406 



Mr. K. H. Kingdon 



represented by the straight line OP in the figure. If we 

 diminish the ordinates of OA try the corresponding ordinates 

 of OP we obtain the curve OB, which is the ionization- 

 pressure curve for the remaining components. 



Fig. 5. 



100 200 300 400 

 Pressure in mm. of Hg 



500 600 700 800 



Again, on the above theory of ionization by thermal 

 collisions, the number of ions produced per c.c. per second 

 varies as the square of the number of molecules per c.c, and 

 therefore as the square of the pressure. Hence the pressure- 

 ionization curve for this component may be represented by 

 the curve OQ. By diminishing the ordinates of OB by the 

 corresponding ordinates of OQ, the curve OC is obtained, 

 which is the pressure-ionization curve for the radiation from 

 the walls of the chamber. This curve shows a very pro- 

 nounced maximum at a pressure of 550 mm. ; and it is evident 

 that if it is possible for a curve such as OC to represent 

 correctly the pressure-ionization curve for a soft radiation, 



