Constitution of Atmospheric Neon. 451 



under which conditions the mixing is very bad. It may 

 therefore be said that the diffusion results are positive but 

 too small to be conclusive. 



Evidence of Positive Rays. 



This is available on three distinct counts : the character 

 of the lines, their position and their intensity. 



Character of the parabolas. 



Plato VIII. shows a dark and a light print taken from a 

 negative obtained in 1913 by Thomson's method of analysis 

 from a gas containing a large percentage of neon. The line 

 due to the lighter constituent which will be culled Ne a can 

 easily be recognized as the brightest on the plate, the Ne' 3 

 i. e. 22 line being the fainter one immediately below it. It 

 can easily be seen that the latter possesses characteristics 

 identical in all but intensity with those of the former. As 

 has already been pointed out (' Rays of Positive Electricity,' 

 p. Ill) the prolongation of the lines towards the vertical 

 axis indicates that the particles causing them are capable of 

 carrying more than one charge; multiple charges not occur- 

 ring on molecules but only on atoms, one is led to infer 

 that both lines are due to elements. 



Position of the parabolas. 



Measurements of plates obtained in this way indicated 

 that it was probable that the lighter constituent did not 

 correspond in mass with the accepted atomic weight of 202, 

 but the accuracy was not sufficient to make this certain. 



Intensity of the jxirabolas. 



The relative intensity of the Ne a and Ne^ parabolas ob- 

 tained from atmospheric neon untreated by diffusion has 

 been estimated by three different observers as about 10 to 1. 

 Its apparent invariability is corroborative evidence against 

 the possibility of the 22 line being due to the presence of 

 other gases in the discharge-bulb. 



It will be seen that although by Thomson's system of 

 analysis the presence of two isotopes in atmospheric neon 

 was indicated by several lines of reasoning, none of them 

 can be regarded as cjuite conclusive, and it was realized that, 

 failing separation, the most satisfactory proof would be 

 afforded by measurements of atomic weight so accurate as 

 to prove beyond dispute that neither constituent corresponded 

 with the accepted atomic weight of atmospheric neon. 



