191 1-] AGGREGATES OF ELECTRONS. 365 



obtained from the spreading out of a beam of rapidly moving 

 electrons when they traverse a layer of matter. Working over such 

 material as was then available Thomson found his conclusion, that 

 the number per atom was comparable with the atomic weight, was 

 strengthened. Quite recently J. A. Crowther has made a very care- 

 ful experimental investigation covering both these lines of inquiry. 

 He finds that Thomson's calculations are borne out very satisfac- 

 torily by his experiments and that the number of electrons which 

 go to make up each atom is three times the atomic weight of the 

 element. 



PRI^'CETON University, 

 April, 1911. 



