14 THE WEALTH OF THE SEA 



of oxygen than nitrogen is dissolved. Moreover cold 

 sea-water dissolves much more gas than warm water, 

 and on this account the waters of the polar regions 

 contain much more dissolved air than do the waters 

 of the tropical seas. 



The presence of the gases dissolved in sea-water 

 is of utmost importance to the animal and vegetable 

 life of the ocean. All marine animals breathe, 

 although few have lungs. The true fishes absorb 

 oxygen from the water through their gills and thus 

 are able to maintain their bodily functions. 



Color and Pressure in the Ocean Depths 



A curious popular misconception is that ships 

 which sink in the deeper parts of the ocean do not 

 reach bottom but float submerged at a great depth, 

 where the density of the water is very high because 

 of the enormous pressure. Nothing can be farther 

 from the truth, for any object that will sink in 

 shallow water will certainly sink to the bottom of 

 the ocean, even though it may be six miles deep. 



The reason for this is not hard to find: water is 

 almost incompressible. Under one additional atmos- 

 phere it is compressed only about one twenty-thou- 

 sandth of its bulk. At the greatest known depth of 

 the ocean, about 5348 fathoms, the water becomes 

 only four and a third per cent heavier than at the 

 surface. The floor of the ocean at great depths is 

 often covered with delicate shells which are only 

 slightly heavier than water, and yet they have sunk 

 from the surface to the bottom. 



