## Stoletov, Aleksandr Grigorievich

# STOLETOV, ALEKSANDR GRIGORIEVICH

(*b.* Vladimir, Russia. 10 August 1839; *d.* Moscow, Russia, 27 May 1896)

*physics*

Stoletov came from a merchant family that had been exiled to Vladimir for sedition by Ivan the Terrible. His father, Grigory Mikhailovich, owned a small grocery store and a tannery; his mother, Aleksandra Vasilievna, was intelligent and well-read. While still a schoolboy he studied French, English, and German.

In 1856 Stoletov entered the Faculty of Physics and Mathematics at Moscow University as one of the first students from the merchant class to receive a government scholarship. His instructors in physics were M. F. Spassky and N. A. Lyubimov; and he received solid mathematical preparation under N. E. Zernov and N. D. Brashman. After graduating in 1860, he remained in the physics department to prepare for an academic career.

In 1862 Stoletov traveled abroad on a fellowship and spent three and a half years in Germany, where he attended the lectures of Helmholtz, Kirchhoff, and Wilhelm Weber and worked in H. G. Magnus’ laboratory. At the end of 1865 he became a physics teacher at Moscow University. Four years later he defended his master’s thesis, “Obshchaya zadacha elektrostatiki i privedenie ee k prosteyshemu vidu” (“The General Problem of Electrostatics and Its Reduction to the Simplest Form”).

In 1871 Stoletov completed plans for his doctoral dissertation, which was based on his experimental research on the magnetic properties of iron. Since there was no laboratory at Moscow University–although Stoletov tried to have one established–he was again obliged to go abroad. At Heidelberg, Kirchhoff offered him the necessary conditions for working on his dissertation, which he defended in Moscow the following year, “Issledovanie o funktsii namagnichenia myagkogo zheleza.”

He became extraordinary professor, and since a physics laboratory had in the meantime been opened at the university, he did his research there. In addition to his lectures, Stoletov also popularized science through his work in the Society of Amateurs of Science, the Society of Amateurs of Natural Sciences, and the Russian Physical-Chemical Society. He attracted a large group of talented young people to the physics. His protracted efforts to establish a physics institute at Moscow University were finally realized in 1887.

In his master’s thesis Stoletov examined the theoretical equilibrium of electricity in an arbitrary number of isolated conductors (continuous and field) in an arbitrarily given field created by arbitrarily complex stationary electric poles. He continued to develop the mathematical method of successive approximation of Robert Murphy, Lipschitz, and William Thomson (Lord Kelvin) for the case of an arbitrary number of conductors. Stoletov had already written his thesis when Lipschitz’s work on the same subject appeared abroad, but the latter was significantly less complete.

In his doctoral dissertation Stoletov examined the relation of the magnetization of iron to the strength of the external magnetic field. Although it was then known that the course of magnetization is not linear, the form of the function in the area of relatively weak fields remained unexplained. A thorough analysis of the experimental material led Stoletov to conclude that previous investigations, carried out in cylindrical models, could not yield satisfactory results because of the demagnetizing effect of the flat end. His use of Kirchhoff’s theory led to the possibility of studying the true relation of magnetization to the field in closed rings magnetized along the perimeter. For this investigation Stoletov developed the method now generally accepted for measuring induction in rings with the aid of a ballistic galvanometer. He was the first to show that magnetic permeability of a ferromagnet increases in proportion to the intensification of the magnetizing field, attains a maximum, and then decreases. Stoletov emphasized the importance of applying these results to electrotechnology.

In his most distinguished work, *Aktinoelek-tricheskie issledovania* (“Actinoelectric Investigations,” 1889), Stoletov experimentally established the basic laws of the external photoelectric effect and certain fundamental regularities of electrical discharge in rarefied gases. The first to develop an experimental method of studying the photoeffect, he showed that during the illumination of metals by ultraviolet light, there is a loss of negative electrical charge. By illuminating the negative plate of a condenser through a latticed-plate positive electrode, he observed a continuous electrical current in the circuit containing the condenser, a cell battery, and a galvanometer. The strength of the current appeared to be proportional to the intensity of the incident light and to the area illuminated. In 1888–1889 Stoletov was the first to show that through the presence of contact difference in potentials between the lattice and the plate, the photoelectric apparatus can, without a supplementary battery, serve as the source of current, converting light energy into electricity. This was the first photoelement, but Stoletov did not patent his invention. In 1890 the German physicists Elster and Geitel independently had the same idea, and received a patent for the photoelement and several of its applications.

Investigating the relation of the photocurrent to the external difference in potential, Stoletov discovered the existence of a saturation current. Further experimental study of this phenomenon at different degrees of rarefaction of air led him to discover an important regularity. If *p*_{m} is the pressure of gas at which the current attains the maximum value, *l* the distance between electrodes, and *v* the potential difference between them, then,

The theory of this phenomenon was provided in 1910 by Townsend, who proposed calling the quantity the Stoletov constant.

In his important four-part *O kriticheskom sostoyanii tel* (“On the Critical State of Bodies,” 1882–1894), Stoletov thoroughly analyzed the experimental data and the theoretical opinions of various authors, introduced clarity into the discussion of the critical state, and showed the correctness of the ideas of Thomas Andrews and van der Waals.

Stoletov’s interest in the history of physics was reflected in an extensive study, *Ocherk razvitia nashikh svedeny o gazakh* ("Sketch of the Development of Our Information on Gases,” 1879), and in articles on Newton, da Vinci, and others.

## BIBLIOGRAPHY

Stoletov’s writings were published as *Sobranie sochineny* (“Collected Works”; Moscow, 1941) and *Izbrannye sochinenia* (“Selected Works”), A. K. Timiryazev, ed. (Moscow, 1950). The Royal Society *Catalogue of Scientific Papers,* VIII, 1024; XI, 507; XII, 707; and XVIII, 978–980, lists 29 of his memoirs and several obituary notices.

On his life and work, see A. I. Kompaneets, *Mirovozrenie A. G. Stoletova* (“The World View of A. G. Stoletov”; Moscow, 1956), with a comprehensive bibliography of his writings and correspondence, pp. 281–286; M. S. Sominsky, *Aleksandr Grigorievich Stoletov* (Leningrad, 1970); and G. M. Teplyakov and P. S. Kudryavtsev, *Aleksandr Grigorievich Stoletov* (Moscow, 1966).

J. G. Dorfman

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