Nikola Tesla U.S. Patent 723,188 - Method of Signaling Patent Wrapper Page 40

fell from its normal rate render the impulses intelligible, but if the operator change at will the period of either circuit alternately, the actuation, or failure of actuation, of an intercepting receiver tuned to a normal rate, will convey no intelligence whatever. For its operation or control is not in any way dependent upon the signal, but upon the mere caprice of the sender. To illustrate another way, perhaps more convenient, for attaining the same result with the apparatus shown in figure 1, the operator need only keep one of the transmitting circuits energized during an arbitrary time interval while he uses the other in the ordinary way for conveying a signal. If he changes during the sending of his message fror one to the other circuit, the intercepting receiver, no matter to which of the two transmitting circuits it may be tuned, will be incapable of recording more than meaningless dashes. There are, however, other ways shown or suggested in the specification which would enable the expert to secure what may be regarded as absolute privacy, as, for example, by arranging the apparatus to vary automatically the order of succession of the impulses transmitted, or the rode in which they are made to co-operate upon the receiver, constantly during the transmission of the message. To illustrate, suppose that in an apparatus of the kind shown in figure 1, a disk, as D, is made to bring into action in any desired way transmitting circuits in groups of two or more, and that at the receiving station there are corresponding circuits which bring the receiver into action, no matter which of the trensmitting circuits are energized. It is now clear that it would be practically impossible to intercept a message, since the number of groupments and their order -4597