2 76 Of the Propagation of Heat 



large as the internal diameter of thejar, and 3-*- inches 

 thick, weighing ic4 oz. 



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This cake of ice being ready, I now poured into the 

 jar 6 Ib. \\ oz., Troy, of boiling-hot water, and, putting 

 the ice gently into it, I found that it was entirely melted 

 in 2 minutes and 58 seconds. 



Having found by this experiment how long the ice 

 was in melting at the surface of the hot water, I now 

 endeavoured to find out whether it would not require a 

 longer time to melt at the bottom of the water. 



Experiment No. 16. 



Into the same jar which was used in the foregoing ex- 

 periment, I now put a cake of ice of the same form and 

 dimensions as that above described, but, instead of letting 



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it swim at the surface of the hot water, I fastened it 

 down on the bottom of the jar and poured the water 

 upon it. 



This cake of ice was fastened down in the jar by 

 means of two slender and elastic pieces of deal about -| 

 of an inch thick, and \ of an inch wide, which, being a 

 trifle longer than the internal diameter of the jar, were 

 of course a little bent when they were introduced into it 

 in an horizontal position, and, on being put down upon 

 the ice at right angles to each other served to confine the 

 ice, and prevent its rising up to the surface when the 

 water was put -into the jar upon it. 



To protect the ice while the boiling-hot water was 

 pouring into the jar, its surface was covered with a cir- 

 cular piece of strong writing-paper, which was afterwards 

 removed as gently as possible by means of a string which 

 was fastened to one side of it ; and to prevent the glass 

 jar from being cracked by the sudden application of the 



