Born Feb. 10 (22), 1849, in Tula; died Feb. 14 (27), 1915, in Petrograd. Russian mathematician. Academician of the St. Petersburg Academy of Sciences (1893; coresponding member, 1891).
Sonin graduated from Moscow University in 1869. In 1877 he became a professor at the University of Warsaw.
Sonin’s principal works extended the research of P. L. Che-byshev. Among them were On the Precision of the Determination of the Limiting Values of Integrals (1892), whose results were associated with a proof of a limit theorem of the theory of probability, and On the Approximation of Definite Integrals and Entire Functions Encountered in This Approximation Process (1887). He studied a class of integral equations of importance in practical applications—namely, integral equations with a variable limit and a kernel that depends on the difference between the independent variables (1884). He also wrote on special functions, particularly cylindrical functions, and on asymptotic expansions of functions.