8 
Professor Leslie on Electrical Theories . 
flame, the electrical communication may be suspended or reite- 
rated at pleasure *. 
We have only, therefore, to investigate the action of an 
electrified body on the ambient air, and to discover how far 
the influence is modified by its shape or magnitude. What 
I am to offer must be regarded rather as a sketch than a com- 
plete solution. The law of electrical action at the various distances 
has not been ascertained*)*; and the theory of the motions of fluids 
is still very incomplete. There are certain principles, however, 
that may direct our investigation. The electrical action resides 
on or near the surface, to whose extent it is nearly proportional ; 
and it decreases rapidly with the distance of the body upon 
which it is exerted. 
The air that surrounds the prime conductor is repelled from 
it in lines perpendicular to its surface ; but the divergency which 
thus results, is rendered regular and uniform by the equal re- 
pulsion of the particles to each other. The stream flows with 
considerable celerity ; and the particles of air, in their passage 
through that slow conducting medium, may reach to the dis- 
tance of a foot or two, with their electricity hardly impaired by 
communication. 
Let A (PI. I. Fig. 1.) be a metallic ball in the vicinity of an 
electrified body, and N, M, L, K, &c. particles of air which have 
acquired the same electricity, and are repelled from the body. 
• It will perhaps be alleged, that this experiment admits of an explanation 
from the common principle, that heated bodies become better conductors of elec- 
tricity. Though air, in its ordinary state, be an exceedingly imperfect conductor, 
yet we might infer from analogy, that, when brought to a high temperature, it 
will profusely transmit the electrical fluid. But this solution, though plausible, 
is wholly inadequate ; for the lighted taper can heat only the ambient air, and 
its effects will therefore be confined to a very narrow sphere, beyond which the 
electrical communication will be as slow as ever. By what magic, therefore, does 
the influence of this flame extend to the distance of several feet ? If the electri- 
city penetrates as slowly as before through thirty inches of air, what though its 
progress be rapid over the remaining inch of its track ? Besides, I am much dis- 
posed to think, that the experiments performed with heated conductors are either 
partly or altogether fallacious, and that the electrical communication is in such 
cases produced by the quick renewal of air along the hot surface of the conductor* 
y The celebrated Coulomb had about this time discovered that electrical action is 
inversely as the square of the distance . 
