Nikola Tesla U.S. Patent 723,188 - Method of Signaling Patent Wrapper Page 19

576 a' respond exclusively to vibrations of one period, is apt to be affected by higher harmonics, and still more so by lower ones. When the oscillations are of a very high frequency, the number of the effective harmonics may be large and the receiver consequently easily disturbed by extraneous influences, to such an extent that, when very short waves, such as those produced by Hertzian spark apparatus, are used, little advantage in this respect, is derived from tuning the circuits. It being an imperative requirement in most practical applications of such systems of signalling or intelligence transmission, that the signals or messages should be exclusive or private, it is highly desirable to do away with the above limitations, especially in view of the fact which I have observed, that the influence of powerful electrical disturbances upon sensitive receivers extends, even on land, to distances of many hundreds of miles and consequently, in accordance with the ory, still fart her on sea. To overcome these drawbacks and to enable a great number of transmitting and receiving stations to be operated, selectively, and exclusively and without any danger of the signals or messages being disturbed, intercepted or interfered with in any way is the object of my present invention. Broadly stated, this invention consists in generating two or more kinds or classes of disturbances or impulses of distinctive character with respect to their effect upon a receiving circuit, and operating thereby a distant receiver which comprises two or more circuits, each of which is tuned so as to respond exclusively to the disturbances or impulses of one kind or class, and so arranged that the operation of the receiver is dependent upon their conjoint or resultant -2