SPECULATIONS ON THE FORCE OF GRAVITY. 351 
are of the celestial sphere described by the moon during 
the interval of time which the astronomers of the exist- 
ing epoch called a day,—in other words, the time re- 
quired by the earth to effect a complete rotation on its 
axis, the velocity of the moon being in fact independent 
of the time of the earth’s rotation. 
Let us now, after the example of Laplace, take from 
the standard tables the least considerable values, if you 
choose, of the expansions or contractions which solid 
bodies experience from changes of temperature; search 
then the annals of Grecian, Arabian, and modern astron- 
omy for the purpose of finding in them the angular 
velocity of the moon, and the great geometer will prove, 
by incontrovertible evidence founded upon these data, 
that during a period of two thousand years the mean 
temperature of the earth has not varied to the extent of 
the hundredth part of a degree of the centigrade ther- 
mometer. No eloquent declamation is capable of resist- 
ing such a process of reasoning, or withstanding the force 
of such numbers. The mathematics have been in all 
ages the implacable adversaries of scientific romances. 
The fall of bodies, if it was not a phenomenon of per- 
petual occurrence, would justly excite in the highest 
degree the astonishment of mankind. What, in effect, is 
more extraordinary than to see an inert mass, that is to 
say, a mass deprived of will, a mass which ought not to 
have any propensity to advance in one direction more 
than in anothers precipitate itself towards the earth as 
soon as it ceased to be supported ! 
Nature engenders the gravity of bodies by a process 
so recondite, so completely beyond the reach of our 
senses and the ordinary resources of human intelligence, 
that the philosophers of antiquity, who supposed that 
