BLUE WATER. 
13 
these waters would submerge it to the depth of more than six hundred 
feet. Again, admitting the mean depth of the sea to be thirteen 
thousand feet, its estimated contents ought to be nearly two thousand 
two hundred and fifty millions of cubic miles of water ; and, if the 
Sea could be imagined to be dried up, all the sewers of the earth. 
O x ^ 
Would require to pour their waters into it for forty thousand years, in 
or der to fill the vast basins anew. 
If we could imagine the entire globe to be divided into one thousand 
8evea hundred and eighty-six parts by weight, we should find approxi- 
m ately, according to Sir John Iderschel, that the total weight of the 
oceanic waters is equivalent to one of these parts. 
The specific weight of sea water is a little above that of fresh water, 
|he proportion being as a thousand to a thousand and twenty-seven. 
I he Bead Sea, which receives no fresh water into its bosom to main- 
hdn itself at the same level as other seas, acquires a higher degree of 
witness, and is equal to a thousand and twenty-eight. The specific 
Suavity of sea water is about the same as the milk of a healthy 
^°Baan. 
The colour of the sea is continually varying. According to the 
testimony of the majority of observers, the ocean, seen by reflection, 
presents a fine azure blue or ultramarine ( cmruleum mare). When 
the air is pure and the surface calm this tint softens insensibly, until it 
h |is t and blended with the blue of the heavens. Near the shore it 
Peonies more of a green or glaucus, 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, 
. 6 green takes a brownish hue. At sunset, the surface of the sea is 
"mined with tints of every hue of purple and emerald. Placed in a 
J ase > sea water appears perfectly transparent and colourless. According 
0 kcoresby, the Polar Seas are of brilliant ultramarine blue. Castaz 
'f-ys °f the Mediterranean, that it is celestial blue, and Tuckey 
1 escribes the equinoctial Atlantic as being of a vivid blue. 
lany local causes influence the colours of marine waters, and give 
■ em certain decided and constant shades. A bottom of white sand 
1 communicate a greyish or apple-green colour to the water, if not 
