2:?T Life of Lagmnge 305 



Lagrange accepted this magnificently expressed invitation 

 and spent the next 21 years at Berlin. 



During this period he produced an extraordinary series 

 of papers on astronomy, on general dynamics, and on a 

 variety of subjects in pure mathematics. Several of the 

 most important of the astronomical papers were sent to 

 Paris and obtained prizes offered by the Academy ; most 

 of the other papers about 60 in all were published by 

 the Berlin Academy. During this period he wrote also 

 his great Mecanique Analytique, one of the most beautiful 

 of all mathematical books, in which he developed fully 

 the general dynamical ideas contained in the earlier paper 

 on libration. Curiously enough he had great difficulty in 

 finding a publisher for his masterpiece, and it only appeared 

 in 1788 in Paris. A year earlier he had left Berlin in 

 consequence of the death of Frederick, and accepted an 

 invitation from Louis XVI. to join the Paris Academy. 

 About this time he suffered from one of the fits of melan- 

 choly with which he was periodically seized and which are 

 generally supposed to have been due to overwork during 

 his career at Turin. It is said that he never looked at 

 the Mecanique Analytique for two years after its publication, 

 and spent most of the time over chemistry and other 

 branches of natural science as well as in non-scientific 

 pursuits. In 1790 he was made president of the Com- 

 mission appointed to draw up a new system of weights 

 and measures, which resulted in the establishment of the 

 metric system ; and the scientific work connected with this 

 undertaking gradually restored his interest in mathematics 

 and astronomy. He always avoided politics, and passed 

 through the Revolution uninjured, unlike his friend 

 Lavoisier the great chemist and Bailly the historian of 

 astronomy, both of whom were guillotined during the Terror. 

 He was in fact held in great honour by the various govern- 

 ments which ruled France up to the time of his death ; 

 in 1793 he was specially exempted from a decree of banish- 

 ment directed against all foreigners ; subsequently he was 

 made professor of mathematics, first at the Ecole Normale 

 ( I 795) J and then at the 6cole Polytechnique (1797), the 

 last appointment being retained till his death in 1813. 

 During this period of his life he published, in addition 



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