Helmholtz, Hermann Von

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Helmholtz, Hermann Von

From the perspective of posterity, Hermann Ludwig Ferdinand von Helmholtz (1821–1894) made his most significant contributions to the fields of sensory physiology and psychology. In particular, he laid the foundations for the experimental investigation of the sensory processes in audition and vision. His successes resulted from his unusual mathematical and mechanical abilities and from his skill in assembling, sifting, and logically interrelating large quantities of information.

Helmholtz was born in Potsdam, the eldest of five children. The atmosphere of his home, although not scientific, was intellectual. Helmholtz mentioned that he frequently listened to the philosophical discussions between his father, August, a distinguished teacher of languages and philosophy in the Gymnasium, and his colleagues. August Helmholtz was most important in guiding his son’s early education. He taught him Greek and Arabic, encouraged him to study poetry, art, and music, and trained him in the writing of expository essays. Even at an early age, however, Helmholtz was attracted more to physics and mathematics than to the humanities. Speaking of his youth, Helmholtz recalled, in 1891, that while the rest of his class in the Gymnasium read Cicero and Vergil, he himself would work out optical and geometrical problems under his desk.

Helmholtz represented a scientific ideal to his contemporaries. He was a man of remarkable talents, universal interests, and indefatigable energy. He published over 200 papers and books making fundamental contributions to the fields of anatomy, medicine, physics, physiology, and psychology. He invented scientific and medical instruments. A contemplative mind led him to consider the philosophic questions raised by developments in science. A sense of social responsibility led him to deplore the gulf separating those trained in the humanities and those trained in the sciences; this gulf he sought to bridge by delivering popular lectures explaining the developments of science to laymen.

For the social sciences, Helmholtz’ views on the methodology of science and the theory of knowledge are of most immediate relevance. The method of studying and interpreting biological and psychological phenomena was a crucial issue for the sci entists and philosophers of the nineteenth century. Helmholtz was convinced that the same scientific method is appropriate for the analysis of vital and mental phenomena as for the analysis of physical phenomena. However, he did not advocate a reductive materialism. For him, memory and learning are facts, the laws of which can be investigated by experimental procedures, even if they cannot be reduced to known physiological processes (Koenigsberger [1902-1903] 1906, p. 305). Rather, he emphasized that the basic method of all scientific inquiry is to discover facts through systematic experimentation and to go beyond these facts to general laws by analysis and abstraction. His lecture on Goethe (see Helmholtz [1853-1870] 1962, pp. 1-21) contains an interesting presentation of his views. After acknowledging Goethe’s insightful contributions on the morphology of the skull and the plant, Helmholtz brought up the matter of Goethe’s obstinate animosity to Newton’s analysis of color. The difference between them, Helmholtz suggested, lay in their attitudes toward the acquisition and conception of knowledge. Goethe, the artist, believed that direct confrontation with a phenomenon is sufficient to provide an understanding of it. He was “accustomed to look as it were, right into the subject, and to reproduce his intuition…. His success [was] proportionate to the vividness of the intuition” (ibid., p. 16). Helmholtz acknowledged that intuitive insight is the source of the creative idea for both the scientist and the artist but insisted that, for the scientist, careful observation and reflection are an initial step sufficient only to suggest a hypothesis. The establishment of scientific truth depends on experimental verification. Moreover, the artist is satisfied simply to describe and hesitates to abstract. “A step into the region of abstract conceptions which must be necessarily taken if we wish to penetrate into the causes of phenomena, scares the poet away” (ibid., p. 16). Goethe objected to Newton’s theory of color because it substitutes quantitative measurements of the color-mixing relationships for direct naturalistic observation of colors. Helmholtz correctly described how observational intuition led Goethe badly astray when he asserted that it is absurd for white light to be the result of a fusion of colored lights. On the other hand, Goethe’s appeal to experience did reveal important phenomenological facts (the distinction between warm and cold colors, the existence of a psychologically unique red, yellow, green, and blue, and the coupling of the colors red and green and yellow and blue) whose potential physiological significance Helmholtz apparently overlooked. Helmholtz’ intellectual attitude was that of the nineteenth-century physicist: it was the source of his acute and penetrating analyses, although it occasionally led him to miss the point.

