178 Sir W. Snow Harris’s Researches in Statical Electricity. 
electrometer now begins to evince an increased action. A third 
application becomes still more sensible. The carrier-ball may 
yet yield up so large a portion of its electricity, that the residue 
on it may be neglected, and the march of an electrometer of 
measure K, fig. 13, will be as the square of the quantity of elec- 
tricity displaced. A stratum of air everywhere surrounding the 
metal becomes in this way charged; or, according to Faraday, 
polarized and inductive action becomes propagated through con- 
tiguous or next particles to bodies at a distance: in this sense, 
simple insulated conductors, as distinguishable from a more regu- 
larly coated surface or stratum, may be conceived to charge upon 
all their surfaces. That this is not only possible but certain, is 
shown in our last experiment 14, the charge itself beimg re- 
solvable into the displaced electricity of the plate itself. When 
the possible displacement becomes exhausted, the charge is at a 
maximum under the given circumstances and conditions of the 
experiment. 
In the case of a coated stratum of air, fig. 19, Exp. 14, in 
which two coatings only, a, c, are employed, plate 6 bemg turned 
aside, the intervening air on one surface of the plate may be 
considered as the more immediate recipient of the charge: still 
the air in contact with the exterior surface of the plate may be 
conceived to participate in the operation. We have here merely 
to suppose, in the case of employing both the plates a, b, that 
plate 6 has been removed to an indefinite distance. It is only 
on account of the small induction of distant matter, as com- 
pared with that of the near and directly opposed coating on 
plate a, that we commonly neglect the charge by distant induc- 
tion upon its opposite surface, and consider only the charge de- 
veloped immediately between the two plates or coatings a, c. 
When we bring into operation, however, a third plate 4, in the 
way shown, Exp. 15, then the equal induction upon the exposed 
surfaces of the centre plate c is complete, and we obtain a full 
or double charge. 
25. It may be worth while to define here more explicitly what 
is to be understood by the term charge, considered as an expres- 
sion of quantitative measurement. By the term electrical charge 
of an insulated conductor, we are to understand the measured 
quantity of electricity it can sustain under a given degree of the 
electrometer as referred to some unit of measure. Thus, fig. 21, 
let a globe S, a circular plate P, of twice the diameter of the 
sphere, and a rectangular plate R, of the same area as the sphere 
and plate, be put successively in connexion with the fixed disc 
p of the electrometer E, fig. 19, or with the fixed ball of the 
balance p, fig. 17 (22). Then the same quantity of electricity 
communicated to these three bodies, S, P, R, affects the electro- 
