33 



Table VII 



The velocity values as they are usually finally shown, represented 

 by Co, page 31, are the differences between the movement on the 

 surface and that at a level 

 where it is believed motionless 

 water lies. But it is important 

 to bear in mind that as a result 

 of dynamic computations, the 

 values of velocities are expressed 

 .in terms normal to the 

 VERTICAL SECTION which may 

 include any two stations. 

 Another step is necessary if it 

 is desired to obtain the value of 

 the real velocity. Let us as- 

 sume that the direction of 

 flow but not the rate is 

 known. In Figure 14 suppose 

 the direction of the current is 

 represented by the parallel 

 lines AM and BMi, between 

 the two stations A and B. Fur- 

 thermore, let it be given that the velocity normal to the section has been 

 computed by means of equation (g) , page '4 1 , and that it is given on the 

 figure as the line K. We now wish to determine the true velocity, 

 V, which lies in a cUrection parallel to the lines AM and BMi, and 

 which forms the angle a with the computed velocity. The value of 



K 



Fig. 14.— Lines AM and BMi indicate the 

 known direction of the circulation. K repre- 

 sents the computed velocity normal to the sec- 

 tional line AB. To find: The true velocity 

 (V) of the current 



V, it is easy to see from the figure, is equal to 



cos a 



The same results 



may be obtained graphically by laying off the angle a and dropping 

 a perpendicular from the end point of the known side K upon the 

 unknown side V, and then measuring the length of the latter in units 

 the same as K. 



