190 Mr. Herschel on certain motions produced in 
lity 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 phsenomena may admit 
of complete explanation from what we already know of the 
passage of electricity through conductors, and the high attrac- 
tive and repulsive powers of the positive and negative elec- 
tricities inter se. It is very possible, for instance, that a highly 
electro-positive body, as potassium, present in the mercury, 
may have its*^atural 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 opposite 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 
phenomena which have been attributed to a similar cause ; 
I mean the tendencies observed in the vapours of electro- 
positive and electro -^negative bodies to conductors 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 me- 
dium is at all necessary, unless we conceive it to retard, or 
otherwise modify the electric current, in its passage through 
