Nikola Tesla U.S. Patent 725,605 - System of Signaling Patent Wrapper Page 36

650 Subsfac. \ful adjustment of the same, these objects may be in a measure attained, but in long experience I have found that notwithstanding all constructive advantages and experimental resources, this method is in many cases inadequate. Thus, while I have. succeeded in so operating, selectively, under certain favorable conditions, more than one hundred receivers, in most cases it is practicable to work successfully but a few, the number rapidly diminishing, either owing to great distance or other causes, as the energy available in the tuned circuits becomes smaller, and the receivers consequently, necessarily more delicate. Evidently a circuit, however well constructed and adjusted to 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 advan.- tage 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 theory, still farther on sca. To overcome these drawbacks and to enable a great number of transmitting and receiving stations to be operated, -2