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Y. The Velocity of the Ions produced, in Gases by Rontgen Rays. 
By John Zeleny, BSc., B.A., Assistant Professor of Physics, University of 
Minnesota. 
Communicated by Professor J. J. Thomson, F.R.S. 
Received February 5,—Read March 1, 1900. 
§ 1. Introduction. 
The electrical conductivity which is imparted to gases by their exposure to Rontgen 
rays has been explained by J. J. Thomson and E. Rutherford* on the hypothesis of 
a formation of oppositely charged carriers throughout the volume of the gas. The 
motion of these carriers or ions when in an electric field constitutes the observed 
conductivity, and the recovery of the insulating property of a gas after an exposure 
to the rays is due partly to the recombination of the oppositely charged ions and 
partly to their impact with the boundaries. 
An estimate of the sum of the velocities with which the positive and negative 
ions move in air when in a unit electric field was first obtained by J. J. Thomson and 
E. Rutherford, and later E. Rutherford,! by the same indirect method, determined 
the sum of the velocities of the ions in a number of gases. This method involved 
the determination of the rate of recombination of the ions, the saturation current 
obtained through the gas by the use of a strong electric field, and the current 
obtained with some small non-saturating electric force. E. Rutherford also 
describes an experiment in which the velocities of the two ions in air were obtained 
separately by a direct method, and found to be approximately equal. The writer^ 
has since shown that in general the two velocities are not equal, and for those gases 
for which the ratio of the two velocities was determined the negative ion moved the 
faster in nearly all cases. 
The values of the velocities of the ions have recently been applied by J. J. 
Thomson§ and J. S. Townsend) | in the determination of important physical quantities, 
and it seemed desirable that a redetermination of the values of the velocities be 
* J. J. Thomson, and E. Rutherford, ‘ Phil. Mag.,’ November, 1896 
t E. Rutherford, ‘ Phil. Mag.,’ November, 1897 
X J. Zeleny, ‘Phil. Mag.,’July, 1898. 
§ J. J. Thomson, ‘Phil. Mag.,’ December, 1898. 
|| J. S. TOWNSEND, ‘Phil. Trans.,’ A, vol. 193, 1899. 
YOL. CXCV-A 266. 2 c 
9.11.1900. 
