118 THE PHYSICAL GEOGRAPHY OF THE SEA. 



see how tlie mountain ranges run ; then turn to Plate VIII. to see 

 how the winds blow, and where the sources are (§ 276) which 

 supply them with vapors. This plate shows the prevailing di 

 rection of the wind only at sea ; but, knowing it there, we may 

 infer what it is on the land. Supposing it to prevail on the land 

 as it generally does in corresponding latitudes at sea, then the 

 Plate will suggest readily enough how the winds that blow over 

 these deserts came to be robbed of their moisture, or, rather, to 

 have so much of it taken from them as to reduce their dew-point 

 below the Desert temperature ; for the air can never deposit its 

 moisture luhen its ierri'perature is higher than its dew-point. We have 

 a rainless region about the Eed Sea, because the Bed 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. Most of New Holland lies 

 within the southeast trade-wind region ; so does most of inter- 

 tropical South America. But intertropical South America is the 

 land of showers. The largest rivers and most copiously watered 

 country in the world are to be found there, whereas almost exact- 

 ly the reverse is the case in Australia. 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 suggest- 

 ed. 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 ; thus that thirsty land is so stinted 

 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 

 vegetable instincts teach them to turn their edges to his rays. In 

 intertropical South America the trade- winds blow perpendicu- 

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

 with their moisture. Here the leaves, measuring many feet 

 square — as the plantain, &c. — turn their broad sides up to the 

 sun, and court his rays. 



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

 The Rainy bide of ^^^^ Other. Wc may uow, fpom what has been said, 

 MoTOTAiua ggQ ^■\^^ j^^ Andes and all other mountains which 



lie athwart the course of the winds have a dry and a rainy side, 



