ey eee 
STABLE EQUILIBRIUM OF THE OCEAN. 347 
should exist which would be capable of neutralizing the 
action of the sun. In a memoir published in February, 
1789, Laplace found that this cause must reside in the 
ellipticity of Saturn produced by a rapid movement of 
rotation of the planet, a movement the existence of 
which Herschel announced in November, 1789. 
The reader cannot fail to remark how, on certain 
occasions, the eyes of the mind can supply the want of 
the most powerful telescopes, and lead to astronomical 
discoveries of the highest importance. 
Let us descend from the heavens upon the earth. 
The discoveries of Laplace will appear not less impor- 
tant, not less worthy of his genius. 
The phenomena of the tides, which an ancient philos- 
opher designated in despair as the tomb of human curi- 
osity,, were connected by Laplace with an analytical 
theory in which the physical conditions of the question 
figure for the first time. Accordingly calculators, to the 
immense advantage of the navigation of our maritime 
coasts, venture in the present day to predict several 
years in advance the details of the time and height of 
the full tides without more anxiety respecting the result 
than if the question related to the phases of an eclipse. 
There exists between the different phenomena of the 
ebb and flow of the tides and the attractive forces which 
the sun and moon exercise upon the fluid sheet which 
covers three fourths of the globe, an intimate and neces- 
sary connection from which Laplace, by the aid of a 
series of twenty years of observations executed at Brest, 
deduced the value of the mass of our satellite. Science 
knows in the present day that seventy-five moons would 
be necessary to form a weight equivalent to that of the 
terrestrial globe, and it is indebted for this result to an 
