ON DEW, &c. 185 



A fourth experiment of , this kind was made 

 by me on the 7th of January, 1814, in the 

 garden of Lincoln's-Inn-Fields, by placing 10 

 grains of wool on a sheet of pasteboard, which 

 lay upon the snow. At the end of 35 minutes 

 the wool was 5 colder than the air, without 

 possessing any additional weight. 



Having thus shown the justness of my former 

 conclusion, that the cold, observed with dew, 

 is the previous occurrence, and, consequently, 

 that the formation of this fluid has precisely 

 the same immediate cause, as the presence of 

 moisture upon the outside of a glass or metallic 

 vessel, when a liquid considerably colder than 

 the air has been poured into it shortly before ; 

 I shall next apply this fact to the explanation 

 of several atmospherical appearances. 



I. The variety in the quantities of dew, which 

 were found by me upon bodies of the same 

 kind, exposed to the air during the same time 

 of the night, but in different situations, is now 

 seen to have been occasioned by the diversity 

 of temperature, which existed among them. 



II. Agreeably to the opinion of Mr. Wilson 

 and Mr. Six, the cold connected with dew 

 ought always to be proportional to the quan- 

 tity of that fluid ; but this is contradicted by 

 experience. On the other hand, if it be 

 granted, that dew is water precipitated from the 



