Nikola Tesla U.S. Patent 649,621 - Apparatus for Transmission of Electrical Energy Patent Wrapper Page 8

C J 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 moves in a circuit one hundred and eighty-five thousand miles long, and each wave would be two hundred miles in length. For such a low frequency, which would be resorted to only when it is indispensable for the operation of 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 D¹, and it should be understood that, whatever length be given to the wires, this requirement should be complied with in order to obtain the best results. P It will be readily understood, that when the above prescribed relations exist, the best conditions for resonance between the transmitting and receiving circuits are attained, and, owing to the fact that the points of highest potential in the coils or conductors A A are coincident with the elevated terminals, the maximum flow of current will take place in the two coils, and this further, 3 205