File:Circuit diagram of d'Arsonval's high frequency apparatus. Wellcome M0014860.jpg

English: High frequency oscillator designed by French physician and pioneering biophysicist Jacques Arsene D'Arsonval for electrotherapy treatment. Beginning in 1889 D'Arsonval did the first experiments on application of high frequency current to the human body, and discovered that frequencies above 10 kHz did not cause the sensation of electric shock, but seemed to have beneficial effects. This circuit consists of a resonant circuit made of two Leyden jar capacitors (B) and an inductor (coil of wire) (C), excited by a spark gap (A) powered by a Ruhmkorff coil (P,S). Sparks across the spark gap would excite resonant oscillating current in the tuned circuit. The high frequency currents generated, 20,000 to 30,000 volts at 100 kHz to 2 MHz at ~100 mA were applied to the patient's body by electrodes attached to either end of the coil (D). By the turn of the century, application of high frequency currents to the body evolved into an early medical field called electrotherapy, and "D'Arsonval currents" were used to treat a wide variety of ailments. After electrotherapy declined in the 1920s the circuit was used in diathermy devices to apply deep heat to body tissues.