112 



Proceedings of the Royal Irish Academy. 



Case II. 



Moon's Transit B, 

 Corr. for Lunar, . . 

 Moon's Hor. Parallax, 

 Lunar Declination, 

 Anti-solar Declination, 



1876, Sept. 10, Morning Tide, 

 Lunar and Anti-solar. 



1877, Aug. 21, Morning Tide, 

 Lunar and Anti-solar. 



d. h. m. ft. in. 



d. 



h. m. ft. in. 



8 3 30 23 2 



29 



3 50 22 8 



+ 5 





+ 5. 



57' 53" 4- 4-7 



55 



50 -3 



20" 0' JST. asc. - 4 



19° 



23' N. asc. - 2 



5° S. +5 



9" 

 23 



S. +4 



24 3 obs. 24 3 



7 obs. 22 11 



Bar. 29-7. No wind. 



Bar 



29'6, WindN.W., 

 strong. 



It is to be observed that, in Case II., although the tide of Sep- 

 tember 10 has almost all its constituents more favourable to its 

 development than those of August 31, still, in consequence of the 

 atmospheric conditions, a higher tide results in the former case than 

 in the latter. 



In the computation of tides, the first thing which is of importance 

 is, that we assign to each tide its proper classification. The transit 

 which is to be employed, as a sort of standard transit from which 

 tides are to be calculated, is the transit nest but two preceding that 

 transit which is nearest to the time of high water of the tide con- 

 sidered. This transit is, in fact, the transit B of Sir John Lubbock's 

 Tables. The rule for determining the classification for the tides of 

 the Irish Sea is as follows : — "Lower transits B are followed by 

 lunar tides, and upper transits B by Anti-lunar tides. All transits B 

 which take place between 23^ hours, and 11^ hours (apparent Green- 

 wich time), give morning tides; and all between 11^ hours, and 

 23^ hours (apparent Greenwich time), give evening tides. All transits 

 B, after 6 hours, and before 18 hours, are connected with solar tides; 

 and all transits B, after 18 hours, and before 6 hours, with anti-solar 

 tides." 



A tabulated comparison of the results of theory and observation is 

 appended, with remarks on the atmospheric conditions in explanation 

 of such discrepancies as are found to occur in them. 



