866 



THE PHYSICAL GEOGRAPHY OF THE SEA. 



The sun assisted by being condensecl upon tlie hill-sides, liberates its 



the latent heat of va- . ^ ^ pi ^ ri 



por. latent caloric, and so, adding lael to the name, as- 



sists the sun to rarefy the air, to cause it to rise up and flow off 

 more rapidly, and so to depress the barometer still more. It is 

 not till the S.W. monsoons have been extended far out to sea that 

 they commence to blow strongly, or that the rainy season begins 

 in India. By this time the mean daily barometric pressure in this 

 place of ascending air, which is also a calm place, has become less 

 than it is in the equatorial calm belt ; and the air which the S.E. 

 trade-winds then bring to the equator, instead of rising up there 

 in the calm belt, pass over without stopping, and flows onward to 

 the calms of Central Asia as the S.W. monsoon. It is drawn over 

 to supply the place of rarefaction over the interior of India. 



687. The S.W. monsoon commences to change at Calcutta, in 

 The rain-fau in India. 22° 34' N., ill February, and extends thence out to 

 sea at the rate of fifteen or twenty miles a day ; yet these winds 

 do not gather vapor enough for the rainy season of Cherraponjie, 

 in lat. 25° 16', to commence with until the middle or last of April, 

 though this station, of all others in the Bengal Presidency, seems 

 to be most favorably situated for wringing the clouds. Selecting 

 from Colonel Sykes's report of the rain-fall of India those places 

 nearest the same meridian, and about 2° of latitude apart, the fol- 

 lowing statement is made, with the view of showing, as far as such 

 data can show, the time at which the rainy season commences in 

 the interior : 



It is June before the S.W. monsoons have backed down as far as 

 the equator and have regularly set. in there. 



688. These positions are selected without regard to elevation 

 Its influences upon the ^bovc the sca Icvcl. Of coursc, whcu the S.W. 

 monsoon?. moiisoou comcs ouly from a short distance out to 



sea, as in April it docs, it is but lightly loaded with moisture. 



