92 Sir W. Snow Harris’s Researches in Statical Electricity. 
_ ever thin we take it, can ever be anything more than a foreign 
body brought to share in the electrical charge of another body, 
on the principles laid down (8), fig. 2; and this will, I ima- 
eine, be satisfactorily conceived by reference to the following 
experiments. 
Exp. 7. Take a small insulated conducting cylinder, a, fig. 9 ; 
suppose a light cylinder of gilded wood, about ‘4: of an inch in 
diameter and ‘6 of an inch high; apply it to the central portion 
of a charged rectangular conducting plate P, as indicated in the 
figure, and then find by the torsion or bifilar balance its reactive 
force. Let this cylinder be now divided into two portions, or 
what comes to the same thing, take a‘cylinder of half the alti- 
tude. Find the force after being applied to the charged plate P, 
as before; the force will be much less. Continue to diminish 
the thickness until a mere disc results; the force will continu- 
ally decrease with the thickness. At last, when the thickness is 
taken indefinitely small, then with a certain charge little or no 
resulting force is apparent. We may here fairly ask, What is the 
limit of thickness at which we may arrest our division so as to 
repose with confidence on the reactive force when transferred to 
the balance, as a measure of the quantity of electricity actually ex- 
isting in the point of the electrified surface to which the disc has 
been applied? Theoretically, we should, in continuing the divi- 
sion, arrive at last at a zero of charge. Now it is notorious that 
if we take a series of proof-planes of variable thickness and apply 
them to different points of a charged surface, we get all sorts of 
proportions of quantity of electricity in the respective points 
touched, as determined by the electrical balance after the method 
of Coulomb; the correctness of which in determining the rela- 
tive quantity of electricity operating between the repellent. balls 
of the balance is quite unquestionable, sufficient attention being 
given to the manipulation. 
I endeavoured to ascertain by very direct experimental pro- 
cesses (Exps. 8 and 9), the altitude above the charged surface 
at which the reactive force imparted to a proof-dise of small 
thickness would be everywhere the same, or nearly so, it bemg 
evident, that, applied to certain points at a distance from the 
centre, the disc takes up a greater charge. 
Exp. 8. A light cylinder of gilded wood, ap, fig. 10, about -4 
of an inch in diameter and 3 inches high, being placed on a 
charged rectangular plate P, as indicated in the figure, the react- 
ive force of a proof-plane, p, applied to the remote face of this 
cylinder was observed for different points of the charged surface, 
and found to be everywhere the same, the plate P bemg charged 
with a given quantity of electricity. At the extremity g the 
reactive force was the same, whether the proof-plane p were 
