1 6^ Count Rumford’s Enquiry concerning the Nature of Heat, 
the rays which proceed from colder bodies, and that these rays, 
like those of light, are reflected, refracted, and concentrated, 
according to certain known laws, by the polished surfaces of 
mirrors and lenses, it might perhaps be imagined, that the 
cooling of a hot body might be accelerated, or retarded, by 
giving it some peculiar form ; or by placing near it, and in 
certain positions with respect to it, two or more highly polished 
reflecting mirrors. 
As these conjectures, if well founded, might lead to experi- 
ments from the results of which the truth or falsehood of the 
hypothesis in question might be demonstrated, it is of much 
importance that this matter should be thoroughly investigated. 
I shall therefore beg the indulgence of the Society, while I en- 
deavour to examine it with that careful attention which it appears 
to me to deserve. 
When different solid substances, heated to the same degree 
of temperature, are exposed in the air to cool, those among 
them which appear to the touch to be the hottest, are not those 
which cool the fastest, or which send off calorific rays, through 
the air, in the greatest abundance. 
As polished metals reflect a great part of the rays from other 
bodies which arrive at their surfaces, and as they are neither 
heated nor cooled by the rays so reflected, their temperatures 
are slowly changed by the actions of the surrounding bodies at 
a different temperature. 
When a hot polished metallic body is exposed in the air to 
cool, surrounded by other bodies at the same temperature as 
that of the cold air, as most of the rays from the surrounding 
bodies are reflected at the polished surface of the hot body, it is 
evident that two sorts of rays must proceed from the surface of 
