114 OF THE INORGANIC 



are spread over the whole surface of the earth ; and 

 being subsequently carried down by the rain, fur- 

 nish to the vegetation those salts necessary to its ex- 

 istence. This is the origin of the salts found in the 

 ashes of plants, in those cases where the soil could 

 not have yielded them . 



In a comprehensive view of the phenomena of 

 nature, we have no scale for that which we 

 are accustomed to name, small or great ; all our 

 ideas are proportioned to what' we see around us, 

 but how insignificant are they in comparison with 

 the whole mass of the globe ! that which is scarcely 

 observable in a confined district appears incon- 

 ceivably large when regarded in its extension 

 through unlimited space. The atmosphere contains 

 only a thousandth part of its weight of carbonic 

 acid ; and yet small as this proportion appears, it 

 is quite sufficient to supply the whole of the present 

 generation of living beings with carbon for a thou- 

 sand years, even if it were not renewed. Sea- water 

 contains TT^OO" f i ts weight of carbonate of lime ; 

 and this quantity, although scarcely appreciable 

 in a pound, is the source from which myriads of 

 marine mollusca and corals are supplied with mate- 

 rials for their habitations. 



Whilst the air contains only from 4 to 6 ten -thou- 

 sandth parts of its volume of carbonic acid, sea- 

 water contains 100 times more, (10,000 volumes of 

 sea-water contain 620 volumes of carbonic acid 



