in Fluids. 281 



factory manner for that fact without being obliged, to 

 abandon my former opinions. 



In about half an hour after the hot water had been 

 poured into the jar, in the last experiment, examining 

 the surface of the ice, I discovered an appearance which 

 fixed my attention and excited all my curiosity ; I per- 

 ceived that the ice had been melted and diminished at 

 its surface, excepting only where it had been covered, or, 

 as it were, shadowed^ by the flat slips of deal by which the 

 cake of ice was fastened down in its place. 



Had the ice been protected and prevented from being 

 melted by that piece of the wood only which, being un- 

 dermost of the two, reposed immediately on the surface 

 of the ice, I should not perhaps have been much sur- 

 prised ; but that part of the surface of the ice being 

 likewise protected which was situated immediately under 

 the other piece of wood, that which, lying across 

 the under piece and resting on it, did not touch the ice any- 

 where except just at its edge^ that circumstance attracted 

 my attention, and I could at first see no way of account- 

 ing for these appearances but by supposing that the ice 

 had been melted by the calorific rays which had been 

 emitted by the hot water, and that those parts of the ice 

 which had been shadowed by the pieces of deal, receiving 

 none of these rays, had, of course, not been melted. 



I was so much struck with these appearances that I 

 immediately made the following experiments, with a view 

 merely to the elucidation of this matter. 



Experiment No. 17. 



Into a cylindrical glass jar, 6| inches in diameter and 

 8 inches high, I put a circular cake of ice, as large as 

 could be made to enter the jar, and about j|- inches 



