Berzelius occupies a pre-eminent position in the history of chemistry, and during a considerable portion of his lifetime exercised an almost unassailable authority as a chemical philosopher. He is distinguished as an experimenter, as a discoverer, as a critic and interpreter, and as a lawgiver. His contributions to chemical knowledge range over every department of the science. He shares with Davy the honour of having established the fundamental laws of electro-chemistry. His experimental work on the atomic weights of the elements—the great work of his life—was of supreme importance at this particular period of the development of chemistry: it served not only to give precision to, and enhance the significance and value of, Dalton’s generalisation, but it furnished chemists, for the first time, with a set of constants, ascertained with the highest exactitude of which operative chemistry was then capable, thereby contributing to the expansion of quantitative analysis, and to a more exact knowledge of the composition of substances. Berzelius, indeed, was an analyst of the first rank—conscientious, patient, and painstaking; an ingenious and skilful manipulator; inventive and resourceful. What determinative chemistry owes to his labours, and not less to his example, is obvious from even the most superficial examination of its literature during the first third of the last century. As a discoverer, Berzelius first made known the existence of _cerium_ (1803), of _selenium_ (1818), and of _thorium_ (1828); and he prepared and investigated a large number of their combinations. He isolated _silicon_ (1823), _zirconium_ (1824), _tantalum_ (1824), and studied the compounds of _vanadium_, discovered by his countryman Sefström. He largely extended our knowledge of groups of substances in which sulphur replaces oxygen; investigated compounds of fluorine (1824), platinum (1828), and tellurium (1831–1833), and made many analyses of minerals, meteorites, and mineral-waters. He discovered _racemic acid_ and investigated the ferrocyanides. It was his investigation of racemic acid—which has the same percentage composition as tartaric acid—that first enabled him to grasp the conception of _isomerism_, a term which we owe to him, and of _metamerism_ and _polymerism_. He was the first to study the phenomena of contact-actions, which he comprehended under the term _catalysis_. [Illustration: JÖNS JAKOB BERZELIUS. From a painting by J. G. Sandberg.] As an author his literary activity was astonishing. His new system of mineralogy marks an epoch in the history of that branch of science. His text-book on chemistry was long the leading manual, and went through many editions, being constantly revised by him. His annual reports on the progress of physics and chemistry extended to twenty-seven volumes and constitute a monument to his industry, thoroughness, perspicacity, and critical ability.