eory
far more probable that it might be detected in a brush than in a spark; for
in a brush, the particles in the line through which the discharge passes
are in very different states as to intensity, and the discharge is already
complete in its act at the root of the brush, before the particles at the
extremity of the ramifications have yet attained their maximum intensity.

1437. I consider _brush_ discharge as probably a successive effect in this
way. Discharge begins at the root (1426. 1553.), and, extending itself in
succession to all parts of the single brush, continues to go on at the root
and the previously formed parts until the whole brush is complete; then, by
the fall in intensity and power at the conductor, it ceases at once in all
parts, to be renewed, when that power has risen again to a sufficient
degree. But in a _spark_, the particles in the line of discharge being,
from the circumstances, nearly alike in their intensity of polarization,
suffer discharge so nearly at the same moment as to make the time quite
insensible to us.

1438. Mr. Wheatstone has already made experiments which fully illustrate
this point. He found that the brush generally had a sensible duration, but
that with his highest capabilities he could not detect any such effect in
the spark[A]. I repeated his experiment on the brush, though with more
imperfect means, to ascertain whether I could distinguish a longer duration
in the stem or root of the brush than in the extremities, and the
appearances were such as to make me think an effect of this kind was
produced.

[A] Philosophical Transactions, 1836, pp. 586, 590.

1439. That the discharge breaks into several ramifications, and by them
passes through portions of air alike, or nearly alike, as to polarization
and the degree of tension the particles there have acquired, is a very
natural result of the previous state of things, and rather to be expected
than that the discharge should continue to go straight out into space in a
single line amongst those particles which, being at a distance from the end
of the rod, are in a lower state of tension than those which are near: and
whilst we cannot but conclude, that those parts where the branches of a
single brush appear, are more favourably circumstanced for discharge than
the darker parts between the ramifications, we may also conclude, that in
those parts where the light of concomitant discharge is equal, there the
circumstances are ne