i68 Count Rumford’s Enquiry concerning the Nature of Heat , 
attentive examination of the matter will show, that no such con- 
centration 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 perfectly evident that 
these are not concentrated ; and, with respect to those which 
are refected , 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 circumstances, 
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 tem- 
perature be not raised by the calorific rays 1'rom 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 polished metallic body 
would do, of any other form, having the same area, or quantity 
of surface opposed to the hot mirror, and being placed at the 
same distance from it. 
By a similar train of reasoning, it may be shown, that the 
form of the hot body (that of a concave mirror) will contribute 
nothing to the effect it will produce on the cold mirror, in 
heating it, by the calorific rays it emits ; and that it will itself be 
cooled neither faster nor slower, on account of its peculiar form. 
Let us now suppose both mirrors to be at the temperature, 
precisely, of the room, (that of freezing water;) and, that a 
bullet, or other small body of a spherical form, at the tempera- 
ture of boiling water, be placed in the focus of one of the 
mirrors ; which mirror we shall call A. 
