Illustrious French thinker and writer, born at Clermont, in Auvergne; was distinguished at once as a mathematician, a physicist, and a philosopher; at 16 wrote a treatise on conic sections, which astonished Descartes; at 18 invented a calculating machine; he afterwards made experiments in pneumatics and hydrostatics, by which his name became associated with those of Torricelli and Boyle; an accident which befell him turned his thoughts to religious subjects, and in 1654 he retired to the convent of Port Royal (q. v .), where he spent as an ascetic the rest of his days, and wrote his celebrated "Provincial Letters" in defence of the Jansenists against the Jesuits, and his no less famous "Pensées," which were published after his death; "his great weapon in polemics," says Prof. Saintsbury, "is polite irony, which he first brought to perfection, and in the use of which he has hardly been equalled, and has certainly not been surpassed since" (1623-1662).