The German physicist and physiologist Hermann Ludwig Ferdinand von Helmholtz (1821-1894) made the first mathematical analysis of the principle of the conservation of energy and invented the ophthalmoscope. He also investigated the physics of tone and color perception.

Born on August 31, 1821, in Potsdam, Hermann von Helmholtz was the eldest of six children of August Helmholtz, a teacher of philosophy and classics in the local gymnasium, and Caroline Penne Helmholtz, a descendant of the family which took prominent part in the founding of Pennsylvania. At the age of 17 he entered the Friedrich Wilhelm Institute as a scholarship student of medicine. Happily for science, Helmholtz had the genius to absorb medical and physiological training with the mind of a physicist. A great help in this respect was a teacher of his at the institute, Johannes Müller, the foremost German physiologist at that time, who insisted on carrying as far as possible the physical and chemical explanation in all problems of physiology. For Helmholtz this also meant the utmost use of mathematics, which he learned on his own to a very advanced degree by studying in his free time such mathematical classics as the works of Euler, Bernoulli, D'Alembert, and Lagrange. His doctoral dissertation (1842) described and analyzed the connections between nerve fibers and nerve cells, a discovery which he made by skillful use of the microscope and which forms the histological basis of the physiology and pathology of the nervous system.

Helmholtz's scholarship status implied the obligation to serve for eight years as army doctor. His first post (1842-1843) was that of a house surgeon at the Charité Hospital in Berlin, followed by a stint of 5 years as assistant surgeon to the Royal Hussars at Potsdam. Despite time-consuming duties, Helmholtz found ways of developing his scientific interests. While at the Charité, he published a demonstration of the strictly chemical nature of fermentation and noted that a vitalistic account would be equivalent to assuming a perpetual-motion process. His papers on metabolism during muscular activity (1845) and on physiological and animal heat (1846, 1847) clearly indicated the great goal toward which his creative mind inevitably tended. In February 1847 he sent the first draft of the introduction of "The Conservation of Force" to Emil Du Bois-Reymond, who immediately declared that it was "an historical document of great scientific import for all time." The 26-year-old Helmholtz read the paper on July 23 before the Physical Society of Berlin. He was not the first to enunciate the idea that physical force (energy) was conserved in its various transformations, but his originality consisted in giving the principle a generalized mathematical form, which readily yielded expressions for kinetic and potential energy in mechanics, thermodynamics, electricity, and magnetism.

Academic World

The impact of the lecture and the availability of a teaching post in anatomy at the Academy of Arts in Berlin made it possible for Helmholtz to transfer to the academic world. In 1849 he accepted the invitation to serve as professor of physiology at the University of Königsberg, where he married Olga von Velten the same year. Among his first papers at Königsberg was "On the Method of Measuring Very Small Intervals of Time and Their Application to Physiological Purposes" (1851). The purpose was the determination of the rate of transmission of sense impressions along the nerves. The value he found shortly afterward was approximately 30 meters per second, in good agreement with subsequent determinations. The next year Helmholtz wrote of a marvelous new device to investigate the eye, the ophthalmoscope, which made its inventor world famous almost overnight.

In 1855 Helmholtz went to Bonn as professor of physiology and anatomy. During the following 3 years he started his incisive analysis of the mathematical relationships underlying tone perception and the esthetical judgment about various tonalities. At the same time he began publishing in a mature form his previous studies of the physiology of vision. The first volume of his famous Handbook of Physiological Optics appeared in 1856. The massive volume was a systematic application of physics to the phenomenon of vision. "On the Integrals of the Hydrodynamic Equations Which Express Vortex Motions" (1858) represented not only a brilliant solution of seemingly insoluble equations, but it also became the foundation for late-19th-century physicists who tried to devise a so-called vortex model of the ether.

Helmholtz spent the next 13 years at the University of Heidelberg. During his first year there his wife died. In 1861 Helmholtz married Anna von Mohl, who became mother of three children. He spent 13 years at Heidelberg, officially a physiologist but in reality a physicist.

