180 Sir W. Snow Harris’s Researches in Statical Electricity. 
to receive, in sharing the charge, twice the quantity of electricity 
which would be retained on the sphere A. Hence, when by con- 
tact the increased induced electrical charge of the sphere in the 
hemisphere s next the plate is communicated to the plate, and 
the sphere and plate are taken together as a whole, then it is 
that the plate receives a quantity proportionate to the magnitude 
of the inductive change in each, without which there would not 
be an equilibrium of distribution between the two bodies (3), 
fig. 2. The perfect success of this experiment is entirely de- 
pendent on insulation, and the absence of foreign induction ; if 
any adventitious circumstance should arise calculated to increase 
the capacity of the sphere by induction, as by the presence of 
near matter, some particular hygrometric states of the air, or 
imperfect insulation, the plate and sphere will appear to share 
equally, as I have found in a great variety of instances, and as 
stated in my paper in the Philosophical Transactions for 1836. 
Such, however, I have since found is not really the case when 
the experiment is very perfectly conducted with due regard to 
disturbing influences. 
27. The result of this experiment, therefore, although it may 
well determine the relative division of the electricity between the 
two bodies, does not really determine their relative capacity for 
electricity or their charge (25). In order to determine this, it 
is requisite to compare each with a third body, on the principles 
laid down by Cavendish, and which may be very well managed 
in employing a third body, suppose a sphere B, fig. 20, which 
may be either equal or not. For the sake of simplicity let it be 
equal. 
Exp. 16. Let the sphere A, charged as before, be touched by 
an equal and similar neutral sphere B; then the charge becomes 
shared equally between the two spheres, and the capacity of a 
sphere equal to the plate P, of twice its diameter, may be repre- 
sented by the fraction 4. Repeat this experiment with the 
plate P; then, as just seen, its capacity deduced in a similar 
way may be represented by the fraction 2. The capacity of the 
sphere, therefore, is to the capacity of the plate of twice the dia- 
meter in the proportion of }: 2; that is, as 1: 2 very nearly, 
oras 1:1°4. And such is really the proportions of charge which 
the two bodies will sustain under a given degree of the electro- 
meter (25). 
Exp. 17. Place 5 measures of electricity on the sphere B, and 
7 measures on the plateP. The respective reactive forces by the 
method of Coulomb will be precisely the same, the plate being 
touched by a free tangent plate (fig. 11), or otherwise near its 
edge; that is to say, 5 measures is to sphere as 7 to plate, that 
is,as 1: 2, or 1: 1° very nearly. 
