Nikola Tesla Books
140 HIGH FREQUENCY APPARATUS is no electrical connection between the two in the case of certain forms of apparatus and, owing to the fact that nothing but the current of high frequency would induce another current in the secondary of this transformer-due to the absence of an iron core-there is no danger whatever of the patient receiving a shock of low frequency current from the secondary terminals. The generation of the high frequency current having been explained, the method of adapting it to the various electrodes and their uses will next be considered. Disregarding for the moment the effects of the various frequencies upon the body, we may turn our attention to the broad classifications given by the manufacturers of apparatus to the currents produced. The classes are in the main but three: the Tesla or high potential current, the D'Arsonval or medium potential current, and the thermo, or as it is sometimes called, the diathermic current which is of comparatively low voltage as high frequency currents go. In order that the respective uses of the three currents may be the more fully understood, it is proposed to treat them under their proper headings. The High Potential or Tesla Current.-This current is that taken from the terminal of the post which tops the high frequency apparatus and it is generally applied through a vacuum electrode of glass which is held in an insulated handle of suitable form. The application is quite without pain, and, in fact, without much of any sensation other than gentle warmth, unless the electrode is lifted from the skin in which case the resultant spark is rather painful. Therefore, one of the first points for the operator to impress upon his mind is the fact that the electrode should never be applied or taken from the patient without the operator placing his own hand upon the glass to divert the current from the patient. The entire success of the electro
