ELECTRO-CHEMICAL POLARITY OF GASES. 375 



platinum wire, giving an extended conducting surface ; and 

 this may be the reason why such rings are formed, though 

 these rings, in all the cases which I have observed, differ 

 broadly from the rings formed by the bare needle or wire, not 

 having the interposed spaces of perfectly bright silver ; and 

 in all the cases the difference of effect produced by the coated 

 and the bare wire is very marked ; in by far the greater 

 number of experiments, when proper precautions are taken, 

 not the slightest formation of rings takes place with the 

 coated wire ; with the bare wire, in the gaseous mixture last 

 mentioned, I have always seen them formed. 



Thus there are three systems of rings which may be 

 formed by the discharge. First, rings such as those seen in 

 the ordinary cases of thin plates ; these I have only observed 

 with olefiant gas, though probably there are many other con- 

 ditions in which they may be produced. Secondly, rings 

 formed by the superposition of layers of oxides, possibly 

 arising from the fact that at certain definite periods portions 

 of the plate become by oxidation inferior conductors, and 

 other portions are attacked, and being at a different distance 

 undergo a different molecular change by oxidation. Thirdly, 

 and to me far the most interesting set of phenomena are pre- 

 sented by the rings alternately bright and oxidated, showing 

 effects of oxidation and reduction by the same current on the 

 same plate, and which only take place in certain gaseous mix- 

 tures, of which, up to this time, one volume oxygen + five 

 volumes hydrogen is the most efficient which I have obtained. 



I cannot at present see any better mode of explaining 

 these phenomena than by regarding them as analogous to the 

 phenomena of interference in light, though doubtless, if this 

 be a right view, the very different modes of action of light 

 and electricity would present very numerous phenomenal dis- 

 tinctions. Alternations of opposite polar electrical actions in 

 the discharges passing in the same direction are, I think, very 

 clearly shown in these experiments, and this appears to me a 

 result worthy of attention. 



Though acquainted with Nobili's beautiful experiments on 

 the formation of coloured rings by deposition in electrolysed 

 liquids, yet as I was working on gases it did not occur to me 



