1814.] Biographical Account of M. Lagrange. 7 



employed the expression " principle ascribed to d'Alembert," as if 

 it did not belong to him with more justice than that of virtual 

 velocities belong to Lagrange himself; as if the solution of the 

 problem of the centres of oscillation by James Bernoulli, in which 

 we find an analogous idea employed, had contained that principle 

 so clearly that we ought to ascribe the discovery of it to him ! Yet 

 that solution was for forty years in the hands of others, of Ber- 

 noulli, Taylor, Cotes, Maclaurin, Fontaine, Clairaut, and Euler 

 himself, who were continually proposing particular questions in 

 dynamics, without ever thinking of this famous principle ; and 

 when once d'Alembert published it, all these mutual attempts 

 ceased for ever. 



Let us return to Lagrange, from whom this long digression has 

 perhaps drawn us too far. 



In speaking of the good fortune of Newton, who had found a 

 system of the world to explain (a good fortune, he observed, with 

 a serious and almost melancholy tone, which we do not meet with 

 every day), he took a pleasure likewise in pointing out what he 

 called the good fortune of one of his associates, whose inventive 

 smd original genius had greatly struck him.* I shall venture like- 

 wise to state an observation of his on a similar subject, which gives 

 a faithful picture of his manner of expressing himself when he was 

 strongly penetrated with his subject : " See," said he, one day, 

 " that confounded ***** with his application of analysis to the 

 generation of surfaces ; he will be immortal, he will be im- 

 mortal !"f 



His candour was equal to his penetration ; and the continual 

 contrast of these two qualities gave to his company a high degree of 

 interest. As his ideas were always perfectly precise, he always 

 wished that the expression of them should be a faithful picture of 

 his conceptions. Hence when he had begun a phrase which he 

 despaired of finishing clearly, those original interruptions, usually 

 followed by his favourite word, I do not know, I do not know, with- 

 out attempting to finish the sentence, he left it abruptly. Often 

 also his unlooked for silence was occasioned by a new idea which 

 came across him, and which rapidly absorbed his faculties of 

 thinking. Who has not seen him interrupt, all of a sudden, the 

 lecture which he was giving at the Polytechnic School, appear 

 sometimes embarrassed like a beginner, quit the table, and sit down 

 opposite to the audience, while masters and scholars, confounded 

 on the benches, waited in a respectful silence till he brought back 

 his thoughts from the spaces through which he had allowed them to 

 watul'i ! 



Real abilities always obtained his suffrage ; I had almost said 

 his homage, such was his modesty. He always spoke of his pre- 

 decessors in the career of mathematics, and of those who had 



■ I presume the person here alluded to it Lavoisier. — T. 



' I conceive the perioa alluded to by Lngiange il Monge.— T. 



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