282 FIRST YEAR SCIENCE 



able. Circulating around each ocean there is a contin- 

 uous drift of surface water extending to a depth of from 

 300 to 600 feet and varying in rate from a few miles up 

 to fifty or more miles a day. In fact these rotating 

 currents are the chief natural basis for the division of the 

 oceanic area into six oceans, as our geographies generally 

 divide them. 



These currents circulate in the northern hemisphere in 

 the direction in which the hands of a watch move and 

 in the southern hemisphere in the opposite direction. In 

 the centers of these rotating areas the water is nearly 

 motionless and here are often found great masses of float- 

 ing seaweed filled with a great variety of small animals. 

 These accumulations of seaweed are called sargasso seas 

 (page 249). 



That these surface drifts have a definite direction of 

 movement is indicated by observations made on the 

 courses taken by a great number of wrecks. The di- 

 rection of these movements has also been determined by 

 throwing from ships in different parts. of the ocean thou- 

 sands of bottles in which had been placed the date and a 

 record of the latitude and longitude of the ship. The 

 places where the bottles came ashore showed the direction 

 of the currents. 



If the movement of the water is slow, ten or fifteen 

 miles a day, it is called a drift; if faster, a current. The 

 principal currents have been given names and have been 

 most carefully charted. The warm current that flows 

 northeastward off the southeast coast of North America is 

 called the G-ulf Stream. That off the east shore of Asia, 

 which also flows northeast, is called the Kuro Siwo or 

 Japan Current. The cold current off the east coast of* 

 Labrador flowing southeast is called the Labrador Current ; 

 and the cold current which flows northward off the west 



