well as volatile metals and other substances; besides which, when
the rarefaction is very considerable, the electricity passes with scarcely
any resistance, and the production of no sensible heat; so that I think
Fusinieri's view of the matter is likely to gain but few assents.

[A] Bib. Univ. 1831, xlviii. 375.

1380. I have no need to remark upon the discharging or collecting power of
flame or hot air. I believe, with Harris, that the mere heat does nothing
(1367.), the rarefaction only being influential. The effect of rarefaction
has been already considered generally (1375.); and that caused by the heat
of a burning light, with the pointed form of the wick, and the carrying
power of the carbonaceous particles which for the time are associated with
it, are fully sufficient to account for all the effects.

1381. We have now arrived at the important question, how will the inductive
tension requisite for insulation and disruptive discharge be sustained in
gases, which, having the same physical state and also the _same
pressure_ and the _same temperature_ as _air_, differ from it in specific
gravity, in chemical qualities, and it may be in peculiar relations, which
not being as yet recognized, are purely electrical (1361.)?

1382. Into this question I can enter now only as far as is essential for
the present argument, namely, that insulation and inductive tension do not
depend merely upon the charged conductors employed, but also, and
essentially, upon the interposed dielectric, in consequence of the
molecular action of its particles (1292.).

1383. A glass vessel _a_ (fig. 127.)[A] was ground at the top and bottom so
as to be closed by two ground brass plates, _b_ and _c_; _b_ carried a
stuffing-box, with a sliding rod _d_ terminated by a brass ball _s_ below,
and a ring above. The lower plate was connected with a foot, stop-cock, and
socket, _e_, _f_ and _g_; and also with a brass ball _l_, which by means of
a stem attached to it and entering the socket _g_, could be fixed at
various heights. The metallic parts of this apparatus were not varnished,
but the glass was well-covered with a coat of shell-lac previously
dissolved in alcohol. On exhausting the vessel at the air-pump it could be
filled with any other gas than air, and, in such cases, the gas so passed
in was dried whilst entering by fused chloride of calcium.

[A] The drawing is to a scale of 1/6.

1384. The other part of the apparatus consisted of two