1815.] _ Equilibrium of Radiant Heat. $83" 
This is explained in the work cited above. (Du Calorique Rayon- 
nant; ‘§ 121.) ; 
A good method of judging of this effect is to take an extreme 
case. Let us suppose the hody to be a perfect: reflector. | In this 
ease the internal cooling of the body would make no alteration in 
its radiation. ‘The thermometer exposed to its influence would not 
be affected by it. In fact, before the cooling, the temperature 
being uniform, the body would radiate by reflection, and this .radia+ 
tion would be precisely equal to that of all the bodies in the same 
place : and since it is supposed a perfect reflector, it would not emit 
any heat. Every thing continues the same after the interior cooling 
of this reflecting body. 
i contine myself to these two objections. They are sufficient for 
pointing out the method of answering all the others. 
Thus it appears that in order to be able to refute objections of this 
nature, nothing more is necessary than to understand well the 
theory against which they are made. Those who have been struck 
with these objections without sufficiently examining this theory ; 
and in particular the celebrated philosophers who have given them 
weight by inserting them in their works, will probably find it just 
and useful to insert also the answers to them, if they appear to 
them, as they do to me, perfectly satisfactory. 
IV. It is doubtless very useful that the ebjections which occur to 
philosophers against a probable theory should be explained at some 
length, and laid before those who are examining that theory. The 
consequence is a discussion which must be of advantage to the side 
of truth. It is therefore always with a kind of gratitude that I meet 
with such objections against the equilibrium of heat: and I expe- 
rience a kind of dissatisfaction when I meet with mere indications 
of some difficulty, without its being possible for me to divine in 
what they consist. ‘Time is lost in seeking for them. One runs the 
risk of being deceived; and it may easily happen that when we 
think we are untying the knot, we are only. pursuing useless re- 
searches without an object. In my Treatise on Caloric (p. 93, note) 
I have given an example of this kind of uncertainty. 
More recently L have been in an equal state of uncertainty on 
reading a note in p. 105 of the excellent work of Dr. Wells on 
Dew. Few works have so much interested me; few, I believe, 
show more completely the genius for observation and the love of 
truth. I could not, therefore, be indifferent to the opinion of so 
distinguished an author respecting an explanation connected with 
the theory of the equilibrium of heat, which I still consider as cor- 
rect. ‘The note to which [allude is as follows :— 
* T once intended to add*here an explanation of some curious 
observations by M. Prevost, of Montauban,* on dew, which were 
published first by himself in the 44th No, of the French Annals of 
* The author bas Inserted here Besancon instead of Montauban, 1 have cor- 
rected this slight mistake. 
