

High Frequency Electric Discharges. 148 



Prof. Eliha Thompson. The secondary of this coil consisted 

 of 500, turns of No. 26 S.W.G. cotton-covered wire wound 

 on a paper tube. Outside this paper tube was a glass tube, 

 upon which the primary, consisting of 10 turns of three 

 No. 16 guttapercha-covered wires, in parallel, was wound. 

 The whole coil was immersed in resin oil contained in a 

 wooden trough. The ends of the secondary were connected 

 through small glass tubes, also filled with oil, to brass balls. 



On approaching the hand to one of the balls forming the 

 terminals of the oil-coil, sparks shot out from the brush dis- 

 charge which surrounds it. If the spark is taken on the skin 

 a sharp prick is felt, but on approaching the terminal or 

 touching it with a piece of metal grasped in the hand, or after 

 grasping the terminal itself, practically no appreciable sensa- 

 tion is felt. If the terminal is grasped in this manner with 

 the right hand, sparks will shoot out from the left hand or 

 indeed from any portion of the body, if brought into proxi- 

 mity with another person, a piece of metal, the gas- or water- 

 pipes, or any conducting body. In the experiment referred 

 to the incandescent lamp was hung by one terminal on a 

 wire connected to earth, and connexion was made between 

 the other lamp terminal and the coil through the two arms 

 and body by the right hand being brought into contact with 

 one terminal of the oil-coil, and a piece of metal grasped in 

 the left hand being approached to the free terminal of the 

 lamp. At the first approach the bulb of the lamp became 

 filled with phosphorescent light, but, on reducing the distance 

 between the metal in the left hand and the free lamp ter- 

 minal, sparks shot out between them and the filament at once 

 became incandescent — the incandescence increasing very 

 nearly to the full normal amount when the piece of metal 

 and the lamp terminal were finally brought into contact. 



To produce a similar incandescence of the filament with 

 continuous or alternating currents of ordinary frequency 

 would require about one fifth of an ampere, and at first sight 

 it would seem that this quantity of current must pass through 

 the arms and body of the operator. 



It has been generally assumed that with high-frequency 

 currents the current is rendered harmless by reason of the 

 high frequency — in fact, that high frequency renders harmless 

 to the human body currents of a strength that would be 

 dangerous and painful, if not fatal, were the frequency lower. 

 The writer is inclined to think that another explanation is 

 possible, and that the true fact is, not that high frequency 

 renders harmless a given strength of current that with ordinary 

 frequency would be harmful, but that with high frequency 

 it is possible to obtain effects with exceedingly small currents. 



