TRADE-WINDS OF THE SOUTHERN HEMISPHERE. 353 



over it and going from warmer to cooler latitudes all tlie time, is 

 the normal condition of the air on the polar side of 40° S., where- 

 as on the polar side of 40° N". a low dew point prevails. The 

 rivers to the north of 40° could not, if they were all converted 

 into steam, supply vapor enough to make up this average differ- 

 ence of dew point between the two hemispheres. 



The symmetry of the rain and storm curves on the polar side 

 of 40° S. suggests that it is the condensation of this vapor which, 

 with the liberation of its latent heat, gives such activity and reg- 

 ularity to the circulation of the atmosphere in the other hemi- 

 sphere. 



1014. On the polar side of 40° S., near Cape Horn, the gauge 

 of Captains King and Fitzroy showed a rain-fall of 153.75 inches 

 in 41 days. 



There is no other place except Cherraponjie where the precipi- 

 tation approaches this in amount. Cherraponjie is a mountain 

 station in India, 4500 feet high, which, in latitude 25° N., acts as 

 a condenser for the monsoons fresh from the sea. But on the 

 polar side of latitude 45° in the northern hemisphere it is, except 

 along the American shores of the North Pacific, a physical impos- 

 sibility that there should be a region of such precipitation as 

 King and Fitzroy found on the western slopes of Patagonia — a 

 physical impossibilty, because the peculiar combination of con- 

 ditions required to produce a Patagonian rain-fall is wanting on 

 the polar side of 45^ IST. 



There is not in the North Atlantic water surface enough to af- 

 ford vapor for such an amount of precipitation. In the North 

 Pacific the water surface may be broad and ample enough to af- 

 ford the vapor, but in neither of these two northern sheets of water 

 are the winds continuous enough from the westward to bring in 

 the requisite quantities of vapor from the sea. Moreover, if the 

 westerly winds of the extra-tropical north were as steady and as 

 strong as are those of the south, there is lacking in the north that 

 continental relief — mountain ranges rising abruptly out of the 

 sea, or separated from it only by lowlands — that seems to be nec- 

 essary to bring down the rain in such floods. 



Colonel Sykes* quotes the rain-faU of Cherraponjie at 605.25 

 inches for the 214 days from April to October, the season of the 



* Report of tlie British Association for 1852, p. 256. 



