48 THE OCEANOGRAPHY OF THE NORTH-WESTERN OCEAN [PART I 



of the annual flooding of the Northern Ocean with Atlantic 

 water is to be found in the annual rise and fall of the waters of 

 the North Sea and Baltic. It is possible to dissociate the rise and 

 fall of the sea due to this cause from the fluctuations in level due 

 to tides, winds, &c. When this was done the water gauges at nine 

 different places on the Dutch North Sea coast, and on the Swedish 

 and German Baltic coasts indicated an annual fluctuation of the level 

 of the sea which could only be due to a yearly flooding of these 

 waters. The rise and fall is in every case only a matter of about 20 

 to 26 centimetres, but the almost exactly synchronous nature of 

 the variations shewed that they were due to a common cause, which 

 can be no other than the variable volume of water which enters 

 these seas in the course of the year from the Atlantic Ocean. 



The North Sea receives high-salinity water from two directions. 

 In the South Atlantic water enters through the Straits of Dover. 

 But this is only a very narrow passage and only a small volume of 

 water enters here. The principal flow is round the north of Scot- 

 land. After passing through the Faeroe Channel the Norwegian 

 Branch of the European Stream, as it is now termed, is deflected 

 by the rotation of the earth, in accordance with the law ^Yhich 

 states that both wind and ocean currents are deflected to the right 

 in northerly latitudes. Passing then round to the north of the 

 Shetlands the stream turns to the south and enters the North Sea. 

 It grows in intensity during the winter and reaches its maximum 

 in the spring, afterwards decreasing in strength. The Dogger 

 Bank in the northern half of the North Sea interrupts the flow 

 of the northerly Atlantic stream so that the southern portion of 

 the area receives its dense water from the Straits of Dover. As 

 the spring advances these two currents gradually cover a large part 

 of the North Sea, approaching each other as north and south 

 tongues of water. They do not however meet, and over the central 

 area of the North Sea the Atlantic water is mixed with fresher 

 water arising from the Rhine, Scheldt, Weser and Elbe, or perhaps 

 coming from the deep Norwegian channel into which it flows from 

 the Baltic. But undercurrents may pass along the deeper de- 

 pressions and guts on the English side and join the north and 

 south Atlantic tongues. It has been estimated that such under- 

 currents may attain a velocity of about five kilometres per day. 



