TRAVELS IN BRAZIL. 71 



experiments of Marcet*, it is true, do not show the 

 specific gravity of the sea water, in the strait, taken 

 fi-om a considerable depth, to be greater than that 

 of the surface. With respect to this difference, we 

 too are unable to state anything positive, on ac- 

 count of the quickness of our passage, and for 

 want of a convenient opportunity of procuring 

 water from a sufficient depth ; the certainty, how- 

 ever, of the greater specific gravity in the Mediter- 

 ranean, may serve as an explanation, whereas, the 

 accuracy of the result of Marcet's experiments 

 may be doubted, on account of the difliculty of 

 obtaining sea water, from a requisite depth. But 

 if there is a difference in the specific gravity of the 

 water of both seas, the countercurrent must really 

 take place as supposed, because in the collision of 

 two fluids of different gravity, the heavier naturally 

 flows under the lighter. Besides the most import- 

 ant cause of the current in the strait, which we 

 have stated, others may contribute. Thus the re- 

 volution of our planet round its axis, which com- 

 municates to the sea that general motion from east 

 to west, probably exercises its influence below 

 the surface of the sea. Another cause of the lower 

 current towards the west, may be looked for in the 

 pressure of the many streams, some of them very 



because the water, which flows out at Gibraltar, can only come 

 from a considerable depth, and consequently from the middle 

 of the sea. 



* Phil. Trans, in the place above quoted. 



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