Marquis De Laplace. 197 



most difficult of all those which had been considered before 

 his time. His perseverance triumphed over every obstacle. 

 When his first efforts were not successful, he renewed them 

 under the most ingenious and diversified forms. 

 , In the motions of the moon, for example, there had been 

 observed an acceleration, the cause of which philosophers were 

 unable to discover. It had been ascribed to the resistance of an 

 ethereal medium in which the celestial bodies moved. If this 

 had been the case, the same cause affecting the orbits of the 

 planets would have tended continually to disturb their primi- 

 tive harmony. These stars would have been constantly dis- 

 turbed in their course, and would have finally been preci- 

 pitated upon the mass of the sun. It would have required 

 the creating power to have been exerted anew in preventing 

 or repairing the immense disorder which the lapse of time 

 would have caused. 



This cosmological question is undoubtedly the greatest which 

 human intelligence can propose: It is now resolved. The 

 first researches of Laplace on the immutability of the dimen- 

 sions of the solar system, and his explanation of the secular 

 equation of the moon, have led to this solution. 



He at first inquired if the acceleration of the moon's mo- 

 tion could be explained by supposing that the action of gravity 

 was not instantaneous, but subject to a successive transmission 

 like that of light. By this means he succeeded in discovering 

 its true cause. A new investigation then gave a better direc- 

 tion to his genius. On the 19th March 1787, he communi- 

 cated to the Academy of Sciences a precise and unexpected 

 solution of this great difficulty. He proved in the clearest 

 manner that the observed acceleration is a necessary effect of 

 universal gravitation. 



This great discovery threw a new light on the most im- 

 portant points of the system of the world. The same theory, 

 indeed, proved to him, that, if the action of gravitation on the 

 stars was not instantaneous, we must suppose that it propa- 

 gates itself more than fifty millions of times faster than light, 

 whose velocity is well known to be 70,000 leagues in a second. 



Hence he concluded from his theory of the lunar motions, 

 that the medium in which the stars revolve does not oppose 



