306 CELESTIAL MECHANICS. I. vii. 36. 



lating to the surface of the sea. It will appear, in the 

 theory of the tides, that this value is very nearly the same 

 for all the particles situated in the same radius of the earth, 

 from the bottom of the sea to the surface : we have there- 



fore, for all these particles, -i-zr^Jy, consequently y must 



be equal to f^y, with the addition of some function inde- 

 pendent of 6, Tsr, and r, as a correction of the fluent: now 

 at the surface of equilibrium of the sea, the quantity ap' 

 must be equal to the pressure of the little column of water 

 ay, which is elevated above this surface, and this pressure 

 is expressed by a^gy: hence it follows, that throughout 

 the interior of the fluid mass, from the surface of the sphe- 

 roid covered by the sea, to the surface of the sea itself, 

 p'—^gy, or that, in other words, any point of the surface of 

 the solid spheroid is more pressed than in the state of equi- 

 librium, by all the weight of the little column of water, con- 

 tained between the surface of the sea and the surface of 

 equilibrium ; and that this excess of pressure becomes ne- 

 gative at the parts in which the sea is depressed below this 

 surface of equilibrium. [There seems, however, to be want- 

 ing in this theory, the consideration of the time required for 

 the transmission of pressure, as well as of the possibility of 

 the divergence of pressure from adirection completely verti- 

 cal. It cannot be supposed that every ripple, which curls the 

 surface of the ocean, produces an instantaneous diversity 

 of pressure at the depth of several miles ; nor is it very 

 probable that each inch of the bottom of the sea at such a 

 depth, is, after any interval of time, afi'ected separately by 

 the transitory inequalities of the surface exactly above it. 

 With respect to the gradual transmission of pressure, it 

 can scarcely be slower in a fluid than it would be in the 

 same substance if congealed into a solid mass: for the 



