674 



WINDS OF THE GLOBE. 



surface of the earth has perpetual calms. The calm-belts themselves are not 

 constant, but move in the different seasons, and besides, the calms are more or 

 less frequently disturbed. 



In the trade-winds belts also, notwithstanding calms are very rare, the velocity 

 of the wind is probably less than the average of the globe. 



Probably the part of the earth where the winds have the greatest velocity, is 

 found between 40° and 60° Lat. S., where very strong westerly winds are prevailing 

 the whole year. The cause of this is the great difference in the pressure of the air 

 at a small distance, or in other words the steep barometric gradient. 



The great difference of the mean velocity of the winds blowing over a region, 

 and of the progress of the air in a certain direction, should be borne in mind. 

 Where the winds are weak, but always from one direction, as in the trade-wind 

 region, the total rate of progress measured in miles will be considerable, frequently 

 greater than in regions where strong winds blow from different directions. It is 

 even possible that the winds may be so counterbalanced by one another, that there 

 will be no resultant direction, so that the definite result, as far as progress of the 

 air is concerned, would be the same as if absolute calms had prevailed all the time. 



So far as regions are considered, where the mean direction of the wind does not 

 vary, or varies but slightly in the different seasons, the mean annual direction with 

 rate of resultant, gives a tolerably fair idea of the character of winds in such 

 regions. 



It is quite different where regions with very great variations in the yearly direc- 

 tion of the wind are considered. Here the annual direction will give but a very 

 imperfect idea of the character of the winds. This is the reason' why, as far as 

 possible, I have always placed at least two contrasting seasons, summer and winter, 

 in giving the percentages of the winds and the mean directions in the small tables 

 which follow, and serve to illustrate the winds of different regions of the world. 

 This is also the reason for constructing the two maps, PI. 5 and 6. The same atten- 

 tion has been given to this subject by Prof. Coffin in his extensive tables arranged 

 in Zones, in Series B of this work, the number of observations being given gene- 

 rally for the four seasons, sometimes even for each month. How far the considera- 

 tion of the annual result alone would mislead, the following table will show : — 





Year. 



Summer. 



Winter. | 



it 



•3 



as 



a 



it 





ra o 



o 



57°-58° N. L.— Eastern Scotland . 



s. 



60° W. 



28 



s. 



65° W. 



18i 



s. 



62° W. 



40 



Greenwich, England 



s. 



62° W. 



17 



s. 



61° W. 



28 



s. 



55° W. 



85 



50°-55° L. N., 0° to 65° long. W.— 





















Atlantic Ocean 



s. 



53° W. 



23 



s. 



46° W. 



23 



s. 



65° W. 



36 



N. W. Ohio 



s. 



65° W. 



35 



s. 



59° W. 



39 



s. 



73° W. 



37 



Middle Tennessee 



s. 



64° W. 



21 



s. 



51° W. 



22 



s. 



65° W. 



28 



Hakodade, N. Japan 



s. 



79° W. 



22 



s. 



12° E. 



42 



N. 



59° W. 



63 



Pekin, N. China 



s. 



64° W. 



11 



s. 



16° E. 



18 



11. 



54° W. 



30 



Madras, Southern India .... 



s. 



30° W. 



18 



s. 



54° W. 



85 



N. 



47° E. 



68 



Colombo, Ceylon 



s. 



61° W. 



29 



s. 



58° W. 



88 



N. 



37° E. 



59 



