ITS SOURCE THE ATMOSPHERE. 17 



oxygen, and they thus supply to the air the loss constantly sus- 

 tained by it. Animals, on the other hand, expire carbon, while 

 plants inspire it ; and thus the composition of the atmosphere, 

 the medium in which both exist, is maintained constantly un- 

 changed. 



It may be asked — Is the quantity of carbonic acid in the atmo- 

 sphere, scarcely amounting to l-10th per cent., sufficient for the 

 wants of the whole vegetation on the surface of the earth, — is it 

 possible that the carbon of plants has its origin from the air alone ? 

 This question is very easily answered. It is known that a 

 column of air of 1427 lbs. weight rests upon every square Hes- 

 sian foot (=0-567 square foot English) of the surface of the 

 earth ; the diameter of the earth and its superficies are likewise 

 known, so that the weight of the atmosphere can be calculated 

 with the greatest exactness. The thousandth-part of this is car. 

 bonic acid, which contains upwards of 27 per cent, carbon. By 

 this calculation it can be shown, that the atmosphere contains 

 3085 billion lbs. of carbon — a quantity which amounts to more 

 than the weight of all the plants, and of all the strata of mineral 

 and brown coal existing on the earth. This carbon is, therefore, 

 more than adequate to supply all the purposes for which it is re- 

 quired. The quantity of carbon contained in sea-water is pro- 

 portionally still greater. 



If, for the sake of argument, we suppose the superficies of the 

 leaves and other green parts of plants, by which the absorption 

 of carbonic acid is effected, to be double that of the soil upon 

 which they grow — a supposition much under the truth in the 

 case of woods, meadows, and corn-fields — let us further sup- 

 pose, that from a stratum of air two feet thick, resting on an acre 

 (Hessian) of land, that is, from 80,000 cubic feet (Hessian) of 

 air, there is absorbed in every second of time, for eight hours 

 daily, carbonic acid equal to 0.00067 of the volume of the air, 

 or ToVo'th of i ts weight ; then those leaves would receive above 

 1000 lbs. of carbon in 200 days.* 



* The quantity of carbonic acid which can be extracted from the air in 

 a given time, is shown by the following calculation. During the white- 

 washing of a small chamber, the superficies of the walls and roof of which 

 we will suppose to be 105 square metres, and which receives six coats of 



