THE SEA 17 



and the angle at which the rays enter. Off Capri in 

 the Mediterranean, photographic plates were not 

 affected by exposure at depths greater than 164) 

 fathoms (300 meters), but in the Atlantic, light rays 

 have affected a plate exposed for eighty minutes at 

 a depth of 547 fathoms (1000 meters}^. 



The red and yellow rays are absorbed by water 

 more readily than the blue and violet; consequently 

 the latter penetrate to a greater distance. This has 

 an important effect upon the animal and vegetable 

 life of the sea. Green algae require yellow light rays 

 for their photosynthetic processes and are on this 

 account found near the surface only. On the other 

 hand red algag can utilize blue light and therefore 

 live in deeper waters. It is probable that the rays 

 used by plants in photosjmthetic processes do not 

 reach deeper than 600 feet, even in the clear water 

 of the tropics. In the polar regions, where the light 

 from the sun strikes the water at an oblique angle, 

 these rays do not penetra+e nearly so far. 



The colors of marine animals are well adapted to 

 these conditions. Dr. Hjort, a famous oceanographer, 

 made a study of the colors of fishes of the Atlantic 

 living at various depths, and found that most of 

 the surface fishes, down to 75 fathoms, are colorless ; 

 from 150 to 250 fathoms the fishes are silvery or 

 gray; and at depths where little light penetrates 

 they are black or dark colored. At these great depths 

 the Crustacea are red in color, but they appear black 

 because no red light rays penetrate the upper layers. 

 Many of the animals, other than fish, living near the 

 surface are blue or bluish violet and so tone in with 



