gg THE PHYSICAL GEOGRAPHY OF THE SEA. 



or, rather, to have so much of it taken from them as to reduce their 

 dew-point below the Desert temperature ; for tlie air can never de- 

 posit its moisture when its temperature is higher than its dew-point. 



135. We have a rainless region about the Red Sea, because the 

 Red Sea, for the most part, lies within the northeast trade-wind 

 region, and these winds, when they reach that region, are dry- 

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

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



136. 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 

 Australia. Whence this dilFerence ? 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 direc- 

 tion. 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 moisture from them ; their instincts, therefore, teach them to 

 turn their edges to his rays. In America, they blow perpendicu- 

 larly upon the shore, penetrating the very heart of the country 

 with their moisture. Here the leaves — as the plantain, &c. — turn 

 their broad sides up to the sun, and court his rays. 



137. Why there is more rain on one side of a mountain than on 

 the other. 



We may now, from what has been said, see why the Andes and 

 all other mountains which run north and south have a dry and a 

 rainy side, and how the prevailing winds of the latitude 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 counter 

 to the southeast trades — which, cooled by the winter temperature 

 of the highlands of Chili, deposit their moisture copiously. Dur- 

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



