Sir W. Snow Harris’s Researches in Statical Electricity. 91 
the surfaces of bodies, did in no way violate sound deduction 
from rigorous thought, or evince in any degree a vague and im- 
perfect apprehension of the probable nature of electrical force. 
When we remove the coatings of a charged electric (7), Exp. 5, 
something is evidently left behind—some agency or source of 
power. What is that something? In what does it consist? It is 
evidently external to the metallic surface with which the dialectric 
surface was previously in contact, although inseparable from it 
so long as the two remain combined ; and it is really from this 
something, which we express by the term electrical stratum or 
atmosphere, that the phenomena we observe arise, and not from 
an hypothetically charged conductor*. 
14. On attentively reviewing these facts, it will be quite ap- 
parent, that in any endeavour to take away or abstract electricity 
from a charged surface through the medium of a conducting sub- 
stance applied to it, it is absolutely essential to maintain in this 
substance a sufficient power of inductive change. This we cannot 
possibly do if the body be of extremely small dimensions and thick- 
ness, and be applied to the charged conductor within the envelope 
of the electrical stratum immediately upon its surface ; because in 
such a position it will approach the conditions of the carrier-ball 
introduced into the hollow sphere (7), Exp. 5: its inductive sus- 
ceptibility, and consequently its power of abstracting electricity, 
“ must become more or less damaged ; indeed it is next to certain, 
that a small and very completely insulated disc of metal of indefi- 
nitely small thickness may under some circumstances come away 
from contact with an electrified surface very nearly neutral. 
These are important facts as affecting the practical operation of 
what is termed the proof-plane, and which consists of an ex- 
trémely thin and small insulated disc of metal applied to the 
surface of a charged conductor, often with a view of determining 
by the quantity of electricity abstracted, the quantity of charge 
disposed in different points of the surface. The received theo- 
retical view of the proof-plane supposes, that when the disc is 
placed upon any point of the charged conducting surface, it 
actually becomes part and parcel of the surface itself, so that on 
removal we may be supposed to have actually abstracted an ele- 
ment of the surface with all the charge belonging to it. Now 
it seems to me extremely difficult to satisfy the mind of the truth 
of this view, or to be assured that a small insulated disc, how- 
* The experiments of Beccaria and Franklin with the smoke of resin and 
colophonia, and which they observed to collect about electrified conductors, 
so as to envelope them, although perhaps no very satisfactory evidence of 
the existence of a similar atmosphere of electricity, are still not without 
very considerable interest. It isnot easy to explain the adherence of these 
atmospheres of smoke to the charged surface, admitting the theory of elec- 
trical repulsive force. 
