nution. It was reserved to Poisson to demonstrate a priori that the non-periodic terms of the order which he considered would mu- tually destroy each other ; a most important conclusion, which re- moved the principal objection that existed to the validity of the demonstration of Lagrange[1].
This brilliant success of Poisson in one of the most difficult pro- blems of physical astronomy, would appear to have influenced him in devoting himself thenceforward almost exclusively to the application of mathematics to physical science ; and the vast number of memoirs and works (amounting to more than 300 in number) which he pub- lished during the last thirty years of his life, made this department of mathematical science, and more particularly whatever related to the action of molecular forces, pre-eminently his own. They comprehend the theory of waves and of the vibrations of elastic substances, the laws of the distribution of electricity and magnetism, the pro- pagation of heat, the theory of capillary attraction, the attraction of spheroids, the local magnetic attraction of ships, important problems on chances, and a multitude of other subjects, which the time allowed for this notice will not permit me to mention. His well-known treatise on Mechanics is incomparably superior to every similar publication in the clear and decided exposition of principles and methods, and in the happy and luminous combination of the most general theories with their particular and most instructive applications.
Poisson was not a philosopher who courted the credit of propound- ing original views which did not arise naturally out of the immediate subjects of his researches ; and he was more disposed to extend and perifect the application of known methods of analysis to important physical problems, than to indulge in speculations on the invention or transformation of formulae, which, however new and elegant, appeared to give him no obvious increase of mathematical power in the prosecution of his inquiries. His delight was to grapple with difficulties which had embarrassed the greatest of his predecessors, and to bring to bear upon them those vast resources of analysis, and those clear views of mechanical and physical principles in their most refined and difficult applications, which have secured him the most brilliant triumphs in nearly every department of physical science.
The confidence which he was accustomed to feel in the results of his analysis — the natural result of his own clear perception of the necessary dependence of the several steps by which they were deduced — led him sometimes to accept conclusions of a somewhat
- ↑ The publication of this memoir recalled the attention of this illustrious mathematician to a subject which he had long neglected, and gave rise to three of his noblest memoirs. Poisson, in his "Memoire sur le Mouve-Dient de la Lune autour de la Terre," has not satisfactorily shown that the major axis of the moon's orbit contains no argument of long period amongst the terms which involve lower powers of a certain quantity m, which denotes the ratio of the sun's mean motion to that of the moon, than the fourt; a demonstration of this most important proposition has been given by Sir John Lubbock in the Philosophical Magazine for the present year.
