Force of the Electric Discharge through Gases. 447 



netic deflexion of the discharge in hydrogen very small, in 

 air many times larger, but less than in carbonic acid gas. 



This is what the explanation given above would lead one to 

 expect, since all the causes mentioned above as tending to 

 prevent deflexion are, so far as we know them, greatest for 

 hydrogen and least for carbonic acid gas. 



In this connexion I may mention that McClelland finds 

 the velocity of the ions produced by an electric discharge 

 many times — five or six — greater in air than in carbonic 

 acid gas, and though he has not yet made a determination 

 for hydrogen, there is no doubt the velocity of the ions in it 

 is much greater than in any other gas. Cf. the velocities 

 found by Rutherford for the ions produced by Rontgen rays 

 (Phil. Mag. vol. xliv. p. 434, 1897). 



Experiments on the Frequency of Discharge. 



In most of the above experiments, in order to make the 

 discharge as steady and regular as possible, a tuning-fork 

 mercury interrupter was employed for breaking the current 

 in the primary of the induction-coil, instead of the ordinary 

 vibrating contact interrupter belonging to the coil. 



Some experiments were made to find whether, by increasing 

 the pitch of the fork used for interrupting the current in the 

 primary coil circuit, the frequency of the discharge could not 

 be increased sufficiently to enable even the abrupt, short dis- 

 charges to be deflected. These experiments, however, were 

 not a success, as the induction-coil would not work with a 

 fork making more than about 120 complete vibrations per 

 second, and for a fork of this pitch the action of the coil was 

 very weak, even when a dangerously high electromotive force 

 was used in the primary circuit. The vibration frequency of 

 the interrupter belonging to the coil was about 60 per second. 



In these abrupt discharges the time between successive dis- 

 charges is practically the same as the time of vibration of the 

 interrupter in the primary circuit of the induction-coil, since 

 each discharge is almost instantaneous, whereas in the ordinary 

 discharge the current begins gradually in the discharge-tube, 

 rises to a maximum, and falls away gradually again, in accord 

 with the rise and fall of electromotive force in the secondary 

 of the coil. In this way the interval between successive dis- 

 charges during which the ionized path through the gas may 

 be destroyed is diminished, and when the resistance in the 

 discharge circuit is small — when the pressure of the gas in 

 the discharge-tube is low — this interval may become small 

 compared with the time of vibration of the interrupter in the 

 primary-coil circuit. 



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