Marquis De Laplace. 37S 



and physical sciences had ah-eady invented, and which formed 

 the foundation of astronomy, but he has added to this science 

 capital discoveries of his own which had escaped all his pre- 

 decessors. He has resolved, either by his own methods or 

 by those of which Euler and Lagrange had pointed out the 

 principles, questions the most important, and certainly the 

 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 foi'ms. 



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 

 primitive harmony. These stars would have been constantly 

 disturbed in their course, and would have final!}' been pre- 

 cipitated 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 v/hich 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 

 dimensions 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 gra- 

 vity was not instantaneous, but subject to a successive trans- 

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

 discovering its true cause. A new investigation then gave a 

 better direction to his genius. On the 19th March 1787, he 

 communicated 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 tile system of the world. The same theory, 

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

 the stars was not instantaneous, we nmst suppose that it pro- 

 pagates itself more than fifty millions of times liister than 

 light, whose velocity is well known to be 70,000 leagues in ii 

 second. 



Ilcncc he concluded from his theory of the lunar motions, 

 that the medium in wliicli the stars revolve does not oppose 



any 



