and the Mode of its Communication. 67 



them both, at the same moment, to the two balls of the 

 thermoscope, and at the same distance. 



The bubble of spirit of wine was immediately driven 

 out of its place to a great distance; and did not return 

 to its former station till after the vessel whose end was 

 covered with gold-beater's skin had been removed to a 

 distance from the ball to which it was presented which 

 was five times greater than the distance at which the 

 other vessel was placed from the opposite ball. 



I was induced to conclude, from the result of this 

 interesting experiment, that an animal substance emits 

 25 times more calorific rays than a polished metallic sur- 

 face of the same dimensions, both substances being at 

 the same temperature. 



Experiment No. 22. Having emptied both the ves- 

 sels used in the last experiment, and refilled them with 

 pounded ice and water, I now presented them again to 

 the thermoscope, at equal distances from their respec- 

 tive balls. 



The result of this experiment confirmed the conclu- 

 sion I had been induced to draw from a former experi- 

 ment of the same kind (No. 13), the motion of the 

 bubble towards the vessel whose surface was covered 

 with gold-beater's skin showing that the rays which 

 proceeded from that animal substance were considerably 

 more efficacious in producing cold than those which 

 proceeded from the naked metal. 



The radiation of cold bodies appearing to me to have 

 been proved beyond all doubt by the preceding experi- 

 ments, I now set about to investigate a very important 

 point which still remained to be determined : I en- 

 deavoured to find out whether the intensity of the 

 action of the frigorific rays which proceed from cold 



