Experiments with High Frequency Discharges. 301 



exhausted tubes by high-frequency discharges, the following 

 experiment may be mentioned. 



A glass tube, two feet in length and two inches in 

 diameter, exhausted to the extent usual in ordinary incan- 

 descent lamps, was supported at its ends on two glass in- 

 sulating pillars. Outside of the tube were wound three turns 

 of fine copper wire, so as to form a coarse pitch spiral, one 

 end of which was connected to the one pole of the high- 

 frequency coil, the other pole of the coil and the other end of 

 the wire spiral being free. 



On starting the coil the wire spiral became luminous, of a 

 dark reddish-purple colour, while there immediately appeared 

 a second bright blue spiral inside the tube, this second spiral 

 keeping exactly half-way between the adjoining turns of the 

 wire. The effect appears to be due to the violent repulsion of 

 the molecules of residual air in the tube, and their bombard- 

 ment of the tube on the other side. 



In the annexed illustration (fig, 1), which is from a photo- 

 graph of the tube taken when in action in a dark room, the 



Fig. 1. 



brighter of the two spirals is the wire, which, though to the 

 eye fainter than the bombardment spiral, appears to be the 

 most strongly actinic. The other fine lines are due to re- 

 flexion. 



The writer has already, in the Philosophical Magazine for 

 February (p. 143), shown how it is possible to incandesce 

 the filaments of ordinary electric lamps with high-frequency 

 currents conveyed through the human body, and has given 

 reasons for believing that the quantity of high-frequency 

 current necessary for this purpose must be much smaller than 

 the quantity of continuous current required to produce a 

 similar effect. The following experiment appears to be in 

 further proof of this. 



One pole of the coil being connected to one terminal of a 

 5 c.-p. 100-volt incandescent lamp, two short wires were 

 connected respectively to the other terminal of the lamp and 

 the other pole of the coil and arranged so that their free ends 



