ws15j Equilibrium of Radian: Heat. 381 
whatever will ensue. Those who make the preceding objection 
ought to be astonished at this result, and to blame the theory for 
not explaining it. j 
Many other objections may be started, and have indeed been — 
raised, in consequence of the same imperfect and erroneous concep- 
tions. I shall only mention one, which, like the preceding, has 
only become known to me by means of a good refutation. 
The refutation is by M. Tremery, who has inserted it in the 
Nouveau Bulletin des Sciences (Aout, 1813, No.7, p; 323) : and 
the objection, the author of which he does not name, is relative to 
the reflection of cold by means of two concave mirrors. It is 
know’ that the theory of ‘the équilibriam explains the result of this 
experiment respecting thie reflection of cold .with the same. facility 
as it does the reflection of heat... It is needless to state this part of 
the theory, which is, I believe,: pretty generally known. 
To this explanation it is objected, that the matrass.of ice or snow 
placed at one of the foci, being supposed to radiate,: ought to send 
by double reflection some rays to the thermometer placed in the 
other focus.’ If the mirrors were withdrawn, these rays would be 
dissipated, and would not come to the thermometer. Therefore 
when the mirrors are removed, the thermometer ought to sink, and 
it ought to rise again when the mirrors are replaced, whieh is con- 
trary to the matter of fact. 
IL. These objections have been forescen and refuted long ago, in 
a work entitled Du Calorique Rayonvant, which [ published in 
1809 (at Geneva and in Paris ; Paschoud). Some of them are 
even peculiarly answered, particularly that one drawn from the ex- 
periment with the conical tube (Du Calorique Rayonnant, § 113). 
{ have therefore only to refer to that work. But as philosophers 
occupied with this subject have been obliged to enter into consider- 
able details in order to get rid of these difficulties, started frequently 
without any regard-to the previous solutions of them, it will not be 
without utility to state here as simply as possible the principles on 
which the theory depends, and on which the answers to these objec- 
tions depend. ‘These principles are at bottom the same as those 
explained by Messrs. ‘T'remery and Davenport; and I shall state 
them more shortly, and perhaps more generally. 
* Y, L suppose that constitution of caloric which agrees best with 
the phenomena of radiation to be known and admitted. It is a dis- 
crete fluid, every particle of which moves rapidly in a straight line. 
These particles go, one in one direction, and another in another 3 
so that every sensible point of the hot space is a centre, from which 
depart, and to which arrive, rows of particles or calorific rays. 
2, A reflector in # place of uniform temperature sends neither 
more nor fewer calorific rays than another body.—In fact, the re- 
flector will not be called of the temperature of the place till the 
assertion Which 1 bave just made be verified ; and in a. short time 
this cannot fail to happen from the laws of the equilibrium of heat. 
As to the thermometrical effect, it is of no consequence whether 
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