nd charge, as being electricity retained upon the surface of
conductors by the mere pressure of the atmosphere!

* * * * *

1451. When the brush is obtained in rarefied air, the appearances vary
greatly, according to circumstances, and are exceedingly beautiful.
Sometimes a brush may be formed of only six or seven branches, these being
broad and highly luminous, of a purple colour, and in some parts an inch or
more apart: by a spark discharge at the prime conductor (1455.) single
brushes may be obtained at pleasure. Discharge in the form of a brush is
favoured by rarefaction of the air, in the same manner and for the same
reason as discharge in the form of a spark (1375.); but in every case there
is previous induction and charge through the dielectric, and polarity of
its particles (1437.), the induction being, as in any other instance,
alternately raised by the machine and lowered by the discharge. In certain
experiments the rarefaction was increased to the utmost degree, and the
opposed conducting surfaces brought as near together as possible without
producing glow (1529.): the brushes then contracted in their lateral
dimensions, and recurred so rapidly as to form an apparently continuous arc
of light from metal to metal. Still the discharge could be observed to
intermit (1427.), so that even under these high conditions, induction
preceded each single brush, and the tense polarized condition of the
contiguous particles was a necessary preparation for the discharge itself.

1452. The brush form of disruptive discharge may be obtained not only in
air and gases, but also in much denser media. I procured it in _oil of
turpentine_ from the end of a wire going through a glass tube into the
fluid contained in a metal vessel. The brush was small and very difficult
to obtain; the ramifications were simple, and stretched out from each
other, diverging very much. The light was exceedingly feeble, a perfectly
dark room being required for its observation. When a few solid particles,
as of dust or silk, were in the liquid, the brush was produced with much
greater facility.

1453. The running together or coalescence of different lines of discharge
(1412.) is very beautifully shown in the brush in air. This point may
present a little difficulty to those who are not accustomed to see in every
discharge an equal exertion of power in opposite directions, a positive
brush being considered by such (perhaps