211 



in which H and H° may be taken as the unadjusted vahies shown in 

 cohimns (19) and (20) of figure 69, and at increases by 15° at each 

 successive half lunar hour. Thus the surface head in the subsection 

 between stations 61 and 77 at zero hour is: 



0.770 cos 22°30'= +0.71 



and at 0.5 lunar hour it is: 



0.770 cos (15° + 22°30') = +0.61 

 and so on. 



The tides at hour are then adjusted to the selected entrance tides 

 as follows: 



Total head, entrance tides 3.35-0.90=2.45 



Primary tides 1.76 



Total correction. 



.69 



The primary heads in the subsections, column (2), total 1.76 feet, 

 while the head between the selected entrance tides is 2.45 feet, giving 

 a correction of 0.69 feet. The correction factors, column (3), are the 

 lengths of the sections divided by the total length of the canal. The 

 corrections derived by applying these factors to the total correction 

 are shown in column (4), an odd hundredth being assigned to the 

 subsection with the largest head. The adjusted tides, column (6), 

 are found by successively adding the adjusted heads, column (5), to 

 the tide at station 5, the initial entrance. 



The tides at ends of the subsections at subsequent intervals of time 

 are adjusted by a repetition of the process. The corrections generally 

 are much smaller than those which, in this case, happen to occur at 

 hour. 



409. The heights above Delaware River datum, of the adjusted tide 

 at any other stations on the canal may be found, at half lunar hour 

 intervals, by linear interpolation between the adjusted tides at the 

 ends of the subsections. The adjusted and observed tides at Biddies 

 Point (station 19 + 500) and at Summit Bridge (station 51+200) are 



