90 THE PHYSICAL GEOGRAPHY OF THE SEA. 



times reaches the enormous depth of twelve or fifteen inches in 

 one day.* 



140. These winds then continue their course to the Himalaya 

 range as dry winds. In crossing this range, they are subjected to a 

 lower temperature than that to which they were exposed in cross- 

 ing the Ghauts. Here they drop more of their moisture in the 

 shape of snow and rain, and then pass over into the thirsty lands 

 beyond with scarcely enough vapor in them to make even a cloud. 

 Thence they ascend into the upper air, there to become counter- 

 currents in the general system of atmospherical circulation. By 

 studying Plate VHL, where the rainless regions and inland basins, 

 as well as the course of the prevailing winds, are shown, these 

 facts will become obvious. 



141. The Regions of Greatest Precipitation. — We shall now 

 be enabled to determine, if the views which I have been en- 

 deavoring to present be correct, what parts of the earth are sub- 

 ject to the greatest fall of rain. They should be on the slopes of 

 those mountains which the trade-winds first strike, after having 

 blown across the greatest tract of ocean. The more abrupt the 

 elevation, and the shorter the distance between the mountain top 

 and the ocean, the greater the amount of precipitation. 



If, therefore, we commence at the parallel of about 30° north 

 in the Pacific, where the northeast trade-winds first strike that 

 ocean, and trace them through their circuits till they first strike 

 high mountains, we ought to find such a place of heavy rains. 



Commencing at this parallel of 30°, therefore, in the North Pa- 

 cific, and tracing thence the course of the northeast trade-winds, 

 we shall find that they blow thence, and reach the region of equa- 

 torial calms near the Caroline Islands. Here they rise up ; but, 

 instead of pursuing the same course in the upper stratum of winds 

 through the southern hemisphere, they, in consequence of the ro- 

 tation of the earth (§ 98), are made to take a southeast course. 

 They keep in this upper stratum until they reach the calms of 

 Capricorn, betw^een the parallels of 30° and 40° ; after which 

 they become the prevailing northwest winds of the southern hemi- 

 sphere, which correspond to the southwest of the northern. Con- 

 tinuing on to the southeast, they are now the surface winds ; they 

 are going from warmer to cooler latitudes ; they become as the 



* Keith Johnston. 



