70 TRAVELS IN BRAZIL. 



the Canary Islands, to deviate from their course, 

 to the south-east. Besides the current in the 

 strait, from the ocean towards the east, a contrary 

 motion of the Mediterranean from east to west, is 

 observable below the surface. The existence of 

 this lower current is further strengthened by the 

 well known reappearance of a ship, sunk in the 

 strait, to the west of it, * The greater specific 

 gravity of the sea water in the Mediterranean, may 

 be perhaps looked upon as the chief cause of this 

 countercurrent. The accounts of travellers agree 

 in this difference in the specific gravity, and our 

 Own observations confirm it, as we found that of 

 the Mediterranean to be 1.03384, and that of the 

 Atlantic ocean, near the strait, 1.02944. f The 



* Drinkwater's History of the late Siege of Gibraltar ; 

 Waiz, in Schwed. Abhandl. 1757 ; Marcet, in Phil. Trans. 1819 ; 

 Patton, in Edinb. Phil. Journ, 1821, vol. iv. p. 243. It is also 

 confirmed by two opposite currents in other straits, as in 

 the Dardanelles, in the Sound, &c. Mr. Von HofF (History of 

 the natural Changes of the Surface of the Earth, Gotha, 1822.8.) 

 has very lately suggested doubts, not indeed of the existence of a 

 sub-marine countercurrent, but of water being conveyed by it 

 from the Mediterranean to the ocean, for he supposes that the 

 motion towards the west, begins in the middle of the strait 

 itself, and therefore proceeds only from the lower parts of the 

 water of the ocean, which are hindered, by a supposed dam at 

 the bottom of the strait, from entering the more shallow Medi- 

 terranean, so that they strike against it, and must return to the 

 west. 



-f- The observation made by Lalande (Voyage en Italic) that 

 the water on the coast of France is lighter than that in the 

 middle of the sea, as it contains only -.l to ^l, and not -^ to 

 .jij, of its weight of salt, does not contradict our supposition, 



