﻿146 Mr. Clinton J. Davisson : Role Played by Gases 



magnetic deflexion of the ions and the maxima draw nearer 

 together. This, of course, causes an apparent decrease in the 

 value of ejm. 



The effects produced by hydrogen and carbon dioxide were 

 found to be similar to those produced by air, except that, as 

 was to be expected on account of the differences in molecular 

 weights, hydrogen produced a smaller effect, at a given 

 pressure, than air, while carbon dioxide produced a greater. 

 This relation is clearly exhibited by the curves, fig. 2, which 



Fig-. 2. 



—pressure-* 



coordinate apparent values of e/m and pressures for the 

 different gases investigated. The curves near the top of the 

 figure are for the emission from the sample of aluminium 

 phosphate. The scale of pressures is in millimetres, as 

 indicated, except in the case of the dotted curve marked 

 " H 2 " for which the scale of pressures is in centimetres. 

 The single curve near the bottom of the figure is for a sample 

 of calcium sulphate which was used in a preliminary 

 experiment. It is interesting to note that in this case the 

 apparent decrease in the value of e/m is less for a given air 

 pressure than in the case of the sodium emission from alu- 

 minium phosphate. This, of course, is what one would 

 expect on account of the difference in mass of the ions. 



