Professor Leslie on Electrical Theories. 31 
The time of transmission is directly as the length of the conduc- 
tor is to the mass electrified, and as the logarithm of the ratio of 
its intensity before and after communication * ; and inversely as 
the celerity of the conducting quality, and as its transverse sec- 
tion. It would follow, that the equilibrium will never be per- 
fectly restored ; but in ordinary cases, the electricity will be im- 
perceptible when diminished to the hundredth part, and the in- 
terval elapsed in the discharge is therefore between five and ten 
! times greater than that required to reduce the intensity to one- 
! half. 
We have hitherto conceived the conducting substance to 
connect both coatings of the charged jar at the same in- 
stant ; but, in ordinary cases, the one * end is made to 
touch the exterior coating, while the other end is brought 
to touch the interior coating. Let All (Plate I. Fig. 11.) re- 
present the conductor communicating with one coating A, and 
the extremity B held near the other coating O. Then, as fast 
as B is electrified, the contiguous stratum of air will acquire 
electricity to the same intensity, and be succeeded by other por- 
tions of air. If the intensity of B’s electricity is constant, the 
communication made in a given interval of time must be pro- 
portioned to the number of aerial particles in contact with B ; 
that is, as the proximate surface of B, and the density of the 
air. We still suppose, that the electrified strata are thrown 
from B to O as quick as they are formed ; if die distance BO be 
considerable, the communication would be somewhat retard- 
ed, and the time of discharge increased. Let AC denote 
the intensity-of the electricity at A; BD, that at B; and con- 
ceive the surface at B, and the density of the air, to remain the 
same. Then a quantity of electricity C c, will be transmitted 
from A to a given distance b , in a given time ; and this must 
be equal to the communication made at B, and consequently 
proportional to BD. Produce CD and AB to meet at E, and 
make E f = Ah ; wherefore BD : fg or C c : : BE : E/; but 
E/is given, and consequently BE is given. Hence the time 
* I have supposed, that the i'ate of the communication of electricity is propor- 
tional to the intensity. Perhaps this is not strictly true, though extremely pro- 
bable : It i3 exactly so in the application of heat. But my aim in this discourse is 
only to obtain an approximation. 
