THE EARTH. 107 



b.uk ar J forward with the tide, they have thus a progressive curreru 

 to the west, which though less observable, is not the less real. 



Besides these two general motions of the sea, there are others which 

 are particular to many parts of it, and are called currents. Theso are 

 found to run in all directions, east, west, north, and south ; being form- 

 ed, as was said above, by various causes ; the prominence of thu 

 shores, the narrowness of the straits, the variation of the wind, and the 

 inequalities at the bottom. These, though no great object to the phi- 

 losopher, as their causes are generally local and obvious, are never- 

 theless of the most material consequence to the mariner ; and, without 

 a knowledge of which, he could never succeed. It oflen has happen- 

 ed, that when a ship has unknowingly got into one of these, every 

 thing seems to go forward with success, the mariners suppose them- 

 selves every hour approaching their wished-for port, the wind fills 

 their sails, and the ship's prow seems to divide the water ; but, at last, 

 by miserable experience they find, that instead of going forward, they 

 have been all the time receding. The business of currents, therefore, 

 makes a considerable article in navigation ; and the direction of their 

 stream, and their rapidity, has been carefully set down. This some 

 do by the observation of the surface of the current ; or by the driving 

 of the froth along the shore ; or by throwing out what is called the 

 log-line, with a buoy made for that purpose, and by the direction and 

 motion of this, they judge of the setting and the rapidity of the current. 



These currents are generally found to be most violent under the 

 equator, where indeed all the motions of the ocean are most perceivable. 

 Along the coasts of Guinea, if a ship happens to overshoot the mouth of 

 any river it is bound to, the current prevents its return ; so that it is 

 obliged to steer out to sea, and take a very large compass, in order to 

 correct the former mistake. These set in a contrary direction to the 

 general motion of the sea westward ; and that so strongly, that a pas- 

 sage which, with the current, is made in two days, is with difficulty 

 performed in six weeks against it. However, they do not extend 

 above twenty leagues from the coast ; and ships going to the East In- 

 dies, take care not to come within the sphere of their action. At Su- 

 matra, the currents, which are extremely rapid, run from south to 

 north : there are also strong currents between Madagascar and the 

 Cape of Good Hope. On the western coasts of America, the current 

 always runs from the south to the north, where a south wind, con 

 tinually blowing, most probably occasions this phenomenon. But the 

 currents that are most remarkable, are those continually flowing in 

 the Mediterranean sea, both from the ocean by the straits of Gibral- 

 tar, and at its other extremity, from the Euxine sea by the Archipe- 

 lago. This is one of the most extraordinary appearances in nature , 

 this large sea receiving not only the numerous rivers that fall into it^ 

 such as the Nile, the Rhone, and the Po, but also a very great infhu 

 from the Euxine sea on one part, and the ocean on the other. At tha 

 same time, it is seen to return none of those waters it is thus known 

 to receive. Outlets running from it fhere are none ; no rivers but 

 such as bring it fresh supplies ; no straits but what are constantly 

 pouring their waters into it : it has, therefore, been the wonder o} 

 mankind in every age, how, and by what means, this vast concours 



