42 



Gulf Stream, and is well illustrated by the velocity diagram (fig. 13, 

 p. 32). In "B," Figure 20, the velocity of ''a" being greater than 

 adjacent particles, or adjacent sheets above and below, is thereby 

 retarded and friction acts to hinder the translatory progress of 

 particle ''a." In '' C," the velocity of particle "a" is less than either 

 of its immediate neighbors, above or below, and friction therefore 



Fig. 20. — Three general types of current velocity diagrams 



tends to accelerate the velocity of ''a." If the water particles in a 

 current be retarded by a constant accelerating force of friction 

 throughout the depth, then the velocity diagram will assume the 

 form of a parabola. 



Cases as shown in '^B" and " C" (fig. 20) may also be illustrated 

 by components and force diagrams in horizontal projection as foUows: 



The dotted lines in Figure 21 represent the direction of flow of the 

 current, and the solid lines are equipotential lines inscribed on the 

 scalar field of the force tending to produce a movement in the sea. 



Fig. 21. — The two types of force diagrams belonging to gradient currents when friction is included 

 either as (1) a retarding or as (2) an accelerating force 



The gradient AE being perpendicular, of course, represents the force 

 due to variations in gravity potential. AC is the force due to terres- 

 tial rotation lying 90° to the right of the direction of the current. 

 By vector analysis we may find the force AF due to friction, where 

 in "A" it retards the current AB, and in ''B" it accelerates the same. 

 If all but one of the parallel lines of flow and aU but one of the parallel 



