300 Ionization Curve for Alpha Rays from Polonium. 



The mercury was later removed from the apparatus by 

 means of a small tube extending through D, but not shown in 

 the diagram, and determinations made for the air-ionization 

 curve when the temperature was 330 degrees centigrade and 



Fin". 2 



the range of the alpha particles the same in the air as it was 

 in the mercury vapour. The range was made the same by 

 adjusting the pressure by means of the manometer. The 

 dotted curve I. in fig. 2 represents the air curve as deter- 

 mined under these conditions. In plotting both curves 

 corrections were made for the loss of range due to the mica 

 over the polonium. 



The full-line curves in fig. 2 represent the theoretical 

 curves for air and mercury vapour, respectively 

 sponding to the theoretical curve 



corre- 



1 = 



(r-x) ir6 



This is the theoretical curve that has been established by 

 other experiments * for air and other gases and vapours. In 

 this formula I is the ionization, c is a constant depending 

 upon the gas, r is the average range of the particles in the 

 beam, and x is the distance the particle has gone in the gas. 

 The value of r was taken as 7*1 centimetres in this case. It 



* Geiger, Proc. Roy. Soc. Series A, vol. lxxxiii. no. A. 5Qo, p. 505; 

 Taylor, Phil. Mag. April 1911. 



