1bow Dew is fformefc, 121 



would be felt if it were not for the great en- 

 velope of atmosphere and its attendant c^oud 

 formations that surround the earth. There 

 are but few days in summer when there is not 

 a haze in the atmosphere, although we call the 

 sky clear, which intensifies the light and gives 

 everything a warmer tone. The heat coming 

 from a full moon on a clear night is absorbed 

 in causing the aqueous vapors that are partly 

 condensed in the higher regions of the atmos- 

 phere, to be reabsorbed into transparent vapor. 

 This clears away the heat screen in the atmos- 

 phere and allows radiation to go on more 

 rapidly at the earth's surface, and thus cools 

 it to a greater extent when the moon is shin- 

 ing brightly than when it is dark and in the 

 shadow of the earth. 



As we have already mentioned, the cold that 

 is produced by radiation through the blades of 

 grass and other radiating substances may be 

 indicated by placing one thermometer on the 

 ground and fixing another at some point in the 

 air. Sometimes the difference is very marked, 

 amounting to as much as 20 or 30 degrees. If 

 under these conditions a cloud floats over- 

 head, forming a heat screen, its presence will 

 be readily noticed by a rise in the thermom- 

 eter. Radiation into the upper regions of the 

 atmosphere is checked, which causes a sudden 

 rise in the temperature near the surface of the 

 earth. By taking advantage of this principle 



