AND THE PREVAILING WINDS OVER THE GLOBE. 585 



the direction of N. This northing of the winds at Mauritius is exactly what 

 should be expected to result from the proximity to the low pressures which 

 prevail in South Africa at this season. This change in the mean direction 

 of the wind being small, the mean annual direction may be regarded as E.S.E. 



Such slight variation, however, is limited to very few regions, for on examin- 

 ing the number of days each wind (N., N.E., E., &c.) has on the mean of the 

 year prevailed at the different stations in Table II., it will be observed that in 

 almost every instance there are two maximum directions, the one being con- 

 siderably greater than the other. These maximum directions may arise in two 

 ways — 1st, At places such as Colombo, Ceylon, where the wind during summer is 

 S.W., and during winter chiefly N,E., the two annual maximum directions are 

 S.W. and N.E. ; in like manner the maximum directions at all places in monsoon 

 regions are occasioned. 2d, At Greenwich two maximum directions, from about 

 S.W. and N.E., appear in the means of every month, from which it is evident that 

 the wind at this place blows oftener, and remains longer, in these two directions 

 than in any other. In cases where the less maximum arises from the prevalence of 

 winds from that direction during a few months of the year, the isobaric charts of the 

 separate months give a ready explanation of both maxima in the annual means. 

 But at places where both maxima appear in the same months, it is evident that 

 the isobaric charts can only furnish data towards the explanation of the greater 

 maximum direction ; and it may be assumed as equally evident that the smaller 

 maximum, of which the east wind of the British Islands is an illustration, can 

 alone be legitimately discussed by daily synoptic charts of the weather. Towards 

 the discussion of this and other questions of meteorology, the value of the 

 Daily Synoptic Charts prepared and issued under the superintendence of M. 

 Leverrier cannot be overrated.* 



There are 115 stations in Table II. situated in the north temperate zone. I 

 have tabulated the two maximum directions at these stations where they occur 

 according to sixteen points of the compass— viz., N., N.N.E., N.E., E.N.E., E., &c. 

 of which the following Table shows the maximum directions most frequently 

 observed : — 



Maximum directions of wind are — S.W. N.E. at 15 stations. 



Greater Max. 



Smaller Max. 







S.W. 



N.E. 



at 



15 



N. 



S. 



)> 



8 



N.E. 



S.W. 



>> 



7 



N.W. 



S.E. 



)> 



6 



S. 



N. 



>» 



•5 



w. 



N.E. 



)> 



5 



N.W. 



S. 



)* 



4 



w. 



E. 



>» 



3 



E. 



W. 



>j 



3 



W.S.W. 



E. 



>> 



3 



W.S.W. 



S.E. 



3) 



3 



Atlas des Mouvements Generaux de 1'Atmosphere pour 1864-5. 



