12 THE WEATHER 



of murky vapor that grows into cloudiness. Usually the higher and 

 more distant the clouds seem to be, the more gradual but general 

 the coming change of weather will prove. Fitzroy. 



If cirrus clouds form in fine weather with a falling barometer, it 

 is almost sure to rain. Howard. 



If cirrus clouds dissolve and appear to vanish, it is an indication of 

 fine weather. Garriott. 



When cloud streamers point upward, the clouds are falling or de- 

 scending, and rain is indicated ; when cloud streamers point downward, 

 the clouds are ascending, and dry weather is indicated. Garriott. 



Clouds flying against the wind indicate rain. 



If in hot weather two strata of clouds appear to move in opposite 

 directions, thunderstorms are indicated. 



Well-defined cumulus clouds forming a few hours after sun-rise, 

 increasing toward the middle of the day, and decreasing toward even- 

 ing are indicative of settled weather ; if instead of subsiding in the even- 

 ing, leaving the sky clear, they keep increasing, they indicate wet 

 weather. Jenyms. 



Birds fly high in fair weather and low in foul weather. The expla- 

 nation is that in fair weather the barometer is usually high, the air 

 heavier and denser and capable of sustaining a given weight at a 

 greater elevation than when less dense during the passage of a storm. 



Frosts, and Methods of Protection 



How frost forms (Wilson). 



In the day, plants usually receive more heat from the sun than they 

 give off (radiate), and consequently become warmer; but at night the 

 process is reversed, and they radiate more heat than they receive and 

 thus grow colder. When the surface of a plant has lost (radiated) 

 sufficient heat to cause its temperature to fall to 32 or below, frost 

 forms. Any condition that causes increased radiation will increase the 

 liability of frost, and conversely, whatever checks radiation or supplies 

 additional heat to the air will tend to ward off frost. 



A clear night is favorable for frost because radiation or loss of heat 

 from the surface of the earth proceeds most rapidly under a clear sky. 

 Clouds act as a blanket. The heat rays do not penetrate them easily, 

 but are reflected back toward the earth, thus checking radiation by 

 confining the heat to the strata of air between the earth and the clouds. 



