Cuar. II., § 2.] 
dynamics and optics; and we shall find very few 
important branches of general physics in which he 
has not left some permanent record of his interest, 
in the course of his career of fifty-five years of 
anxious devotion to science. ~ 
His largest and most systematic work, the T'raité 
de Mécanique Céleste, in five quarto volumes, was 
not only most ably executed, but exceedingly well 
timed, The applications of analysis to physical astro- 
nomy had been accumulating for nearly a century. 
Hundreds of memoirs relating to them, dispersed 
through many volumes in different languages, written 
with varying ability, in various stages of scientific pro- 
gress, and with differing notations, presented a mass 
of reading almost beyond the reach of the most reso- 
- lutestudent. Laplace undertook to digest the whole 
into one body of doctrine, composed throughout on 
a uniform plan, with the best mathematical aids which 
were known at the commencement of this century. 
And though improvements and discoveries have been 
since made, the methods and most of the results of 
the Mécanique Céleste remain, with little variation, 
the preferable ones of our own time. As a work of 
labour, it may compete with the Principia of New- 
ton; as an original work, it is of course immeasur- 
ably inferior. Its principles are, in fact, the same 
with those laid down in that immortal code, and its 
deductions are collected (as we have said) from the 
writings of Clairaut, D’Alembert, Euler, and Lagrange, 
as well as from the previous memoirs of the author 
himself. Laplace has been too sparing of his cita- 
tions and acknowledgments, and a consequence of 
this literary avarice has been that he is sometimes 
considered as more of a compiler and less of a dis- 
coverer than is justly his due, For however ill he 
could have dispensed with the skilful preparations 
of his illustrious rivals and contemporaries, his pre- 
eminent sagacity furnished on several occasions the 
key-stone of the arch which imparted at once strength 
and completeness to the fabric. We have seen in 
the last section that though the credit of the theo- 
rems respecting the stability of the solar system is very 
generally attributed to Lagrange, who, indeed, prin- 
cipally furnished the methods, and gave great gene- 
gives ‘ality to the results, yet the capital discovery of the 
dim justly invariability of the major axes of the planetary orbits 
a high re- is due to Laplace. It was he, again, who removed 
(89.) 
His Traité 
de Mé- 
canique 
Céleste. 
Far less 
original 
than the 
Principia ; 
P * from the theory of gravity the two greatest and 
most impracticable difficulties with which it had 
ever been assailed—the anomaly of the lunar ac- 
celerations, and the great inequalities of Jupiter and 
Saturn, and by so doing rendered it almost infinitely 
improbable that any future discrepancy should more 
than temporarily embarrass a theory which had tri- 
PHYSICAL ASTRONOMY—LAPLACKE. 
821 
umphed in succession over such formidable causes of 
doubt. True that Lagrange, in his memoir of 1783, 
had come within a single step of the first of these 
discoveries, and, by a process of exclusion, had almost 
forced attention in the right direction respecting the 
latter ; still Laplace seized the prize in both cases, 
after a fair, prolonged, and arduous struggle: Now 
these three discoveries were the greatest in physical 
astronomy between those of D’Alembert and Clairaut 
on the precession of the equinoxes, the motion of the 
lunar apse, and the periodicity of comets,—and that 
of Leverrier and Adams on the perturbations of 
Uranus about a century later. 
The universal testimony of mathematicians is to | ~~ 
the effect that Lagrange was unrivalled as a pure comgined 
analyst, in his power of generalization, and in the with La- 
inherent elegance of his methods; that Laplace, stange- 
with nearly equal power in using the calculus, had 
more sagacity in its mechanical and astronomical 
applications, or rather, perhaps, we should say, in 
directing it to the discrimination of causes, and the 
revelation of consequences. 
In other respects he differed far more widely from _(91.) 
his illustrious compeer. He rather courted popu- His public 
larity, and was pleased at being considered worthy “aracter- 
of political distinction. For a short time he was one 
of Napoleon’s ministers; but the Emperor, it is said, 
was more satisfied with his mathematical than with 
his diplomatic talents. He had none of the shyness of 
Lagrange, nor his repugnance to general society. He 
received with affability and kindness those who were 
introduced to him, and his attentions were after- 
wards recollected with gratitude by rising men of 
science abroad. He had a villa at Arceuil, adjoining 
that of Berthollet, and was one of the original mem- 
bers of the “Societé d’Arceuil,” to whose memoirs 
he contributed. He exercised a powerful influence and as a 
in the Academy of Sciences, of which for a time he — of 
acted as dictator, and he was not very tolerant of demy of 
views in science opposed to his own. The undula- Sciences. 
tory theory of light he always opposed, and was 
mainly determined in doing so by the facility with 
which the attraction of luminous corpuscles could be 
subjected to calculation. 
The weak point of his scientific character was one so 
natural, and perhaps so inseparable from his prevail 
ing studies, that it is not fair to criticise it too severely, 
This was a love of analytical display in treating ques- 
tions which it rather embarrassed than illustrated ; 
and generally, a disposition to overrate the sphere of 
mathematical discovery. This he had in common 
with Euler, to whom he was very superior in physical 
attainments and sagacity. His language, and that of 
his eulogists,? often amounts to the assumption that 
(92.) 
Love of 
analytical 
display 
1 For instance Arago says (speaking of the invariability of the major axes): “ Enfin par la toute-puissance d’une formule 
fand. 
ts” (A ire, 1844, p. 304). This is indeed the idolatry 
mathématique, le monde materiel se trouva raffermi sur ses 
of mathematics. Many examples may be found in Laplace’s writings on Probability ; which occasioned Mr Ellis to say of him, that 
“ to Laplace all the lessons of History were merely confirmations of the ‘ resultats de caleul.’ » To the same effect was the mot 
of Napoleon, “ that Laplace carried into the art of government the principles of the infinitesimal calculus.” 
