THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] J^V" 



.U. WM 

 MARCH 1899. V. „ r fpV 



XIX. On the Theory of the Conduction of Electricity through 

 Gases by Charged Ions. By J. J. Thomson, M.A., F.R.S., 

 Cavendish Professor of Experimental Physics, Cambridge*. 



rilHE electrical conductivity possessed by gases under cer- 

 JL tain circumstances — as for example when Rontgen or 

 uranium rays pass through the gas, or when the gas is in a 

 vacuum-tube or in the neighbourhood of a piece of metal 

 heated to redness, or near a flame or an arc or spark-discharge, 

 or to a piece of metal illuminated by ultra-violet light — can be 

 regarded as due to the presence in the gas of charged ions, 

 the motions of these ions in the electric field constituting the 

 current. 



To investigate the distribution of the electric force through 

 the gas we have to take into account (1) the production of 

 the ions ; this may either take place throughout the gas, or 

 else be confined to particular regions ; (2) the recombina- 

 tion of the ions, the positively charged ions combining with 

 the negatively charged ones to form an electrically neutral 

 system ; (3) the movement of the ions under the electric 

 forces. We shall suppose in the subsequent investigations 

 that the velocity of an ion is proportional to the electric 

 intensity acting upon it. The velocity acquired by an ion 

 under a given potential gradient has been measured at the 

 Cavendish Laboratory by several observers — in the case of 

 gases exposed to the Rontgen rays by Rutherford and 

 by Zeleny; for gases exposed to uranium radiation or to 



* Communicated by the Author. 

 Phil. Mag. S. 5. Vol. 47. No. 286. March 1899. T 



