JOSEPH BL A CK. i 7 1 



whose attention and reflection has been occupied with this sub- 

 ject. He infers that the wood, takes a Httle heat from the hand, 

 but is soon heated so much as to take no more. The lead 

 takes more heat before it be as much satiated ; and the ice con- 

 tinues to feel equally cold, and to carry off heat as fast as in the 

 first moment till the whole be melted. This, then, was the 

 inference made by Dr. Black. 



" Boerhaave has recorded an interesting observation by Fah- 

 renheit, namely, that water would sometimes grow considerably 

 colder than melting snow without freezing, and would freeze 

 in a moment when shaken or disturbed, and in the act ol 

 treezing give out many degi'ees of heat. Founded on this ob- 

 servation, it appears that Dr. Black entertained some vague 

 notion or conjecture that the heat which was received by the 

 ice during its conversion into water was not lost, but was still 

 contained in the water. And he hoped to verify this conjec- 

 ture, by making a comparison of the time required to raise a 

 pound of water one degree in its temperature, with the time 

 required to melt a pound of ice, both being supposed to 

 receive the heat equally fast. And that he might ascertain 

 how much heat was extricated during congelation, he thought 

 of comparing the time required to depress the temperature of a 

 pound of water one degree, with the time required for freezing 

 it entirely. The plan of this series of experiments occurred to 

 him during the summer season ; but for want of ice, which he 

 could not then procure, he had no opportunity of putting it to 

 the test. He therefore waited impatiently for the winter. 



" The winter arrived, and the decisive experiment was per- 

 formed in the month of December, 1761. From this experi- 

 ment, it appeared that as much heat was taken up by the ice 

 during its liquefaction as would have raised the water 140 degrees 



