Hermann Ludwig Ferdinand von Helmholtz (August 31, 1821 – September 8, 1894) was a German physician and physicist. In the words of the 1911 Britannica, "his life from first to last was one of devotion to science, and he must be accounted, on intellectual grounds, as one of the foremost men of the 19th century."

Helmholtz is notable in a number of areas of science. In physiology and physiological psychology, he is known for his mathematics of the eye, theories of vision, ideas on the visual perception of space, color vision research, and on the sensation of tone, perception of sound, and empiricism. In physics, he is known for his theories on the conservation of force, work in electrodynamics, chemical thermodynamics, and on a mechanical foundation of thermodynamics. As a philosopher, he is known for his philosophy of science, ideas on the relation between the laws of perception and the laws of nature, the science of aesthetics, and ideas on the civilizing power of science. A large German association of research institutions, the Helmholtz Association, is named after him.

Helmholtz was the son of the Potsdam Gymnasium headmaster, Ferdinand Helmholtz, who had studied classical philology and philosophy, and who was a close friend of the publisher and philosopher Immanuel Hermann Fichte. Helmholtz's work is influenced by the philosophy of Fichte and Kant. He tried to trace their theories in empirical matters like physiology.

As a young man, Helmholtz was interested in natural science, but his father wanted him to study medicine at the Charité because there was financial support for medical students.

Helmholtz wrote about many topics ranging from the age of the Earth to the origin of the solar system.

His first important scientific achievement, an 1847 physics treatise on the conservation of energy was written in the context of his medical studies and philosophical background. He discovered the principle of conservation of energy while studying muscle metabolism. He tried to demonstrate that no energy is lost in muscle movement, motivated by the implication that there were no vital forces necessary to move a muscle. This was a rejection of the speculative tradition of Naturphilosophie which was at that time a dominant philosophical paradigm in German physiology.

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Drawing on the earlier work of Sadi Carnot, Émile Clapeyron and James Prescott Joule, he postulated a relationship between mechanics, heat, light, electricity and magnetism by treating them all as manifestations of a single force (energy in modern terms). He published his theories in his book Über die Erhaltung der Kraft (On the Conservation of Force, 1847).



In the 1850s and 60s, building on the publications of William Thomson, Helmholtz and William Rankine popularized the idea of the heat death of the universe.

The sensory physiology of Helmholtz was the basis of the work of Wilhelm Wundt, a student of Helmholtz, who is considered one of the founders of experimental psychology. He, more explicitly than Helmholtz, described his research as a form of empirical philosophy and as a study of the mind as something separate. Helmholtz had in his early refutal of the speculative early nineteenth century tradition of Naturphilosophie stressed the importance of materialism, and was focusing more on the unity of "mind" and body.

In 1851, Helmholtz revolutionized the field of ophthalmology with the invention of the ophthalmoscope; an instrument used to examine the inside of the human eye. This made him world famous overnight. Helmholtz's interests at that time were increasingly focused on the physiology of the senses. His main publication, entitled Handbuch der Physiologischen Optik (Handbook of Physiological Optics), provided empirical theories on spatial vision, color vision, and motion perception, and became the fundamental reference work in his field during the second half of the nineteenth century. His theory of accommodation went unchallenged until the final decade of the 20th century.

Helmholtz continued to work for several decades on several editions of the handbook, frequently updating his work because of his dispute with Ewald Hering who held opposite views on spatial and color vision. This dispute divided the discipline of physiology during the second half of the 1800s.

In 1863 Helmholtz published Die Lehre von den Tonempfindungen (On the Sensations of Tone as a Physiological Basis for the Theory of Music), once again demonstrating his interest in the physics of perception. This book influenced musicologists into the twentieth century. Helmholtz invented the Helmholtz resonator to show the strength of the various tones.

The book was translated by Alexander J. Ellis in 1885 (first English edition from third German edition completed June 1885, and second English edition from fourth German edition completed July 1885).

In 1871 Helmholtz moved from Heidelberg to Berlin to become a professor in physics. He became interested in electromagnetism. Oliver Heaviside stated that there were longitudinal waves in Helmholtz theory. Although he did not make major contributions to this field, his student Heinrich Rudolf Hertz became famous as the first to demonstrate electromagnetic radiation. Helmholtz had predicted E-M radiation from Maxwell's equations, and the wave equation now carries his name.

Other students and research associates of Helmholtz at Berlin included Max Planck, Heinrich Kayser, Eugen Goldstein, Wilhelm Wien, Arthur König, Henry Augustus Rowland, A. A. Michelson, and Michael Pupin. Leo Koenigsberger, who studied at Berlin while Helmholtz was there, wrote the definitive biography of him in 1902.

*Helmholtz free energy *Helmholtz coil which was named in his honor. *Helmholtz pitch notation *Helmholtz resonance *Helmholtz theorem *Helmholtz decomposition *Helmholtz equation *Kelvin-Helmholtz instability *Young-Helmholtz theory, about the trichromatic colour vision

*1971. Selected Writings of Hermann von Helmholtz. Kahl, Russell, ed. Wesleyan Uni. Press. *1977. Helmholtz: Epistemological Writings. Cohen, Robert, and Wartofsky, Marx, eds. and trans. Reidel. *Ewald, William B., ed., 1996. From Kant to Hilbert: A Source Book in the Foundations of Mathematics, 2 vols. Oxford Uni. Press. **1876. "The origin and meaning of geometrical axioms," 663-88. **1878. "The facts in perception," 698-726. **1887. "Numbering and measuring from an epistemological viewpoint," 727-52. *Leo Koenigsberger, translated by Frances A. Welby Hermann von Helmholtz (Dover, 1965)

* "Hermann von Helmholtz" (Obituary). Royal Society (Great Britain). (1894). Proceedings of the Royal Society of London. London: Printed by Taylor and Francis. * * J. G. McKendrick Hermann Ludwig Ferdinand von Helmholtz (London : Unwin, 1899) *On the Conservation of Force Introduction to a Series of Lectures Delivered at Carlsruhe in the Winter of 1862–1863, English translation *Treatise on Physiological Optics 1910, three volumes. English translation by Optical Society of America (1924-5). * Biography and bibliography in the Virtual Laboratory of the Max Planck Institute for the History of Science