112 



TIDES. 



[Sect. IV. 



in any obvious way upon the moon, the periods of maxi- 

 mum and minimum should be carefully and exactly ob- 

 served, in order to determine upon what the rise and fall 

 does depend. This is the case in some parts of the 



Pacific, the rise and fall at those places beino- small. 



9. If the tides are tolerahly regular, it will not be ne- 

 cessary to observe, except for every five minutes near the 

 time of high water and low water ; say for an hour so 

 as to include the exact time near the middle of the hour. 

 From these observations, by laying down the heio-hts as 



ordinates, and drawing curves, as directed in Art. 6 

 the height and time of high water and of low water will 

 be deduced. 



10. It is desirable to compare tlie observations of the 

 time of high water and low^ water with the time of the 

 moon's transit (see Art. 1) wMle the observations ar(i 

 goivg on : for if the tide follow this transit at very irre- 



comrnon modes of observation will 



gular intervals, the 



probably be of no use, and the time and trouble employed 



in making them wdll be lost. 



11. The time of high w^ater at any place on the day of 

 new or full moon is commonly called the establishment of 



cause 



this being established, the time of 

 high water on any other day may, in most cases, be 

 known. 



12. But if the tides are very irregular, this is not the 

 case ; and then the establishment of the place is of no 

 use : or, rather, there is no proper establishment. And if 

 the tides be regular the establishment may be got from 



ations made on other days, just as w ell as from those 

 made on the day of new or full moon. See Note A. 



1^ - 



^I^ 



13. 



of tli^ 

 riioon I 



howTi 



flioon 



cane<^ 

 Su] 



high 



V 



the h 



traiisi 

 are g 

 on til 



1 



1S4/ 

 Jan 



11 A. 

 p 



P. 



13 A. 



p. 



14 A. 



p. 



A. 

 P. 



15 



14 



* 



Iti 



differea, 

 at Grt. 



