ese experiments were made with rods of brass about a quarter of an
inch thick having rounded ends, these being opposed in a glass globe 7
inches in diameter, containing the gas to be experimented with. The
electric machine was used to communicate directly, sometimes the positive,
and sometimes the negative state, to the rod in connection with it.

1478. Thus we see that, notwithstanding there is a general difference in
favour of the superiority of the positive brush over the negative, that
difference is at its maximum in nitrogen and air; whilst in carbonic acid,
muriatic acid, coal gas, and oxygen, it diminishes, and at last almost
disappears. So that in this particular effect, as in all others yet
examined, the evidence is in favour of that view which refers the results
to a direct relation of the electric forces with the molecules of the
matter concerned in the action (1421. 1423. 1463.). Even when special
phenomena arise under the operation of the general law, the theory adopted
seems fully competent to meet the case.

1479. Before I proceed further in tracing the probable cause of the
difference between the positive and negative brush discharge, I wish to
know the results of a few experiments which are in course of preparation:
and thinking this Series of Researches long enough, I shall here close it
with the expectation of being able in a few weeks to renew the inquiry, and
entirely redeem my pledge (1306.).

_Royal Institution,
Dec. 23rd, 1837._

THIRTEENTH SERIES.

S 18. _On Induction (continued)._ P ix. _Disruptive discharge
(continued)--Peculiarities of positive and negative discharge either as
spark or brush--Glow discharge--Dark discharge._ P x. _Convection, or
carrying discharge._ P xi. _Relation of a vacuum to electrical phenomena._
S 19. _Nature of the electrical current._

Received February 22,--Read March 15, 1838.

P ix. _Disruptive discharge (continued)._

1480. Let us now direct our attention to the general difference of the
positive and negative disruptive discharge, with the object of tracing, as
far as possible, the cause of that difference, and whether it depends on
the charged conductors principally, or on the interposed dielectric; and as
it appears to be great in air and nitrogen (1476.), let us observe the
phenomena in air first.

1481. The general case is best understood by a reference to surfaces of
considerable size rather than to points, which involve (as a secondary