Harvey on the Deposition q/Deiv. 37 



2d. A narrow zone of exceedingly fine particles, having distinct 

 boundaries. 



3d. A zone composed of particles increasing in size from both 

 its boundaries to its middle. 



4th. A narrow zone of exceedingly fine particles, having distinct 

 boundaries. 



5th. A dry transparent circle. 



At midnight, the only perceptible changes were an increase in 

 the magnitudes of the drops of dew, a small diminution in the dia- 

 meters of the dry circles, and also in the breadth of the dry zone. 

 At two in the morning, the drops in the larger zones had farther 

 increased, and the dry parts still remained without moisture. At 

 four, the moment which marked the greatest depression of tempe- 

 rature, the larger drops had increased considerably; and the finer 

 particles in the narrow zones, had also augmented in size. 

 The breadths of the latter were, however, still preserved, in 

 common with the other zones, and the dry portions of the crystals. 



The appearance of the glasses at each period of observation, was 

 extremely interesting. After the particles of dew had increased to 

 a certain size, the glassy surface very much resembled the white 

 metallic paper used in ornamental works. About an hour before 

 sunrise, a small pellucid drop appeared in the centre of the dry 

 circular space, formed from the moisture which had been deposited 

 on the outside of the glass, and which had descended to the lowest 

 part of the crystal. When the glass was raised, the drop re- 

 mained on the metal. The sudden application of heat to the 

 crystals, was always accompanied by a partial disappearance of the 

 minuter particles of moisture. This was observed, both when the 

 glasses were handled, and when a candle was brought near them, 

 for the purpose of examination : — affording an indirect proof of the 

 theory of Dr. Wells, that the primary cause of dew, and all the in- 

 teresting and beautiful phenomena arising from its numerous modi- 

 fications, are to be traced to changes and varieties of temperature. 



To the feeble manner in which heat is emitted from highly po- 

 lished metallic surfaces, and the check which their influence com- 

 municates to bodies having considerable radiating powers, and in 



