THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] 



NOVEMBER 1916. / ffl 



2 



XL VIII. The Mobility of the Negative Ion. 

 By S. Ratner, of the University of Petrograd*. 



IT is well known that in general the mobility (k) of a 

 gaseous ion varies inversely as the pressure (p), so that 

 the product kp is constant for a given gas, but at low 

 pressures the mobility of the negative ion becomes abnormally 

 great, and kp increases rapidly with diminution of pressure. 

 The phenomenon of the abnormal mobility of the negative 

 ion has been studied by a large number of experimenters. 

 Langevin f, Kovarik J, Lattey §, and others could observe 

 the abnormal increase of the mobility only in the case when 

 the pressure was reduced below a certain value (75-200 mm.) 

 and therefore assumed the existence of a " critical " pressure 

 at which the abnormality sets in. Frank || , and later Haines U, 

 have shown that in carefully purified nitrogen, argon, 

 helium, and hydrogen, the mobility of the negative ion is 

 abnormally great, even at atmospheric pressure. Kovarik 

 and Lattey (loc. eit.) drew attention to the fact that at low 

 pressure the mobility of the negative ion varies with the 

 electric force. J. S. Townsend** has shown that the mobility 

 of the negative ion may in general be expressed as a function 



* Communicated by Sir J. J. Thomson, O.M., F.E.S. 

 t P. Langevin, Annates de Ch. et de Physique, xxviii. (1903). 

 X Kovarik, « The Physical Review,' xxx. p. 415 (1910). 

 § It. T. Lattey, Proc. Rov. Soc. A, lxxxiv. p. 173 (1910). 

 || Frank, Verh. d. D. Phi/s. Ges. xii. pp. 221 & 613 (1910). 

 H Phil. Mag. xxx. p. 503* (1915). 



** J. S. Townsend, 'Electricity in Gases.' Oxford, 1915. 

 Phil Mag. S. 6. Vol. 32. No. 191. Nov. 1016. 2 H 



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