On this day 131 years ago, on September 8, 1894 (August 9, 1894 lunar calendar), German scientist Helmholtz died. German physicist and physiologist. Born in Potsdam, Berlin on October 31, 1821, died on September 8, 1894 in Charlottenburg, near Berlin. After graduating from high school, he served in the army for 8 years and was admitted to the Royal Academy of Medical Sciences in Berlin at public expense. After receiving a doctorate in medicine in 1842, he was appointed a military doctor in the Potsdam garrison. In 1847 he gave a lecture on the conservation of force at the German Physical Society, which won great prestige in the scientific community. The following year he served as an associate professor of physiology at the University of Königsberg. In this lecture, Helmholtz first proposed the law of conservation of energy mathematically. The main argument is: ¢Ù All science can be reduced to mechanics. ¢Ú Emphasizes that Newtonian mechanics and Lagrangian mechanics are mathematically equivalent, so that the Lagrangian method can be used to measure the force in terms of the energy transmitted by the force or the work it does. ¢Û All such energy is conserved. Helmholtz developed the work of J.R. Mayer, J.P. Joule, and others, discussing the known scientific achievements of mechanics, heat, electricity, and chemistry, and rigorously demonstrating the laws of conservation of energy in various motions. The content of this lecture was later written in the monograph "Conservation of Force" and published. While working in Königsberg, Helmholtz measured the propagation rate of neural stimuli and published research results in physiological mechanics and physiological optics. In 1851 he invented the ophthalmoscope used in ophthalmology and proposed the mathematical theory of this instrument. In 1855 he moved to the University of Bonn as professor of anatomy and physiology, published the first volume of the Handbook of Physiology, and began the study of eddy currents in fluid mechanics. From 1857 he was professor of physiology at the University of Heidelberg. He used a resonator (called the Helmholtz resonator) to separate and strengthen the homophony of sound. In 1863 he published his magnum opus "The Physiological Basis of Tone". Comments: A rare multi-disciplinary outstanding scientist!