1892.] on Alternate Currents of High Potential and Frequency. 639 



of tbe currents from tlie machine is raised by means of an induction 

 coil. In consequence of the enormous rate of change obtainable in 

 the primary current, much higher potential differences are obtained 

 than with coils operated in the usual ways, and, owing to the high 

 frequency, the secondary discharge possesses many striking peculi- 

 arities. Both the electrodes behave generally alike, though it appears 

 from some observations that one current impulse preponderates over 

 the other, as before mentioned. 



The physiological effects of the high tension discharge are found 

 to be so small that the shock of the coil can be supported without 

 any inconvenience, except perhaps a small burn produced by the 

 discharge upon approaching tbe band to one of the terminals. 



The decidedly smaller physiological effects of these currents are 

 thought to be due either to a different distribution through the body 

 or to the tissues acting as condensers. But in the case of an induc- 

 tion coil with a great many turns the harmlessness is principally due 

 to the fact that but little energy is available in the external circuit 

 when the same is closed through the experimenter's body, on account 

 of the great impedance of the coil. 



In varying the frequency and strength of the currents through 

 the primary of the coil, the character of the secondary discharge is 

 greatly varied, and no less than five distinct forms are observed: — A 

 weak, sensitive thread discharge, a powerful jQaming discharge, and 

 three forms of brush or streaming discbarges. Each of these 

 possesses certain noteworthy features, but the most interesting to 

 study are the latter. 



Under certain conditions the streams, which are presumably due to 

 the violent agitation of the air molecules, issue freely from all points 

 of the coil, even through a thick insulation. If there is the smallest 

 air-space between the primary and secondary, they will form there 

 and surely injure the coil by slowly warming the insulation. As they 

 form even with ordinary frequencies when the potential is excessive, 

 the air-space must be most carefully avoided. 



These high frequency streamers differ in aspect and properties 

 from those produced by a static machine. The wind produced by 

 them is small and should altogether cease if still considerably higher 

 frequencies could be obtained. 



A peculiarity is that they issue as freely from surfaces as from 

 points. Owing to this, a metallic vane, mounted in one of the terminals 

 of the coil so as to rotate freely, and having one of its sides covered 

 with insulation, is spun rapidly around. Such a vane would not rotate 

 with a steady potential, but with a high frequency coil it will spin, 

 even if it be entirely covered with insulation, provided the insula- 

 tion on one side be either thicker or of a higher specific inductive 

 capacity. A Crookes' electric radiometer is also spun around when 

 connected to one of the terminals of the coil, but only at very high 

 exhaustion or at ordinary pressures. 



There is still another and more striking peculiarity of such a 



