[footnote] *Bravais, in Daemtz and Martins, 'Meteorologie', p. 263. At Halle (51 degrees 29' N. lat.), the oscillation still amounts to 0.28 lines. It would seem that a great many observations will be required in order to obtain results that can be trusted in regard to the hours of the maximum and minimum on mountains in the temperate zone. See the observations of horary variations, collected on the Faulhorn in 1832, 1841, and 1842 (Martins, 'Meteorologie', p. 254.)
The supposition that, much nearer the pole, the height of the barometer is really less at 10 A.M. than at 4 P.M., and consequently, that the maximum and minimum influences of these hours p 315 are inverted, is not confirmed by Parry's observations at Port Bowen (73 degrees 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 degrees and 45 degrees.
[footnote] *Humboldt, 'Essai sur la Geographie des Plantes', 1807, p. 90; and in 'Rel. Hist.', t. iii., p. 313; and on the diminuation of atmospheric pressure in the tropical portions of the Atlantic, in Poggend., 'Annalen der Physik', bd. xxxvii., s. 245-258, and s. 463-486.
If with Kämtz we connect together by 'isobarometric' 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 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 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 Daussey, by an elevation of the mean level of the sea.•
[footnote] *Dausay, in the 'Comptes Rendus', t. iii., p. 136.
As the most important fluctuations of the pressure of the atmosphere, whether occurring with horary or annual regularity, 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.
[footnote] *Dove, 'Ueber die Sturme', in Poggend., 'Annalen', bd. lii., s. 1.
Tables of atmospheric pressure during different winds, termed 'barometric windroses', afford a deeper insight into the connection of meteorological phenomena.*
[footnote] *Leopold von Buch, 'Barometrische Windrose', in 'Abhandl. der Akad. der Wiss. zu Berlin aus den Jahren', 1818-1819, s. 187.