35 
Professor Leslie on Electrical Theories. 
tion will therefore be equal to the amount of all the successive 
impulses ; in the same manner as the motion acquired by a fall- 
ing body is proportional to the time of descent. It is of no 
consequence, that, in the one case, we perceive the accumulation 
gradually effected, while the time required in the other is to- 
tally insensible ; for the quantify must be finite in both. How- 
ever, since the cohesion of the particles occasions a certain re- 
sistance, the total obstruction will also be as the duration ; and 
hence the force which effectually tends to produce disruption, 
will increase more slowly than the time, just as a body falling 
through air or water receives, at equal intervals, smaller and 
smaller additions to its velocity. Nay, the reaction made by 
the distended particles of a solid substance may at last coun- 
terbalance their difference of repulsion ; in which case the con- 
tinuance of the exertion will produce no farther effect, just as, 
to continue the allusion, a body, in its descent through a resist- 
ing medium, acquires a certain uniform motion. And hence 
the incessant working of the electrical machine is insufficient to 
burst the prime conductor. 
We can now ascertain the effect produced by a shock on different 
conductors. If the length is constant, the disturbing forces will 
be the same, and the absolute exertion will depend on the time 
of transmission, though in a less ratio ; and will therefore be 
determined by the slow transmitting quality of the substance, 
but much more by the smallness of the transverse section. When 
the distance of communication is shortened, the time of action 
is indeed diminished, but the successive impulses on which the 
effect mostly depends are proportionally more powerful. It is 
also very probable that the repulsions increase faster than the 
intensity of the electricity ; and consequently both causes will 
conspire to burst the short conductor. Suppose that AB and 
DE, (PL I. Fig. 13.), are two similar conductors connected to the 
two coatings of a charged jar, and the intervening part B33 of 
the same breadth, but of a slower conducting substance. Let 
the celerity of transmission from A to a be to that through the 
equal distance from B to h, as i to n. Then, since the quan- 
tity of communication must be the same through the whole of 
the compound conductor, the difference of intensity, F f must 
be to G e as i is td n , in order that G e el, transmitted in the time n , 
c 2 
