The Motion of Ions and Electrons through Gases. 33 



To the Editors of the Philosophical Magazine. 



Foxcombe, 

 ~ near Oxford. 



Gentlemen, — 



By courtesy of the Editors I have been permitted to see 

 Mr. Snorter's letter. 



The limitation to which proposition (6) is subject is ex- 

 plicitly stated in the first two paragraphs of p. 268 of my 

 paper. I am disposed to think that had Mr. Shorter realised 

 the importance of these paragraphs, the irrelevance of his 

 criticisms would have been apparent. 



I am, 



Yours faithfully, 



April 11th, 1917. BERKELEY. 



III. The Motion of Ions and Electrons through Gases. By 

 E. M. Wellisch, Lecturer in Applied Mathematics at the 

 University of Sydney *. 



1. Introduction. 



THE experiments described in the present paper were 

 carried out in the Sloane Laboratory of Yale University, 

 and are a continuation of those which have already been 

 described in the American Journal of Science for May 1915. 

 In determining the mobility (k) of the ion as a function of 

 the pressure (p) of the gas, previous investigators had found 

 that the product pk showed an abnormal increase as the 

 pressure of the gas was reduced. This result had been inter- 

 preted as indicating a diminution in the size and mass of the 

 ion at relatively low pressures ; for the negative ion in air this 

 diminution appeared to set in at pressures below 10 cm., 

 while for the positive ion it did not occur till the pressure was 

 reduced below 1 mm. 



The investigation to which reference has already been 

 made provided experimental and theoretical indications which 

 were entirely different from the foregoing. For the posi- 

 tive ion in air no anomalous results were found ; the law 

 pk = const, held good to the lowest pressure employed 

 (*05 mm.). The negative carriers were found to consist of 

 two distinct kinds, electrons and ions, the former coming 

 more and more into evidence as the pressure of the 



* Communicated by the Author. 

 Phil. Mag. S. 6. Vol. 34. No. 199. July 1917. D 



