Mr. Grove on the Electro-chemical Polaritxj of Gases. 511 



force, it is diflBcult 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 

 electricity to be propagated by undulations, there would be inter- 

 ference ; 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 ordinary colom-s 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. Ex- 

 periment 14. shows clearly that the action by which the polished 

 ring is foi-med 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 sur- 

 face of the needle. 



If the phsenomena 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 flat surface 

 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 character, might occasion pulsations by the inrush- 

 ing of the surrounding gas, and thus vacua in circles might be 

 formed at the places where the action of oxidation is rendered 

 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 Experiments 13 

 and 14, though not perhaps the least valuable one given iu 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. 

 December 27, If^.'il. 



Postscript, April 24th. 



I may, I trust, be ])ermitted to add to this ])apcr one or two 

 experiments on the subject last discussed. Assuming that the 



