Professor Leslie on Electrical Theories. 
communication. The air immediately environing an electrical 
body becomes also similarly electrified ; its particles are hence re- 
pelled by each other, and also by the body, from which, as from 
the centre, they stream in all directions. Thus, let a large board 
be covered with tinfoil to within half an inch of its edge, and the 
surface be made smooth. Place it perpendicular on an insulated 
stool, parallel with the prime conductor, and at the distance of 
half a foot. On working the machine, the tinfoil will continue 
dark; but if a knob be brought near it, it will shew considerable 
sparks. Hence the reason of the difficulty of performing elec- 
trical experiments in open air, especially in cvindy weather ; 
lienee, likewise, the great improvement has been made in ma- 
chines, by covering the upper part of the cylinder with a flap 
of silk, and coating the conductor with a thin surface of sealing- 
wax *. 
But if the air, in consequence of the successive application of 
its particles, be thus capable of making an electrical communi- 
cation, may we not infer, with a considerable degree of proba- 
bility, that, whenever a body acquires the electricity of a distant 
one, it derives this quality merely from the motion and transfer- 
ence of the intervening aerial particles ? Let a pointed wire be 
held a foot or half a foot behind the electrified conductor, and it 
will be tipped in a darkened room with a lucid spangle. But, 
while in this situation, let an insulated sheet of glass, of paper. 
* Air is constantly blown from an electrified body , whether this be in the state of 
what is called positive or negative electricity ; or whether it is connected with the 
jxrime conductor , or with the cushion of a cylindrical machine . Thus , a whirl placid 
on either of these , will yet revolve always the same way , or in a direction opposite to 
the ends of the bent wires. In like manner , a thick tapering wire , electrified either 
positively or negatively , will still project a stream of air , as indicated by the turning 
of a small wheel of card . Hence , the explication of a seemingly paradoxical fact, 
that any hot body will cool faster, if kept electrified. To make this experiment in a 
satisfactory manner , gild a very large mercurial thermometer , having a ball perhaps 
of an inch, and a half diameter, and a long stem bearing only 30 or 40 degrees : Sus- 
pend the instrument from an insulated stand at the distance of two or three yards from 
the prime conductor , with which it communicates by a silver thread. Apply the hand 
to the bulb of the thermometer, and heat it up 20° above the temperature of the room, 
and note the time it takes to fall to the middle point. Repeat the operation , and then 
keep turning the machine , and the mercury will be found to sink down in less than 
half that time. 
