GEANTHAM ADDRESS. 289 



The great discoveries which have been made by Lagrange 

 and Laplace upon the results of disturbing forces, have estab- 

 lished the law of periodical variation of orbits, which secures 

 the stability of the system by prescribing a maximum and a 

 minimum amount of deviation ; and this is not a contingent but 

 a necessary truth, deduced by rigorous demonstration as the 

 inevitable result of undoubted data in point of fact the eccen- 

 tricities of the orbits, the directions of the motions, and the 

 movement in one plane of a certain position. That wonderful 

 proposition of Newton,* which with its corollaries may be 

 said to give the whole doctrine of disturbing forces, has been 

 little more than applied and extended by the labours of 

 succeeding geometricians. Indeed, Laplace, struck with 

 wonder at one of Newton's comprehensive general statements 

 on disturbing forces in another proposition, f has not hesitated 

 to assert, that it contains the germ of Lagrange's celebrated 

 inquiry, exactly a century after the ' Principia ' was given to 

 the world. J 



The wonderful powers of generalization, combined with the 

 boldness of never shrinking from a conclusion that seemed the 

 legitimate result of his investigations, how new and even 

 startling soever it might appear, was strikingly shown in that 

 memorable inference which he drew from optical pheno- 

 mena, that the diamond is 'an unctuous substance coagu- 

 lated ;' subsequent discoveries having proved both that such 

 substances are carbonaceous, and that the diamond is 



that Koemer had given some conjectural explanation of the phenomena of 

 what he termed vacillation; but no date is assigned Koemer died in 1710. 

 In the same passage it is said that before Bradley's discovery, Newton had 

 " suspected the nutation." He had deduced it from the propositions above 

 referred to, and was considered so to have done by Clairaut. Bradley' K 

 paper was published in the 'Phil. Trans.' 1747; and it is not a little 

 singular that he makes no mention at all of Newton. 



* Lib. I. Prop. LXVI. 



t The XVHth's two last Corollaries. 



J ' Mem, de Berlin,' 1786, p. 253, is the memoir referred to by Laplace. 

 The memoir is by Duval le Koi, but adopted by Lagrange as a supplement 

 to his two memoirs, 1782 and 1784. 



U 



