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. 
VOR RS), 
Aucust 13, 1925. 
