VI 



This paper endeavors to encompass in a general way the foregoing 

 subject with its various aspects. The contents deal with the fol- 

 lowing : The causes of currents ; static consideration of a water mass ; 

 dynamics and Bjerknes' theory; and a practical method for mapping 

 currents. Other related subjects discussed are friction; effect of 

 bottom configuration; tides; variations in atmospheric pressures; 

 and the winds. The writer has tried to present a rather technical 

 scientific subject in such a manner that it may easily be understood 

 by the ordinary student. Always there has been the hope that the 

 methods elucidated herein would serve some practical economic 

 service. 



I wish to recognize with appreciation the advice and suggestions 

 made with regard to this paper by the curator of the Museum of 

 Comparative Zoology, Harvard University, and the hydrographic 

 engineer, United States Hydrographic Office. 



The foreword is not complete unless this place is reserved to express 

 a sincere appreciation and acknowledgment of the untiring, generous 

 assistance and instruction given me in this work by the director of 

 the Geo-Physical Institute, Bergen, Norway. He has in many in- 

 stances placed even his personal notes at my disposal, and in a hun- 

 dred other ways has shown an unselfish spirit of cooperation and 

 friendship. As I leave Norway I bid him a fond farewell. 



E. H. S. 



August 13, 1925. 



