﻿Thermions from the Salts of the Alkaline Earths. 123 



than those of the alkali metals. It seemed advisable, how- 

 ever, to terminate these tests temporarily with an examination 

 of the salts of the alkaline earths and to devote a part of the 

 available time to experiments suggested by recent investi- 

 gations of Garrett and of Horton. The results of these latter 

 experiments appear in another paper. The present paper 

 includes an account of determinations of ejm for the positive 

 thermions from various salts of barium, strontium, calcium, 

 and magnesium. 



Experimental Method. 



The method by which these determinations have been 

 made is that which Richardson devised for determining the 

 specific charge of the positive thermions from different 

 metals, and which w T as used by him in determining the same 

 characteristic for the positive thermions from the salts of 

 alkali metals in the experiments mentioned above. The 

 rationale of this method together with a detailed description 

 of the apparatus may be found in an article by Richardson 

 in the Philosophical Magazine for Nov. 1908. It will be 

 unnecessary in the present case, therefore, to give more than 

 the essential features of the method and a few words con- 

 cerning certain alterations in the apparatus. 



In the schematic diagram (fig. 1) AA and BB represent 



Vcac^o 



sections of the parts of a parallel plate condenser. A slot 

 with its length normal to the plane of the drawing is cut in 

 the plate AA to admit the platinum strip C. C carries on 



