278 ESSAY 



been shown, by the last experiment, independ- 

 ently of what; was said before in this Essay, not 

 to be evaporation. It is also clear, that the 

 cold, induced on the water in those experi- 

 ments, had a common cause with that observed, 

 at the same time, upon the grass and the straw ; 

 which latter cold must, in consequence of proofs 

 formerly given, be admitted to have arisen from 

 the radiation of the heat of those substances to 

 the heavens. A necessary inference, therefore, 

 appears to be, that the formation of ice in Ben- 

 gal, in the circumstances described by Sir R. 

 Barker and Mr. Williams, must likewise be 

 attributed, in by far the greater measure, if 

 not altogether, to a loss of heat, which the 

 water suffers by its own radiation, while situated 

 in such a manner, that it can receive little heat 

 from other bodies, either by radiation or con- 

 duction*. 



* On the evenings preceding the nights, during which ice 

 is produced in Bengal, the temperature of the water exposed 

 in the pans is, probably, often 60 or more. But water of 

 the heat of 60, if exposed in a shallow earthen vessel to air 

 of the same temperature, during the day, while the weather 

 is calm and clear, will lose about 3 of heat by evaporation. 

 A cold from this cause may, therefore, concur with that from 

 radiation, and, consequently, may, in Bengal, accelerate 

 somewhat the formation of ice. The influence, however, of 

 evaporation there, in this respect, should the state of the air 



