156 LAPLACE. 



No person was more sagacious than Laplace in discovering intimate 

 relations between phenomena apparently' very dissimilar; uo person 

 sliovvcd liiinself more skillful in deducing important conclusions from 

 those unexpected aliinities. 



Toward the close of liis days, for example, he overthrew with a stroke 

 of the i)en, by the aid of (certain observations of the moon, the cosmo- 

 gonic theories of Butlbn and Bailly, wiiich were so long in favor. Ac- 

 cording to these theories, the earth was inevitably advancing to a state 

 of congelation which was close at hand. Laplace, who never contented 

 himself with a vague statement, sought to determine in numbers the 

 rapid cooling of our globe which Buffon had so eloqucntlj' but so gra- 

 tuitously announced. Nothing could be nsore simple, better connected, 

 or niort^ demonstrative than the chain of deductions of the celebrated 

 geometer. 



A body diminishes in volume when it cools. According to the most 

 elementary principles of mechanics, a rotating body which contracts in 

 dimensions ought inevitably to turn upon its axis with greater and 

 greater rapidity. The length of the day lias been determined in all 

 ages by the time of the earth's rotation ; if the earth is cooling, the 

 length of the day must be continually shortening. Now, there exists a 

 means of ascertaining whether the length of the day has undergone any 

 variation ; this consists in examining, for each century, the arc of the 

 celestial sphere described by the moon during tlie interval of time which 

 the astronomers of the existing epoch called a day ; in other words, the 

 time required 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 DOW, after the example of Laplace, take from the standard tables 

 the least considerable values, if you choose, of the expansions or con- 

 tractions wliich solid bodies experience from changes of temperature; 

 search then the annals of Grecian, Arabian, and modern astronomy 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 2,000 years the mean tempera- 

 ture of tlie earth has not varied to the extent of the hundredth i)art of 

 a degree of the centigrade thermometer. No eloquent declamation is 

 capable of resisting such a juocess of reasoning, or withstaiuling the 

 force of such numbers. The mathematics have been in all ages the im- 

 placable adversaries of scientitic romances. 



The <all of bodies, if it was not a phenomenon of perpetual 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 sa.v, a mass deprived of will, a mass which ought not to have any 

 propensity to advance in one direction more than in another, precipitate 

 itself toward the earth as soon as it ceased to be supported ? 



Nature engenders the gravity of bodies by a process so recondite, so 



