Heinrich Friedrich Emil Lenz

(in Russian, Emilii Khristianovich Lents). Born Feb. 12 (24), in Tartu; died Jan. 29 (Feb. 10), 1865, in Rome. Russian physicist and electrical engineer. Academician of the St. Petersburg Academy of Sciences (1830).

In 1820, Lenz enrolled in the University of Dorpat (now Tartu). In 1823, without completing his studies, he took the post of physicist on the sloop Predpriiatie, which embarked on a voyage around the world (1823–26) under the command of O. E. Kotzebue. Lenz conducted oceanographic studies, in recognition of which he was elected an adjunct member of the St. Petersburg Academy of Sciences in 1828. In 1830 he was elected academician extraordinary, and in 1834 a full academician. In 1836 he was appointed to the chair of physics and physical geography at the University of St. Petersburg, becoming the university’s rector in 1863.

In 1883, Lenz formulated a law, now known as Lenz’s law, which determines the direction of induced currents. In a work written with M. H. von Jacobi (B. S. Iakobi), On the Laws of Electromagnets (parts 1–2, 1838–44), he proposed methods of designing electromagnets. (These methods were used until the 1880’s, when the laws of magnetic circuits became known.) Lenz also established the reversibility of electric machines. He discovered the phenomenon of “armature reaction,” and as a means of reducing its effect proposed shifting the brushes of the machine. In 1842 he substantiated by exact experiments the law of the heating effects of electric currents discovered in 1841 by J. Joule. Lenz also devised an instrument for studying the shape of alternating current curves. He conducted research on determining the dependence of resistance in metals on temperature and authored works on the derivation of Ohm’s law and the establishment of a ballistic method for measuring magnetic flux (with M. H. von Jacobi).

Lenz is also known for his works in geophysics. He investigated the vertical distribution of water temperature and salinity in oceans and the daily variations of air temperature for different latitudes. He was one of the first to propose a method of barometric leveling. Lenz attributed great importance to the teaching of physics in secondary schools. His Handbook of Physics, Compiled for... Russian Gymnasiums (1839) was published in 11 editions.