Nikola Tesla Books
138 HIGH FREQUENCY APPARATUS voltage of the current induced in the second wire is in direct proportion to the ratio between the numbers of turns of wire in the first and second coils. Therefore, if the first coil contains one hundred turns and the second coil one thousand turns, the voltage induced in the second coil will be ten times that applied to the first. Accordingly, let us assume that in our transformer there are one hundred turns of wire in the first coil or primary, as it is called, and thirtyfive hundred turns in the second coil or secondary. If we impress a voltage of 110 on the primary we shall have a voltage of thirty-five times 110 or 3850 volts at the secondary terminals. This high voltage makes it necessary to employ highly specialized methods of insulating the windings of the transformer for the tendency of the very high potential current is to leap through the air for a fraction of an inch or to tear its way through even the best of insulators unless they present sufficient resistance to its passage. We shall next see how this high voltage is applied to the operation of the apparatus and what measures are taken to safeguard the patient from the dangerous current. We have learned that the alternating current, after entering the apparatus within the instrument case, is transformed or stepped up in voltage to a value perhaps hundreds of times as high as that at which it enterd the instrument. This voltage would prove dangerous or fatal under certain circumstances if it were applied to the body of a patient in its existing state. Before it can be used, therefore, it must be converted to a current of very high frequency, i. e., one which changes its direction of flow hundreds of thousands or perhaps even a million times per second. The astonishing characteristic of such a current is that it may be applied to the human body in quantities which would prove fatal if the current were of the commercial frequency.
