Page:Proceedings of the Royal Society of London Vol 4.djvu/297

Rh startling character *. such were his views of the constitution and finite extent of the earth's atmosphere, which some distinguished philoso- phers have ventured to defend. It is not in mathematical reason- ings only that we are sometimes disposed to forget that the conclu- sions which we make general are not dependent upon our assumed premises alone, but are modified by concurrent or collateral causes, which neither our analysis nor our reasonings are competent to comprehend.

The habits of life of this great mathematician were of the most simple and laborious kind ; though he never missed a meet- ing of the Institute, or a lecture, or an examination, or any other public engagement, yet on all other occasions, at least in his later years, he denied access to all visitors, and remained in his study from an early hour in the morning until six o'clock at night, when he joined his family at dinner, and spent the evening in social con- verse, or in amusements of the lightest and least absorbing charac- ter, carefully avoiding every topic which might recall the severity of his morning occupations. The wear and tear, however, of a life devoted to such constant study, and the total neglect of exercise and healthy recreations, finally undermined his naturally vigorous con- stitution, and in the autumn of 1838 the alarming discovery was made that he was labouring under the fatal disease of water in the chest. The efforts of his physicians contributed for a time to mitigate the more serious symptoms of his malady ; but every relaxation of his sufferings led to the resumption of his labours ; and to the earnest remonstrances of his friends, and the entreaties of his family, he was accustomed to reply, that to him la vie cetait le travail; naj, he even undertook to conduct the usual examinations of the Ecole Polytechnique, which occupied him for nearly ten hours a day for the greatest part of a month. This last imprudent effort ended in an attack of paralysis, attended by loss of memory and the rapid ob- scuration of all his faculties ; he continued to struggle, amidst alter- nations of hope and despondency, for a considerable period, and died on the 25th of April last, in the fifty-ninth year of his age.

Poisson was eminently a deductive philosopher, and one of the most illustrious of his class ; his profound knowledge of the labours of his predecessors, his perfect command of analysis, and his extra- ordinary sagacity and tact in applying it, his clearness and precision in the enunciation of his problems, and the general elegance of form which pervaded his investigations, must long continue to give to his works that classical character, which has hitherto been almost exclusively appropriated to the productions of Lagrange, Laplace, and Euler. If he was inferior to Fourier or to Fresnel in the largeness and pregnancy of his philosophical views, he was in- comparably superior to them in mathematical power : if some of his contemporaries rivalled or surpassed him in particular departments of his own favourite studies, he has left no one to equal him, either in France or in Europe at large, in the extent, variety, and intrinsic value of his labours.

The last work on which he was engaged was a trealise on the theory of light, with particular reference to the recent researches of