EASTING OF THE TRADE -WINDS, ETC. 177 



rainless regions of the northern hemisphere. — According to the views 

 presented in § 358 and Plate VII., the south-east 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 circulation, Avould 

 be carried, after crossing the Andes and rising up in the belt of 

 equatorial calms, towards Northern Africa, Spain, and the South 

 of Europe. They might carry with them the infusoria of Ehren- 

 berg (§ 358), 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 pre- 

 cipitation ? 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 south- 

 east trade- wind region of the earth, should have a scanty supply 

 of rain, and vice versa. Let us try this rule : The extra-tropical 

 part of New Holland comprises a portion of land thus situated in 

 the southern hemisphere. Tropical India is to the northw^ard 

 and westward of it ; and tropical India is in the north-east 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 countiy. 



366. Each hemisphere receives from the sun the same amount of 

 heat. — The earth is nearer to the sun in the summer of the 

 southern hemisphere than it is in the summer of the northeiTL ; 

 consequently, it has been held that one hemisphere annually 

 receives more heat than the other. But the northern summer is 

 7*7 days longer than the southern; and Sir John Herschel has 

 shown, and any one who will take the trouble may demonstrate, 

 that the total amount of direct solar heat received annually 

 by each hemisphere is identically the same, and therefore the 

 northern hemisphere in its longer summer makes up with heat 

 for the greater intensity but shorter duration of the southern 

 summer. But though the amount of heat annually impressed by 

 the sun upon each hemisphere be identically the same, it by no 

 means follows that the amount radiated oft' into space by each 

 hemisphere again is also identically the same. There is no 

 reason to believe that the earth is growing warmer or cooler, and 



