Tides and Tidal Currents in the Proximity of Land 



357 



an acute angle with the direction of the current maximum (Fig. 147c). If on 

 the contrary, H.W. precedes by one quarter period the maximum current 

 we have \ti < e < and < y> < \n and \n< y/ < \n, the position of the 

 isolines is exactly the reverse of the previous one (Fig. 147c/). 



If there is friction, the systems of curves are no longer perpendicular to 

 each other, and the essential point is whether or not frictional terms are 

 predominant in the equations for tany> and tany' in (XI. 33). Both for the 

 progressive and the standing tide wave we get tan y. tan y' = —FIG. When 

 the friction is small, F will not be very different from G; and F.G will not 

 deviate considerably from 1 ; the angle enclosed by the two systems of curves 

 will not deviate much from 90°; with other conditions, there can be strong 

 deviations from 90°. 



6. Conditions Along Shores and Disturbances on Account of Bays and Islands 



If the current runs parallel to a shore (jc-direction) we have in its proximity 

 V = 0, and we obtain from (XI. 34) 



tany 



tany 



/ 



COtf 



7 



tane 



(XI. 35) 



If we consider a short stretch of shore, the variations in the time of the 

 maximal current and in the occurrence of the high water will be small, although 

 the variations in the magnitude and in the direction of the currents are large. 



ziyMwwv,. 



Fig. 148. Co-tidal lines in the vicinity of a Cape and in a Bay. 



In (XI. 35) £ is to be considered as nearly constant, i.e. the slope of the co- 

 tidal and co-range lines towards the shore line will be almost constant. 

 Although this seems to be the case, great variations show up in the direction 

 of the slope. Figure 148 illustrates the course of the co-tidal lines in the im- 

 mediate vicinity of a cape and of a small bay. Both the time of high water 

 and the range vary much more rapidly around the cape and much slower 

 in front of the bay than farther outside, where they have a more uniform 

 course. 



