312 COSMOS. 



of the atmospheric pressure, successively propagated from east 

 to west, and occurring with such regularity in the tropics. 

 These currents present a remarkable spectacle ; like rivers of 

 uniform breadth, they cross the sea in different directions, whilst 

 the adjacent strata of water which remain undisturbed form, as 

 it were, the banks of these moving streams. This difference 

 between the moving waters and those at rest, is most strikingly 

 manifested where long lines of sea weed borne onward by the 

 current, enable us to estimate its velocity. In the lower 

 strata of the atmosphere, we may sometimes during a storm 

 observe similar phenomena in the limited aerial current, 

 which is indicated by a narrow line of trees which are often 

 found to be overthrown in the midst of a dense wood. 



The general movement of the sea from east to west between 

 the tropics (termed the equatorial or rotation current), is con- 

 sidered to be owing to the propagation of tides and to the trade 

 winds. Its direction is changed by the resistance it experi- 

 ences from the prominent eastern shores of continents. The 

 results recently obtained by Daussy regarding the velocity of 

 this current, estimated from observations made on the dis- 

 tances traversed by bottles that had purposely been thrown 

 into the sea, agree within one-eighteenth with the velocity of 

 motion (10 French nautical miles, 952 toises each, in 24 hours) 

 which I had found from a comparison with earlier experiments.* 

 Christopher Columbus during his third voyage, when he was 

 seeking to enter the tropics in the meridian of Teneriffe, 

 wrote in his journal as follows :f " I regard it as proved that 

 the waters of the sea move from east to west, as do the 

 heavens (las aguas van con los cielos), that is to say, like the 

 apparent motion of the sun, moon, and stars." 



The narrow currents or true oceanic rivers which traverse the 

 sea, bring warm water into higher and cold water into lower 

 latitudes. To the first class belongs the celebrated gulf stream 



* Humboldt, Relat. hist., t. i. p. 64 ; Nouvelles Annales dea Voyages, 

 1839, p. 255. 



t Humboldt, Examen crit. de I'hist. de la Oeogr., t. iii. p. 100. 

 Columbus adds shortly after, (Navarrete, Coleccion de los viages y de~ 

 scubrimientos de los Espanoles, t. i. p. 260,) that the movement is 

 strongest in the Caribbean sea. In fact, Rennell terms this region, " not 

 a current, but a sea in motion" (Investigation of Currents, p. 23). 

 ' J Humboldt, Examen critique, t. ii. p. 250; Relat. hist., t. i. 

 pp. 66-74. 



