Mayer, JULIUS ROBERT VON, physicist, was born at Heilbronn, 25th November 1814, studied medicine at Tübingen, Munich, and Paris, began life as a ship's surgeon, and settled in his native town to practise his profession in 1841. Whilst at Batavia in 1840 his attention was first attracted to the studies he afterwards pursued in every interval of leisure. In 1842 he published in Liebig's Annalen a preliminary statement of the mechanical theory of heat, in which he clearly determined the numerical relation between heat and work. Three years later he restated his views with admirable clearness and with a great wealth of illustration, and at the same time gave a forecast of his theory of the meteoric origin of the sun's heat, elaborated in 1848. Contemporaneously with Mayer the mechanical theory of heat was worked out independently by Joule (q.v.) in England. Nevertheless a controversy arose as to the priority of discovery. The Royal Society gave him the Copley medal in 1871, and he was ennobled by the king of Württemberg two years before his death, on 20th March 1878. Mayer's papers were collected under the title Mechanik der Wärme (2d ed. 1874), and his Correspondence appeared in 1889.
See Tyndall in Nature (vol. v.; cf. vol. xvii.), and monographs by Dühring (1879) and Weyrauch (1889).