122 
THE PHYSICAL GEOGRAPHY OF THE SEA. 
227. According to this view, and not taking into account any 
of thie exceptions produced by the land and other circumstances 
upon the general circulation of the atmosphere over the ocean, the 
southeast trade-winds, which reach the shores of Brazil near the 
parallel of Rio, and which blow thence for the most part over the 
land, should be the winds which, in the general course of circula- 
tion, would be carried, after crossing the Andes and rising up in 
the belt of equatorial calms, toward Northern Africa, Spain, and 
the South of Europe. 
They might carry with them the infusoria of Ehrenberg 158), 
but, according to this theory, they would be wanting in moisture. 
Now, are not those portions of the Old World, for the most part 
dry countries, receiving but a small amount of precipitation ? 
228. Hence the general rule : those countries to the north of 
the calms of Cancer, which have large bodies of land situated to 
the southward and westward of them, in the southeast trade-wind 
region of the earth, should have a scanty supply of rain, and vice 
versa. 
229. Let us try this rule : The extra-tropical part of New Hol- 
land comprises a portion of land thus situated in the southern hem- 
isphere. Tropical India is to the northward and westward of it ; 
and tropical India is in the northeast trade-wind region, and should 
give extra-tropical New Holland a slender supply of rain. But 
what modifications the monsoons of the Indian Ocean may make 
to this rule, or what effect they may have upon the rains in New 
Holland, my investigations in that part of the ocean have not been 
carried far enough for final decision ; though New Holland is a 
dry country. Referring back to p. 79 for what has been already 
said concerning the " Meteorological Agencies" 115) of the 
atmosphere, it will be observed that cases are there brought for- 
ward which afford trials for this rule, every one of which holds 
good. 
230. Thus, though it be not proved as a mathematical truth 
that magnetism is the power which guides the storm from right 
to left and from left to right, which conducts the moist and the 
dry air each in its appointed paths, and which regulates the "wind 
in his circuits," yet that it is such a power is rendered very prob- 
able ; for, under the supposition that there is such a crossing of the 
air at the five calm places, as Plate, p. 70, represents 106), we 
