ON DEW, &c. Ml 



every hour, and by weighing each of them, after 

 exposure for an hour, found, that they had all 

 attracted dew. 



When dew forms upon a smooth dense body 

 as glass, and it is only by means of such a body, 

 that the process can be accurately observed, the 

 appearances are altogether similar to those, 

 which occur on a like body, when exposed to 

 the steam of water, a little warmer than itself. 

 The exposed surface has first its lustre dimi- 

 nished, by a slight damp uniformly spread over 

 it. As the moisture increases, it gathers into 

 irregularly shaped flat drops, which are, at first, 

 very small, but afterwards enlarge and run into 

 one another, forming streamlets, by means of 

 which a great part escapes from the body which 

 had received it. 



During nights, that are equally clear and 

 calm y dew often appears in very unequal quan- 

 tities, even after allowance has been made, for 

 any difference in their lengths. One great 

 source of these differences is very obvious. 

 For, it being manifest, whatever theory be 

 adopted concerning the immediate cause of 

 dew, that the more replete the atmosphere is 

 with moisture, previously to the operation of 

 that cause, the more copious will the precipita- 

 tion of water be, after this operation has com- 

 menced, all the circumstances, which tend to 



K 2 



