98 
MR. GROVE ON THE ELECTRO-CHEMICAL POLARITY OF GASES. 
The results detailed in Experiment 13th, appear to open a new field of research. 
Priestley observed concentric circles produced by the electrical discharge from a 
powerful Leyden battery, which he describes as consisting of minute cavities and 
globules of fused metal*. In my experiments there is an alternation of oxidation 
and reduction, a medium capable of producing both being present; the lateral effect 
and complementary colours have to my mind something closely resembling the 
phenomena of interference in light, although from the polar character of the force, it 
is difficult to imagine any precisely analogous condition of electricity. The discharge 
taking place from different parts of the needle and extending from its point to a 
considerable distance over its surface, would give different lengths for the lines of 
polarization and discharge to the different parts of the disc on the silver plate affected 
by the discharge ; and assuming eleetricity to be propagated by undulations, there 
would be interference ; but instead of alternations of light and darkness we get 
alternations of positive and negative electricity. The ring of polished metal between 
the central spot and the exterior ring, quite distinguishes these rings from the ordi- 
nary colours of thin plates, i. e. colours, the annular succession of which depends 
only on the different thicknesses of the film ; here doubtless the colours of the 
oxidated portions are colours of thin plates. Experiment 14 shows clearly that the 
action by which the polished ring is formed is a polar action of the discharge, and 
not a mere absence of action. 
When the plate is negative, the effect is, as I have observed, less marked and more 
uncertain ; but in this case it should be recollected that the visible discharge issues 
from the point, and does not extend, or extends to a very small degree, over the 
surface of the needle. 
If the phenomena were such that the central portion were always clear, while 
around it was one, and one only circle of oxide, it might be accounted for by the 
hypothesis, that the lines of polarization and discharge between a point and fiat sur- 
face, assume the form of a hollow cone ; but a cone of negative bounded by cones 
of positive action, still gives the idea of some lateral fits or phases of undulation. 
The high rarefaction of the medium by the discharge, and its intermitting cha- 
racter, might occasion pulsations by the inrushing of the surrounding gas, and thus 
vacua in circles might be formed at the places where the action of oxidation is ren- 
dered null ; but this view is, I think, inadmissible ; it does not account for the effects 
obtaining only in certain mixtures, it does not account for the reducing action, the 
plate being positive, and presents other difficulties. The point involved in Experi- 
ments 13 and 14, though not perhaps the least valuable one given in this paper, 
presents apparently a wide field of inquiry ; I therefore will not further dilate on it 
at present, and hope to make it the subject of future investigation. 
* History of Electricity, 2nd edition, p. 624. 
December 27, 1851. 
