412 D'ALEMBERT. 



pily applied to the equilibrium and pressure of fluids, in 

 his first work upon that difficult subject. 



The subject of fluids was, perhaps, the one which 

 most occupied D'Alembert's attention, and for the 

 greatest number of years. His 'Opuscula' contain several 

 interesting tracts upon its various departments, espe- 

 cially the first and fifth volumes, which were published in 

 1761 and 1768 respectively. But above half the eighth 

 volume relates to the same subject, and it appeared as 

 late as 1780, so that this inquiry had retained its hold 

 on his mind for a period of nearly forty years. * 



We may further observe, that the extreme interest 

 which he took in it seems to have made him some- 

 what susceptible, when he conceived others had not 

 done justice to his labours in this favourite department 

 of science. Not only is he anxious, perhaps beyond 

 what is altogether beseeming the calm and disinterested 



* The readers of D'Alembert's papers on these subjects will have 

 real obligations to Bossut, if they read with D'Alembert that 

 great didactic writer's admirable treatise, ' Hydrodynamique,' 

 second edition. He was an intimate friend and, indeed, may be 

 said to have been a pupil, of D'Alembert and of Condorcet. His 

 ' Calcul Integral et Diflerentiel,' is also a truly excellent and useful 

 work. Of the four great elementary treatises on this subject, 

 Lacroix's, Bougainville's, Cousin's, and Bossut's, the last appears 

 to me the best; but I am aware of the high opinion which 

 D'Alembert entertained of Bougainville's. He was accustomed to 

 refer to Bossut those who applied to him for explanations of his 

 writings, as Newton did to Demoivre. Why, may it be permitted 

 us respectfully to ask, why will so many mathematicians fancy it 

 beneath them to write clearly, simply, and, as didactic matter should 

 be written, intelligibly and always proceeding from what is 

 known and explained to what is not, without anticipation? Surely 

 Bossut was as great a geometrician as themselves, and he con- 

 descended to write as if he were teaching and not commenting, 

 alluding, or referring. 



