no Inquiry concerning the Nature of Heat, 



surfaces of spheres being to each other as the squares 

 of their radii. 



Supposing now (what, indeed, appears to be incontro- 

 vertible) that the intensity of the rays which hot and 

 cold bodies emit, in a medium perfectly transparent, 

 follows the same law, we can determine what effects 

 must be produced by the largeness or smallness of the 

 confined space (of a room, for instance) in which a hot 

 body is placed to cool. 



To simplify this investigation, we will suppose this 

 confined space to be a hollow sphere of ice 9 feet in 

 diameter, at the temperature of freezing water; and the 

 hot body to be a solid sphere of metal 2 inches in 

 diameter, at the temperature of boiling water, placed in 

 the centre of it ; and we will suppose, farther, that this 

 hollow sphere is void of air, and that the cooling of the 

 hot body is effected solely by the frigorific rays from 

 the ice. 



The question to be determined is, in what manner 

 the cooling of the hot body would be affected by in- 

 creasing the diameter of this hollow sphere of ice. 



Let us suppose its diameter to be increased to 18 

 feet. Its internal surface will then be to the surface of 

 a sphere 9 feet in diameter as the square of 18 to the 

 square of 9, that is to say, as 324 to 8 1, or as 4 to i. 

 And as the quantity of frigorific rays emitted are, cteteris 

 paribns, as the surface from which they proceed, the 

 quantity of rays emitted by the internal surface of the 

 larger sphere will be to the quantity emitted by the 

 internal surface of the smaller as 4 to i. 



But the intensities of these rays at the common cen- 

 tre of these spheres (where the hot body is placed) be- 

 ing as the squares of the distances from the radiating 



