HELMHOLTZ, HERMANN LUDWIG FERDINAND VON German philosopher and man of science, was born on Aug. 31, 1821, at Potsdam, near Berlin. He lived in Berlin from 1842 to 1849, when he became professor of physiol ogy in Konigsberg. There he remained from 1849 to 1855, when he removed to the chair of physiology in Bonn. In 1858 he be came professor of physiology in Heidelberg, and in 1871 he occu pied the chair of physics in Berlin. To this professorship was added in 1887 the post of director of the physico-technical insti tute at Charlottenburg, near Berlin, and he held the two positions together until his death on Sept. 8, 1894.
His investigations occupied almost the whole field of science, from physiology to mechanics. In 1847 Helmholtz read to the Physical Society of Berlin a famous paper, (Yber die Erhaltung der Kraft (on the conservation of force), which became one of the epoch-making papers of the century; indeed, along with J. R. Mayer, J. P. Joule and W. Thomson (Lord Kelvin), he may be regarded as one of the founders of the law of the conservation of energy. In 1851, he invented the ophthalmoscope.
Helmholtz's contributions to physiological optics are of great importance. He investigated the optical constants of the eye, measured by his invention, the ophthalmometer, the radii of curva ture of the crystalline lens for near and far vision, explained the mechanism of accommodation by which the eye can focus within certain limits, discussed the phenomena of colour vision, and gave a luminous account of the movements of the eyeballs so as to secure single vision with two eyes. In particular he revived and gave new force to the theory of colour-vision associated with the name of Thomas Young, showing the three primary colours to be red, green and violet, and he applied the theory to the explana tion of colour-blindness. His great work on Physiological Optics (1856-66) is by far the most important book that has appeared on the physiology and physics of vision. Equally distinguished were his labours in physiological acoustics. He explained accu rately the mechanism of the bones of the ear, and he discussed the action of the cochlea on the principles of sympathetic vibration.
Perhaps his greatest contribution, however, was his attempt to account for our perception of quality of tone. He showed, both by analysis and by synthesis, that quality depends on the order, number and intensity of the overtones or harmonics that may, and usually do, enter into the structure of a musical tone. He also developed the theory of differential and of summational tones. His work on Sensations of Tone (1862) may well be termed the principia of physiological acoustics. He may also be said to be the founder of the fixed-pitch theory of vowel tones, according to which it is asserted that the pitch of a vowel depends on the resonance of the mouth, according to the form of the cavity while singing it, and this independently of the pitch of the note on which the vowel is sung. For the later years of his life his labours may be summed up under the following heads : (1) On the con servation of energy ; (2) on hydro-dynamics; (3) on electro dynamics and theories of electricity; (4) on meteorological physics; (5) on optics; and (6) on the abstract principles of dynamics. In all these fields of labour he made important con tributions to science, and showed himself equally great in all.
Helmholtz continued his study of the phenomena of electrical oscillations from 1869 to 1871, and in the latter year he announced that the velocity of the propagation of electromagnetic induction was greater than 314,00o metres per second. This work is interest ing in view of the fact that Hertz was a pupil of Helmholtz at this time and that later he demonstrated the existence of electro magnetic waves while studying a problem suggested to him by Helmholtz. This was followed by a series of papers on electro dynamics which were published from 187o onwards. Helmholtz started with a formula due to F. E. Neuman for the potential of two current elements, and investigated the terms which must be added to give a general expression which agreed with the phe nomena of closed circuits. There followed a controversy on the relative merits of the work of Helmholtz, Weber and Clerk Maxwell on this problem. In his paper on the "equations of motion of electricity in conductors at rest" (1874), Helmholtz applied his generalized formula to the propagation of electric and magnetic disturbances through bodies capable of electric or mag netic polarization. He contributed papers on the theory of the electrical double layer and on electrolysis. Towards the end of his life he wrote on the physical meaning of the Principle of Least Action and applied the principle to electrodynamics. Helm holtz also wrote and lectured on philosophical and aesthetic prob lems. His position was that of an empiricist, denying the doc trine of innate ideas and holding that all knowledge is founded on experience, hereditarily transmitted or acquired.
See Engelmann, Gedactnissrede auf Hermann von Helmholtz (1894) ; Konigsberger, Hermann von Helmholtz (1902; Eng. trans. by F. A. Welby, 1906) ; J. G. McKendrick, II. L. F. von Helmholtz (1899).