ADDRESS SECTION A, B.A. 1876. 261 



attraction. Happily, however, for our object, there 

 is no meteorological or other disturbing cause 

 which produces periodic changes of sea-level in 

 either the fortnightly declinational or the monthly 

 elliptic period ; and the lunar gravitational tides in 

 these periods are therefore to be carefully inves- 

 tigated in order that we may obtain the answer to 

 the interesting question, How much does the earth 

 as an elastic spheroid yield to the tide-generating 

 influence of sun or moon ? Hitherto in the 

 British Association Committee's reductions of 

 Tidal Observations we have not succeeded in 

 obtaining any trustworthy indications of either of 

 these tides. The St. George's Pier landing-stage 

 pontoon, unhappily chosen for the Liverpool tide- 

 gauge, cannot be trusted for such a delicate inves- 

 tigation : the available funds for calculation were 

 expended before the long-period tides for Hilbre 

 Island could be attacked, and three years of 

 Kurrachee gave our only approach to a result. 

 Comparisons of this with an indication of a result 

 of calculations on West Hartlepool tides, con- 

 ducted with the assistance of a grant from the 



