■_* 



•*;.!! 



I 



i. 



L^i - 



.r> 



i 



Sect. IV.J 



TIDES. 



115 



or more, the curve (Art. 14) will descend and ascend 

 alternately every fortnight, as in fig. o. 



This curve is the curve of the semi -jmnsual inequality ; 

 and when this curve has been determined by obcsrvations 

 at any place, the hour of high water at any thae at that 



place may be predicted. 



17. But the curve will be better determined if, instead 

 of taking for the abscissa the day of the month, as in 

 fig. 2, we take for the abscissa the time of the moon's 

 transit as in fig. 3.* 



Tiines H. W. 



Fig. 3 



Sh.. 



^J 



[ 



^ 



/ 



/ 



1 



* 



Jh- 



6b 



4^ 



9»' 



1^^ 



7h bb 9h i^.h \\h !*■ ^** ^'^ "^^ 



Jan. 7, 89, 10, 11. 12, 13, M, 15, 15, 17, IS 



L ^ 



i»l 



•; 



!i 



r 



\, 



lu this case the establishment is the orclirxate of this 

 curve which corresponds to the time of moon s transit 

 Oh. or 12h, In the figure it is 2h. 16m. 



The mode of calculating the hour of high water on 



* Since the moon's transit is about 48 minutes later every day, there 

 will be along the abscissa five days of the month for ev^./ tour hours of 

 moon's transit. 



