668 WINDSOPTHEGLOBE. 



througli the zenith of a parallel. The greatest heat m our summer would be 

 about the Tropic of Cancer, in our winter about the Tropic of Capricorn, and 

 this would also be the belt of low pressure at that time. The S. E. trade would 

 cross the equator into the northern hemisphere when the 'sun has a northern 

 declination, and the N. E. trade follow into the southern hemisphere during the 

 other half of the year, giving a variation of the inner limits of the trades of 

 perhaps 40°, instead of the 10° or 12° which are now observed. Further, 

 as dry continents cool also more rapidly, the cold in the polar region of each 

 hemisphere during the winter would be more intense than now, extending to 

 the whole polar region, and coinciding with a very high pressure. 



These hypothetical conditions are much more imperfectly realized than those I 

 have sketched before, as the extent of continents is much less than that of oceans. 

 The nearest approach to realization is on the greatest continent, that of Asia, 

 where the highest pressure of winter is a little north of 50° N. If it is not found 

 further north, it is because the continent does not extend much beyond 73° N. 

 In summer, on the contrary, we find the highest temperature in N. W. India 

 between 30° and 35° N., and also the lowest pressure there and in N. China. 



The larger the continent the more it approaches to the ideal conditions I have 

 supposed. In Africa, for example, there is a belt of lowest pressure in summer at 

 about 17° N., and the highest temperature is probably still more to the north. 



The narrower continents of North and South America are more under the in- 

 fluence of oceans than Africa. 



As already seen, the highest mean pressure on the surface of the globe is found 

 in winter on the Asiatic continent. It is necessary to mention here a feature of 

 the climate of this continent, explained by geographical conditions, which lias a 

 great influence on the winds, namely, the steadiness of pressure in winter. 

 Pressure is so constant here that, though the barometrical range generally increases 

 with latitude, it is not greater at Jakutsk in N. E. Siberia, under 62° N. L., than 

 in Vienna in Central Europe, Lat. N. 48°, or even in St. Louis in North America, 

 under 39° N. L. The coldest and heaviest stratum of air over Eastern Siberia is 

 prevented from floAving towards the south and east, where pressure is low, by the 

 intervening mountains and plateaus, from 3000 ft. to 5000 ft. high. So long as the 

 cold of winter continues, pressure must, therefore, be high over the cold region 

 of Northern Asia. As it is low in the Pacific Ocean and the equatorial regions, 

 air will flow there from the region of high pressure above the mountains and 

 plateaus. But, as above said, the coldest and heaviest lowest stratum cannot 

 flow towards the Pacific on account of the intervening heights; the quantity of 

 air moving in this direction will not be great enough to supply the deficiency. 

 Thus pressure being lower the whole winter in the S. and E., the Avinds should 

 be regular from the N. and W., and this is really the case. 



On the whole southern and eastern slope of Asia we see a mutual reaction of 

 continental and oceanic influences — the great monsoons. The Europeans were first 

 made acquainted with tlie regular change of wind and weather in India through 

 the campaigns of Alexander the Great. Not only did the Greeks see this change 

 themselves, but they also learned from the natives with how great a regularity this 



