Electrical Conductivity in Gases traversed hy Cathode Rays. ,375 

 The following Papers were read : — 



I. " The Circulation of the Surface Waters of the North Atlantic 

 Ocean." By H. N. Dickson. Communicated by Sir John 

 Murray, F.R.S. 



11. " On Cerebral Anaemia and the Effects which follow Ligation of 

 the Cerebral Arteries." By Dr. Leonard Hill. Communi- 

 cated by Dr. MoTT, F.E.S. 



II L " The Influence of Increased Atmospheric Pressure on the Circula- 

 tion of the Blood. Preliminary Note." By Dr. Leonard 

 Hill. Communicated by Dr. Mott, F.R.S. 



IV. " Contributions to the Comparative Anatomy of the Mammalian 

 Eye, chiefly based on Ophthalmoscopic Examination." By Dr. 

 G. L. Johnson. Communicated by Dr. Gadow, F.R.S. 



The Society adjourned over Ascension Day to Thursday, May 31. 



*' 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.RS. 

 Received December 7, 1899— Read February 1, 1900. 



(Abstract.) 



The object of the experiments which are described in this papei^ 

 was to investigate the nature of the conductivity produced in different 

 gases when cathode rays of definite strength passed through them. 



In a series of papers,"^ Professors J. J. Thomson and Rutherford 

 have recently shown that gases become conductors, when traversed 

 either by Rontgen or by uranium rays, owing to the production of 

 positive and negative ioQS throughout their volume. 



In the present investigation cathode rays were found to impress a 

 condition of the same kind upon a gas, and laws have been de- 

 veloped which connect the absorption of these rays with the number 

 of ions produced by them in the absorbing gases. 



The investigation is described under the following subdivisions : — 



(1) Form of tube adopted for the production of cathode rays. 



(2) lonisation by cathode rays. 



(3) Discharging action of cathode rays. 



(4) lonisation not due to RontgCD rays. 



* 'Phil. Mag.,' Korember, 1896, p. 393 ; iUd., January, 1899, p. 109.. 



2 F 2 



