352 Proceedings of the Royal Irish Academy. 



■were handed down from father to son, for several generations, as a 

 family possession; and the publication of new tables, accompanied 

 by a statement of the mode of calculation, was resented as an infringe- 

 ment of the rights of property." I am not aware that the mystery 

 has even yet been divulged, though I am sure much progress has 

 been made towards its solution by an independent inquiry. 



The fii'st object of such an inquiiy is to ascertain the laws which 

 regulate what is technically called the " diui'nal ineq^uality." This it 

 is which causes the spring-tides sometimes to increase successively by 

 iiTegular steps, each being alternately greater and less than the one 

 preceding, and sometimes to succeed each other by continuous incre- 

 ments of height. This, though due to the changes of the moon's and 

 sun's declination, as its ultimate cause, is much dependent on the con- 

 figuration of land and water in the regions through which the tidal 

 ■wave has to traverse; and Dr. "Whe well's statement may still be safely 

 endorsed — '"'Although Laplace's conjecture, that in the moving fluid 

 the motions must have a periodicity corresponding to that of the forces, 

 may in some cases of the problem be verified, this cannot be done in 

 the actual case where the revolving motion of the ocean is prevented 

 by the intrusion of tracts of land, running nearly from pole to pole." 

 He adds: "I am not aware that for such a case anything has been 

 done to bring the hydrodynamical theoiy of oceanic tides into agree- 

 ment with observation." 



jS'ow it is precisely for the object of bringing theory into agree- 

 ment with observation that the method has been devised to which I 

 wish to call attention — a method which has been embodied for several 

 years past in the Admiralty Tables. It is based on a modification of 

 Sir John Lubbock's Tables, and rests on the equilibnum theory of 

 Bemouilli, and it embodies the law which regulates the diurnal 

 inequality. I propose to submit the method to the same test to which 

 all the other consequences of gi^avitation have been submitted, viz. — 

 the calculation of tables, and the continued and orderly comparison of 

 these with observation. In order to do this satisfactorily, we shall 

 select a period of time when settled weather indicates that atmo- 

 spheric disturbing causes have had a minimum effect, the error from 

 accuracy being in each case pointed out, and a note being made of the 

 atmospheric conditions. 



Our fii'st record will show ten successive tides in February, 

 1878:— 



