ii] RHYTHMICAL CHANGE IN THE SEA 35 



earth they are continually deflected to the east in 

 the northern hemisphere, and to the west in the 

 southern hemisphere. In the North Atlantic the 

 northerly flowing current is what we call the Gulf 

 Stream ; and the southerly flowing one consists of 

 the East Greenlandic and Icelandic currents, and 

 the Labrador current. 



The Gulf Stream spreads out in the Atlantic in 

 the form of a gigantic whirlpool the northern margin 

 of which is never higher than the latitude of the 

 Azores. Looking at an astronomical diagram we 

 see that for six months in the year most heat falls 

 on the part of the sea immediately north of the 

 equator, while for other six months most heat falls 

 on the sea immediately south of the equator. There- 

 fore the equatorial stream shifts a little way north 

 and south of the equator in the course of the year, 

 and the whole area covered by the Gulf Stream 

 circulation (which is caused by the equatorial stream) 

 also shifts a little way north or south as the earth 

 swings round the sun in the course of the year. 

 There is just the same annual variation in the 

 amount of water flowing south from the north pole, 

 for more ice is melted during the summer than 

 during the winter and therefore more fresh water 

 forms and flows away to the south. 



What we call the Gulf Stream in our latitudes 

 is really the drift of comparatively warm and salt 



32 



