of this may occur, i.e. that the charging of the air may not extend even so
far as the light. We do not know as yet enough of the electric light to be
able to state on what it depends, and it is very possible that, when
electricity bursts forth into air, all the particles of which are in a
state of tension, light may be evolved by such as, being very near to, are
not of, those which actually receive a charge at the time.

1446. The further a brush extends in a gas, the further no doubt is the
charge or discharge carried forward; but this may vary between different
gases, and yet the intensity required for the first moment of discharge not
vary in the same, but in some other proportion. Thus with respect to
nitrogen and muriatic acid gases, the former, as far as my experiments have
proceeded, produces far finer and larger brushes than the latter (1458.
1462.), but the intensity required to commence discharge is much higher for
the muriatic acid than the nitrogen (1395.). Here again, therefore, as in
many other qualities, specific differences are presented by different
gaseous dielectrics, and so prove the special relation of the latter to the
act and the phenomena of induction.

1447. To sum up these considerations respecting the character and condition
of the brush, I may state that it is a spark to air; a diffusion of
electric force to matter, not by conduction, but disruptive discharge, a
dilute spark which, passing to very badly conducting matter, frequently
discharges but a small portion of the power stored up in the conductor; for
as the air charged reacts on the conductor, whilst the conductor, by loss
of electricity, sinks in its force (1435.), the discharge quickly ceases,
until by the dispersion of the charged air and the renewal of the excited
conditions of the conductor, circumstances have risen up to their first
effective condition, again to cause discharge, and again to fall and rise,

1448. The brush and spark gradually pass into one another, Making a small
ball positive by a good electrical machine with a large prime conductor,
and approaching a large uninsulated discharging ball towards it, very
beautiful variations from the spark to the brush may be obtained. The
drawings of long and powerful sparks, given by Van Marum[A], Harris[B], and
others, also indicate the same phenomena. As far as I have observed,
whenever the spark has been brushy in air of common pressures, the whole of
the electricity has not