The second part of Helmholtz's Handbook of Physiological Optics was published in 1862. The next year saw the publication of another systematic application of physics in physiology, Theory of the Sensations of Tone as Physiological Basis of the Theory of Music. In 1867 followed the third, and final, volume of the Handbook. Helmholtz's last 3 years at Heidelberg were marked by portentous investigations in theoretical physics. His interest was now in fluid mechanics, the foundations of geometry and electricity. Characteristically enough, when the chair of physics became vacant in Bonn, the university tried to get Helmholtz back as professor of physics. Helmholtz declined the opportunity, but in his reply he made no secret of his lifelong ambition: "Physics was really from the outset the science which principally attracted my interests. I was mainly led to medicine and thereby to physiology by the force of external circumstances. What I have accomplished in physiology rests mainly upon a physical foundation."

Life in Berlin

The same letter also gives a clue to the inspiration that animated Helmholtz during the last two major assignments of his life. The first of these was the professorship of physics at the University of Berlin (1871-1888). Following the Franco-Prussian war of 1870-1871, Berlin emerged as the capital of the First Reich, and as a professor of physics at the University of Berlin Helmholtz could be most influential in promoting the cause of scientific instruction in German schools and universities. There was much to be done if, in a predominantly humanistic and classical educational system, science courses were to gain a rightful place. It was the professorship of physics at the University of Berlin which he finally found most promising to reward him "for taking the new work of a new post" upon himself. His request was immediately granted that a chair in physics be complemented by an Institute of Physics reserved exclusively for advanced research. Shortly after his arrival in Berlin, Helmholtz gave evidence of the high level in physical research which he had in mind. His memoir read in 1872 before the Berlin Academy of Sciences, "On the Theory of Electrodynamics," represented a remarkable effort to provide a generalized form of electrodynamics, of which even James Clerk Maxwell's theory was but a particular case. In 1873 he was invited to lecture in the United States, but he felt that acceptance would hinder his researches at his institute, which had begun to attract the most promising young physicists in Germany. The foremost among them was Heinrich Hertz, who developed under Helmholtz's guidance the interest to test experimentally a chief consequence of Maxwell's theory, the propagation of electromagnetic oscillations in space. A high point in Helmholtz's own reflections on the problems of electricity was his Faraday lecture in 1881, in which he emphasized the essentially atomic structure of electricity, a contention fully confirmed a few years later by J. J. Thomson's work with cathode rays.

During this period Helmholtz began to achieve the status of a chief adviser to the state in scientific matters. He played a prominent part in the establishment of the Imperial Physico-Technical Institute (Physikalisch-Technische Reichsanstalt), of which he became the first director in 1888. Although a chief aim of the new institute was to carry out high-precision measurements, Helmholtz wanted the new institute to serve pure science as well as technology. During his last years acclaim and honors poured in from every side. His seventieth birthday became an occasion for nationwide celebrations. He died on September 8, 1894, after months of struggle with paralysis. In no small measure, through his inspiration physics in Germany rose to unparalleled heights by the end of the 19th century, a position which remained unchallenged for another generation.

Further Reading

• Leo Koenigsberger's classic three-volume biography is available in English in a one-volume abridgment by Frances A. Welby as Hermann von Helmholtz (1906). It covers equally well the personal and scientific aspects of Helmholtz's career and discusses his influence on science in the second half of the 19th century. A specialized study of Helmholtz is Richard M. Warren and Roslyn P. Warren, Helmholtz on Perception, Its Physiology and Development (1968). A detailed biographical account of Helmholtz's life is in Bessie Zaban Jones, ed., The Golden Age of Science: Thirty Portraits of the Giants of 19th-Century Science by Their Scientific Contemporaries (1966). Good discussions of Helmholtz are also in Henry Ernst Sigerist, The Great Doctors: A Biographical History of Medicine (1933), and Ralph Hermon Major, A History of Medicine (vol. 2, 1954).