ON DEW, &c. 203 



by another wise arrangement, tends to prevent 

 the injury, that might arise from its own cause ; 

 since the precipitation of water, upon the tender 

 parts of plants, must lessen the cold in them, 

 which occasions it. I shall observe in the last 

 place, that the appearance of dew is not confined 

 to any one part of the night, but occurs during 

 its whole course, from means the most simple 

 and efficacious. For after one part of the air 

 has deposited its moisture, on the colder surface 

 of the earth, it is removed, in consequence of 

 that agitation in the atmosphere which exists 

 during its stillest states, and gives place to an- 

 other having its quantity of water undiminished ; 

 and, again, as the night proceeds, a portion of 

 air, which had before deposited all the moisture, 

 which circumstances at that time permitted, is 

 rendered fit, by the general increase of the cold 

 of the atmosphere, to give out a fresh parcel, 

 when it comes anew into contact with the 

 ground. 



I. The first fact, which I shall here attempt 

 to explain, is the prevention, either wholly or 

 in part, of cold, from radiation, in substances 

 on the ground, by the interposition of any solid 

 body between them and the sky. This evi- 

 dently appears to arise in the following manner. 

 The lower body radiates its heat upwards, as if 

 no other intervened between it and the sky j 



