THE OCEAN. 



327 



Analogy thus leads us to infer a general correspondence between the height of the 

 land and the depth of the sea. If this be so, then the greatest depth of the ocean 

 will be nearly 30,000 feet, equal to the elevation of the loftiest peaks of the Himalaya 

 mountains. Perhaps, without much inaccuracy, its mean depth may be taken at a 

 quarter of a mile ; according to which its solid contents, allowing the ocean to occupy 

 three fourths of the superficies of the earth, will be about 32,058,939J cubic miles. 

 The level of the ocean, however, is not the same in all places, nor at all times in the 

 same place, for astronomical and atmospherical causes, producing tides and winds, 

 operate to effect a change. Apart also from these disturbing causes, it is found that the 

 level of the water in some gulfs and inland seas has in general a greater elevation than 

 that of the main deep. Thus the waters of the Red Sea, separated by the Isthmus of 

 Suez from the Mediterranean, were found by the French engineers 321 feet higher than 

 those of the latter. A fact of a similar kind was demonstrated by Humboldt, with refer- 

 ence to the waters of the Gulf of Mexico, which he estimated to be from 20 to 23 feet 

 higher than those of the Pacific Ocean, on the opposite shore of the Isthmus of Panama. 

 This effect appears to be occasioned by the tropical current of the ocean from east to west, 

 caused by the earth's rotation upon its axis from west to east, which accumulates the 

 water in those gulfs opening eastward. 



The saltness of the ocean is one of its prime characteristics ; but, as yet, we have 

 nothing but hypothesis, with reference to its cause and design. In addition to pure water, 

 it has been ascertained, by the experiments of different chemists, to hold in solution mu- 

 riate of soda, or common salt, muriatic and sulphuric acid, fixed mineral alkali, magnesia, 

 and sulphate of lime, besides the animal and vegetable matter, in a state of decomposition, 

 with which it is impregnated. The great specific gravity of the sea, resulting from these 

 ingredients, explains its buoyancy. The proportional specific gravity of different kinds 

 of water is stated to be as follows : .*'' 



Sea water 

 River water 



- 1 -028 



- 1 -010 



Pure spring water 

 Distilled water - 



- 1 -001 to 1 -005 



- I'OOO 



The quantity of salts in the water of the ocean varies in different places. Lord Mulgrave 

 found the proportion at the back of Yarmouth sands to be 3*125 per cent of the weight 

 of the water ; and Captain Scoresby, in N. lat. 77 40' and E. long. 2 30', found the pro- 

 portion to be 3 '56 per cent in a quantity of water taken from the surface. Different 

 observers have given the following results : 



Quantity of 

 Saline Matter. 



Quantity of 

 Saline Matter. 



N. lat. 80 60 fathoms under ice 354 percent. S. lat. 49 50' 60 fathoms under ice 4-16 per cent. 



74 3-60 46 4-50 



60 3-40 40 30 4-00 



45 4-00 25 54 do. 



39 do. 20 3-90 



34 do. I 16 3-50 



14 do. 



The s^a was formerly supposed by physical enquirers to be the saltest under the equator ; 

 but Humboldt has deduced from good experiments conclusions as follows : 



Proportion of salt between and 14 lat. =0-0374 



15 25 =0-0394 



30 44 =0-0386 



50 50 =0-0372 



From this table it appears that the saltness of the ocean is greater towards the tropics 

 than at the equator, and least towards the poles ; for which a reason may be found in the 



