THE SEA AND THE ATMOSPHERE. 11 



and 20,000 feet. In America, from the line south to the tropics, 

 as also, as there is now every reason to believe, in Africa within 

 similar latitudes, vast ridges of mountains, covered with per- 

 petual snow, run northward and southward in the line of the 

 meridian right across the path of the trade-winds. A similar 

 rid^^e, though of less magnificent dimensions, traverses the 

 peninsula of Hindoostan, increasing in altitude as it approaches 

 the line, attaining an elevation of 8500 feet at Dodabetta, and 

 about 6000 in Ceylon. The Alps in Europe, and the gigantic 

 chain of the Himalayas in Asia, both far south in the temperate 

 zone, stretch from east to west, and intercept the aerial current 

 from the north. Others of lesser note, in the equatorial or 

 meridional, or some intermediate direction, cross the paths 

 of the atmospherical cun-ents in every direction, imparting 

 to them fresh supplies of cold, as they themselves obtain from 

 them warmth in exchange : in strictness the two operations are 

 the same. 



33. Water. — " Magnificent and stupendous as are the effects 

 and results of the water and of air acting independently on each 

 other, in equalizing the temperature of the globe, they are still 

 more so when combined. One cubic inch of water, when in- 

 vested with a sufficiency of heat, will form one cubic foot of steam 

 — the water before its evaporation, and the vapour which it forms 

 being exactly of the same temperature ; though in reality, in the 

 process of conversion, 1100 degrees of heat have been absorbed or 

 carried away from the vicinage, and rendered latent or imper- 

 ceptible ; this heat is returned in a sensible and perceptible 

 form the moment the vapour is converted once more into water. 

 The general fact is the same in the case of vapour carried 

 ofi" by dry air at any temperature that may be imagined ; for, 

 down far below the freezing-point, evaporation proceeds unin- 

 terruptedly. 



34. Latent heat. — " The air, heated and dried as it sweeps 

 over the arid surface of the soil, drinks up by day myriads of 

 tons of moisture from the sea — as much, indeed, as would, were 

 no moisture restored to it, depress its whole surface at the rate 

 of eight or ten feet annually. The quantity of heat thus con- 

 verted from a sensible or perceptible to an insensible or latent 

 state is almost incredible. The action equally goes on, and 

 with the like results, over the surface of the earth, where there 

 is moisture to be withdi'awn. But ni^'ht and the seasons of the 



