712 



WINDS OF THE GLOBE. 



Barometric observations are numerous on the Atlantic Ocean, and are important 

 as giving us tlie key to the winds. (See Plate 14.) Unfortunately their tabula- 

 tion and reduction is not all that can be desired. They are calculated without 

 regard to longitude, and from 5° to 5° of latitude only. Thus we do not knovv^ the 

 difference of pressure in the eastern and western parts of the ocean, although it 

 must be great, especially in latitude from 20° to 35° N. and S. as shown by the 

 great difference in the polar limits of the trades. 



The Meteorological Institute of the Netherlands has undertaken the calculation 

 of the barometric means of the Atlantic Ocean for every degree of latitude, distin- 

 guishing also, in the southern hemisphere, the outward and homeward voyages. 

 This would give two sets of figures, one for the eastern and one for tlie middle part 

 of the ocean, as the ships going to the East Indies take a course more to the west- 

 ward, while on returning they go nearer to the coast of Africa. This expected 

 publication will shed light on many obscure problems. 



The most complete barometrical table for the Atlantic we now possess is pub- 

 lished in the Pilot Charts. It is calculated from 5° to 5°, for every month. I 

 have calculated from it the pressure of the two contrasting reasons, and have 

 given in the following table the pressure observed on some islands and coast stations 

 reduced to sea-level. (See also Plate 1-4.) The mean pressure is at 32° Fahr. 





June. 



Dec. 





June. 



Dec. 





June. 



Dec. 





July. 



J.in. 





July. 



J.in. 





July. 



Jan. 





Aug. 



Feb. 





Aug. 



Feb. 





Aug. 



Feb. 



Atlantic Ocean — 







Atlantic Ocean — 







32° 38' N. 16°36'W. 







35°-40" N. . . 



30.18 



30.13 



10^-15° S. . . 



30.05 



29.98 



Funclial, Madeira . 



30.11 



30.16 



30 -35 N. . . 



30.21 



30.21 



15 -20 S. . . 



30.10 



30.03 



32= 23' N. 64° 40' W. 







25 -30 N. . . 



30.20 



30.20 



20 -25 S. . . 



30.14 



30.06 



Bermuda Islands . 



29.97 



29.93 



20 -25 N. . . 



30.11 



30.07 



25 -30 S. . . 



30.13 



30.07 



5° 24' N. 0° 10' E. 







15 -20 N. . . 



30.01 



30.03 



30 -35 S. . . 



30.09 



30.03 



Christiansb'g, Guinea 



30.00 



29.91 



10 -15 N. . . 



29.93 



29.96 



35 -40 S. . . 



29.96 



30.00 



4° 56' S. 55° 39' W. 







5 -10 N. . . 



29.96 



29.92 



40 -45 S. . . 



29.92 



29.94 



Cayenne, Fr. Gniana 



29.95 



29.91 



- 5 N. . . 



29.96 



29.90 



45 -50 S. . . 



29.72 



29.72 



33° 56' S. 18° 27 E. 







- 5 S. . . 



29.98 



29.91 



50 -55 S. . . 



29.52 



29.43 



Cape Town, S. Africa 



30.17 



30.00 



5 -10 S. . . 



30.02 



29.95 



55 -eo S. . . 



29.27 



29.23 



34° 37' S. 58° 21' W. 

 Buenos Ayres . . 



30.15 



30.01 



The polar boundaries of the N. E. and S. E. trades are marked by a high pres- 

 sure (at 30° to 35° N. and at 20° to 30° S.), while the space intervening between 

 the two trades — the belt of equatorial calms and variable winds, has a compara- 

 tively loAV pressure. It should be remarked that this low pressure remains on 

 the northern hemisphere, changing from 10° to 15° N. in our summer and from 

 0° to 5° in our winter. The air from north and south is attracted towards this 

 belt of low pressure, and, as the conditions of the tropics are very uniform, the 

 winds also are very regular. 



A comparison of stations in the west and east of the ocean will show that pres- 

 sure is generally higher in the east (as in Madeira compared with Bermuda, in 

 Christiansburg compared with Cayenne, and Cape Town compared with Buenos 

 Ayres). This is an additional cause for the easting of the trade-winds near the 

 American continent. 



Pressure is extremely low in the higher latitudes of the southern hemisphere. 



