->-B 



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 

 section (see fig. 12, p. 30) or in a 

 horizontal view called a dynamic 

 topographical chart (see fig. 19, p. 

 39). Both vertical and horizontal 

 projections, it will be found, assist 

 to reveal particular knowledge 

 regarding the types of forces in- 

 volved. It will lead also to a 

 clearer understanding of the rel- 



FiG. 15.— ResolutiotLof the two principal forces in . . . r .\, jt j 



a gradient current AB; AE, the forces due to atlVC pOSltlOU Ot the torCCS, and, 



Archimedean tendencies; AC, the Ferrelian morCOVCr, tO the COUrSC of the 

 force J ■!• • c 



current, it we now review some oi 

 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- 



M 

 O 



N 

 P 



C 



Fig. 16. — A diagram offerees 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 AE, 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, etc., then, correspond to the 



