RECENT HYDROBIOLOGICAL INVESTIGATIONS 475 



Gulf of Mexico, and issues from the latter as the well-known 

 Gulf Stream. This ocean current is joined by a current which 

 flows outside the West Indian Islands, and the stream so 

 formed enters the North Atlantic and flows to the north-east. 

 It is, at the outset, an " Ocean river " only a few miles wide, 

 and possessing a velocity of about a hundred miles a day. 

 Coming from a region of high temperature and rapid evapora- 

 tion, the water is relatively warm and dense, having a 

 temperature of about 20 C, and a salinity of over 36 per 

 thousand. Soon after issuing from the Straits of Florida the 

 Gulf Stream loses its individuality and fans out into the North 

 Atlantic in about latitudes 40 N. to 45 N. and longitudes about 

 41 to 42 W. At about latitude 41 N. and longitude 50 W. 

 it encounters the waters of the Labrador Stream coming down 

 from Baffin Bay and Davis Straits, and the two currents interfere 

 to some extent, the waters of the colder pushing through and 

 underneath those of the warmer. All the time, however, the 

 tendency is for the waters of the Labrador Stream to be pushed 

 to the west, and for those of the Gulf Stream to flow to the 

 east. After this collision the Gulf Stream becomes diffuse, 

 and splits up into three badly defined " drifts." One of these 

 turns round to the east and south, as the Canaries Current, 

 and, ultimately rejoining the North Equatorial Stream, com- 

 pletes the gigantic anti-cyclonic eddy of the North Atlantic 

 Ocean which encloses the Sargasso Sea. A second drift flows 

 to the north-east and enters the region of the Bay of Biscay 

 and English Channel. The third drift flows on to the north- 

 east, to the west of the British Isles, as the Norwegian Branch 

 of the European Stream. 



These facts have long been known, but it is important to 

 remember them when discussing the details of the circulation 

 in the more northern regions. It is also necessary to remember 

 that the strength and volume of the Gulf Stream itself are 

 periodic, varying throughout the year in a definite manner. 

 With regard to this annual periodicity, however, much still 

 remains to be investigated. The Gulf Stream circulation also 

 varies in strength from year to year. The fact that water of 

 sub-tropical origin reaches the northerly coasts of Europe is, 

 as is well known, of the utmost importance to the climate of 

 the British Islands and that of the Scandinavian countries. 

 It is not so well known that the periodicity in volume of the 



