118 



TIDES. 



[Sect 1 V. 



And hence, it has sometimes been stated as a rule, at such 

 places, that the afternoon tides are always the highest or 

 the reverse. But this is not the rule. If the afternoon 

 tides are the highest at one time of the year, they arc 



lowest at another. 



the 



The rule of the diurnal inequality depends on th^ 

 moon s dechnation, and will be given in Note B. 



26. There is often a diurnal inequality of ihe height 

 of low water, and at some places it is greater than % 

 diurnal mequallty of high water (as at Sincapore, and at 

 Port Essmgton in Australia) . 



^ 27. Also there is often a diurnal inequality in the 

 time«. 



When this is the case, if we set off the Imntidal inter- 

 vals as ordinates (see Art. 14), the line drawn through 

 their extremities will have a zigzag form, like that of the 

 heights in fig. 4. 



28. When this is the case, we cannot determine the 

 establishment (see Art. 17) without making allowance for 

 the diurnal inequality. 



dr 



We make allowance for the diurnal inequality bv 

 ...... a curve, cutting off from the zigzags equal per- 



a »v J n 



tions above and below. (Sop fio. 4. ^ q^i,:„ 7- mi 



^ . "tiuw. ^^^oee ng. 4.; ling mean line will 



■" of a wavy form in consequence of the semi-mensual 

 inequality ; and the ordinate corresponding to the new or 

 run moon, or to the hour or 12 of moon's transit, will 

 give the establishment. 



But if 



we a 



^ pply this eptablishrnent to predict the time 



- tide on any day, we must also apply the diurnal 



N 



(S 



7 



\ 



f>«t' 



b^^' 



TV.] 



29. 



that 

 have 



thei 

 si/! 



t 



happen 

 few day^ 

 are two 

 should 1 



every 



h 



5 minnt( 



30. Ii 



the U h 



ticularly 



They 



observati 



These 



1. A, 

 commoni 

 If thp""^ 



examine, 

 the objec 

 area, it 



region 0: 

 32. It 



flood 



an 





urns. 



w 



tu 



'ii 



rn 



e 1] 



e 



^^iistak 



observati 

 ^^ the ti, 

 '^ the SI 



