to each other I was able to
show the difference of specific inductive capacity when only thin plates of
shell-lac were used, the rest of the dielectric space being filled with
air. By bringing B and C nearer to A another great increase of sensibility
was made. By enlarging the size of the plates still further power was
gained. By diminishing the extent of the wires, &c. connected with the gold
leaves, another improvement resulted. So that in fact the gold leaves
became, in this manner, as delicate a test of _specific inductive action_
as they are, in Bennet's and Singer's electrometers, of ordinary electrical
charge.

1313. It is evident that by making the three plates the sides of cells,
with proper precautions as regards insulation, &c., this apparatus may be
used in the examination of gases, with far more effect than the former
apparatus (1187. 1290), and may, perhaps, bring out differences which have
as yet escaped me (1292. 1293.)

1314. It is also evident that two metal plates are quite sufficient to form
the instrument; the state of the single inducteous plate when the
dielectric is changed, being examined either by bringing a body excited in
a known manner towards its gold leaves, or, what I think will be better,
employing a carrier ball in place of the leaf, and examining that ball by
the Coulomb electrometer (1180.). The inductive and inducteous surfaces may
even be balls; the latter being itself the carrier ball of the Coulomb's
electrometer (1181. 1229.).

1315. To increase the effect, a small condenser may be used with great
advantage. Thus if, when two inducteous plates are used, a little condenser
were put in the place of the gold leaves, I have no doubt the three
principal plates might be reduced to an inch or even half an inch in
diameter. Even the gold leaves act to each other for the time as the plates
of a condenser. If only two plates were used, by the proper application of
the condenser the same reduction might take place. This expectation is
fully justified by an effect already observed and described (1229.).

1316. In that case the application of the instrument to very extensive
research is evident. Comparatively small masses of dielectrics could be
examined, as diamonds and crystals. An expectation, that the specific
inductive capacity of crystals will vary in different directions, according
as the lines of inductive force (1304.) are parallel to, or in other
positions in relation to the axes