Nikola Tesla U.S. Patent 723,188 - Method of Signaling Patent Wrapper Page 39

596 There are a nudber of ways by which ary desired degree of privacy may be secured, several of which we will explain somewhat in detail. Since the number of the co-operative elements may indefinitely increased, privacy could be thus secured without resorting to any other expedient. For it is evident that if the total energy transmitted be divided into a considerable. number of series of irpulses, only an instrument of extreme delicacy could be operated by, or "pick up", one of the series. That is, while the preper receiver is actuated by the energy of all the co-operative impulses, the intercepting receiver could be brought into action only by one, or at most by comparatively few, of the impulses, and to intercept a message a degree of delicacy practically unattainable would therefore be required. But with the apparatus illustrated privacy may be attained in a variety of ways without increasing the number of circuits, as, for example, by arbitrarily varying the periods of vibration of either of the transmitting elements. Referring to figure. 1, suppose the circuit of the source S be kept closed and both transmitter circuits normally excited; then the receiving circuit will be continuously energized. If now, however, the period of one of the transmitter circuits be varied, the corresponding circuit at the receiving station will cease to be energized, and the receiver will be affected thereby. Thus the arbitrary variation of the period of one of the transmitting circuits produces the same effects upon the receiver as opening or closing the circuit S. Even now, a receiver tuned to the ordinary rate of the varying transmitter circuits would by its failure to operate as the period of the transmitter rose or -3