ON DEW, &c. 187 



the night just spoken of, I made the following 

 experiment. To 10 grains of wool having the 

 same form and extension, as the parcels em- 

 ployed for the collection of that fluid, were 

 added 21 grains of water, this being the quan- 

 tity of moisture, which had been attracted by 

 10 grains of wool, lying on the grassplat, in the 

 space of 8 hours on that night. The wet wool 

 having been then placed in a china saucer, laid 

 on a feather-bed in a room, the door and win- 

 dows of which were shut, its heat during the 

 following 8 hours was, at frequent examina- 

 tions, uniformly found to be about 4 less, 

 than that of a dry china saucer on the same 

 bed ; the temperature of the air in the room 

 not having altered more than \ a degree, in the 

 course of the experiment. At the end of the 

 8 hours, the wool still retained 2j grains of 

 moisture. If this quantity had also evaporated, 

 the cold uniformly produced during the 8 hours 

 would, in all probability, have been about 4j. 

 From this experiment, therefore, I think it may 

 be inferred, that the mean quantity of cold, 

 which was prevented, by the formation of dew, 

 from appearing on the ground, during the night 

 which has been mentioned, was also aoout 4^, 

 But, as the production of dew, during some 

 parts of the night, was at a greater rate, than 

 that of 211 grains for 8 hours, 1 or 2 degrees 



