196 



379. Primary currents in other subsections. — The amplitudes and 

 phases of the currents which would be produced at the other velocity 

 stations under the initial assumption are computed from equations 

 (283) and (284). These computations are tabulated in figure 62, 

 facing page 198. The coordinate components of the tide at the 

 entrances and at the storage stations, found in paragraph 377, are 

 entered in columns (2) and (3). Since the canal has a constant 

 cross section. 



7=aAx/i:>=0.000,140,5X40,000/30=0.187. 



This value is entered in column (4) . A much larger value of I would 

 indicate that the canal should be divided into shorter subsections. 

 The resulting coordinate velocity increments, I A sin a and I A cos a, 

 are entered in columns (5) and (6) . For these and for the subsequent 

 computations, the slide rule affords satisfactory accuracy. 



The coordinate amplitudes, Bq sin /3o and B^ cos /So, of the current 

 at station 100, determined in paragraph 378, are entered opposite this 

 station in columns (7) and (8). The values of (B/m) sin /3 and 

 (B/m) cos jS at station 60 are found by subtracting, algebraically, the 

 coordinate velocity increments lA sin a and lA cos a at station 80 from 

 the coordinate amplitudes of the currents at station 100 (since the 

 summation is in the negative direction) ; and the values at station 20 

 by subtracting the increments at station 40 from the values found at 

 station 60. The values of (B/m) sin 13 and (B/m) cos /3 at station 

 140 are similarly found by adding, algebraically, the coordinate 

 increments at station 120 to the coordinate amplitudes at station 100; 

 and at station 180 by again adding the increments at station 140. 

 The totals of columns (5) and (6) may be checked against the differ- 

 ences between the last and first lines of columns (7) and (8) respec- 

 tively. 



The values of tan /3, from columns (7) and (8) are entered in column 

 (9), and the corresponding values of jS in column (10). Since, in the 

 present example, the area of the cross section of the canal is the same 

 at all stations, m = l and B/m=B. The entries in columns (11) and 



(12) therefore are omitted, and the amplitudes, B, of the current at the 

 velocity stations entered in column (13) from the relation: 



B=(B/m) sin/3/sin p=(B/m) cos i8/cos /3. 



The values of /3 and B at station 100 derived in columns (10) and 



(13) should check with those found in paragraph 378. 



380. Surface heads corresponding to computed currents in subsec- 

 tions. — The computation is continued in columns (14) to (24) of 

 figure 62. The value of p, column (14) for all subsections is, from 

 equation (287) : 



:P=0.000,005,148Xl20'X30=2.224. 



