320 



Mr Campbell, Dmontinuities in Light Emission. 



Fig. 2 gives the relation between the potential ditferenee on one 

 of the cells and the current through it. It will be seen that very 

 complete saturation is attained : the point on the curve which is 

 marked by the cross corresponds to the P.D. actually used in the 

 observations. 



The electrodes of the two photo-electric cells Avere connected 

 with the battery of small accumulators, which provided the po- 

 tential used, in such a way that the currents through them to the 

 electrometer were opposite in sign. See fig. 3 which shows the 

 connections of the measuring circuit. 



o 



0-1 



p. D. (E.S.U.) 



0-2 



Fig. 2. 



§ 13. The electrometer employed was of the Dolezalek pattern. 

 The constants a and /3 (real for low potentials on the needle, and 

 imaginary for high potentials) were changed by altering the 

 potential on the needle. These constants were determined in the 

 ordinary way by observing the motion of the needle when dis- 

 placed from its zero position with the quadrants kept at constant 

 potential. The sensitiveness in most cases was about 10", the 

 scale being 1 1 metres distant and capable of readings to |- division. 



A tilted electroscope was also connected to the common 

 electrode of the cells. It was more convenient than the electro- 

 meter for some purposes, such as the measurement of the total 

 current through either cell. It was for such measurements that 

 the capacity box (9 x 10- to 9 x 10^) shown in fig. 3 was employed. 



