THE SEA 19 



tion of the moon, once at full and once at new moon. 

 The highest spring tides occur a short time before 

 the March and September equinoxes. 



The tides are lowest in mid-ocean, where they 

 range from two to three feet. On the coasts of con- 

 tinents they rise to much greater heights, and 

 when forced up narrow, shelving bays, deep gulfs, 

 or broad river mouths, they attain considerable 

 heights. In the Bay of Fundy the spring tides, aided 

 by favoring winds, sometimes reach seventy feet in 

 height. 



Although the water of waves appears to move for- 

 ward, it really moves up and down vertically. There 

 is a slight surface drift, however, as is shown by 

 the finding of golf balls from Scotland off the coast 

 of the Lofoten Islands in the north of Norway. On 

 approaching the shore the wave breaks, and its 

 crest topples forward, and gives rise to a distinct 

 horizontal movement of the water. 



In the open sea, with a moderate wind, the height 

 of the average wave is only about six feet. Reason- 

 ably authentic cases of waves measuring fifty feet 

 above the level of the trough have been reported, but 

 such waves occur only during exceedingly violent 

 storms. 



True ocean currents are bodies of water of definite 

 constitution, often differing markedly from the sur- 

 rounding water, through which they flow like a 

 river. The Gulf Stream, which has already been 

 discussed, is a typical ocean current. Other important 

 Atlantic Ocean currents are the North Equatorial 



