Nikola Tesla Books
HIGH FREQUENCY APPARATUS and still obtain effects bordering upon the marvelous. When the electric current is made to oscillate or change its direction of flow several thousand times per second, it partakes of some astonishing characteristics. All of the preconceived theories of electricity as applied to the commercial current are overthrown and the phenomena exhibited are contradictory in the extreme to the conventional ideas the everyday electrical worker. For example, if an alternating current of the commercial sort having a frequency of 60 or 125 cycles per second, be passed through the human body, a muscular contractive effect is produced and the sensation of an electric "shock" is felt. If the voltage of the applied current should be higher than the hundred mark, the shock is unpleasant and perhaps dangerous; let it reach 1,000 volts or perhaps even half that amount, and the shock is in most cases fatal. On the other hand, if the current be made to oscillate or change its direction of flow with a frequency of 10,000 or more cycles per second, it may be applied to the body without danger or even discomfort at potentials running well into the tens of thousands. Let the frequency be increased still further, say into the millions, and the sensation of shock and muscular contraction is quite absent. Its place is taken by one of gentle warmth. Spectacular Demonstrations.-The importance of this one peculiarity alone will be appreciated by those who have seen the self-styled electrical marvels upon the stage. Their claims to the effect that they are "taking thousands of volts through their bodies" are perhaps well founded for the presence of a spark several inches long is pretty good evidence of a very high potential. It is usually conceded that every inch of spark between points through the air represents a potential of between five and ten thousand volts. The secret of the performer's apparent power
