﻿468 Dr. Norman Campbell on 



the presence of two different electrodes. I have no explana- 

 tion to offer of the effect, but it does not seem to prevent the 

 conclusion that the delta rays from aluminium and from 

 gold excited by the same alpha rays are the same both in 

 quantity and in quality. Several other experiments of a 

 similarly qualitative nature were made and, though some 

 unexpected phenomena were found, none of the measurements 

 threw the smallest doubt on that conclusion. At length it 

 appeared desirable to investigate the matter quantitatively 

 by the aid of the detailed theory of Townsend ; for this 

 purpose more accurate and more extensive measurements 

 were required. 



Pabt II. 

 Quantitative Measurements. 



6. In the experiments of Townsend, the theory of which 

 is examined in the previous paper (Phil. Mag. March 1912, 

 p. 400), the distance between the electrodes and not the 

 pressure of the gas was altered. It appeared more convenient 

 here to change the pressure of the gas and not the distance 

 between the electrodes. An algebraic transformation suffices 

 to reduce the equations to a suitable form. Adopting the 

 notation of the previous paper, 



V V 



let n / = n l, fju=fi l, af = a l, v = N 7, — =?/, — = c. 



Then (13) becomes 



i/ e=e ,P^n 1+ n'(^+e'jje-^_^. . . (1) 



(15) becomes /jl = ci / e~ IJC , (2) 



(16) becomes a f =ve~ vc , (3) 



(18) becomes log fju-\- fxc — log v — vc (4^ 



It will be seen that if i, n, n', p are measured for a sufficient 

 number of values of ?/, it will be possible to determine the 

 constants v and V'. 



The Experiments. 



7. The experiments were carried out in the apparatus 

 already described. The gas used was air dried by P 2 5 . 

 The pressure was read by a McLeod gauge calibrated ex- 

 perimentally. The different ratios (15, 20, 40, 200, 1000) 

 were compared among themselves, and their relative values 



