221 years ago today, on February 24, 1804 (January 14, 1804 lunar calendar), Russian physicist and geophysicist Lenz was born. Lenz was born in Estonia on February 24, 1804. At the age of 16, he was admitted to the Dauphat University in his hometown with honors. In 1828, he was selected as a junior scientific assistant of the St. Petersburg Academy of Sciences in Russia. In 1830, he was elected as an academician of the St. Petersburg Academy of Sciences. In 1834, he was elected as an academician. He served as the head of the Department of Physics and Mathematics of St. Petersburg University for a long time, and was later elected as the first president by the faculty. Lenz's main achievements in physics were the discovery of Lenz's law of electromagnetic induction and Joule-Lenz's law of electrothermal effect. In 1833, Lenz presented his paper entitled "On Determining the Direction of Induced Current by Electromechanical Method" at the St. Petersburg Academy of Sciences, proposing Lenz's law. Helmholtz proved that Lenz's law is the law of conservation of energy for electromagnetic phenomena. In 1831, Lenz used the shock method to quantitatively study electromagnetic phenomena based on the instantaneous and shock-like effects of induced currents, and determined that the induced electromotive force in the coil is equal to the sum of the electromotive forces in each coil turn, regardless of the thickness and type of wires used. In 1838, Lenz also studied the convertibility of electric motors and generators, using Lenz's law to explain its conversion principle. In 1844, Lenz studied the parallel connection of any electromotive force and resistance, and obtained the law of shunt current, 4 years before Kirchhoff published the more general circuit law. In the winter of 1865, Lenz died of a stroke in Rome, Italy.