ccur, and particles
must, to a certain degree, be displaced. A third mode, namely, that by
sparks or brushes, may, because of its violent displacement of the
particles of the _dielectric_ in its course, be called the _disruptive
discharge_; and a fourth may, perhaps, be conveniently distinguished for a
time by the words _convection_, or _carrying discharge_, being that in
which discharge is effected either by the carrying power of solid
particles, or those of gases and liquids. Hereafter, perhaps, all these
modes may appear as the result of one common principle, but at present they
require to be considered apart; and I will now speak of the _first_ mode,
for amongst all the forms of discharge, that which we express by the term
conduction appears the most simple and the most directly in contrast with
insulation.

P vii. _Conduction, or conductive discharge._

1320. Though assumed to be essentially different, yet neither Cavendish nor
Poisson attempt to explain by, or even state in, their theories, what the
essential difference between insulation and conduction is. Nor have I
anything, perhaps, to offer in this respect, _except_ that, according to my
view of induction, insulation and conduction depend upon the same molecular
action of the dielectrics concerned; are only extreme degrees of _one
common condition_ or effect; and in any sufficient mathematical theory of
electricity must be taken as cases of the same kind. Hence the importance
of the endeavour to show the connection between them under my theory of the
electrical relations of contiguous particles.

1321. Though the action of the insulating dielectric in the charged Leyden
jar, and that of the wire in discharging it, may seem very different, they
may be associated by numerous intermediate links, which carry us on from
one to the other, leaving, I think, no necessary connection unsupplied. We
may observe some of these in succession for information respecting the
whole case.

1322. Spermnceti has been examined and found to be a dielectric, through
which induction can take place (1240. 1246.), its specific inductive
capacity being about or above 1.8 (1279.), and the inductive action has
been considered in it, as in all other substances, an action of contiguous
particles.

1323. But spermaceti is also a _conductor_, though in so low a degree that
we can trace the process of conduction, as it were, step by step through
the mass (1247.); and even when the elect