131 



o 



0) 



if) 



c 

 a; 



Q. 



O 6 12 



Lunar Hour after Transit 



Prinnary current Corrected 



Figure 41. — Distortion of primary current when = 10°. 2. 



Id 



-2 



Lunar 



Hour 



12 



Primary current 



Corrected current 



Figure 42. — Distortion of primary current when 0=36°. 



264. Correction for remaini'ng approximations. — The coiTection of 

 the primary current for the remaining approximations introduced in 

 its derivation may be computed by a variation of the procedure by 

 which the corrections shown in table X are derived. The computations 

 determine the corrections at selected ti.me intervals through the tidal 

 cycle. In order that they may apply to repetitions of the cycle, the 

 intervals should be parts of the component hour of the simple har- 

 monic fluctuation of the head used for the deterjtnination of the 

 primary current, ordinarily the lunar hour of 1.035 mean solar hours. 

 Since the computations depend, in part, on the changes in the velocity 

 during these intervals, their accuracy is increased, but the labor mul- 



