1 1 6 Inquiry concerning the Nature of Heat, 



which, coming from the surface of the cold mirror, im- 

 pinge against the surface of the hot mirror, will be the 

 same, whatever may be the degree of polish, or reflect- 

 ing power, of the cold mirror. And, if this be the case, 

 we may conclude that the presence of this mirror will 

 have no effect whatever on the hot mirror ; or that it 

 will no more expedite its cooling than any other body, 

 of any other form, would do, at the same distance and 

 occupying the same space. 



It might perhaps be imagined that the form of the 

 cold mirror might concentrate the rays it emits and 

 reflects, and, by such concentration, produce a greater 

 effect on the opposite mirror than if its surface were 

 flat, or of any other form ; but a more attentive exami- 

 nation of the matter will show that no such concentra- 

 tion actually takes place : for, with regard to those rays 

 which are emitted by this cold body, as they proceed 

 from each point of its surface in all directions^ it is per- 

 fectly evident that these are not concentrated ; and with 

 respect to those which are reflected, it is equally certain 

 that they are not concentrated, because, in order to 

 their being concentrated, they must arrive at the surface 

 of the mirror in parallel lines, and in the direction of 

 the axis of the mirror, which, under the given circum- 

 stances, is evidently impossible. 



Hence we see that the presence of the cold mirror 

 will not tend, in the smallest degree, either to accelerate 

 or to retard the cooling of the hot mirror; that is to 

 say, provided its temperature be not raised by the calo- 

 rific rays from the hot mirror. 



If its temperature be raised by those rays, it will 

 tend to retard the cooling of the hot mirror ; but, even 

 in this case, it will not retard it more than any other 



