[ 49 ] 
II. Electrical Conductivity in Gases Traversed by Cathode Rays. 
By J. C. McLennan, Demonstrator in Physics, University of Toronto. 
Communicated by Professor J. J. Thomson, F.R.S. 
Received December 7, 1899—Read February 1, 1900. 
Though it has been known that a gas becomes a conductor when traversed by cathode 
rays, yet the laws connecting this electrical conductivity have not hitherto been 
studied. 
The theory has been put forward by J. J. Thomson and Rutherford^ that when a 
gas becomes a conductor under a radiation, it does so in virtue of the production of 
positive and negative ions throughout its mass. This view has been established by 
their experiments on Ptontgenised gases, and confirmed by those of ZelenyI on the 
same subject. The recent work of Rutherford on Uranium Radiation^ also affords 
another example of such a process in the gases traversed. 
The object of the experiments which are described in this paper was to investigate 
the nature of the conductivity in different gases when cathode rays of definite 
strength passed through them, and to measure the number of ions produced. With 
this in view, I have worked with cathode rays produced, after the method of Lenard, 
outside the discharge tube, as these were found to be more easily dealt with than 
those inside. 
The investigation is described under the following subdivisions:— 
1. Form of tube adopted for the production of cathode rays. 
2. Ionization by cathode rays. 
3. Discharging action of cathode rays. 
4. Ionization not due to Rontgen rays. 
5. Discussion of methods for measuring the ionizations produced in different 
gases. 
6. Description of apparatus used. 
7. Explanation of the method adopted for comparing ionizations. 
8. Ionization in different gases at the same pressure. 
9. Ionization in air at different pressures. 
* ‘Phil. Mag.,’ November, 189G, p. 393. 
t ‘Phil. Mag.,’ July, 1898, p. 120. 
\ ‘Phil. Mag.,’ January, 1899, p. 109. 
VOL. CXCV.—A 263 . 
H 
3.11.1900. 
