ATMOSPHERIC PRESSURE. 29A 



iLc Equator and in the tropics, owing to the effect of the 

 rising current,* than in the temperate zones, and it appear" 

 to attain its maximum in Western Europe between the paral- 

 lels of 40 and 45. If with Kamtz we connect together by 

 isnbarometric lines those places which present the same mean 

 difference between the monthly extremes of the barometer, we 

 shall have curves whose geographical position and inflections 

 yield important conclusions regarding the influence exercised 

 by the form of the land and the distribution of seas on the 

 oscillations of the atmosphere. Hindostan, with its high moun- 

 tain-chains and triangular peninsulas, and the eastern coasts of 

 the New Continent, where the warm gulf stream turns to the 

 east at the Newfoundland banks, exhibit greater isobarometric 

 oscillations than do the group of the Antilles and Western 

 Europe. The prevailing winds exercise a principal influence 

 on the diminution of the pressure of the atmosphere, and this, 

 as we have already mentioned, is accompanied, according to 

 Daussy, by an elevation of the mean level of the sea.f 



As the most important fluctuations of the pressure of the 

 atmosphere, whether occurring with horary or annual regu- 

 larity, or accidentally, and then often attended by violence 

 and danger,]: are, like all the other phenomena of the wea- 

 ther, mainly owing to the heating force of the sun's rays, it 

 has long been suggested, (partly according to the idea of 

 Lambert,) that the direction of the wind should be compared 

 with the height of the barometer, alternations of temperature, 

 and the increase and decrease of humidity. Tables of atmo- 

 spheric pressure during different winds, termed barometric 

 iv ind roses, afford a deeper insight into the connection of 

 meteorological phenomena. Dove has, with admirable 

 sagacity, recognised, in the " law of rotation" in both hemi- 

 spheres, which he himself established, the cause of many 

 important processes in the aerial ocean. || The difference of 



* Humboldt, Essai sur la Geograpliie des Plantes, 1807, p. 90 ; and 

 in Rel. hist., t. iii., p. 313 ; and on the diminution of atmospheric pressure 

 in the tropical portions of the Atlantic, in Poggend. Annaien der Phy* 

 eik, bd. xxxvii. s. 245-258, and s. 468-486. 



f Daussy, in the Comptes rendus, t. iii. p. 1 36. 



J Dove, Ueber die Sturme, in Poggend. Annaien, bd. Iii. s. 1. 



Leopold von Buch, Baromeirische Windrose, in Abhandl. dff 

 Akad. der Wiss. zu Btrlin aus den J. 1818-1819, s. 187. 



li See Dove, Meieorologitche Untermchungen, 1837. s, 99-843; and 



Tf 



