750 W I N D S O F T H E G L B E . 



the late Prof. CofEu on the maps of the "AViiuls of the Northern Hemisphere." In the mind of the 

 deceased author this was the boundary between the prevailing polar winds of the Arctic regions and 

 the equatorial (westerly) winds of the middle latitudes of the Northern Hemisphere. He traced it at 

 a distance of 28° 20' from an imaginary point which he called the "Meteorological Pole," and located 

 in 84° N. lat. and 105° W. loug. 



PLATE 3. 



Mean Annual Direction between 80° N. Lat. and 56° S. Lat. 



The general prevalence of westerly winds will be seen here in the middle latitudes of the Northern 

 Hemisphere. Yet they are not always true equatorial winds, but incliue somewhat to the north in 

 some regions. On the tropical seas easterly winds largely prevail, as indicated by the length of the 

 arrows. This is the region of the trade- winds which prevail more largely in the Southern Hemisphere 

 than in the Northern. In the middle latitudes of the Southern Hemisphere westerly winds again 

 prevail, and this to a large extent, while further south there are again easterly (polar) winds. In 

 some parts of the globe, where monsoon winds prevail, the length of the arrow showing the mean 

 annual direction is rather small (as in India, China, Japan). This does not come from an un- 

 decided character of the winds, but is caused by the nearly opposite direction of the winds in 

 winter and summer. As they counteract one another in the yearly resultant, the ratio of the latter 

 is small. A reference to Plates 5 and 6, giving the mean direction of the wind in summer and 

 winter, shows that at each season the arrows in China, India, Japan, and the surrounding seas, have 

 a great length, showing largely prevailing winds at both seasons. 



3Ionsoon comes from the Arabic word llauaim, or wind of the season. We call monsoon regions 

 those that have winds of nearly opposite character in winter and summer, each of these winds 

 prevailing during some month of the year nearly to the exclusion of all others. On the greatest 

 scale we see such winds along all the southern and eastern coast of Asia, and on the surrounding 

 seas, the winds in the tropical part of this country being N. E. in winter and S. W. in summer, 

 while further north, in the interior of India, China, Japan, and the Russian Amoor provinces, the 

 winds are rather N. and N. W. in winter, and S. and S. E. in summer. Monsoon winds are caused 

 by the mutual reaction of great continental masses and the ocean, and thus they are most prevailing 

 where the greatest continent — Asia — approaches the greatest oceans — the Pacific and Indian. In 

 winter the pressure of the air is high on great continents, and thus air flows out from there, while in 

 summer, on the contrary, the land-masses being highly heated, an ascending current is produced and the 

 air from the surrounding oceans is drawn in to supply the deficiency. In all parts of the earth, where 

 continents and oceans adjoin, we see a tendency to produce monsoons. This is what Prof. Coflin 

 has called monsoon influences, but not everywhere monsoon winds are dominant. Monsoon influ- 

 ences may be considered as small deflections from the mean annual direction in regions where no 

 great differences in the mean direction of the wind in the difi'erent seasons are experienced, and thus 

 this relative influence of land and sea is small. In monsoon regions, on the contrary, this influence 

 is experienced on the largest scale. 



PLATE 4. 



Mean Direction in the Four Seasons in the Antarctic Region. 



The direction of the wind is here represented by broken arrows, thus : "^-'O' ^_^'~^ A 



straight lino drawn from the tail to the head of the arrow gives the mean annual direction. The 

 sequence is always — spring, summer, autumn, winter. Thus the nearest part to the tail of the arrow- 

 indicates the mean direction and ratio of resultant in the spring, and the nearest to the head that of 

 winter. As before stated, June, July and August are denominated "summer," etc. 



