428 D'ALEMBEBT. 



investigated the figure of the earth upon the hypothesis 

 of a variable density in the different zones, but the 

 same throughout each, D'Alembert was not satisfied 

 with giving his own solution more generally and more 

 rigorously, but assailed Clairaut's hypothesis. However, 

 this controversy was carried on with much less heat 

 than the former. Geometricians appear to be agreed 

 that in the one case, that of the lunar tables, Clairaut 

 had the decided advantage over his adversary, whose 

 mind did not easily lend itself to such details ; but that 

 the balance inclined in his favour upon the question of 

 the earth's figure, D' Alembert's solution being certainly 

 more general and less dependent upon assumption. His 

 treatise on this subject is universally admired by geo- 

 metricians, and it contains both the differential equa- 

 tions, then first given, of the equilibrium of fluids, and 

 the new and most important theorem upon the relation 

 between the polar oblateness and increase of gravita- 



cuting the Pere all his life. But little reliance can be placed on this 

 assertion, at least if we may judge by the manifest falsehood of his state- 

 ment, that "D'Alembert attacked Boscovich in his ' Opuscule,' vol. i. 

 p. 246 ; " for all the attack consists in defending himself against an objec- 

 tion made by " an Italian geometrician of note in the science." The utter 

 incompetency of a person like Lalande to edit such a work as Montucla's, 

 can hardly be conceived without reading what he has done. Such ignor- 

 ance or want of judgment is inconceivable, as could make him call Priest- 

 ley's ' History of Optics' (so he terms it) a work of great importance, and 

 one of its author's best, while by speaking of it as a book in 813 4to pages, 

 he shows that he never had seen it ; such ignorance as could also make 

 him speak of Priestley's "universal erudition," vol. iii. p. 604, 5.) 

 The entire want of common care as to dates is shown in his quoting 

 Black's experiments as published in 1777 instead of 1755, if indeed this 

 be a mere error, for the error is made to support the absurd argument that 

 Priestley by his experiments, 1772, preceded Black as founder of the new 

 chemical system. But nothing can be worse than Lalande's edition. The 

 analytical expressions so abound with errors, possibly of the press, but 

 which Lalande was incapable of correcting, that nothing can be more 

 unsatisfactory than reading the book ; nothing more tiresome than using 

 the formulas, and finding, after perhaps a laborious investigation, as has 

 happened to myself, that there was a gross error in them. Lalande's great 

 merits, in his own department, both as a writer and a professor, beside his 

 labours as a practical astronomer, stand wholly apart from his labours as 

 an editor of a work in its main branches above him. 



