314 LAPLACE. 



sphere was then wanted to account for a movement in 

 which all the stars participated at the same time. 



Copernicus having deprived the earth of its alleged 

 immobility, gave a very simple explanation of the most 

 minute circumstances of precession. He supposed that 

 the axis of rotation does not remain exactly parallel to 

 itself; that in the course of each complete revolution of 

 the earth around the sun, the axis deviates from its posi- 

 tion by a small quantity ; in a word, instead of supposing 

 the circum polar stars to advance in a certain way towards 

 the pole, he makes the pole advance towards the stars. 

 This hypothesis divested the mechanism of the universe 

 of the greatest complication which the love of theorizing 

 had introduced into it. A new Alphonse would have 

 then wanted a pretext to address to his astronomical 

 synod the profound remark, so erroneously interpreted, 

 which history ascribes to the king of Castile. 



If the conception of Copernicus improved by Kepler 

 had, as we have just seen, introduced a striking im- 

 provement into the mechanism of the heavens, it still 

 remained to discover the motive force which, by altering 

 the position of the terrestrial axis during each successive, 

 year, would cause it to describe an entire circle of nearly 

 50 in diameter, in a period of about 26,000 years. 



Newton conjectured that this force arose from the 

 action of the sun and moon upon the redundant matter 

 accumulated in the equatorial regions of the earth : thus 

 he made the precession of the equinoxes depend upon 

 the spheroidal figure of the earth ; he declared that 

 upon a round planet no precession would exist. 



All this was quite true, but Newton did not succeed in 

 establishing it by a mathematical process. Now this 

 great man had introduced into philosophy the severe and 



