130 WORLD-POWER AND EVOLUTION 



lower latitudes. When the air rises, heat is removed from the 

 earth's surface. As the air stays aloft a long time before coming 

 down again, the heat is radiated into space and lost. When the air 

 finally descends in clear areas of high pressure, it has become 

 decidedly cold. Because this cold air is heavy it flows under the 

 warm air in the storm center and raises it. Thus cold waves 

 follow warm waves. When the sun is active this process takes 

 place more rapidly than when the sun's surface is at rest. Hence, 

 even though the sun gives out more heat than usual, the increased 

 storminess causes the earth's surface to become cool. The amount 

 of cooling is greatest at the equator, and least in high latitudes. 



Still another point deserves special study. It bears not only 

 on the problem of the kind of climate under which man's mental 

 evolution took place, but on his historic activities and the con- 

 ditions of such modern matters as financial crises. When sun- 

 spots are abupdant, the ordinary cyclonic storms which bring our 

 frequent changes of weather tend to become concentrated in 

 certain belts. The main belt, both in the United States and 

 Europe, lies well to the north. At present, during times of the 

 greatest solar activity, its center lies in southern Canada and 

 southern Scandinavia. With greater solar activity the belt 

 would apparently lie still farther north. South of the northern 

 storm belt, that is, in the central parts of the United States and 

 Europe, the storminess declines when sunspots are numerous. 

 Hence these regions tend toward aridity when those farther north 

 are moist. Still farther south lies a second belt of increased 

 storminess at times of solar activity. This belt extends from the 

 southwestern United States to the Gulf of Mexico, and reappears 

 east of the Atlantic where it embraces the Mediterranean region, 

 Syria, Persia, northern India, and other parts of central Asia. 

 Here the increase in storminess is like that of the northern belt, 

 although much less intense. 



Having seen what happens at present during times of increased 

 sunspots, let us go back to the fourteenth century. Many lines 



