The Chemical Statics of Organised Beings. 9 



solar influence only ; as in winter the earth is stript, whilst in 

 summer it is covered with verdure , it has been supposed that 

 the air must transfer all these influences into its constitution. 



Carbonic acid should augment by night and diminish by day. 

 Oxygen, in its turn, should follow an inverse progress. 



Carbonic acid should also follow the course of the seasons, 

 and oxygen obey the same law. 



All this is true, without doubt, and quite perceptible as to a 

 portion of air limited and confined under a jar ; but, in the mass 

 of the atmosphere, all these local variations blend and disappear. 

 Accumulated centuries are requisite in order effectually to put in 

 action this balance of the two kingdoms, with regard to the 

 composition of air; we are then very far .from those daily or 

 yearly variations, which we had been apt to look upon as being 

 as easy to observe as to foresee. With regard to oxygen, cal- 

 culation shows that, exaggerating all the data, not less than 

 800,000 years would be required for the animals living on the 

 surface of the earth to consume it entirely. 



Consequently, if we suppose that an analysis of the air had 

 been made in 1800, and that during the entire century plants 

 had ceased to perform their functions on the surface of the whole 

 globe, the animals at the same time all continuing to live, the 

 analysts in 1900 would find the oxygen of the air diminished by 

 ] -8000th of its weight, a quantity which is beyond the reach of 

 our most delicate methods of observation, and which, assuredly, 

 would have no influence whatever on the life of animals or plants. 



As to this, then, we cannot be deceived ; the oxygen of the 

 air is consumed by animals, who convert it into water and car- 

 bonic acid; it is restored by plants, which decompose these two 

 bodies. 



But nature has arranged everything so that the store of air 

 should be such with relation to the consumption of animals, that 

 the want of the intervention of plants for the purification of the 

 air should not be felt until centuries have elapsed. 



The air which surrounds us weighs as much as 581,000 cubic 

 kilometres of copper; its oxygen weighs as much as 134,000 of 

 these same cubes. Supposing the earth peopled with a thousand 

 millions of men, and estimating the animal population at a quan- 

 tity equivalent to three thousand millions of men, we should find 

 that these quantities united consume in a century only a weight of 

 oxygen equal to 15 or 16 cubic kilometres of copper, whilst the 

 air contains 134,000 of-it. It would require 10,000 years for all 

 these men to produce a perceptible effect upon the eudiometer 

 of Volta, even supposing vegetable life annihilated during all this 

 time. 



In regard to the permanence of the composition of air, we 

 may say with all confidence that the proportion of oxygen 

 which it contains is secured for many centuries, even reckoning 



