jXatural History of the Ocean, 8fc» 131 



which they may sound 80 fathoms, while the vessel is go= 

 ing three miles per hour. 



Soilness of the Sea. — Varies in different latitudes and lo= 

 calities. In the Tropical and Polar regions, the saltness is 

 the same, diminishing gradually on either side to the tem- 

 perate. In bays, arms, and at the mouths of rivers, the 

 water contains less salt. 



It is doubtful if the saltness does not vary with the depth. 



The salt is deposited when sea water freezes. 



The Mediterranean is Salter than the Atlantic ; the Bal* 

 tic less salt. 



Generally speaking, the saline matter of the Atlantic is 

 from three to four per cent, say in 1000 grains of sea wa- 

 ter are the following, viz. : — 



Muriate of Soda, - - 30.80 



Magnesian Salts, ... 04.00 



Sulphate of Lime, - - 00.80 



35.60 or 3.56 per cent. 



Sea Ice. — Sea water freezes at 28®. Buffon doubted if 

 it ever froze. Sea ice varies in colour from white and 

 grey, to greenish and sappharine. Its forms are various 

 presenting every shape which fancy can create. Scoresby 

 notices sixteen kinds, known among sailors. Sea ice when 

 melted affords fresh water. Mountains of ice have been 

 seen on the banks of Newfoundland, above 2,000 miles 

 from the place of its formation. They are heavier than 

 the water, and only one eighth appears above the surface. 

 Their approach is known by the effect they produce on 

 the atmosphere — and by the ice-blink, a luminous appear- 

 ance in the air above them. It is supposed that the poles 

 are surrounded by ice, which prevents access to them. 

 The nearest approach to the North Pole has been the lati- 

 tude of 82", or within 510 miles. The nearest approach 

 to the South Pole, has been latitude 72, by Cook, or within 

 1 1 30 miles. It is a matter of conjecture if either pole will 

 ever be visited. 



Motions of the Sea, are of three kinds, viz :— 



1. Motion of Waves. II. Motion of Currents. III. Mo- 

 tion of Tides. 



1. The motion of waves is preserved by the law of grav- 

 itation ; the sinking of one wave raising others. It is not 

 known how deep the sea is agitated : divers say to a great 



