30 
dynamic contours of a given isobaric surface as illustrated by the 
dynamic topographical chart described on page 37 (see fig. 19). 
Therefore it follows that the dynamic isobaths recorded on such charts 
possess a tremendous significance in as much as they delineate the 
courses of the water particles over any given area that has been 
investigated. Not only may the paths of the currents be traced on 
such charts, but the degree of compactness of the dynamic isobaths 
along the gradient at right angles to the current, is a measure of the 
relative velocity of the current. The closer together the contours lie 
in any given latitude indicates the more rapidly the current is flowing 
at that time and place. 
DIRECTION OF FLOW 
The direction toward which the water moves is, of course, requisite 
information which may be obtained best perhaps by reference to a 
vertical section—i. e., the dynamic section. If a plane be passed 
ROG SE ROS ROS <—_—_—_ ROR 
— ARCH IMEDEAN TENDENCY 
Cosco FERRELIAN TENDENCY 
Fic. 17.—Showing the two types of distribution of specific yolume in vertical section and the resultant 
tendency toward flow of the water in consequence 
vertically downward through the plane of the forces AC and AE (fig. 
_ 16 p. 34) and a distribution of specific volume be secured, a dynamic 
section similar to Figure 12, page 30, will result. Consideration of the 
closed curve formed by the two verticals at stations 206 and 205 will 
reveal the fact that the water being lighter to a greater depth at 206 
than at 205 tends to be forced upward at 206 and downward at 205. 
But when the current is constant there is no actual movement of the 
water particles in these planes, as the real forces are exactly counter- 
balanced by the Ferrelian force (effect of earth rotation), the latter 
of which acts in a direction opposite to the tendency of the Archi- 
medean forces. The real movement of the water particles, as repre- 
sented by the foregoing figure, takes the form of a current which 
flows at right angles to the plane of the dynamic section. In such 
a distribution of forces as shown by Figure 17 the current would 
Tun in a direction through the paper, either toward or away from the 
