GENERAL VIEW. 279 



and vertical elevation. We then come to the two coverings 

 or envelopes of our planet, of which one, composed of 

 elastic fluids, the atmosphere, is general ; and the other, the 

 sea, is local, or restricted to portions of the earth's sur- 

 face. These two envelopes, air and sea, constitute a natural 

 whole, materially affecting the distribution of the various 

 climates of the surface of the globe, according to the relative 

 extent of land and sea, the form and aspect of the land, and 

 the height and direction of the mountain chains. It results 

 from this reciprocal influence of the atmosphere the sea 

 and the land, that great meteorological phsenomena cannot 

 be well studied apart from geological considerations. Me- 

 teorology, as well as the geography of plants and of animals, 

 have only begun to make real progress, since the mutual 

 connection and dependence of the phaenomena to be investi- 

 gated have been recognised. It is true that the word cli- 

 mate has especial reference to the condition of the atmo- 

 sphere ; but this condition is itself subjected to the double 

 influence of the ocean, whose agitated waters are traversed 

 by currents differing greatly in temperature, and of the dry 

 land, which radiates heat with very different degrees of in- 

 tensity, according to its varying characters of form, eleva- 

 tion, and colour, and whether bare or clothed with forests, 

 or with grasses or other low growing plants. 



In the present state of our knowledge, the superficial ex- 

 tent of dry land compared to that of the liquid element, is 

 as 1 : 2-8; or, according to Kigaud, as 100 : 270. ( 335 ) The 

 islands form scarcely one-twenty-third part of the continental 

 masses, which are so unequally distributed, that the northern 

 hemisphere contains three times as much land as the southern, 

 t which is pre-eminently oceanic. Prom 40 South latitude 



