262 Meteorological Sketches. 
prevail in the temperate and lower latitudes. On the western shores 
of the Atlantic, in North and South America, where the aerial cur- 
rent is passing from the equator towards the higher latitudes, we find 
on the other hand that there are adequate supplies of rain. The 
same is generally true of the western shores and islands of the Pa- 
cific ocean; and the westerly monsoons being of this latter character, 
generally afford copious rains, while the easterly monsoons, or regular 
trade winds, which incline towards the equator, are equally remark- 
able for their dryness, at least within the latitudes above mentioned. 
In the atmospheric basin of the North Atlantic, we have the most 
striking exhibition of this effect in the great African desert of Sa- 
hara. Continuing our survey eastwardly under the same parallels, 
we find also the great deserts of Lybia, Egypt and Arabia, which 
for the most part are subject to the same course of general winds, 
the blighting effects of which fully exemplify the position which is 
here assumed. In the atmospheric basin of the South Atlantic, we 
find also, in South Africa, an arid region, extending across the same 
parallels of latitude, where a southerly wind is found to prevail, 
which in its progress towards the equator, becomes merged in the 
southeast trade-winds. ‘The same effects are produced on the east- 
ern shores of the Pacific ocean, where, upon the coasts of Chili, 
Bolivia and Peru, we have a like section of the general winds, 
which, notwithstanding the near proximity of the Andes, causes the 
desert of Atacama, and a remarkable absence of rain on other parts 
of the same coast. The same general effect is produced by the 
corresponding winds which prevail upon the western coast of North 
America, where, owing to the peculiar direction of the sea-coast and 
mountain ranges, the arid influence is extended, as in some parts of 
Asia, far into the temperate latitudes. ‘The phenomena attending 
the general winds in the basin of the Indian ocean, and New Hol- 
land, are of the same character. It seems to follow, that the gene- 
ral sterility, or periodical drought of the regions referred to, .is not 
to be ascribed to the peculiar constitution or composition of the nat- 
ural surface, or to excessive heat, but must be attributed to the pe- 
culiar course and the consequent hygrometric condition of the gen- 
eral winds which there prevail. 
Of the Variations of the Barometer. 
The fluctuations in the height of the mercurial column have long 
excited attention, and the proximate causes of these changes are 
