arly equal also. The single successive brushes are by
no means of the same particular shape even when they are observed without
displacement of the rod or surrounding objects (1427. 1433.), and the
successive discharges may be considered as taking place into the mass of
air around, through different roads at each brush, according as minute
circumstances, such as dust, &c. (1391. 1392.), may have favoured the
course by one set of particles rather than another.

1440. Brush discharge does not essentially require any current of the
medium in which the brush appears: the current almost always occurs, but is
a consequence of the brush, and will be considered hereafter (1562-1610.).
On holding a blunt point positively charged towards uninsulated water, a
star or glow appeared on the point, a current of air passed from it, and
the surface of the water was depressed; but on bringing the point so near
that sonorous brushes passed, then the current of air instantly ceased, and
the surface of the water became level.

1441. The discharge by a brush is not to all the particles of air that are
near the electrified conductor from which the brush issues; only those
parts where the ramifications pass are electrified: the air in the central
dark parts between them receives no charge, and, in fact, at the time of
discharge, has its electric and inductive tension considerably lowered. For
consider fig. 128 to represent a single positive brush;--the induction
before the discharge is from the end of the rod outwards, in diverging
lines towards the distant conductors, as the walls of the room, &c., and a
particle at _a_ has polarity of a certain degree of tension, and tends with
a certain force to become charged; but at the moment of discharge, the air
in the ramifications _b_ and _d_, acquiring also a positive state, opposes
its influence to that of the positive conductor on _a_, and the tension of
the particle at _a_ is therefore diminished rather than increased. The
charged particles at _b_ and _d_ are now inductive bodies, but their lines
of inductive action are still outwards towards the walls of the room; the
direction of the polarity and the tendency of other particles to charge
from these, being governed by, or in conformity with, these lines of force.

1442. The particles that are charged are probably very highly charged, but,
the medium being a non-conductor, they cannot communicate that state to
their neighbours. They travel, there