Nikola Tesla U.S. Patent 723,188 - Method of Signaling Patent Wrapper Page 51

608 will be readily seen that the relay R3 will be operated only when both contacts cl and d2 are closed. D The apparatus at the sending station may be controlled in any suitable manner, as for instance, by momentarily closing the circuit of the source S, two different electrical vibrations be ing emitted simultaneously, or in rapid succession, The two reas may be desired, at each closure of the circuit. ceiving circuits at the distant station, each tuned to respond to the vibrations produced by one of the elements of the transmitter, affect the sensitive devices al and a2 and cause the relays R and R2 to be operated and contacts and c2 to be closed, thus actuating the receiver or relay R³, which in turn establishes a contact c3 and brings into action a device a3 by means of a battery d4 included in a local circuit, as shown. But evidently, if through any extraneous disturbance only one of the circuits at the receiving station is affected, the relay R3 will fail to respond. In this way a communication may be carried on with greatly increased safety against interference, and privacy of the messages may be secured. The receiving station shown in Fig. 2 is supposed to be one requiring no return nessage, but if the use of the system is such that this is necessary, then the two stations will be similarly equipped and any well known means, which it is not thought necessary to illustrate here, may be resorted to for enabling the apparatus at each xtation to be used in turn as transmitter and receiver. In like manner the operation of a receiver, as R3³, may be made dependent instead upon two, upon more than two such transmitting systems or circuits, and thus any desired degree of exclusiveness or privacy and safety against extraneous dis-7