35 



d3niamic 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 djmamic 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 wliich the water moves is, of course, requisite 

 information which may be obtained best perhaps by reference to a 

 vertical section — i. e., the d3niamic section. If a plane be passed 



20fc> 



2o5 



205 



20X 



AROHIMEDEAtM " 

 RERRELIAN 



:ndemoy 

 en deisjcv 



Fig. 17.— Showing the two types of distribution of specific volume 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 dowTiward 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 

 run in a direction through the paper, either toward or away from the 



