336 OUTLINES OF NATURAL PHILOSOPHY. 



For since -j and - are as the forces of the Sun and 



Moon on the waters of the Sea, : ^- : : 1 : 3 ; 



* ' 1 



and therefore m r = m r is thus found 



a 1 



- 5 the mass of the Earth being 1. 

 68.5 h 



\. The two tides immediately following one 

 another, or the tides of the day and of the night, 

 should be very unequal when the Sun and Moon 

 are distant from the equator, if the theory of 

 the spheroid, 336, were just. They are, how- 

 ever, nearly equal j and this has been shewn, by 

 LA PLACE, to be what must necessarily happen 

 in the oscillations of a sea of uniform depth. 



The depth of the Sea is therefore nearly the same 

 throughout, or, though not exactly the same, there 

 is a certain mean depth, from which the deviations 

 are not considerable, if we take in a large extent 

 of ocean. If this were not the case, the consecu- 

 tive tides would not approach so near to equality 

 as they actually do. 



343. Great 

 i 



