e whose particles cannot be
permanently polarized. If I be right in my view of induction, then I
consider the reduction of these two effects (which have been so long held
distinct) to an action of contiguous particles obedient to one common law,
as a very important result; and, on the other hand, the identity of
character which the two acquire when viewed by the theory (1326.), is
additional presumptive proof in favour of the correctness of the latter.

* * * * *

1339. That heat has great influence over simple conduction is well known
(445.), its effect being, in some cases, almost an entire change of the
characters of the body (432. 1340.). Harris has, however, shown that it in
no respect affects gaseous bodies, or at least air[A]; and Davy has taught
us that, as a class, metals have their conducting power _diminished_ by
it[B].

[A] _Philosophical Transactions_, 1834, p. 230

[B] Ibid. 1821, p. 431.

1340. I formerly described a substance, sulphuret of silver, whose
conducting power was increased by heat (433. 437. 438.); and I have since
then met with another as strongly affected in the same way: this is
fluoride of lead. When a piece of that substance, which had been fused and
cooled, was introduced into the circuit of a voltaic battery, it stopped
the current. Being heated, it acquired conducting powers before it was
visibly red-hot in daylight; and even sparks could be taken against it
whilst still solid. The current alone then raised its temperature (as in
the case of sulphuret of silver) until it fused, after which it seemed to
conduct as well as the metallic vessel containing it; for whether the wire
used to complete the circuit touched the fused fluoride only, or was in
contact with the platina on which it was supported, no sensible difference
in the force of the current was observed. During all the time there was
scarcely a trace of decomposing action of the fluoride, and what did occur,
seemed referable to the air and moisture of the atmosphere, and not to
electrolytic action.

1341. I have now very little doubt that periodide of mercury (414. 448.
691.) is a case of the same kind, and also corrosive sublimate (692.). I am
also inclined to think, since making the above experiments, that the
anomalous action of the protoxide of antimony, formerly observed and
described (693. 801.), may be referred in part to the same cause.

1342. I have no intention at present of go