ATMOSPHER.C PRESSURE. 315 



are inverted, is not confirmed by Parry's observations at Port 

 Bowen (73° 14')- 



The mean height of the barometer is somewhat less under 

 the equator and in the tropics, owing to the effect of the rising 

 current,* than in the temperate zones, and it appears to attain 

 its maximum in Western Europe between the parallels of 40° 

 and 45°. If with Kamtz we connect together by isobaromet- 

 ric 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 im- 

 portant 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 mountain 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 oscil- 

 lations than do the group of the Antilles and Western Europe. 

 The prevailing winds exercise a principal influence on the 

 diminutioi 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.t 



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 weather, 

 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 atmospheric 

 pressure during different winds, termed barometric windroses, 

 afford a deeper insight into the connection of meteorological 

 phenomena. § Dove has, with admirable sagacity, recognized, 

 in the " law of rotation" in both hemispheres, which he him- 

 self established, the cause of many important processes in the 

 aerial ocean. !l The difference of temperature between the 



* Humboldt, Essai stir la Geographic des Plantes, 1807, p. 90; and 

 iu Rel. Hist., t. iii., p. 313 ; and on the diminution of atmospheric press- 

 ure in the tropical portions of the Atlantic, in Poggend., Annalen der 

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



t Daussy, in the Comptes Rendus, t. iii., p. 136. 



X Dove, Ueber die Sturme, iu Poggend., An?ialen, bd. Hi., s. 1. 



$ Leopold von Buch, BaromeLrische Windrose, iu Abhandl. der Akad. 

 der Wiss. zu Berlin aus den Jahren 1818-1819, s. 187. 



II See Dove, Meteorologische Uniersuchungen, 1837, s. '^'^-313; and 



