A PRACTICAL METHOD FOR DETERMINING OCEAN 
CURRENTS 
Epwarp H. Smita 
THE ORIGIN OF CURRENTS 
In order to make a systematic exposition of the circulation taking 
place in the oceans with especial regard to the origin of currents, 
we have found it convenient to divide the forces into two general 
classes: (1) Internal and (2) external. 
(1) Internal forces appear in an ocean mass whenever any change 
takes place in the physical character of the water itself; that is, if 
either the temperature or the salinity varies in the sea then the 
dynamic equilibrium is upset and a tendency to readjust must follow. 
The internal system of forces in an ocean are disturbed whenever 
that mass radiates or absorbs heat; evaporates from the surface; 
receives additions of fresh water; or suffers internal physical trans- 
formation as a result of its turbulent activity. Radiation is simply a 
gain or loss of heat by the ocean, which tends to vary the temperature 
of the surface layers. Evaporation tends to vary the salinity of the 
surface. The ocean receives fresh water from rain, snow, or melting 
ice. When an ocean mixes internally it alters its physical character 
within the region of mixing. 
(2) Forces classified as external and provocative of currents are 
winds, tides, and variations in atmospheric pressure. The winds 
we shall divide into two groups, determined primarily by their 
extent and duration: (a) Those winds which by a tangential pressure 
on the surface of the sea frictionally propagate a pure wind current 
only; and (6) those winds which by virtue of friction drive water 
particles against boundary surfaces in the sea and give rise to gradient 
currents. Winds classified as (6) are by far the most important of the 
external forces assisting to maintain the more or less prevailing system 
of circulation in the oceans. 
There are, however, two other forces which are classified as second- 
ary, but only in so far as they tend to deform the components estab- 
lished by (1) and (2). They are, nevertheless, of the utmost im- 
portance in the consideration of currents, namely, (a) the quasi 
force due to terrestial rotation which acts simultaneously as soon as a 
movement as described in paragraph (1) or (2) begins; and (0), fric- 
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