74 Inquiry concerning the Nature of Heat, 



But it is time to consider these emanations in a new 

 point of view. What difference can there be between 

 calorific rays and frigorific rays ? Are not the same 

 rays either calorific or frigorific according as the body at 

 whose surface they arrive is hotter or colder than that 

 from which they proceed ? 



Let us suppose three equal bodies, . A, B, and C, 

 (the globular bulbs of three mercurial thermometers, 

 for instance,) to be placed at equal distances (3 inches) 

 in the same horizontal line ; and let A be at the tem- 

 perature of freezing water, B at the temperature of 72 

 F., and C at that of 102 F. The rays emitted by B 

 will be calorific in regard to the colder body A, but in 

 respect to the hotter body C they will be frigorific ; 

 and, from the results of the two last experiments, we 

 have abundant reason to conclude that they will be 

 just as efficacious in heating the former as in cooling 

 the latter. 



Before I proceed to give an account of the experi- 

 ments which were made with a view to determine the 

 relative quantities of rays emitted from the surfaces of 

 various substances, from living animals, dead animal 

 matter, &c. (which I must reserve for a future com- 

 munication), I shall lay before the Society the results 

 of several experiments, of various kinds, which were 

 made with a view to the farther investigation of the 

 radiations of hot and of cold bodies, and of the effects 

 produced by them. 



Experiment No. 25. Having found, from the re- 

 sults of the experiments No. 21 and No. 22, that great 

 quantities of rays are thrown off from the surface of the 

 animal substance used in those experiments (gold-beat- 

 er's skin), I now covered the whole of the -external sur- 



