0_ appears upon the chemically prepared paper P.
The method by means of which the musical signals may be sent simultaneously in both directions along the same circuit is shown in our next illustration, figures 8, 9, and 10. The arrangement is similar to that shown in figures 3, 4, and 5, excepting that the intermittent current from the transmitting instruments is passed through the primary wires of an induction coil, and the receiving instruments are placed in circuit with the secondary wire. In this way free earth communication is secured at either end of the circuit, and the musical signals produced by the manipulation of any key are received at all the stations upon the line. The great objection to this plan is the extreme complication of the parts and the necessity of employing local and main batteries at every station. It was also found by practical experiment that it was difficult, if not impossible, upon either of the plans here shown, to transmit simultaneously the number of musical tones that theory showed to be feasible. Mature consideration revealed the fact that this difficulty lay in the nature of the electrical current employed, and was finally obviated by the invention of the _undulatory_ current.