Sir W. Snow Harris’s Researches in Statical Electricity. 181 
Ezp. 18. Place the plate and sphere successively in commu- 
nication with the fixed disc of the hydrostatic electrometer 
(fig. 18), or the fixed disc of the balance, fig. 17. Deposit 5 
measures on the sphere, and 7 measures on the plate: the index 
will stand at the same number of degrees in each case as before. 
A great many such experiments may be adduced to show that 
this is really the proportionate electrical capacities of a sphere 
and circular plate of twice the diameter of the sphere; and that 
if we attempt to place twice the quantity of electricity on the 
plate, according to the ordinary deduction, that it charges in 
proportion to its double surface, we entirely fail: the plate will 
not receive any other proportion of charge than that just stated. 
28. The fact that simple insulated conductors do not always 
take up electricity in proportion to their surfaces has been long 
known. It was first observed by Le Monnier in 1746, by Volta 
in 1779, and was observed in certain cases by Coulomb himself in 
his justly celebrated memoirs on electricity in L’Histoire de 
P Académie, in 1785. The law, however, of this species of elec- 
trical action has never been fully investigated in all its generality. 
In the case of spheres, circular plates, and plane surfaces, I have 
been enabled to arrive at a very simple expression for the rela- 
tive quantities of electricity which such bodies can sustain under 
a given degree of the electrometer, that is to say, their charge ; 
and which comes very near the result of experiment in almost 
every instance. If P represent the circumference or perimeter, 
S the surface, and C the charge, then we have C= /Sx P, 
taking P and S as abstract numbers. That this is true for 
spheres, circular plates, and plane surfaces of other forms, may 
be most satisfactorily shown in the way just described, Exps. 17 
and 18. Take, for example, two spheres, Q, R, whose diameters 
are 5°67 inches and 9 inches respectively; then we have for 
charge of sphere Q, of diameter 5-67, and surface 101, 
V¥S+P= W101 x 17=42-4 nearly ; 
and for charge of sphere R, of diameter 9, and surface 2545, 
VSx P= V 2545 x 28°27 =84'8 nearly ; 
that is to say, the relative quantities of electricity which may be 
accumulated on these two globes under the same electrometer 
indication, or in other words, their relative charge, will be as 
42°4 : 84°8, or as 1:2, their surfaces being as 1 : 2°5. 
Exp. 19. Place 5 measures on globe Q, and 10 measures on 
globe R, and take the reactive forces by the method of Coulomb ; 
these reactive forces will be alike. If the relative charges had 
been in proportion to their surfaces, they should have been in 
