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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 



