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^ 





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4 "'* 



(1 



1 ^ 



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INF' 



Ti ff 



N.- 



' 1 . 



1 ' 



r 



L 





Appeiidix.] 



TIDES. 



125 



(2.) Tide two days and a half old: 



Hour of Moon's Transit 



Correction of the Ksta- ) 

 blishmeiit • . , ( 



h. i h. 



2 



3 





1 



1 



m. 



ra. ' 



-31 



4 J^ 1 



i 



h. I h 



' 7 







o-^\ 



I 



w. 



j h. i h. 



I 10 n 





Uui + JO 



t 



T* 



This table is to be used in ti}e same way as th^ othei 



IJence we see that the age of the tide most affects the lunitidal inter- 

 nal when the time of moon's transit is between 7 and 8 hours.* 



The mean lunitidal interval, or ivean establishiwnt, is IG minutes less 

 than the former, and 31 minutes less tl'^n the latter establishment sup- 

 posed in the above tables. (See Art, 87.) 



If the tides are observed for a semilunation, or any com.plete number 

 of semilunations, the mean lunitidal interval, or mean establishment (sec 



7), Will be found by taking the mean of all the lunitidal intervals 

 observed. 



The lunitidal interval corresponding to any given distance of the moon 

 from the sun may be found by the follo>ting table. But the tide cor- 

 responding to the given distance may not really occur till one, two, 

 three days later, according to the age of the tide. 



Art. 3 



or 



(3.) Correction of 7?ieau establishment. 



^_ 



Hour of Moon's Tran--v 

 sit (1, a^ 3 days pre- > 

 ceding) , , . , ; 



Corresponding Cor- 

 rection of Mean La- 



nitidaUnterval , , 







p 

 i 



h. 



i ; 2 1 3 



1 i 



i 



* 



1 



h. 



ni. 







m, m. 



-K) -3i 



m. I m. . 

 -41 -44 



I 





h. I h. 



10 ; 11 



m. I in. m. 



+ 31 +44 +4 



-•1 



+ 31 



1 



i 



m. 



+ lfi 



i 



? 



This table may be used ^f hen we know the age of the tide. Thus, let 

 the age of the tide be a day and a quarter, and the mean luTiitidal inter* 

 val 2 h. 11 m.; let the moon's transit take jplace at 4 h. ; then at the birth 

 of the tide, a day and a quarter earlier, the transit took place at 3h. 

 therefore the correction of the lunitidal interval is, by the table. - 41 m., 

 and the interval so corrected is 1 h. 30 m., which, added to 4h., the time 

 ofmoon'stransi* jives 5 h. 30 m. as the time of high water. 



To find the Estahlishment at any place when the Hour of Hiyh Water on a 



given day is observed. 

 On the given day, the time of moon's transit is known- and hence the 

 lunitidal interval ; and, by the above tables, the correction by which this 

 differs from the establishment is known. 



• Hence it is desirnlle to make tide observations in the first and ^ourtli quarters of 

 the moon, rather than in the second and third quarters. 





^!^^- 



