WEATHER PROVERBS 437 



lower temperature they maintain through radiation to space, just as, 

 and for the same reason that it collects on blades of grass and other 

 exposed good radiators. But in order that the marked radiation, es- 

 sential to the formation of the water droplets, may take place, it is 

 necessary that the atmosphere above them be dry, for water vapor does 

 not allow radiation freely to pass through it. Hence a gray morning 

 sky implies a dry atmosphere above the dew droplets, and, therefore, 

 justifies the expectation of a fair day, or even a clear one, for the drop- 

 lets themselves to which the gray is due are soon evaporated by the 

 rising sun, and convection, in this case, because it mixes the moist 

 lower with a dry upper air, seldom causes precipitation. 



A red morning sky commonly implies that the lower and heavier 

 dust particles have been protected from excessive night radiation by a 

 blanket of overlying moisture, else it would be gray; and at the same 

 time it also implies the presence, in the lower atmosphere, of suflBcient 

 moisture to enlarge the dust particles through incipient condensation, 

 else the sky would have some shorter wave-length color, such as yellow 

 to green. Hence when the morning sky is red the whole atmosphere, 

 to considerable elevations, is moist, and rain, therefore, probable. 



Convection in the main, as we have seen, prepares the way for the 

 phenomena of the evening sky, and radiation for those of the morning 

 sky. Hence the amount and distribution of moisture most favorable 

 to any given sky color, such as a gray or a red, are radically different 

 in the two cases. There is, therefore, a real physical basis for, and 

 much truth in, the proverbs that declare one result to follow the red 

 of morning and quite another that of evening. There is also justifica- 

 tion for some proverbs, two of which have already been given, that 

 refer to or include other colors. 



Additional good examples of the latter are as follows : 



"Evening gray and morning red 

 Make the shepherd hang his head." 



' ' An evening gray and a morning red 

 "Will send the shepherd wet to bed." 



"Evening red and morning gray 

 Two sure signs of one fine day." 



"Evening red and morning gray 

 Help the traveler on his way; 

 Evening gray and morning red 

 Bring down rain upon his head. ' ' 



CoBONAs AND Haloes 



"For I fear a hurricane; 

 Last night the moon had a golden ring, 

 And to-night no moon we see." 



— LongfeUow. 



