142 A TEXTBOOK OF OCEANOGRAPHY 



and other causes, it is not easy to détermine the influence of 

 the earth's rotation in causing a déviation of océan currents. 

 In the case of atmospheric currents the same difficulties are 

 not présent, or if présent, then not felt to the same degree, so 

 that the déviation of atmospheric currents caused by the earth's 

 rotation is easy to détermine. 



The most suitable localities for investigation are those free 

 from tidal streams and strong océan currents, such as the 

 Baltic and Mediterranean, Hère the only influence causing 

 currents is the wind, and since the direction of the wind can 

 be observed, we can tell in what direction the current should 

 flow if it is caused by wind alone. Investigations into the 

 influence of the earth's rotation hâve been made both in the 

 Baltic and the Mediterranean Seas, and the resuit of one such 

 séries of investigations is recorded briefly hère. Records were 

 kept for 294 days on the Adlergrund Lightship in the Baltic. 

 Every two hours the direction of the wind, its strength (on the 

 Beaufort scale), the direction and strength of the current in 

 ths sea at 5 mètres depth, were recorded. Tidal streams were 

 absent. The wind caused a current, and this was readily 

 observed up to the depth of 5 mètres. Occasionally the wind 

 changed too rapidly to enable satisfactory observations to be 

 made, so that only 226 days gave suitable records. On many 

 days, however, the wind was too feeble (below 3 on Beaufort's 

 scale) to cause a sufïiciently strongly-marked current to be 

 noted, so that finally the records of 131 days were selected for 

 analysis. On thèse days the wind exceeded 3 on the Beaufort 

 scale, and the stream over 37 miles, in the twenty-four hours. 

 The angle was measured between the actual direction of the 

 current and the wind, and this gives the déviation due to the 

 rotation of the earth, ail other possible causes being excluded. 

 There is found to be a marked déviation to the right, and, as 

 will be seen on référence to the figure (Fig. 27), the maximum 

 déviation is 25° to the right. 



