Lenz, Emil Khristianovich (Heinrich Fridrich Emil)
Lenz, Emil Khristianovich (Heinrich Fridrich Emil)
(b. Dorpat, Russia [now Tartu, Estonian S.S.R.], 24 February 1804;d. Rome, Italy, 10 February 1865)
Lenz’s father, senior secretary of the Dorpat magistracy, died in 1817, leaving his widow and two sons in straitened circumstances.
After graduating from secondary school with highest honors in 1820, Lenz entered Dorpat University. At the university he studied chemistry under his uncle, J. E. F. Giese, and physics under G.F Parrot, who had founded the physics department and its physical cabinet and was the first rector of the university. Soon Parrot recommended the nineteen-year-old student to Admiral I. F. Krusenstern as a geophysical observer during Kotzebue’s second scientific voyage around the world (1823-1826) on the sloop Predpriatie.
In 1828 Lenz was elected junior scientific assistant of the St. Petersburg Academy of Sciences. In 1829-1830 he traveled in southern Russia, where he participated in an ascent of Mt. Elbrus in the caucasus and determined its height, conducted magnetic observations at Nikolayev according to Humboldt’s program of simultaneous observations, initiated accurate measurements of variations in the level of the Caspian Sea by setting up a surveying rod in Baku, and took samples of petroleum and natural gas. In 1830 he was elected associate academician and in 1834 a full academician.
In the spring of 1831 Lenz began his investigations of electromagnetism, which he continued until 1858. At the same time he lectured on physics at the Naval Military School (1835-1841), the Artillery Academy (1848-1861), the Central Pedagogical Institute (18517-1859), and the University St. Petersburg (1836-1865), where from 1840 to 1863 he was dean of the physics and mathematics department and later the first rector to be elected by the professorial in accordance with the new statutes of the university. Lenz died of and apoplectic stroke while on vacation. In 1830 he had married A. P. Helmersen, sister of the geologist G. P. Helmersen; they had seven children. Robert became a physicist and headed the physics department of the St. Petersburg Technological Institute. Lenz’s students A. S. Savelyev, F. F. Petrushevsky, F. N. Shvedov, and M. P. Avenarius became university professors. His physics textbook for secondary schools ran to thirteen editions, and that on physical geography for higher military educational institutions ran to four.
Lenz’s services as an expert were frequently enlisted to solve scientific and engineering problems. Many decorations were conferred on him, and he held the rank of privy councillor. He was an honorary member of many Russian universities, the Physical Society in Frankfurt am Main, and the Berlin Geographical Society, and was corresponding member of the Turin Academy of Sciences. His papers were published in the Mémoires and Bulletin of the St. Petersburg Academy of Sciences and, as a rule, in Poggendorff’s Annalen at the same time. Some papers were also published in England, France, and Switzerland.
Lenz’s name survives in the history of physics as the result of his discovery of two fundamental physical laws—soon seen as special cases of the law of conservation of energy—and a great many empirical quantitative relationships of electromagnetic, electrothermal, and electrochemical phenomena; his development of precise measuring methods, instruments, and standards; and his investigations of the theoretical principles of electrical engineering. All three of these aspects of his work can be found in almost any of his publications. His application of Ohm’s law and Gauss’s method of least squares and his graphical representation of various laws have distinguished his work from the scientific papers of most of his contemporaries.
In November 1833, Lenz read his paper ( “Ueber die Bestimmung der Richtung durch elektodyanamische Vertheilung erregten galvanischen Ströme” ) before the St. Petersburg Academy. It established Lenz’s law, relating the phenomena of induction to those of the ponderomotive interaction of currents and magnets discovered by Oersted and Ampère. Lenz’s law states that the induced current is in such a direction as to oppose, by its electromagnetic action, the motion, of the magnet or coil that produces the induction. F. Neumann’s derivation of the mathematical expression for the electromotive force of induction (1846) and Helmholtz’s proof of the law of conservation of energy for electromagnetic phenomena (1847) were based on Lenz’s law. This law also includes the principle of invertibility of motor and generator, which Lenz demonstrated on Pixii’s magnetoelectric machine in 1838. The same law explains the phenomenon of armature reaction, discovered by Lenz in 1847 in his experiments with Störer’s machine. This enabled Lenz to disprove W. Weber’s incorrect hypothesis that the failure of current to increase with increased armature speeds was due to delay in the rate of magnetization of the iron, and to indicate the necessity of providing brushes at the neutrals of the machine. Continuing his experiments with Störer’s machine, Lenz devised a method for plotting curves showing the phase relationship between current and magnetization (1853-1858).
Independently of Joule and with greater accuracy, in 1842-1843 Lenz established the law of thermal action of a current, appreciating that the quantity of heat obtained was limited by the chemical processes of the battery. In 1838 he gave a visual and conclusive proof of J. C. A. Peltier’s discovery by freezing water with an electric current on a layer of bismuth and antimony.
