42 
Gulf Stream, and is well illustrated by the velocity diagram (fig. 18, 
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 
Qa oT s 
aA 
Fia. 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 follows: 
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, 
Fic. 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 all but one of the parallel 
