66 Inquiry concerning the Nature of Heat, 



from which it had set out ; and, as often as I wiped off 

 the ice from the surface of the flat end of the vessel 

 which was not blackened, and presented it clean and 

 bright to the ball of the instrument, the bubble began 

 again to move towards the opposite side, which, by 

 the bye, shows that ice emits a greater quantity of frigo- 

 rific rays than a bright metallic surface, at the same 

 temperature. 



Having frequently observed, on presenting my hand 

 to one of the balls of the thermoscope, that the instru- 

 ment was greatly affected by the calorific rays which 

 proceeded from it, apparently much more so than it 

 would have been by a much hotter body of the same 

 quantity of surface, but of a different kind of substance, 

 placed at the same distance, I was extremely curious to 

 find out whether animal substances do not emit calorific 

 (and consequently frigorific) rays much more copiously 

 than other substances, and whether living animal bodies 

 do not emit them in greater abundance than dead ani- 

 mal matter. 



The first experiment I made, with a view to the 

 investigation of this particular point, was as simple as 

 its result was striking and conclusive. 



Experiment No. 21. Having procured a piece of 

 gold-beater's skin (which, as is well known, is one of 

 the membranes that line the larger intestines in cattle, 

 and is exceedingly thin), I moistened it with water; and, 

 applying it, while moist, to the flat circular end of one 

 of my horizontal cylindrical vessels, it remained firmly 

 attached to the surface of the metal when it became 

 dry. I now filled this vessel, and another, of equal 

 dimensions, the end of which was not covered, with 

 hot water (at the temperature of 180), and presented 



