Page:Physical Geography of the Sea and its Meteorology.djvu/483

Rh with those which rule at sea. There is barely a resemblance between this profile of the atmosphere over the land and the profile of it (Plate XVI.) 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, seem to serve as chimneys to the atmosphere. The latent heat which is liberated by the vapour they condense has the effect of bringing down the barometer, and of causing, during the rainy season, an indraught thitherward from many miles at sea. Such is the rare-faction produced by the liberation of this heat, that its effects are, 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 Sandwich Islands. Thus the land and the islands give us in the circulation of the atmosphere systems within system. In the Mississippi 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 atmosphere: its general movements are indicated by observations at sea; its eddies and whirlpools are created by the mountains, and the islands, and other inequalities, which obstruct its flow in the regular channels. The mean reading of the barometer when the rainy season in India is at its height is 0*4 inch less than it is in the midst of the dry.

860. Agreement of observations at sea.—The diagram (Plate XVI.) shows the observations in the southern hemisphere to be so accordant, and