34 
In Figure 15, AB represents the path of the current; AE, the result- 
ant of the real physical forces; and AC, the quasi force due to earth 
rotation, acting with the same magnitude but in the opposite direc- 
tion. The two vectors AE and AC lie in one and the same plane, 
EAC, which is perpendicular to the course of the current. The fields 
of forces may be investigated by regarding them graphically in either 
a vertical view, called a dynamic 
i section (see fig. 12, p. 30) or in a. 
horizontal view called a dynamic. 
topographical chart (see fig. 19, p- 
39). Bothvertical and horizontal 
projections, it will be found, assist. 
to reveal particular knowledge 
regarding the types of forces in- 
C volved. It will lead also to a 
: sig é clearer understanding of the rel- 
Fic. 15.—Resolution of the two principal forces in 5 Bo 
a gradient current AB; AE, the forces due to ative position of the forces, and, 
Archimedean tendencies; AC, the Ferrelian moreover, to the course of the 
Be current, if we now review some of 
the fundamental notions pertaining to such representations of forces. 
The well-known method of regarding a force as represented by equi- 
scalar surfaces and unit scalar sheets is especially applicable here. 
The potential value of an irregularly formed equiscalar surface, 
obviously, can be traced by its intersections with a series of unit 
parallel horizontal planes. The rate of variation of contours (inter- 
sections) measured along a normal vector called the gradient is a 
direct expression of the acceleration of the scalar force. In Figure 16 
E N 
P 
M 
O 
Cc 
Fic. 16.—A diagram of forces similar to that shown in Fig. 15, but with the addition 
of dynamic isobaths MN, OP, etc., which show the position of such contours 
(when friction is disregarded) relative to the actual movement of the water 
particles 
the vector AE representing the acceleration due to primary forces in 
the sea provoking currents may be regarded as a gradient force due to 
the variations in level. These variations are in horizontal projection 
shown by a series of horizontal lines (dynamic isobaths) MN, OP, etc., 
all perpendicular to line AH, and inscribed on the scalar field of the 
force. But MN, OP, etc., are also parallel to the line AB, the stream 
line of the current. Lines MN, OP, etce., then, correspond to the 
