THE TIDES. (APP. Z>.) 219 



ago maintained x to be a consequence of friction 

 would prove that the crowns of the luni-tidal 

 spheroid are in advance of those of the soli-tidal 

 spheroid ; and therefore that those of the latter 

 are less advanced by friction than those of the 

 former. It is easily conceived that a know- 

 ledge of the heights of the tides and of the 

 intervals between the spring tides and the 

 times of greatest force, somewhat more extensive 

 than we have at present, would afford data for a 

 rough estimate of the proper mean amount of the 

 average interval in question, that is, of the interval 

 between the times of high water of the mean luni- 

 tidal and mean soli-tidal spheroids. The whole 

 moment of the couple retarding the earth's rota- 

 tion, in virtue of the lunar tide, must be something 

 more than that calculated on the hypothesis that 

 the obliquity of the mean luni-tidal spheroid is 

 only equal to the hour-angle corresponding to that 

 interval of time. 



8. We know, however, but little at present re- 

 garding the actual time of the spring tides in dif- 

 ferent parts of the ocean, and it is not even quite 

 certain, although, as Airy remarks, it is extremely 

 probable, that in the southern seas they take place 

 at an interval after the full and change, although it 

 may be at a less interval than on the Atlantic coast 

 of Kurope. There must be observations on record 

 (such as those of Sir Thomas Maclear at the Cape 



1 See Airy's Tides and Waves, 544. 



