Argon and Helium when submitted to Electric Discharge. 257 



February 13, 1896. 



Sir JOSEPH LISTER, Bart,, President, in the Chair. 



A List of the Presents received was laid on the table, and thanks 

 ordered for them. 



The following Papers were read : — 



I. " On the Behaviour of Argon and Helium when submitted 

 to the Electric Discharge." By J. N. Collie, Ph.D., 

 F.R.S.E., and William Ramsay, Ph.D., F.R.S. Received 

 February 4, 1896. 



The experiments to be described fall into two classes; the first 

 series relates to the distance through which electric sparks from an 

 induction coil will strike through argon and through helium at 

 atmospheric pressure contrasted with the length of the spark-gap in 

 other gases ; and also with the pressures at which the spark-discharge 

 changes into a ribbon-like discharge in different gases. The second 

 series, which was made with the object of ascertaining how much 

 of one gas is detectable in its mixture with another, at different 

 pressures, deals with the spectra of gases in electrodeless vacuum 

 tabes. As both sets of phenomena relate to the passing of electric 

 discharge through gases, we have thought it well to consider them 

 together. 



The attention of one of the authors was drawn to the spark-gap, as 

 a possible means of obtaining information regarding the atomicity of 

 argon and helium, by Mr. batterer, who was kind enough to send 

 copies of his paper on the subject (' Wied. Ann.,' 1889, p. 663). 

 batterer's conclusion, drawn from a great many experiments, was 

 that the spark-gap at atmospheric pressure varied in length inversely 

 as the atomicity of the gas ; thus, in mercury gas, which is acknow- 

 ledgedly monatomic, the distance traversed by a spark from electrodes 

 of approximately constant potential, was very much greater than in 

 diatomic gases, such as oxygen, hydrogen, nitrogen, or carbon mon- 

 oxide ; and in these, greater than in gases of more complex molecular 

 structure. Our experiments show that while with argon, the distance 

 traversed by the spark is considerably greater than with air, oxygen, 

 or hydrogen, with helium the spark is capable of passing through 

 most unusual distances. 



To carry out such experiments the tube must contain movable 



