EQUATORIAL STREAM. 197 



everywhere see how the wind rouses the water and 

 increases the force of the waves, and we know that 

 by mighty storms the flow of rivers may be 

 stopped, and the sea stirred up to great depths ; 

 must we not then expect that long-lasting winds, 

 even of moderate strength, must tend powerfully 

 to impress upon the sea a movement in their own 

 direction ? 



Such indeed is the case, and especially with the 

 constant easterly winds of the tropics, and with 

 the west winds which are so prevalent in higher 

 latitudes. The influence of these winds joins with 

 that of the differences of temperature in urging 

 the waters of the tropical seas to the west, and 

 those of the temperate zones to the east. Lastly, 

 the tides whose course is from east to west tend to 

 establish currents in the same direction, and these 

 may enhance the general westward flow of the 

 tropical seas. 



The sea-currents have been most carefully 

 studied in the Atlantic Ocean. In this ocean too 

 the conditions of their origin and direction are 

 very obvious, although the latter suffers consider- 

 able modifications from the form of the coast, and 

 most likely of the sea-bottom. Near the equator, 

 and close to the African coasts, the mighty 

 Equatorial Stream sets out. Here, to the 

 south of the islands of St. Thomas and 

 Anna Bon, it lias a speed of forty miles in 



