Harvey on the Deposition ofDeio. 39 



condition did not exist, but a close approximation to it took place. 

 This new state of the metallic surface necessarily restored, in some 

 degree, the diminished radiating power of the glass ; and hence 

 produced the narrow zones of fine particles, formed after the first 

 deposition. Nor is it improbable, though I have not met with an 

 experiment to verify it, but that the moment marked by the depo- 

 sition of dew on a metallic surface, would also be distinguished by 

 the appearance of moisture on the dry portions of the crystal. And 

 from the principle also, that dew is deposited more readily on ho- 

 rizontal, than on vertical, surfaces, we may anticipate that moisture 

 would appear earlier, as well as more copiously, in the dry circular 

 space at the bottom of the glass, surrounded with the ferrule, than in 

 the dry zone round the border of the same crystal. 



On the 10th of June the following observations were made 

 on the temperature of glass resting on the green herbage, and that 

 of the air twelve inches above it. The experiment was instituted 

 to observe if the deposition of dew immediately succeeded the de- 

 pression of the temperature of the body on which it was formed, 

 below that of the stratum of air hovering over its surface. From 

 the table this appears to have been the case. 



The first perceptible trace of moisture was observed on the 

 vitreous surface resting on the grass, at six ; and at a quarter of an 

 hour after, it was distinctly visible. At fifteen minutes before six, 



