78 Inquiry concerning the Nature of Heat, 



and disposed to be cooled with the greatest facility will 

 be the least likely to be oppressed by the accumulation 

 of the heat generated in them by respiration, or of that 

 excited by the sun's rays. 



With a view to throw some light on this interesting 

 subject, I made the following experiments. 



Experiment No. 27. Having covered the flat ends 

 of both my horizontal cylindrical vessels with gold- 

 beater's skin, I painted one of these coverings (of this 

 animal substance) black, with Indian ink; and then, 

 filling both vessels with boiling-hot water, I presented 

 them, at equal distances, to the two opposite balls ' of 

 the thermoscope. 



The bubble of spirit of wine was immediately driven 

 out of its place by the superior efficacy of the calorific 

 rays which proceeded from the blackened animal sub- 

 stance. 



On repeating this experiment a great number of 

 times, and when the water in the vessels was at different 

 degrees of temperature (the temperature being the same 

 in the two vessels in each experiment), the results uni- 

 formly indicated that calorific rays were thrown off 

 from the black surface in greater abundance than from 

 the equal surface which was not blackened. 



Although the results of these experiments appeared 

 to me to be so perfectly conclusive as to establish the 

 fact in question beyond all possibility of doubt, yet, in 

 so interesting an inquiry, I was desirous, by varying 

 my experiments, to bring, if possible, a variety of 

 proofs to support the important conclusions which 

 result from it. 



Experiment No. 28. Having covered the two large 

 cylindrical vessels, No. 3 and No. 4, with gold-beater's 



