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Helmholtz, Hermann (Ludwig Ferdinand) von

physics physiology law medical

(1821–94) German physicist and physiologist: a discoverer of the law of conservation of energy; achieved major results in theories of electricity and magnetism, and on the physiology of vision and hearing.

Helmholtz must be the most versatile scientist of his century: he did first-class work in physics and physiology, both theoretical and experimental, and he was no mean mathematician. He has been claimed to be the last scholar whose work ranged over the sciences, philosophy and the arts. He believed that his diversity of interests was helpful to him in giving novel viewpoints in his researches.

As a child he was ‘delicate’ and often ill, but his parents did their best to amuse him. At school he found he did badly at memory work and rote-learning, but he enjoyed the logic of geometry and was delighted by physics. However, his father knew of no way of studying physics except as a medical student, for which he could get a university grant, provided he followed it by some service as an army surgeon. He must have done well as a medical student at Berlin, because after a short time as an army surgeon he became professor of physiology at Königsberg and later at Bonn and Heidelberg, and of physics at Berlin.

He was 26 and working in medicine when he published his pamphlet On the Conservation of Force in 1847; his ideas in it on the law of conservation of energy were much more precise than the ideas on the law given by J R Mayer (1814–78), and more wide-ranging than those of ; Helmholtz gave examples of the law in mechanics, heat, electricity and chemistry, with numerical values.

By 1850 he had moved to physiological optics and colour vision. An early success for him in this area was his invention of the ophthalmoscope for viewing the human retina. ( had invented a similar device 3 years earlier, but his medical friends failed to use it.) Helmholtz was more successful, and his device not only revolutionized the study of diseases of the eye but also was of value to physicians generally in giving the only direct view of the circulatory system. His study of the sense organs was continued in work on the ear and the mechanism of hearing, where he argued that the cochlea resonates for different frequencies and analyses complex sounds; and he developed a theory on the nature of harmony and musical sound (he was a skilful musician).

Earlier he had worked on the speed of nerve impulses and showed that this was of the order of a tenth of the speed of sound. He was a masterly experimenter, but in later life he gave up physiology for physics and became more interested in theoretical work, including on electromagnetic radiation. He encouraged his pupil and friend to work in this area, with important results: Hertz discovered radio waves in 1888. Other pupils included ; he had a great many pupils, his fame as a physicist compared with that of his friend in England, and in Germany he was said to be ‘the most illustrious man next to Bismarck and the old Emperor’.

Helmont, Jan Baptista van [next]

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