m 



the Air and in the Sea. 175 



and part to the south-west. The north-west branch of this cur- 

 rent unites in the Caribbean Sea with the northern equatorial, 

 and in this way impels almost the whole of the warmed water of 

 the surface of the Atlantic equatorial zone into the Gulf of 

 Mexico. The great mass of this warmer and therefore lighter 

 water driven together by the equatorial current must, of course, 

 have the tendency to spread over the colder and heavier water, 

 and to now off northward. Thus arises, then, a current of warm 

 water flowing out of the Gulf of Mexico, commonly known by 

 the name of the Gulf-stream. 



The motive force of the Gulf-stream must therefore be derived 

 partly from the pressure of the equatorial current, partly from 

 the tendency of the warm water to spread over the cold of the 

 higher latitudes, but partly also from the attraction of the cur- 

 rent, directed eastward, of the middle latitudes ; but all these 

 causes spring directly from the attraction of the sun and moon, 

 which thus must be regarded as the prime motive force of the 

 Gulf- stream*. 



The eastward current of the middle latitudes and the north- 

 east movement of the entire northern portion of the Atlantic 

 Ocean form the continuation of the Gulf-stream, and hence are 

 often designated by the same name — to which we have no ob- 

 jection, if it be kept in view that the prime cause of motion of 

 the two last-mentioned currents lies in the force of the ebb-cur- 

 rent. As already said, in about 30° latitude this force com- 

 mences to overpower the force of the flood-current, and develops 

 the maximum of its effect somewhere between the 40th and 50th 

 degrees of latitude ; further polewards it diminishes considerably, 

 and becomes so feeble that it is no longer perceived as a current. 

 Nevertheless a slight movement eastwards appears to extend 

 considerably further towards the pole, and gradually to collect 

 the warmer water on the coasts of England and Norway. This 

 warmer water is derived partly from the Gulf of Mexico ; but 

 part of it may have been heated on the surface of the ocean in 

 higher latitudes. The ebb-current, therefore, collects the su- 

 perficial warmer water in the eastern part of the ocean ; and the 

 tendency of the warm water to spread over the colder impels it 

 north-eastward, and thus accounts for the motion of the north- 

 ern portion of the Atlantic. 



The principal force of the ebb-current, flowing eastward, is 

 deflected south by the coasts of Europe, and, following the coast 

 of Africa, returns again into the equatorial stream. The attrac- 

 tion of the latter perhaps forms the principal cause of thesouth- 



* Self-evidently it is not meant that the sun and moon's attraction heats 

 the water of the Gulf of Mexico ; but it is that which generates the equa- 

 torial current and thus collects the warm water in the gulf. 



