Nikola Tesla U.S. Patent 725,605 - System of Signaling Patent Wrapper Page 21

1 T 1 J 3 J 3 Sub. Oper. powerful electrical disturbances upon sensitive receivers extends, even on land, to distances of many hundreds of miles and consequently, in accordance with theory, still farther on sea. To overcome these drawbacks and to enable a great number of transmitting and receiving stations to be operated, selectively, and exclusively, without any danger of the signals or messages being disturbed or intercepted, or interfered with in any ways, is the object of my present improvement. Broadly stated, my invention involves the employment of means for generating two or more kinds or classes of disturbances, waves or impulses of distinctive character, with respect to their effect upon a receiving apparatus, and a distinct receiver which comprises two or more elements, severally responsive to the different disturbances or impulses, and which is dependent for operation upon the conjoint or resultant action of two or more of such elements. By employing only two kinds of disturbances or impulses instead of as has heretofore beer done, to operate a receiver, I have found that safety against the disturbing influences of other sources is increased to such an extent, that I believe this number to be amply sufficient in most cases for rendering the exchange of signals or messages between two stations quite reliable and exclusive, but in exceptional instances, a greater number may be used, and a degree of safety against extraneous interference attained such as is comparable to that afforded by a combination lock. The liability of a receiver being affected by dis-3This page retyped from microfilm for better readability - Ed.] 635