ice) THE OCEAN WORLD. 
the rivers of the earth would require to pour their waters into it for 
40,000 years, in order to fill the vast basins anew. 
If we could imagine the entire globe to be divided into 1,786 
parts by weight, we should find approximately, according to Sir John 
Herschel, that the total weight of the oceanic waters is equivalent to 
one of these parts. 
The specific density of sea water is a little above that of fresh 
water, the proportion being as 1,000 to 1,027. The Dead Sea, 
which receives no fresh water so as to enable it to maintain itself at 
the same level as other seas, acquires a higher degree of saltness 
each year: its present density is equal to 1,028. 
The colour of the sea is continually varying, and is chiefly caused 
by filtration of the solar rays. According to the testimony of the 
majority of observers, the ocean, seen by reflection, presents a fine 
azure blue or ultramarine (ceruleum mare). When the air is pure 
and the surface calm, this tint softens insensibly, until it is lost and 
blended with the blue of the heavens. Near the shore it becomes 
more of a green or glaucous tint, and more or less brilliant, according 
to circumstances. There are some days when the ocean assumes a 
livid aspect, and others when it becomes a very pure green ; at other 
times, the green is sombre and sad. When the sea is agitated, the 
green takes a brownish hue. At sunset the surface of the sea is 
illumined with tints of every hue of purple and emerald. Placed in 
a vase, sea water appears perfectly transparent and colourless. 
According to Scoresby, the Polar seas are of brilliant ultramarine 
blue. Castaz says of the Mediterranean, that it is celestial blue, and 
Tuckey describes the equinoctial Atlantic as being of a vivid blue. 
Many local causes influence the colours of marine waters, and 
give them certain decided and constant shades. A bottom of white 
sand will communicate a greyish or apple-green colour to the water, 
if not very deep ; when the sand is yellow, the green appears more 
sombre; the presence of rocks is often announced by the deep 
colour which the sea takes in their vicinity. In the Bay of Loango 
the waters appear of a deep red, because the bottom is there naturally 
red. It appears white in the Gulf of Guinea, yellow on the coast of 
Japan, green to the west of the Canaries, and black round the 
Maldive group of islands. The Mediterranean, towards the Grecian 
Archipelago, sometimes becomes more or less red. The White and 
Black Seas appear to be named after the ice of the one and the 
tempests to which the other is subject. 