Lenz worked out the theoretical and practical aspects of the ballistic method of measuring electrical and magnetic quantities (1832) on the basis of his conception of the instantaneous, impactlike effect of induction current. Employing this method, he was able to make the first quantitative investigation of the induction phenomena themselves. (He established that the induced electromotive force in a coil is the sum of the electromotive force in each turn and does not depend upon the diameter of the turns, the thickness of the wire, or the metal of which it is made.) He also made a quantitative comparison of the resistivity of wire of different metals, established the laws of temperature dependence of resistivity in quadratic form for eight metals, derived the squarelaw variation of the attractive force of electromagnets with the magnetization current (under the conditions of the experiment, the magnetic field was proportional to the magnetic induction), and plotted curves showing the intensity distribution of magnetization along an iron core of a coil of finite length. The last of these measurements was made by Lenz as a member of a special committee which investigated the possibility of using Jacobi’s electric motor for propelling ships. In their joint investigations (1837-1840) it was shown that the magnetization of electromagnets and, consequently, the available power of the motor depend upon the amount of zinc dissolved in the battery. Therefore all hopes of obtaining “free work” by means of electromagnets had to be abandoned.
In 1844 Lenz deduced the law of the branching of currents in a system of parallel-connected elements with arbitrary electromotive forces and resistances—four years before the publication of Kirchhoff’s more general laws.
Lenz’s most significant investigation in electrochemistry, conducted with A. S. Savelyev (1844-1846), established the additivity of electrode potentials in a galvanic cell; the existence of a series of electrode potentials at the metal-electrolyte boundary, similar to the Volta series; and the additivity laws of the electromotive forces of polarization on the cathode and anode, as well as of the electromotive forces of polarization and initial electrode potential of each electrode.
In the first half of the nineteenth century, data were being accumulated in geophysics; and the main problem was to ensure their reliability. This work was done by Lenz in his own observations and in the instructions he drew up for expeditions of the Russian Geographic Society, which he helped to organize in 1845.
During the voyage of the Predpriatie, Lenz’s use of instruments, invented by Parrot for determining the specific gravity and temperature of seawater to a depth of about two kilometers, yielded results that were not excelled in accuracy by the Challenger expedition or on the voyages of S. O. Makarov on the Vityaz at the end of the nineteenth century.
Lenz also discovered and correctly explained the existence of salinity maximums in the Atlantic and Pacific oceans north and south of the equator, the greater salinity of the Atlantic in comparison with the Pacific, and the decreasing salinity of the Indian Ocean encountered in traveling east. He noted that at definite latitudes, water at the ocean’s surface is wrmer than the air above it; and he found two maximums and two minimums of barometric pressure in the tropics.
I. Original Works. Some of Lenz’s works were collected as Izbrannie trudy ( “Selected Works” ; Moscow, 1950), with articles by T. P. Kravetz, L. S. Berg, and K. K. Baumgart and a bibliography of 251 items. This collection does not include the following important works: “Ueber die Gesetze, nach welchen der Magnet auf eine Spirale einwirkt, wenn es ihr plötzlich genähert oder von ihr entfernt wird, und über die vortheilhafteste Konstruktion der Spiralen zu magneto-elektrischem Behufe,” in Mémoires de l’Académie impériable des sciences de St.-Pétersbourg, 6th ser., 2 (1833), 427-457, also in R. Taylor, ed., Scientific Memoirs, I (London, 1837), 608—630; “Ueber einige Versuche im Gebiete der Galvanismus,” in Bulletin scientifique de l’Académie impériale des sciences de St.-Pétersbourg,3, no. 21 (1838), cols. 321-326, also in Annals of Electricity, Magnetism and Chemistry;3 (1838), 380-385; Rukovodstvo k fizike, sostavlennoe dlya russkikh gimnazy ( “Manual of Physics, Prepared for Russian Secondary Schools” ; St. Petersburg, 1839; 13th ed., Moscow, 1870); “Ueber galvanische Polarisation und elektromotorische Kraft in Hydroketten,” in Bulletin de la classe physico-mathématique de l’Académie impériale des sciences de St.-Pétersburg,5 (1847), 1-28; and Fizicheskaya geografia. S prilozheniem osobennogo atlasa ( “Physical Geography. With Special Atlas Appended”; St. Petersburg, 1851; 4th ed., 1865), also translated into Swedish (Kuopio, Finland, 1854).
II. Secondary Literature. On Lenz or his work, see W. K. Lebedinsky, “E. K. Lenz kak odin iz osnovateley nauki ob elektromagnetisme” ( “E. K. Lenz as One of the Founders of the Science of Electromagnetism” ), in Elektrichestvo, nos. 11-12 (1895), 153-161; O. A. Lezhneva, “Die Entwicklung der Physik in Russland in der ersten Hälfte des 19. Jahrhunderts,” in Sowjetische Beiträge zur Geschichte der Naturwissenschaften (Berlin, 1960); O. A. Lezhneva and B. N. Rzhonsnitsky, Emil Khristianovich Lenz (Moscow-Lemomgrad, 1952), which has a bibliography of 114 titles; and W. M. Stine, “The Contribution of H. F. E. Lenz to the Science of Electromagnetism,” in Journal of the Franklin Institute,155 (Apr.-May 1903), 301-314, 363-384.
Olga A. Lezhneva