144 AIR AND LIFE. 



Some special points are to be noted concerning salt water. Of course 

 the constituents of atmospheric air are met with in sea water. But, 

 generally speaking, the variations in the proportions of these constit- 

 uents are less numerous and of less importance. The seas, generally 

 considered, make up a more homogeneous whole than any river of large 

 dimensions. Between the south Atlantic and the north Atlantic less 

 differences are to be expected, and less found, than in the Thames or 

 the Seine, below and above London or Paris. A priori it is obvious that 

 there are less causes of difference in aeration in the two parts of the 

 Atlantic than there are in any of the two rivers in two x>oints not 10 

 miles apart. It is quite obvious also that local differences, such as 

 exist at the mouth of a great river that has just passed through a 

 large town, as is the case with the Hudson, the Thames, or the Gironde, 

 must be very soon dissipated in the enormous mass of the ocean 

 through the agency of tides, currents, and -winds. Upon the whole, 

 generally speaking, none of those local differences are of any real 

 importance. There are, however, differences which should be noticed, 

 but their causes are quite different from those which obtain in the pre- 

 ceding case. The most important are observed when we compare speci- 

 mens of water obtained from different depths. Carpenter noticed the 

 fact and comparing specimens of water obtained in the same vertical 

 line, at depths of 750, 800, and 862 fathoms, he observed the following 

 composition of the air extracted : 





750 fathoms. 



800 fathoms. 



862 fathoms. 





18.8 

 49.3 

 31.9 



17.8 

 48.5 

 33.7 



17.2 





34.5 





48.3 







While the proportion of oxygen decreases with increasing depth, that 

 of carbonic acid increases in a marked manner. No very satifactory 

 explanation of this fact has been yet provided. 



We have now sufficiently dwelt upon this topic, and none will doubt 

 that air — that is, the constituents of air, to put it in exact terms — inti- 

 mately mingles with the waters that cover three-fourths of our planet. 

 While waters do not contain atmospheric air as such, and while the 

 gases dissolved in them do not make up normal air, they contain the 

 elements of the latter, and the proportions are sufficient to maintain 

 aquatic life. We may consider that these elements are found in water, 

 even at the most considerable depths, although we have no positive 

 proof of it. 



Now, it is quite clear that since th^ mass of the waters contains 

 organisms that breathe and live, and since life goes on notwithstand- 

 ing the unceasing production of carbonic acid and the destruction of 

 oxygen, both necessary consequences of their life and respiration, there 



