Danysz and Duane — Electric Charges of a- and (3-Rays. 307 



as the number of a-particles emitted per second by one gram 

 of radium alone. 



Columns 6 and 12 in the table contain the ratios of the nega- 

 tive to the positive charges projected vertically upward from 

 the little spheres. The negative charge was estimated by tak- 

 ing the difference between the minimum and the saturated 

 values of the currents, the former for field strengths of about 

 80 gauss, and the latter, 8000 gauss. The average value of the 

 ratio is '63, and, assuming that a /3-particle carries half the 

 charge of an a-particle, this corresponds to the emission in the 

 vertical direction of 3*8 /3-particles for every three a-particles. 



It must be borne in mind that some of the /3-particles come 

 from the surface of the mercury in the little spheres either by 

 reflection or as secondary rays. A rough estimate of the num- 

 ber of /3-particles due to this effect may be obtained from the 

 following experiment. A. very small thin-walled sphere of 

 glass was filled with emanation, but no mercury was allowed 

 to flow into it. On measuring the charges with this sphere as 

 the source of rays the following ratios were found : 



Charge + *52, -535, -52, -485, -485, -48 ; average -505 



which corresponds to three /3-particles for every three a-parti- 

 cles. In this experiment there was no metal in the immediate 

 neighborhood of the sphere. On placing a small sheet of brass 

 about l mm thick close under the sphere, however, the ratio was 

 found to increase, the values being 



Charge =F '605, -615, -625, *61 ; average *615. 



This is approximately the ratio obtained with mercury in the 

 sphere. 



From these experiments we conclude that the number of 

 /3-particles emitted by the emanation and radium ABC, and 

 capable of traversing the thin walls of the spheres, is about 

 equal to the number of a-particles emitted in the same length 

 of time.* To get the total number of /3-particles actually pro- 

 jected from the active substances we must add to the above 

 those few slow /3-partieles that are known to come from radium 

 B with perhaps other slow ones that may be emitted by the 

 emanation and radium A. 



* Eutherford, Phil. Mag. 1905 ; Makower, Phil. Mag. 1909. 



