JAN, a Polish astronomer and mathematician, was born at Znin on the 29th of August 1756. He began his education at Pozen, continued it at Cracow, and completed it at Göttingen. While at the university he was distinguished for his classical attainments, and it is told by his biographer, Balinski, that he had the whole of Horace by heart. In 1777 he was appointed teacher of statics, hydraulics, logic, and political economy at Nowodwòp in Cracow. Some time after he visited Paris, where he made the acquaintance of Laplace, Condorcet and D'Alembert; and in 1787 he visited England, having previously mastered the English language so far as to be able to read the mathematical writings of Maclaurin and Simson. He visited Sir William Herschel and his observatory at Slough, and made the acquaintance of some eminent English mathematicians and astronomers. After his return to Poland he seldom left his post as professor of mathematics and astronomy at Cracow, till 1806, when he was transferred to the university seat of Wilna. Sniadecki here engaged in numerous astronomical observations, many of which will be found published in the Transactions of the St Petersburg Academy, and in the Berlin Astronomische Jahrbücher. On the suppression of the university of Wilna, Sniadecki retired, and died in 1880. A collected edition of his works, with a life by Balinski, was published in 8 vols., Warsaw, 1837-39. The mathematician and astronomer had a younger brother, ANDREJEZ SNIADECKI, who was an eminent physiologist. He was born in 1768, and died in 1838. He studied successively at Cracow, Pavia, and Edinburgh, and returned home to profess chemistry and physiology at the university over which his elder brother presided in his later years. The most important work of this writer was his Theory of Organic Existences, 2 vols., 1804-11, which has been translated into German and French, and is much esteemed.