-1859] WRITINGS OF JOSEPH HENRY. 165 



restored to supply the place of that previously abstracted, 

 and the whole quantity of carbon in the atmosphere remains 

 nearly the same from age to age, the measurable variations 

 being only perceptible during the lapse of the ages which 

 constitute a geological period. When we consider however 

 the great amount of coal consumed at the present day in the 

 mechanical arts and locomotion, it would appear that the 

 amount of carbonic acid is increasing in the atmosphere ; 

 but when we compare with this the improvements made in 

 agriculture, and the stimulus thus afforded to the growth of 

 plants and animals, the effects of these artificial conditions 

 would apparently nearly balance each other. There is 

 another source of abstraction of carbonic acid from the at- 

 mosphere, namely, that which takes place through the agency 

 of animal life in the production of coral ; but this again may 

 be probably balanced by the carbonic acid emitted from the 

 various active volcanoes of the globe. We do not however 

 by these remarks attempt to establish the fact that in all 

 parts of nature there is an exact compensation, and that our 

 globe has always remained in the state in which it now exists, 

 but that the great changes which affect our planet are ex- 

 ceedingly gradual, and the conditions may be considered 

 constant during the age of individuals, or even of nations. 



Should the carbonic acid of the air sensibly increase over 

 the limits before mentioned, the vegetation of the earth would, 

 as we have seen, become more luxuriant, and animal life de- 

 generate into a lower type. If on the other hand, the car- 

 bonic acid should be diminished, the reverse would proba- 

 bly take place, vegetable life would become less, and animals 

 would either correspondingly diminish in number, or they 

 would assume a higher type. M. Flourens supposes that the 

 amount of organic life on the surface of the globe has re- 

 mained the same through all periods, though exhibited 

 under different forms, but this would be dependent upon the 

 permanency of the amount of organizing force from the sun. 

 Saline matter in the atmosphere. — Air from the surface of 

 the ocean contains a portion of the saline ingredients which 

 in positions near the sea, and in some cases further inland, 



