THE ASTRONOMICAL VIEW OF NATURE. 319 



after many able mathematicians and observers had gen- 

 erally investigated the numberless problems contained in 

 the ' Principia,' Laplace published his ' Exposition du 

 Systeme du Monde,' followed in the course of the first 

 quarter of this century by the ' Mecanique celeste ' ; l and 

 at the close of the present century the most learned 

 astronomer of the age could say that the ' Principia ' 

 still formed the sole foundation of all investigations in 

 that domain. 2 



It is interesting to see how in a simple formula the 12. 



... Thegravita- 



mathematician is able to condense an almost immeasur- won for- 

 mula. 



able volume of thought, bringing the theory and the 

 observations of past ages to a focus from which new lines 

 of thought diverge in many directions. Every mathe- 



1 The ' Exposition du Systeme 

 du Monde' appeared, 1796, in 2 

 vols. 8vo : the first and second 

 volume of the ' Mecanique celeste,' 



gravitation," which was given by 

 Newton in such a way that the 

 action of one or more third (dis- 

 turbing) bodies could be taken into 



1799, 4to ; the third, 1802 ; the j account, dealing thus with the case 

 fourth, 1805 ; the last, 1825. Be- j of nature, which had in the first 

 fore publishing this work, which instance presented itself in treating 

 has been termed a second edition ! of the complex motion of the moon, 

 of the ' Principia,' Laplace had ; Laplace himself, who in number- 

 himself during thirty years assisted ' less passages of his works re- 

 in dispelling the last doubts as to curs to the discoveries of Newton, 

 the sufficiency of the doctrine of announced the object of the ' Me- 

 universal gravitation to explain all canique celeste ' to be the treat- 

 cosmical phenomena; and he had ment of astronomy "as a great 

 especially brought the investiga- , problem of mechanics, from which 

 tions of Clairaut, Euler, d'Alem- it was important to banish as much 

 bert, Lambert, and Lagrange to a as possible all empiricism," and to 

 final result by publishing in sue- j perfect it so as "to borrow from 

 cessive memoirs between 1773 and f observation only the most indis- 

 1786 the doctrine of "the stability pensable data" (' Mec. c6\.,' vol. L 



of the system of the universe," 

 based upon the invariability of the 

 major axes and the periods of re- 

 volution of the planetary orbits. 

 He and his predecessors also ex- 

 tended the solution of the problem 

 "to find the orbit of two bodies, 

 acting under the law of mutual 



introd. ) 



2 The late Professor Rudolf Wolf 

 of Zurich, whose ' Handbuch der 

 Astronomic, ihrer Geschichte und 

 Litteratur,' 2 vols., 1890-93, as well 

 as his earlier ' Geschichte der As- 

 tronomic,' Miinchen, 1877, 1 warmly 

 recommend. 



