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 

 admitted to originate. 



In paragraph (xxxi,) you say "that at one time there was a 

 distinction 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 v/ould 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 sinallest 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, and 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, 



