BLUE WATEK. 11 



soundings show that the mean level of the Pacific and Atlantic 

 Oceans are identical. 



It has been calculated that all the waters of the several seas 

 gathered together would form a sphere of fifty or sixty leagues in 

 diameter, and, supposing the surface of the globe perfectly level, that 

 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 

 would require to pour their waters into it for forty thousand years, in 

 order to fill the vast basins anew. 



If we could imagine the entire globe to be divided into one thousand 

 seven hundred and eighty-six parts by weight, we should find approxi- 

 mately, according to Sir John Herschel, 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,, 

 the proportion being as a thousand to a thousand and twenty -seven. 

 The Dead Sea, which receives no fresh water into its bosom to main- 

 tain itself at the same level as other seas, acquires a higher degree of 

 saltness, and is equal to a thousand and twenty-eight. The specific 

 gravity of sea water is about the same as the milk of a healthy woman. 



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 (cseruleum 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 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, 

 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. 



