174 



OBSERVATIONS ON THE WINDS. 



We perceive with remarkable clearness the double period of the decrease 

 of the N.B. to S.E. winds in winter and summer, in contrast to an increase 

 of the South to N.W. winds in the same seasons, and conversely an in- 

 crease of N.E. to S.E. winds in spring and autumn, and a less frequent 

 occurrence of the South to West winds at the same time. The reason why 

 the N.W. and North winds are proportionally less frequent in summer may 

 be because the region of average uniform heating of the oceanic atmosphere 

 then extends beyond 55° N., whilst in all other seasons the limit fails dowu 

 to 50° N., and so gives the cold polar wind an opportunity of breaking into 

 the warmer equatorial current at, or to the South of, 50° N. But if we 

 look at the distribution of the N.W. and North winds in separate meridional 

 strips, we find them decidedly more frequent in the Eastern parts ot the 

 ocean, as far as 35° W. in summer (23 _2;.c.* against 21 j^.c. ; 27 p.c. against 

 Mp-c.) ; on the contrary, in the Western parts, as far as 74° W., they 

 occur much less often (16 p.c. against 24 p.c. ; 15 p.c. against 25 p.c). 

 Here the summer heating of the European as well as the American con- 

 tinent evidently exerts its influence, and it attracts the cold N.W. wind of 

 the ocean towards the European coasts lying trom S.W. to N.E. ; while 

 for the same reason it diminishes the frequency of this wind on the 

 American coast, and, on the other hand, must increase the S.E. and South 

 winds (the Tables give 24: p.c. against 19 p.c). These explanations as to 

 the causes of the prevailing summer winds on our coasts are Here snown 

 by Tinequi vocal numerical values. 



B. An enquiry into the distribution of the winds with reference to Longi- 

 tude only, seems still called for from our special considerations. 



Our General Wind Table gives the followmg mean vames of the winds' 

 fi-equency ; the per-centages are now doubled : — 



From which it at once appears that between 35° and 55° W., that is, in 

 the middle of the North Atlantic Ocean, the Easterly winds throughout 

 are less frequent than in the districts bordering it to the East and West ; 

 that the South winds are equally numerous in all three districts ; the 

 remaining winds, between S.W. and North, are decidedly more frequent 

 in the central strip than to the West and East of it. 



But if we again compare the per-centages of the same longitudinal 

 section in the year with the separate quarters, and keep to the above 

 notation, we obtain — 



» These figures are obtained by comparing the results for the summer, in Table B, 

 page 173, with those for the year, in Table A, page 172. 



