747. Whence the Red Sea derives its name.—These discolourations are no doubt caused by organisms of the sea, but whether wholly animal or wholly vegetable, or whether sometimes the one and sometimes the other, has not been satisfactorily ascertained. I have had specimens of the colouring matter sent to me from the pink-stained patches of the sea. They were animalculæ well defined. The tints which have given to the Red Sea its name may perhaps be in some measure due to agencies similar to those which, in the salt-makers' ponds, give a reddish cast (§ 71) to the brine just before it reaches that point of concentration when crystallization is to commence. Some microscopists maintain that this tinge is imparted by the shells and other remains of infusoria which have perished in the glowing saltness of the water. The Red Sea may be regarded, in a certain light, as the scene of natural salt-works on a grand scale. The process is by solar evaporation. No rains interfere, for that sea (§ 376) is in a riverless district, and the evaporation goes on unceasingly, day and night, the year round. The shores are lined with incrustations of salt, and the same causes which tinge with red (§71) the brine in the vats of the salt-makers probably impart a like hue to the arms and ponds along the shore of this sea. Quantities, also, of slimy, red colouring matter are, at certain seasons of the year, washed up along the shores of the Red Sea, which Dr. Ehrenberg, after an examination under the microscope, pronounces to be a very delicate kind of sea-weed: from this matter that sea derived its name. So also the Yellow Sea. Along the coasts of China, yellowish-coloured spots are said not to be uncommon. I know of no examination of this colouring matter, however. In the Pacific Ocean I have often observed these discolourations of the sea. Red patches of water are most frequently met with, but I have also observed white or milky appearances, which at night I have known greatly to alarm navigators by their being taken for shoals.
748. The escape of warm waters from the Pacific.—These teeming waters bear off through their several channels the surplus heat of the tropics, and disperse it among the icebergs of the Antarctic. See the immense equatorial flow to the east of Australia, and which I have called the Polynesian Drift. It is bound for the icy barriers of that unknown sea, there to temper climates, grow cool, and return again, refreshing man and beast by the way, either as the Humboldt current, or the ice-bearing current which
