THE 



LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



NOVEMBER 189!). 



XLIV. On the Velocity and Mass of the Ions in the Electric 

 Wind, in Air. By A. P. Chattock, Professor of Physics, 

 University College, Bristol* . 



IT is a generally accepted theory of what happens when a 

 sharp point discharges electricity through a non-conduct- 

 ing gas onto a smooth metal plate, that the strong field at the 

 point dissociates the gas into + and — ions, and that a one- 

 way flow of the ions of like sign to the point thereupon ensues 

 from point to plate. 



Rutherford (Phil. Mag. Nov. 1897) has measured the 

 velocity of ions dissociated in gases by Rontgen and by 

 uranium rays, and finds that for air the sum of the + and — 

 velocities in a field of one volt per centimetre is 3 '2 centi- 

 metres per second. Zeleny (Phil. Mag. July 1898) has since 

 shown that the ratio of the velocity of the negative to that 

 of the positive ions in the same field is 1*25 for air. 



One object of the present paper is to show that the ions 

 dissociated at a sharp point in air are probably identical with 

 those studied by Rutherford and Zeleny. 



Theory of the Method. 



Let B, fig. 1, be a sharp positively electrified metal point 

 in a non-conducting gas, opposite and at distance z from an 



* Communicated by the Author. A small portion of this paper was 

 read at the Bristol Meeting of the British Association last year. 



Phil. Mag. S. 5. Vol. 48. No. 294. Nov. 1899. ' 2 F 



