142 SOCIAL EVOLUTION 



taneously throughout the northern hemisphere. It is 

 held, with some evidence, that once in thirty-six years, 

 on the average, we pass through what may be called a 

 climatic cycle. There are two extremes during a cycle, 

 at one of which the climate of continental regions for a 

 series of years is unusually cool and rainy, with a low 

 barometric pressure and relatively frequent storms; 

 while at the other it is comparatively warm and dry, 

 with high pressure and few storms. These changes are 

 most extreme in mid-continental regions, decreasing 

 toward the sea-coast. Thus the Glacial period as a 

 whole represents the largest type of pulsation. But upon 

 it are superposed the great pulsations known as Gla- 

 cial epochs, each with a length measured probably in 

 tens of thousands of years. The steady progress of these 

 cycles is interrupted by smaller changes of climate, such 

 as those of which there is evidence during historic times 

 in Central Asia. Finally the climate of the world pul- 

 sates in cycles of thirty-six years, and even these are in- 

 terrupted by seasonal changes and by storms. 



We have often heard it said that civilization has ad- 

 vanced from east to west. Mr. Huntlngton considers it 

 more accurate to say that civilization has advanced from 

 south to north. The civilizations which started in Egypt 

 and Babylonia, we know, spread to Persia, slightly farther 

 north. Then Syria, Greece, and Carthage became dom- 

 inant. Next, Rome until its decline, and then an obscure 

 period of transition until France, Austria, and the states 

 of southern Germany grew in prominence. Finally, 

 during modern times, the northern nations of Europe 

 have risen to power. The common explanation has been 

 that as man became more civilized he also became better 

 adapted to colder and moister climatic conditions. Mod- 



