258 HISTORY OF PHYSICAL ASTRONOMY. 



general result was, that the facts agreed with the 

 condition of equilibrium at a certain anterior time, 

 but that this anterior time was different for dif- 

 ferent phenomena. In like manner it appeared to 

 follow from these researches, that in order to ex- 

 plain the facts, the mass of the moon must be 

 supposed different in the calculation at different 

 places. A result in effect the same was obtained 

 by M. Daussy 42 , an active French hydrographer ; 

 for he found that observations at various stations 

 could not be reconciled with the formulae of La- 

 place's Mecanique Celeste (in which the ratio of 

 the heights of spring-tides and neap-tides was com- 

 puted on an assumed mass of the moon) without 

 an alteration of level which was, in fact, equivalent 

 to an alteration of the moon's mass. Thus all things 

 appeared to tend to show that the Equilibrium- 

 theory would give the formulce for the inequalities 

 of the tides, but that the magnitudes which enter 

 into these formulae must be sought from observation. 



Whether this result is consistent with theory, 

 is a question not so much of physical astronomy 

 as of Hydrodynamics, and has not yet been solved. 

 A Theory of the Tides which should include in its 

 conditions the phenomena of derivative tides, and 

 of their combinations, will probably require all the 

 resources of the mathematical mechanician. 



As a contribution of empirical materials to the 

 treatment of this hydrodynamical problem, it may 

 42 Connaissance des Terns, 1838. 



