Purple eBooks

Absolutely pure
water, like pure air, is colourless, but all seas and lakes, however
clear and translucent, contain abundance of very finely divided matter,
organic or inorganic, which, as in the atmosphere, reflects the blue
rays in such quantity as to overpower the white or coloured
light-reflected from the fewer and more rapidly sinking particles of
larger size. The oceanic dust is derived from many sources. Minute
organisms are constantly dying near the surface, and their skeletons, or
fragments of them, fall slowly to the bottom. The mud brought down by
rivers, though it cannot be traced on the ocean floor more than about
150 miles from land, yet no doubt furnishes many particles of organic
matter which are carried by surface currents to enormous distances and
are ultimately dissolved before they reach the bottom. A more important
source of finely divided matter is to be found in volcanic dust which,
as in the case of Krakatoa, may remain for years in the atmosphere, but
which must ultimately fall upon the surface of the earth and ocean.


Pages:
479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503