CHAPTER IX 



OCEAN CURRENTS— THE GULF STREAM 



There are several distinct types of movement of the 

 water in the oceans : — 



1. The Tidal Wave (caused by the attraction of the sun 

 and moon), which rises and falls every 12 J hours, and is only 

 seen in its unmodified form in the great Southern Ocean, 

 where it has a free and uninterrupted course around the 

 globe. This gives rise to branch waves that extend up the 

 oceans between the continents, and may become very much 

 compUcated where they meet with obstruction. The rise 

 and fall of the tidal wave gives origin to tidal currents in 

 shallow water near land, or over oceanic shoals. Such tidal 

 currents have been detected down to the considerable depth 

 of 400 fathoms in the open ocean. Higher tides (" spring 

 tides ") occur at the time of full moon and new moon, and 

 less high (" neap tides ") at the time of the first and third 

 quarters of the moon. Further details are more a matter 

 for the astronomer than the oceanographer. 



2. Waves and Storms and drift of surface water are 



caused by the wind. As proof of the existence of surface 



drifts for great distances, we have the evidence of golf -balls 



from Scotland found at the Lofoten islands in the north of 



Norway, and Siberian drift-wood carried into the Norwegian 



seas. The waves of the open sea may give rise to a current 



on approaching a shore. As a general rule, what Murray 



has called the " mud-line," at a depth of about 100 fathoms 



on the coast of a continent facing the open sea, is the 



region where the finest particles are undisturbed by wave 



action, but it is said that there is evidence of waves affecting 



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