THE ATMOSPHERE. 95 



winds, for tliey have as yet, in their course, crossed no wide sheets 

 of water from which they could take up a supply of vapor. 



198. Most of New Holland lies within the southeast trade-wind 

 region ; so does most of inter-tropical South America. But inter- 

 tropical South America is the land of showers. The largest riv- 

 ers and most copiously watered country in the world are to be 

 found there, whereas almost exactly the reverse is the case in Aus- 

 tralia. Whence this difference ? Examine the direction of the 

 winds with regard to the shore-line of these two regions, and the 

 explanation will at once be suggested. In Australia — east coast 

 — the shore-line is stretched out in the direction of the trades ; in 

 South America — east coast — it is perpendicular to their direction. 

 In Australia, they fringe this shore only with their vapor, and so 

 stint that thirsty land with showers that the trees can not afford to 

 spread their leaves out to the sun, for it evaporates all the moist- 

 ure from them ; their instincts, therefore, teach them to turn their 

 edges to his rays. In inter-tropical South America, the trade- 

 winds blow perpendicularly upon the shore, penetrating the very 

 heart of the country with their moisture. Here the leaves, meas- 

 uring many feet square — as the plantain, &c. — turn their broad 

 sides up to the sun, and court his rays. 



199. Wh?/ there is more rain on one side of a inountain than 

 on the other. 



We may now, from what has been said, see why the xA.ndes and 

 all other mountains which lie athwart the course of the winds have 

 a dry and a rainy side, and how the prevailing winds of the lati- 

 tude determine which is the rainy and which the dry side. 



Thus, let us take the southern coast of Chili for illustration. 

 In our summer time, when the sun comes north, and drags after 

 him his belts of perpetual winds and calms, that coast is left with- 

 in the regions of the northwest winds — the winds that are coun- 

 ter to the southeast trades — which, cooled by the winter temper- 

 ature of the highlands of Chili, deposit their moisture copiously. 

 During the rest of the year, the most of Chili is in the region of 

 the southeast trades, and the same causes which operate in Cali- 

 fornia to prevent rain there, operate in Chili ; only the dry season 

 in one place is the rainy season of the other. 



