82 Inquiry concerning the Nature of Heat, 



merits, that the radiations of cold bodies affected my 

 thermoscope very sensibly, even when placed at a con- 

 siderable distance from it, and in situations where cur- 

 rents of cold air could not be suspected to exist, I was 

 desirous of finding out whether the cooling of a hot 

 body would or would not be 'sensibly accelerated by 

 those rays. To determine that point, I made the fol- 

 lowing experiment. 



Experiment No. 29. Having provided two conical 

 vessels, made of thin sheet brass, each 4 inches in diam- 

 eter at the base, and 4 inches high, ending above in a 

 cylindrical neck, 0.88 of an inch in diameter, I enclosed 

 each of them in a cylinder of thin pasteboard, covered 

 with gilt paper, and then covered them up with rabbit- 

 skins, which had the hair on them, in such a manner that 

 no part of these vessels, except their flat bottoms, was 

 exposed naked to the air. I then covered their bottoms 

 with gold-beater's skin, painted black with Indian ink, 

 in order to render them as sensible as possible to calo- 

 rific and frigorific rays. 



This being done, I suspended these two vessels in 

 an erect position, or with their bottoms downwards, to 

 the two opposite horizontal arms of a wooden stand, 

 provided for the experiment; and I placed under each 

 of them a pewter platter, blackened on the inside by 

 holding it over a lighted wax candle. 



Each of these platters was 12 inches in diameter, 

 and they were supported on the top of two shallow 

 earthen dishes, each of which was n inches in diameter 

 at its brim ; these earthen dishes being supported on 

 circular wooden stands 10 inches in diameter. 



A circular piece of thick drawing-paper, ia-J inches 

 in diameter, with a circular hole in its centre, just 6 



