72 Inquiry concerning the N attire of Heat, 



frigorific emanations from cold bodies, analogous to 

 those calorific emanations from hot bodies which he 

 calls radiant heat. He everywhere speaks of the reflec- 

 tion of cold (by metallic mirrors) as being merely appar- 

 ent ; and it is on that supposition that the explanation 

 he has given of the phenomena is founded. 



On a supposition that the caloric of modern chemists 

 has any real existence, and that heat, or an increase of 

 temperature in any body, is caused by an accumulation 

 of that substance in such body, the reflection of cold 

 would indeed be impossible ; and the supposition that 

 such an event had taken place would be absurd, and 

 could not be admitted, however striking and convincing 

 the appearances might be which indicated that event. 

 But, to return from this digression : 



Having found that the intensity of the calorific rays 

 emitted by a hot body, at any given temperature, de- 

 pends much on the surface of such body, that a pol- 

 ished metallic surface, for instance, throws off much 

 fewer rays than the same surface, at the same tempera- 

 ture, would emit if painted, or blackened in the smoke 

 of a lamp or candle, I was desirous of finding out 

 whether the frigorific rays from cold bodies are affected 

 in the same manner, by the same means, and in the 

 same degree. 



It was to ascertain that point that the experiment 

 No. 20 was made ; and although the result of that ex- 

 periment afforded abundant reason to conclude that 

 those substances which, when hot, throw off calorific 

 rays in the greatest abundance, actually throw off great 

 quantities of frigorific rays when they are cold, yet, as 

 the relative quantities of these rays could, not be ex- 

 actly determined by that experiment, in order to ascer- 



