442 HISTORY OF FORMAL ASTRONOMY. 



had courage to go through it. Delambre 4 acknow- 

 ledges that his patience often failed him during the 

 task; and subscribes to the judgment of Bailly; 

 "After this sublime effort, Kepler replunges himself 

 in the relations of music to the motions, the dis- 

 tance, and the eccentricities of the planets. In all 

 these harmonic ratios there is not one true rela- 

 tion ; in a crowd of ideas there is not one truth : he 

 becomes a man after being a spirit of light." Cer- 

 tainly these speculations are of no value, but we 

 may look on them with toleration, when we recol- 

 lect that Newton has sought for analogies between 

 the spaces occupied by the prismatic colours and 

 the notes of the gamut 5 . The numerical relations 

 of concords are so peculiar that we can easily sup- 

 pose them to have other bearings than those which 

 first offer themselves. 



It does not belong to my present purpose to 

 speak at length of the speculations concerning the 

 forces producing the celestial motions by which 

 Kepler was led to this celebrated law, or of those 

 which he deduced from it, and which are found in 

 the Epitome Astronomies Copernicance, published 

 1622. In that work also (p. 554), he extended this 

 law, though in a loose manner, to the satellites of 

 Jupiter. These physical speculations were only a 

 vague and distant prelude to Newton's discoveries ; 

 and the law, as a formal rule, was complete in 

 itself. We must now attend to the history of 

 4 A. M. a. 35a 6 Opticks, B. 2. p. iv. Obs 5. 



