rent unless combination take
place, so as to allow other particles to act successively in the same
manner, and not even then unless one set of the particles be present as an
element of an electrolyte (923. 963.); i.e. mere quiescent contact alone
without chemical action does not in such cases produce a _current_.

[A] Philosophical Transactions, 1807, p. 31.

1746. Still it seems very possible that such a relation may produce a high
charge, and thus give rise to excitement by friction. When two bodies are
rubbed together to produce electricity in the usual way, one at least must
be an insulator. During the act of rubbing, the particles of opposite kinds
must be brought more or less closely together, the few which are most
favourably circumstanced being in such close contact as to be short only of
that which is consequent upon chemical combination. At such moments they
may acquire by their mutual induction (1740.) and partial discharge to each
other, very exalted opposite states, and when, the moment after, they are
by the progress of the rub removed from each other's vicinity, they will
retain this state if both bodies be insulators, and exhibit them upon their
complete separation.

1747. All the circumstances attending friction seem to me to favour such a
view. The irregularities of form and pressure will cause that the particles
of the two rubbing surfaces will be at very variable distances, only a few
at once being in that very close relation which is probably necessary for
the development of the forces; further, those which are nearest at one time
will be further removed at another, and others will become the nearest, and
so by continuing the friction many will in succession be excited. Finally,
the lateral direction of the separation in rubbing seems to me the best
fitted to bring many pairs of particles, first of all into that close
vicinity necessary for their assuming the opposite states by relation to
each other, and then to remove them from each other's influence whilst they
retain that state.

1748. It would be easy, on the same view, to explain hypothetically, how,
if one of the rubbing bodies be a conductor, as the amalgam of an
electrical machine, the state of the other when it comes from under the
friction is (as a mass) exalted; but it would be folly to go far into such
speculation before that already advanced has been confirmed or corrected by
fit experimental evidence. I do not wish it to be suppos