10 On Delambre's Biographical Account of Lagrange* [July, 



" Finally, I always took care every day to assign myself a task 

 for the next. The mind is indolent. We must get the better of 

 this natural inactivity, and keep our industry in full vigour, in order 

 to be able to exert all our powers when occasion requires them. 

 Nothing but exercise can accomplish this. It is likewise an excellent 

 practice to accustom oneself as much as possible to do the same 

 things at the same hours, reserving the most difficult for the 

 morning. I learned that custom from the King of Prussia, and I 

 have found that this regularity gradually renders labour more easy 

 and more agreeable." * 



As to his fourth principle, I may state that when he was scarcely 

 acquainted with the first rudiments of the differential and integral 

 calculus, he undertook the perusal of Euler's Mechanic?, in which 

 he not only learned dynamics, but likewise the integral calculus, 

 properly so called ; and he assured me that this labour had greatly 

 improved his mathematical skill. The fine problems with which 

 that book is filled greatly facilitated the perusal of Newton's Prin- 

 ctpia, the study of which he combined with that excellent work. 

 * 4 Read it therefore with care," he would say, " as well as the 

 beautiful theory of the motion of solid bodies, which follows it." 

 Then yielding to his admiration of Euler, he placed him at the head 

 of all who have written upon mathematics for clearness, method, 

 and for the beautiful examples which recur without end. He 

 finished by repeating, " If you wish to be a mathematician, you 

 must study Euler." Every other person would liave said, Euler 

 and Lagrange. f 



» I can assure the reader that all these statements were communicated to me by 

 M. Lagrange one evening, the first part of which he had employed in assuring me 

 sgain that he did not like to talk about the method of studying the mathematics. 

 He had sometimes the custom of making such professions, and then gradually 

 watering upon the subject that he disclaimed, provided hi~. hearers took great care 

 not to appear themselves to be sensible of his procedure, but allowed him to be 

 tarried away by the momentary impulse which directed him. During an intimacy 

 •f fifteen years, during which I was very frequently in his company, such a con- 

 versation took place only once. 1 listened to him with more than usual avidity, 

 and I took care, when I returned home, to write down a faithful abstract of the 

 whole conversation. 



+ Mathematicians, and, above all, those who are endeavouring to become 

 cnalheu:aticians, must be anxious for the publication of a collection of the most 

 important dissertations of Lagrange. His principal treatises on analysis, mecha- 

 nics, and the system of the world, are scattered through various academical col- 

 lections, which it is difficult, and sometimes impossible, to procure, llesides, it 

 is very inconvenient to have to turn over thirty or forty volumes for what migbt 

 easily be united in three or four. The author of this notice can assure his readers 

 that in such a space might be united about thirty-five of the most rare and most im- 

 portant papers of Lagrange. He would with pleasure set about the publication, 

 if he thwight that it wou'd be encouraged by the lovers, so numerous at present, 

 of the mo«t perfect of all Ike sciences. If their wishes should reach him, he w ill 

 put info the bands of a bookseller a list of the memoirs, accompanied with the 

 reasons for selecting thern, and with the classification to which it is couceived they 

 *oght to be subjected. 



