PAPEES 



OF THE 



EOYAL SOCIETY OF TASMANIA^ 



1913. 



ON THE RELATION BETWEEN THE LOSS OF 

 ENERGY AND THE lONISATION PRODUCED 

 BY CATHODE RAYS. 



By J. L. Glasson, B.A., D.Sc. 



(Read 14th April, 1913.) 



In a previous paper {Phil. Blag., October, 1911) I have 

 shown that the number of ions made by a cathode ray in 

 traversing unit length of air varies inversely as the square 

 of the velocity of the ray. If a be this number we have the 

 relation 



where A is a constant. W. Wilson has shown (Proc. Roy. 

 Soc, vol. 85, p. 240) that the law represented by equation 

 (i) holds also for the ]3 rays given out by radium. These 

 rays had a velocity as high as 2*9 x lO^*^ cm. per second. 

 The cathode rays I used had velocities as low as 3 x 109 

 cm. per second. So that the law (i) holds over a consider- 

 able range of velocities. From data given in my paper, it 

 is easy to calculate the constant //. One cathode ray moving 

 with a speed of 4*8 x 109 cm. per second makes 1*5 pairs 

 of ions per cm. of air at a pressure of 1 m.m. of mercury. 



So that for air at atmospheric pressure we find that 

 a = 1140 and A = 2*5 x lO^s. 



In a recent paper {Proc. Ilotj. Soc, April, 1912) Whid- 

 dington has shown that when cathode rays pass thi^ough 



