rge ball was inductric positively; it consisted of a little
brushy part on the small negative ball, then a dark space, and lastly a
dull straight line on the large positive ball (fig. 134.). The position of
the dark space was very constant, and is probably in direct relation to the
dark space described when negative glow was produced (1544.). When by any
circumstance a bright spark was determined, the contrast with the peculiar
spark described was very striking; for it always had a faint purple part,
but the place of this part was constantly near the positive ball.

1560. Thus dark discharge appears to be decidedly established. But its
establishment is accompanied by proofs that it occurs in different degrees
and modes in different gases. Hence then another specific action, added to
the many (1296. 1398. 1399. 1423. 1454. 1503.) by which the electrical
relations of insulating dielectrics are distinguished and established, and
another argument in favour of that molecular theory of induction, which is
at present under examination[A].

[A] I cannot resist referring here by a note to Biot's philosophical
view of the nature of the light of the electric discharge, Annales de
Chimie, liii. p. 321.

* * * * *

1561. What I have had to say regarding disruptive discharge has extended to
some length, but I hope will be excused in consequence of the importance of
the subject. Before concluding my remarks, I will again intimate in the
form of a query, whether we have not reason to consider the tension or
retention and after discharge in air or other insulating dielectrics, as
the same thing with retardation and discharge in a metal wire, differing
only, but almost infinitely, in degree (1334. 1336.). In other words, can
we not, by a gradual chain of association, carry up discharge from its
occurrence in air, through spermaceti and water, to solutions, and then on
to chlorides, oxides and metals, without any essential change in its
character; and, at the same time, connecting the insensible conduction of
air, through muriatic acid gas and the dark discharge, with the better
conduction of spermaceti, water, and the all but perfect conduction of the
metals, associate the phenomena at both extremes? and may it not be, that
the retardation and ignition of a wire are effects exactly correspondent in
their nature to the retention of charge and spark in air? If so, here again
the two extremes in proper