SUNLIGHT 15 



10. Winds. — The heat wav..- from tin- sun perform 

 an important duty in making winds. When the surface 

 of the earth is vanned l>\ the heal varee from the sun, 

 it in turn warms up the air which is pressing against it 

 Warm air rises, and cold air, which is heavier, moves in 

 to take its place. Tims the air i- constantly moving 



■bout, and the motion is called wind. The motion of 



the air helps to k« ep the eartli from hecoming too hot. 

 Seated air ri<e< and takes with it a quantity of heat 

 from the earth; eohler air comes in its place, and this 

 in it- turn is warmed up and carries ofT more heat. So 

 changing may go on until the earth is cooled off. 

 Notice tlic air near a Btone or hrick wall some hot day 

 and see the waves of hot air rising. When a fire is built 

 on a hearth it fir.-t heats the air, which, rising up the 

 chinni' eft I drailght Winds arc distrihut. 



rain; moving orer the country they carry with them 

 clouds of moisture, which, when condensed, fall M rain. 

 'Plie winds from the oceans bring in to the land great 

 <|iiantities of rain clou. 



11. Radiation. — During the rammer, when the sun 



p«.iir- down greal quantities of heat day after day. the 

 earth becomes thoroughly warmed up. The land is 

 wanned by the sunshine, and bodies of water are 

 warmed even more thoroughly than the soil. Thus the 



earth is storing up heat in hind ami water for use at 

 night and in the cold winter. At night, when the sun 

 has set and the rapplj of heel waves is temporarily shut 

 ofT. the air would become very cold but for the heat the 

 earth DM luring the day. The air pressing 



against the earth is warmed by the stored heat, and thua 



