10 Second Letter from Dr. Hare to Prof. Faraday. 
dependent of any energy of theirs, and proceeds altogether from 
that electrical accumulation with which the inductive change is 
Be to originate. 
In paragraph (xxxi,) you say * « that at one time there was a 
quibetion between heat and cold. At present that theory is 
done away with, and the phenomena of heat and cold are referred 
to the same class, and to different degrees of the same power.”’ 
_ In reply to this I beg leave to point out, that although, in ordi- 
nary acceptation, cold refers to relatively low temperature; yet 
we all understand that there might be that perfect negation of 
_ heat, or abstraction of caloric, which may be defined absolute 
cold. I presume that, having thus defined absolute cold, you 
- would not represent it as identical with caloric. For my own 
part this would seem as unreasonable as to confound matter with 
nihility. 
Assuming that there is only one electric fluid, there appears 
to me to be an analogy between caloric and electricity, so far that 
negative electricity conveys, in the one case, an idea analogous 
to that which cold conveys in the other. But if the doctrine of 
Du Fay be admitted, there are two kinds of electric matter, 
which are no more to be confounded than an acid and an alkali. 
Let us, upon these premises, subject to further examination your 
argument (1330,) that insulation and conduction should be iden- 
tified, “since the moment we leave in the smallest degree per- 
fection at either extremity, we involve the element of perfection at 
the opposite end.” Let us suppose two remote portions of space, 
one, replete with pure vitreous electricity, the other with pure re-— 
sinous : let there be a series of like spaces containing the resinous 
_ and vitreous electricities in as many different varieties of admix- 
ture, so that in passing from one of the first mentioned spaces, 
through the series to the other, as soon as we should cease to be 
exposed to the vitreous fluid, in perfect purity, we should begin 
to be exposed minutely to the resinous, or that, in passing from 
the purely resinous atmosphere, we should begin to be exposed to 
a minute portion of the vitreous fluid; would this be a sufficient 
reason for confounding the two fluids, ind treating the phenomena 
to which they give rise as the effect of one only ? 
But the discussion, into which your illustrations have led me, 
refers to things, whereas conduction and insulation, as I un- 
derstand them, are opposite and incompatible properties, so that, 
