THE 



AMERICAN JOURNALOFSCIENCE 



[FOURTH SERIES.] 



Art. I. — The Motion of Ions and Electrons through Gases ; 

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

 the Universitj of Sydney. 



1. Introduction. 



The experiments described in the present paper were carried 

 out in the Sioane Laboratory of Yale University and are a con- 

 tinuation of those which have already been described in this 

 Journal (May, 1915). In determining the mobility {h) of the 

 ion as a function of the pressure {p) of the ^as, previous 

 investigators had found that the product ^A; showed an abnormal 

 increase as the pressure of the gas was reduced. This result 

 had been interpreted as indicating a diminution in the size 

 and mass of the ion at relatively low pressures ; for the nega- 

 tive ion in air this diminution appeared to set in at pressures 

 below 10^=™ while for the positive ion it did not occur till the 

 pressure was reduced below l"""". 



The investigation to which reference has already been made 

 provided experimental and theoretical indications which were 

 entirely different from the foregoing. For the positive ion in 

 air no anomalous results were found ; the law j9^ = const, held 

 good to the lowest pressure employed ("05™""). 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 gas was reduced. WJien once this separa- 

 tion had been effected all the preceding anomalies disappeared ; 

 the law ph = const, was verified for the negative ion in air 

 from 1 atmosphere down to -15™™, indicating that the ion 

 remains unaltered in character over this range of pressures. 

 The electrons appeared to travel freely through the gas with- 

 out attaching themselves to molecules. No indication was 

 found of any intermediate stage in the nature of the negative 



Am. Jour. Sci.— Fourth Series, Vol. XLIV, No. 259.— July, 1917. 



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