Nikola Tesla U.S. Patent 645,576 - System of Transmission of Electrical Energy Patent Wrapper Page 58

176 same which are liable to be approached, touched or handled, will be at or nearly the same potential as the adjacent portions of the ground, this insuring, both in the transmitting and receiving apparatus, and regardless of the magnitude of the electrical pressure used, perfect personal safety, which is best evidenced by the fact, that although such extreme pressures of many millions of volts have been for a number of years continuously experimented with, no injury has been sustained, neither by myself or any of my assistants. The length of the thin-wire coil in each transformer should be approximately one quarter of the wave length of the electric disturbance in the circuit, this estimate being based on the velocity of propagation of the disturbance through the coil. itself and the circuit with which it is designed to be used. By way of illustration, if the rate at which the current traverses the circuit including the coil, be one hundred and eighty-five thousand miles per second, then a frequency of nine hundred and twenty-five per second would maintain nine hundred and twenty-five stationary waves in a circuit one hundred and eity-five thousand miles long, and each wave would be two hundred miles in length. For such a low frequency, to which I shall resort only when it is indispensible to operate motors of the ordinary kind, under the conditions above assumed, I would use a secondary of fifty miles in length. By such an adjustment or proportioning of the length of wire in the secondary coil or coils, the points of highest potential are made to coincide with the elevated terminals D, D', and it should be understood that, whatever length be given to the -9This page retyped from microfilm for better readability - Ed.