368 EXPERIMENTAL INVESTIGATIONS. 



I have above selected all the experiments which I con- 

 sider material in this, I believe, new class of phenomena. 

 The spots produced by electrical discharges, both on con- 

 ducting bodies and on electrics, have been before noticed and 

 experimented on, one class by Priestley,* and another class 

 by Karstenf and others, but as far as I am aware no distinct 

 electro-chemical action in dry gases, depending upon the 

 antithetic state of the terminals, and presenting a definite 

 relation of the chemical to the electrical actions in gaseous 

 media, has been pointed out. I now proceed to consider the 

 relation which these results bear to other electrical phenomena. 



As may be gathered from my opening remarks, the ex- 

 periments above detailed appear to me to furnish a previously 

 deficient link in the chain of analogy connecting dielectric 

 induction with electrolysis. The only satisfactory rationale 

 which I can present to my own mind of these phenomena is 

 the following : The discharges being interrupted (as is evident 

 from the nature of the apparatus, and may be easily proved 

 by agitating a mirror near them and regarding their reflected 

 images in the moving mirror), the gaseous medium is polarised 

 anterior to each discharge, and polarised not merely physically, 

 as is generally admitted, but chemically, the oxygen or anion 

 being determined to the positive terminal or anode, and the 

 hydrogen or cation being determined to the negative terminal 

 or cathode ; at the instant preceding discharge there would 

 then be a molecule or superficial layer of oxygen or of electro- 

 negative molecules in contact with the anode, and a similar 

 layer of hydrogen or of electro-positive molecules in contact 

 with the cathode ; in other words, the electrodes in gas would 

 be polarised, as the electrodes in liquid are. The discharge 

 now takes place, by which the superficial termini of metal or 

 of oxide, as the case may be, are highly ignited or brought 

 into a state of chemical exaltation at which their affinities can 

 act ; the anode thus becomes oxidated, and the cathode, if an 

 oxide, reduced. I have elsewhere { shown strong reasons for 



* History of Electricity, 2nd edit., p. 624. 

 f Archives de V Electricite , vol. ii. p. 647 ; vol. ill. p. 310. 

 \ Phil. Trans., 1847, pp. 10, 16, 21. Correlation of Physical Forces, p. 50, 

 2nd edit. 



