ON THE COASTS OF IRELAND. 



47 



must be 13'' 7% or the day mast be about October 12; if it happens at six in the 

 morning, the sun's right ascension must be 19^' 7'", and the day must be about January 

 6. In the same way the day may be found for other hours. The coefficient may be 

 taken from the table in page 28, doubling the mean of the quantities in the three 

 high water columns (without regard of sign) for the difference of two tides. Thus 

 the following Table is formed. 



Station. 



Kilbaha .... 

 Kilrush .... 

 Foynes Island 

 Limerick. ... 

 Casleh Bay . . 

 Galway .... 

 Old Head . . . 

 Mullaghmore , 

 Buncrana . . . 

 Port Rush . . . 

 Carrowkeel . . . 



Greatest 

 difference 

 of two high 

 waters on 

 same day. 



ft. 



0-71 



0-55 

 0-72 

 0-77 

 0-65 

 0-61 

 M4 

 1-65 

 1-37 

 1-11 

 1-31 



Day when | Day when 

 the excess of the excess of 

 noon tide !morning tide 

 over mid- over evening 



night tide is 

 greatest. 



tide is 

 greatest. 



Oct. 12. 

 Oct. 14. 

 Oct. 30. 

 Nov. 7. 

 Oct. 14. 

 Oct. 17. 

 Oct. 17. 

 Oct. 26. 

 Nov. 5. 

 Nov. 14. 

 Nov. 26. 



Jan. 6. 

 Jan. 8. 

 Jan. 22. 

 Jan. 30. 

 Jan. 8. 

 Jan. 10. 

 Jan. 10. 

 Jan, 18. 

 Jan. 28. 

 Feb. 3. 

 Feb. 18. 



Station. 



Ballycastle 



Glenarm 



Donaghadee . . . 



Ardglass 



Clogher Head. . . 



Kingstown 



Dunmore East . 



New Ross 



Passage West . , . 

 Castle Townsend 



Greatest 



difference 



of two high 



waters on 



same day. 



ft. 



M6 



1-48 



1-41 



1-32 



1-29 



1-16 



0-44 



0-53 



0-30 



0-08 



Day when | Day when 

 the excess of the excess of 

 noon tide morning tide 



over mid- 

 night tide is 

 greatest. 



over evening 



tide is 



greatest. 



Nov. 24. 

 Jan. 7- 

 Jan. 13. 

 Jan. 13. 

 Jan. 16. 

 Jan. 19. 

 Oct. 21. 

 Nov. 2. 

 Oct. 21. 

 Oct. 13. 



Feb. 16. 

 April 10. 

 April 17. 

 April 17. 

 April 20. 

 April 23. 

 Jan. 5. 

 Jan. 24. 

 Jan. 14. 

 Jan. 7. 



Section X. — Method of expressing the height of the water, throughout evei^ individual 

 tide, by sines and cosines of arcs, and expr^essions in this form for evert/ tide in 

 the whole series of observations, except those at Courtown. 



The times of iiigh water (and similarly those of low water) having had their prin- 

 cipal irregularities smoothed down by the operations described in Section II., and 

 being corrected for the diurnal equation in time ascertained by the operations of 

 Section III., present a series of times, which are liable perhaps to something like 

 constant error from the method involuntarily adopted by the computer in fixing on 

 the time of high water, and which are affected by the peculiar form of the tidal func- 

 tion at each station, but which nevertheless follow at intervals equal (with very con- 

 siderable accuracy) to the true tidal day of the place. This being understood, it will 

 be seen that the following process entirely corrects any error of the supposed times 

 of high or low water in its exhibition of the time of maximum of the first tidal argu- 

 ment, and is entirely free from the effects of such error in the exhibition of other 

 quantities. 



The whole number of observations, equidistant in time, made in the course of one 

 tide, being about 150, if we divide this duration into sixteen equal parts we shall 

 have at least nine observations in each part ; and the mean time of these nine ob- 

 servations cannot in any case be more than 2^ minutes from the middle of that part. 

 It appears evident here that we may use the mean of all the heights in one portion 

 to represent (with smaller error than unavoidably occurs in the observations) the 



