NICHOLSON, WILLIAM, an eminent chemist and mechanician, was born in London in 1753. His early years were spent in commercial pursuits, but he soon abandoned that occupation for the more congenial walk of scientific research. He opened a school in the metropolis in 1775, which he continued to conduct with great success for a long series of years. Meanwhile he prosecuted mechanical invention and scientific inquiry with great zeal. Besides English translations of the chemical works of Fourcroy, Chaptal, &c., he wrote numerous treatises on natural philosophy and chemistry, and was unquestionably the most eminent philosophical journalist of his day. His most valued works are his Dictionary of Chemistry, 2 vols. 4to, 1795; and his Journal of Natural Philosophy, Chemistry, and the Arts, 5 vols. 4to, 1797-1802, of which a new series appeared in 36 vols. 8vo, 1802-14. He invented an areometer and other instruments, but so impoverished himself by these pursuits that he was imprisoned for debt. He died in London in June 1815. (See DISSERT. SIXTH, chap. vii.)