458 



THE PHYSICAL GEOGRAPHY OF THE SEA. 



858. Eesorting to the graphic method, and using the table (§ 855) 

 Barometric curve at ^^^ ^^^ puppose, the barometric curve of the dia- 

 ^"""^ gram (p. 457) has been projected from pole to pole. 



859. Professor Schouw has given us the mean height of the ba- 

 Ditto over the land, romctcr for 32 placcs ou the 



land between the parallels of 83° S. and 75° 

 SO' N. They afford materials for the an- 

 nexed diagram, and show the exceptional 

 character of the meteorological influences 

 which rule on shore when compared with 

 those which rule at sea. There is barely a 

 resemblance between this profile of the at- 

 mosphere over the land and the profile of 

 it (§ 858) over the sea, so different are these 

 influences. The irregularities over the 

 land are chiefly owing to the difference in 

 the amount of precipitation at one station 

 as compared with the amount at another. 

 Those islands, as the Sandwich and Society, 

 which are so situated as to bring down a 

 heavy precipitation, are as chimneys to the 

 atmos2J>here. The latent heat which is liber- 

 ated by the vapor they condense has the 

 effect of bringing down the barometer, and 

 of causing, during the rainy season, an in- 

 draught thitherward from many miles at 

 sea. Such is the rarefaction produced by 

 the liberation of this heat, that its effect is, 

 as the pilot charts show, felt and confessed 

 by the winds at the distance out to sea of 

 more than a thousand miles from the Sand- 

 wich Islands. Thus the land and the isl- 

 ands give us, in the circulation of the atmos- 

 phere, systems within systems. In the Mis- 

 sissippi and all great rivers, the general 

 movement of the waters, notwithstanding 

 the eddies and the whirlpools, is down 

 stream with the current. So with the at- 

 mosphere : its general movements are indi- 



