12 



THE THEORY OF IONIZATION OF GASES 



increases in electromotive force are made, the cor- 

 responding increases of current are very small. In this 

 case the negative ions travel outwards, and only a few 

 of those produced by the rays pass through the field of 

 strong electric force, so that the number of new ions pro- 

 duced by collisions is comparatively small. Experiments 



eoo 



too 



50 



I 



SO 100 150 200 50 300 3So 4OO 



Electromotive Force. 

 Figure 5. 



on the currents between concentric cylinders have been 

 made by Mr. Kirkby, which show in a striking manner 

 the effect of changing the direction of the electric force. 

 The curves, figure 5, for air at a pressure of 3*53 milli- 

 metres give the currents between a cylinder of 4'15 

 centimetres diameter and a concentric wire of *206 

 millimetres diameter when the air is ionized by Eontgen 

 rays. 1 



P. J. Kirkby, Philosophical Magazine, February, 1902. 



