45 



volumes in five thousand volumes of air, is quite 

 sufficient to supply carbon for the growth of a 

 most luxuriant vegetation all over the globe. For 

 the prodigious extent of the atmosphere raises the 

 total amount of carbonic acid contained therein to 

 about 8,440 billions of pounds. 



The plant absorbing this gaseous compound 

 retains the carbon and returns the oxygen to the air. 

 This continuous absorption would, in course of time, 

 naturally diminish the percentage of carbonic acid 

 in the atmospheric air, if an all-wise Nature had not 

 provided for such an exigency. For, while plants 

 inhale carbonic acid and exhale oxygen, animal 

 respiration does just the reverse ; animals absorb 

 oxygen and expel carbonic acid a wonderful con- 

 nection between these two kingdoms, by which the 

 one supplies the necessary means of existence for 

 the other. Then the decay of the plants them- 

 selves, which sets in immediately on then* vital 

 power becoming extinct, contributes towards the! 

 supply for succeeding generations. Further, any 

 loss incurred by nature in storing up carbon in 

 coal, peat, turf, &c., is made good by the periodical 

 eruptions of volcanoes, which supply from time to 

 time enormous quantities of carbonic acid, and also 

 ammonia, to our atmosphere ; so that the constitu- 

 tion of the atmosphere is rarely changed to a 

 perceptible degree. 



But although the larger quantity of carbonic acid 



