282 Mr. Hersc/iel on certain Motions produced in Fluid [Oct. 



a little obscure : in all probability it forms a Voltaic combination 

 with the mercury and the liquid. 



48. In reasoning upon the facts detailed in this Paper, we 

 have to consider, as probably materially influencing the results, 

 first, the vast difference of conducting power between the metallic 

 bodies set in motion, and the liquid under which they are 

 immersed. This is not unlikely to enter as one of the essential 

 conditions of the phenomenon, especially as it appears to result 

 from all the experiments, that the peculiar action, whatever it 

 be, by which the currents are produced, is exerted only at the 

 common surface of the fluids. I have never been able to pro- 

 duce the least trace of such currents without the presence of a 

 fluid metal. This leads us to conclude that a second essential 

 condition is a perfect immiscibility of the conducting fluids, so 

 as to render the transition from one to the other quite sudden. 

 Besides these, a third essential condition is to be found in a 

 certain chemical, or electrical relation between them. Under 

 these conditions, it is by no means impossible, that the phaeno- 

 mena may admit of complete explanation from what we already 

 know of the passage of electricity through conductors, and the 

 high attractive and repulsive powers of the positive and negative 

 electricities inter se. It is very possible, for instance, that a 

 highly electro-positive body, as potassium, present in the mer- 

 cury, may have its natural electric state exalted by its vicinity 

 to the positive pole ; and, being thus repelled, may take the 

 only course the resistance of the metal on the one hand, and 

 attraction of cohesion on the other, will permit; viz. along the 

 surface, to recede from the positive pole. It may even act as a 

 carrier of positive electricity, which may adhere to it too strongly 

 to be transmitted through the mercury (which, though a good, 

 is far from a perfect conductor ;) and when arrived at the oppo- 

 site side of the globule, may there, by the influence of the 

 opposite pole, lose its exalted electrical state. This explanation 

 tallies with that of other phamomena which have been attributed 

 to a similar cause ; I mean the tendencies observed in the 

 vapours of electro-positive and electro-negative bodies to con- 

 ductors electrified oppositely, which Mr. Brande has described 

 in a Bakerian Lecture formerly read to this Society. Yet it must 

 not be concealed that this explanation is beset with difficulties, 

 and that the mode of action of the less-conducting medium in it 

 is far from clear ; it does not even appear why such a medium is 

 at all necessary, unless we conceive it to retard, or otherwise 

 modify the electric current, in its passage through it, and dispose 

 it thereby to ready combination with the metallic molecules. 



49. Another course is doubtless open to us, which is to con- 

 sider the action which takes place at the common surface of two 

 unequally conducting media, as one, sui generis, and to depend 



