70 Inquiry concerning the Natiire of Heat, 



From these experiments, which I lately repeated at 

 Geneva, in the presence of Professor Pictet, Mons. de 

 Saussure, M. Senebier, and several other persons, we 

 may venture to conclude, that, at equal intervals of tem- 

 perature, the rays which generate cold are just as real, 

 and just as intense, as those which generate heat ; or, 

 that their actions are equally powerful in changing the 

 temperatures of neighbouring bodies. 



On a superficial view of this subject, it might appear 

 extraordinary that so important a fact as that of the 

 frigorific radiations of cold bodies should have been so 

 long unnoticed, while the calorific radiations of hot 

 bodies have been so well known ; but, if we consider 

 the matter with attention, our surprise will cease. 

 Those radiations by means of which the temperatures 

 of neighbouring bodies are gradually changed and equal- 

 ized are not sensible to our feeling unless the intervals 

 of temperature be very considerable ; and the constitu- 

 tion of things is such, that, while we are often exposed 

 to the influence of bodies heated several thousand de- 

 grees (as measured by the thermometer) above the 

 mean temperature of the surface of the skin, it is very 

 seldom that we have opportunities of experiencing the 

 effects of the radiations of bodies much colder than 

 ourselves, and we have no means of producing degrees 

 of cold which bear any proportion to the intense heats 

 excited by means of fire. 



From the result of the experiment of which an ac- 

 count has just been given, it is evident that we should 

 be just as much affected by the calorific rays emitted by 

 a cannon bullet at the temperature of 160 degrees of 

 Fahrenheit's scale (= 64 degrees above that of the 

 blood) as by the frigorific rays of an equal bullet, ice 



