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himself to form the North Hempstead Library Association and Library. In 1792 he was appointed Professor of Chemistry, Natural History, and Philosophy in Columbia College, where, while dissenting from some of the principles of the French chemist, he introduced, for the first time in the United States, the chemical nomenclature devised by Lavoisier. His dissent from Lavoisier led to a controversy with Dr. Priestley, at the end of which the two disputants found themselves on a footing of mutual esteem and warm personal friendship. He records himself in 1794 as having exhibited at full length, in a printed essay, the actual state of learning in Columbia College. At about this time, too, he was co-operating with Chancellor Livingston and Simeon De Witt in the establishment of the Society for the Promotion of Agriculture, Manufactures, and the Useful Arts, before which he delivered his first public address. Having executed a commission from this society for that work, he made a detailed report, in 1796, of geological and mineralogical observations on the banks of the Hudson, for coal, etc.—a performance which, he mentions, was respectfully quoted by Count Volney. This was the first work of the kind undertaken in the United States, and the report helped to secure a wide European as well as American reputation for the author. Referring to it, Dr. J. W. Francis says, "He may fairly be pronounced the pioneer investigator of geological science among us, preceding McClure by several years." The report was published in the Medical Repository, a quarterly magazine begun in 1797 by Dr. Mitchill, with Drs. Edward Miller and Elihu H. Smith, and continued by Dr. Mitchill for more than sixteen years. After his marriage, in 1799, to Mrs. Catharine Cock, which brought him the enjoyment of an ample fortune, Dr. Mitchill was able to devote himself entirely to scientific and public occupations. Among the scientific works with which he accredits himself during the few years succeeding this event is the publication of a chart of chemical nomenclature, with an explanatory memoir, in which he contended that metals in their malleable and ductile state are compounds of a base with hydrogen (phlogiston), as in their calciform state they consist of a base with oxygen; and that in several there is an intermediate condition in which there is no union either with hydrogen or oxygen. And he extended the same doctrine to the greater part of inflammable bodies. In 1802 he records a correspondence with Albert Gallatin, Secretary of the Treasury, on a project for illuminating the lighthouses of the United States with inflammable air. In 1806 he wrote the introduction to the American edition of Assalini's Observations on the Plague, Dysentery, and Ophthalmy of Egypt; and in the ensuing winter translated from the Latin Lancisi's book on the noxious exhalations of marshes at Washington—a