involved in the Formation of Complex Atoms. 121 



equation. The evaluation of this integral gives the value 

 l/2a, so 



— 47rac 2 

 The mass represented by this value of Gr is 



Am= + 



— 4:7TG 2 a ' 



where Am is the change of mass due to the overlapping of 

 the fields of the electrons. Now the longitudinal mass is 



1 6tt C 2 R' 



where R=the radius of the electron. By division 



Am _ 3R 



mi 2a ' 



If Am is expressed in ordinary units, and a is replaced 

 by d/2, where d is the total distance apart of the electrons, 



2e 2 



and the total mass of a positive and a negative electron is 



2 /e 2 . e 2 3e* 



2^ /£ e_ &r\ 



< +e -~ 3c 2 \R r dF 



m 

 or in a general form 



This equation in the form last given was derived by 

 Nicholson in a paper presented to the London Physical 

 Society on February 26, 1915 *, almost the same time 

 that the paper by the authors was sent to the National 

 Academy. Nicholson derived the equation in a different 

 manner. He points out the fundamental nature of this 

 equation, and states that the effect of mutual mass must be 

 considered in practically all of the work on the structure 

 of atoms. 



It may be well to consider here one or two points of 

 Nicholson's paper which seem to be open to question. It is 

 difficult to see how even the elements supposed to exist in 



* Proc. Pbys. Soc. London, xxvii. pp. 217-229 (April 15, 1915). 



