THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 





[SIXTH SERIES.] 



. — r 

 APRIL 190 



XXXVIII. The Conductivity produced in Gases by the aid 

 of Ultra- Violet Light. By John S. Townsend, M.A. } 

 Wyheham Professor of Physics , Oxford*. 



i 



[Plate IX.] 



N a former paper f on this subject, I gave an account of 

 some experiments which were made with a view to 

 finding the nature o£ the conductivity which is obtained when 

 ultra-violet light falls on the negative electrode in a gas. 

 The results confirmed the theory of the genesis of ions by 

 collision which had been previously deduced J from experi- 

 ments with Rontgen rays and from Stoletow's experiments. 

 It was also shown that the negative ions thus produced in a 

 gas are identical with the negative ions set free from the 

 electrode by the action of the ultra-violet light. The gases 

 which were examined were air, carbonic acid^ and hydrogen. 



I propose in this paper to give the results of some experi- 

 ments which I have made with hydrochloric acid gas and 

 water vapour, and to compare the results with those obtained 

 with the other gases. In all cases the same general theory 

 affords an explanation of the phenomena, and we are led to 

 conclude that negative ions are generated in air, carbonic 

 acid gas, hydrogen, water vapour, or hydrochloric acid gas. 

 which are all identical with the negative ions set free from a 

 zinc plate by the action of the ultra-violet light. 



* Communicated by the Author. 



f Phil. Mag. June 1902. J Ibid. February 1901. 



Phil. Mag. S. 6. Vol. 5. No. 28, April 1903. 2 D 



