1894.] Prof. J. J. Thomson on Electric Discharge through Gases. 239 



WEEKLY EVENING MEETING, 

 Friday, April 13, 1894. 



Sir Frederick Bramwell, Bart. D.C.L. LL.D. F.R.S. Honorary 

 Secretary and Vice-President, in the Chair. 



Professor J. J. Thomson, M.A. Sc.D. F.RS. 



Electric Discharge through Gases. 



One of the most important and interesting branches of physical 

 science is that which deals with the connection between electrical 

 and chemical effects. 



The investigations on electrolysis made within these walls by 

 Davy and Faraday proved that the important class of electrical 

 phenomena associated with the passage of electricity through 

 liquids, are connected in the closest way with chemical action. They 

 proved that no electricity will pass through most liquids unless 

 chemical action occurs, and that for each unit of electricity which 

 passes through the liquid there is a definite amount of chemical 

 decomposition. 



This case, though it is one where the laws are most accurately 

 known, is but one among many electrical phenomena which are 

 inseparable from chemical action. 



So many instances of this kind have been discovered that we 

 may perhaps venture to hope that we are not far from the time when 

 it will be universally recognised that many of the most fundamental 

 questions in chemistry and electricity are but different aspects of ono 

 and the same phenomenon. 



Anything which throws light on the connection between elec- 

 tricity and matter, interesting as it is on its own account- acquires 

 additional interest when regarded as elucidating the connection 

 between chemical and electrical effects, and no phenomena seem 

 more suitable for this purpose than those which are the subject of 

 the discourse this evening — the discharge of electricity through gases. 

 For in gases we have matter in the state in which its properties 

 have been most carefully studied, while the investigation of the 

 electrical effects is facilitated by the visibility of the discharge, 

 affording us ocular, and not merely circumstantial, evidence of what 

 is taking place. 



The points to which I wish to refer particularly this evening are, 

 firstly, some phenomena connected with the passage of electricity 

 from the gas to the electrode, or from the electrode to the gas ; and 

 secondly, some of the properties of the discharge when its course lies 

 entirely in the gas. 



