100 
MR. GROVE ON THE ELECTRO-CHEMICAL POLARITY OF GASES. 
When the experiment is continued for some time, a dark deposit is formed on 
the glass around the extremity of the 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 conditions 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 presented 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 
mixtures, 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 v^ry different modes of action of light and elec- 
tricity would present very numerous phenomenal distinctions. 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 electrolyzed liquids, yet as I was working on gases it did not 
occur to me to refer to his memoirs* ; 1 have done so since making the experiments 
given in this Postscript, and find tliat with regard to the rings so formed by electro- 
lysis, he suggests interference as a possible explanation. 
The dark space in the discharge to which Faraday has called attention, may 
possibly be conneeted with these phenomena. I have observed, that in a well-ex- 
hausted receiver containing a small piece of phosphorus, the discharge is throughout 
its course striated by transverse non-luminous bands, presenting a very beautiful 
effect, and a yellow deposit, which, as far as I have yet examined it seems to be 
allotropic phosphorus, is deposited on the plate of the air-pump and on tlie neigh- 
* Ann. de Ch. et de Phys. vol. xxxiv. 
