PHYSICAL OCEANOGRAPHY 



269 



In August 1906, a series of current-measurements was made c 



by the "Michael Sars " 

 the Ling Bank in the North Sea, 

 Sea. Fig. 179 shows the 

 currents at depths of 2, 20, 

 and 75 metres (the depth of 

 water being 80 metres). In 

 the lower row the direction 

 j- and velocity of the current 

 ^ are indicated by arrows for 

 ^ every hour from 5 p.m. on the 

 ? 7th August to 6 A.M. on the 

 ? 8th August. It is seen how 

 I the water moved at the differ- 

 ^ ent depths, varying in direc- 

 j tion and velocity ; in the 

 I course of twelve or thirteen 

 ^ hours the direction of the 

 5 current had passed through 

 I all the points of the compass. 

 I In the top row all the arrows 

 5 are joined, thus forming a 

 ^ line which shows roughly the 

 I motion of the water during 

 ^ the period of thirteen hours. 

 I The course proved to be 

 '^ somewhat elliptic, the water 

 S returning very nearly, but 

 ^ not quite, to its point of 

 J departure. This is a typical 

 ^ case, for tidal currents are, as 

 ]* a rule, characterised by this 

 g turning, the water arriving at 

 ": its Starting-point again after 

 ^ a period of about twelve and 

 a half hours. The displace- 

 ment in the course of this 

 time, as exhibited by the 

 current-lines, is attributable 

 to a general motion of the 

 water, towards the east at 

 2 metres, north-east at 20 

 metres, and north - north - east at 75 metres. But this 



measurements 

 n the North 



