Helmholtz, Hermann Ludwig Ferdinand von [key], 1821–94, German scientist. Although known especially as a physicist and biologist, he was also a physician, mathematician, philosopher, and lecturer on popular science. He extended the application of the law of conservation of energy and in 1847 formulated it mathematically. He contributed to the knowledge of thermodynamics and electrodynamics and studied vortex motion in fluids. A pioneer in physiological optics and author of a Treatise on Physiological Optics (1867; tr., 3 vol., 1924–25), he extended Thomas Young's theory of color vision, explained the mechanism of lens accommodation in the eye, and invented (1851) the ophthalmoscope. He was an authority on acoustics, especially on the perception of tone quality, and wrote On the Sensations of Tone (4th ed. 1877, tr. 1954). Helmholtz was professor of physics at the Univ. of Berlin from 1871 and also director of the physicotechnical institute at Charlottenburg from 1887.
See his Selected Writings, ed. by K. Russell (1971); study by R. M. Warren and R. P. Warren (1968).
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