Work in physics . At the age of 16, Helmholtz announced to his father that he wanted to study physics. His father, however, could not support the cost of an academic course and enrolled him in the Friedrich Wilhelm Medical Institute in Berlin. This institute gave free instruction on the condition that those enrolled later spend some years as surgeons in the Prussian army. In Berlin, Helmholtz came under the influence of Johannes Miiller, professor of physiology at the University of Berlin, and Miiller’s influence is apparent throughout his physiological research. In 1842, at 21, he received his doctorate for a thesis in anatomy confirming Miiller’s conjecture that the nerve fibers originate in the ganglion cells. Yet Helmholtz was to join Du Bois-Reymond, Brücke, and Virchow, all Müller’s students, in a pact to abolish Miiller’s notion that within the living organism there exists a separate vital force distinct from chemical and physical forces. These men realized that physiology needed to be securely established as a branch of chemistry and physics. Liebig had placed the question of vitalism within the domain of experimental science by transforming the philosophic question into the experimental problem of whether or not the mechanical energy and the heat produced by an organism result entirely from its own metabolism. Helmholtz realized that this problem is closely connected to the law of the conservation of energy and turned his attention to that law. Joule had already established the equivalence between mechanical work and heat, and Helmholtz sought to extend the principle of the conservation of energy to physiology. He began by investigating the relation between muscular activity and heat. For this purpose he devised the myograph, a device which records the twitching of a muscle, a thermal galvanometer sensitive to temperature changes of .001° centigrade, and a means by which a muscle can be stimulated by electric shocks of short duration. He found that a single muscle contraction can give rise to an increase in temperature of from .001° centigrade to .005° centigrade, showing that the chemical processes in muscle contraction produce heat. Helmholtz then turned to determining the equivalence between the heat produced by an animal and the caloric value of the food taken in. He calculated the amounts of heat given off in various ways and the efficiency of an animal’s metabolism and concluded that the total heat given off corresponds to the heat generated by the oxidation of the food consumed. Unknown to Helmholtz, the extension of the law of the conservation of energy from inanimate to animate phenomena had already been suggested by Robert Mayer. Helmholtz next set himself the task of showing the universal application of the conservation of energy principle by theoretically deriving it from more fundamental physical principles. He showed that if all matter consists of particles, and if these interact according to forces acting along the lines joining the particles, and if all forms of energy depend upon the motion and position of the particles, then the conservation of energy must hold. These results he announced in a lecture he gave (at the age of 26) to the Physical Society of Berlin on July 23, 1847.

Work in physiology . Helmholtz’ scientific ability now became generally recognized, and with the aid of Alexander von Humboldt, president of the Academy of Sciences in Berlin, he was released from further military service. After a year as a lecturer in anatomy at the Academy of Arts in Berlin, Helmholtz became professor of physiology at Königsberg. He remained in Königsberg from 1849 to 1855.

Nerve impulses. The first important physiological problem to concern Helmholtz after his move to Königsberg was the rate of nerve transmission. Müller had stated that the speed of the nerve impulse is comparable to the speed of light and unmeasurable. Du Bois-Reymond’s theory of the polarization of molecules in nervous tissue suggested to Helmholtz that the nerve impulse, although electrical in nature, is not simply an electric current. Helmholtz stimulated nerves near and far from a muscle and measured the time it takes for the muscle to contract. The difference in time divided by the distance between the two points showed that the rate of the neural impulse in the motor nerve of a frog is about 27 meters per second. Helmholtz also devised the reaction time experiment to measure the speed of nerve transmission in humans. An electric shock was given to a point on the skin and the observer was directed to move his hand as quickly as he could. Although variable, the results showed that the rate of transmission of the impulse is between 50 and 60 meters per second. The novelty of these studies provoked opposition from physiologists. In fact, both Muller and von Humboldt refused at first to believe the results and it was only through the continued arguments of Du Bois-Reymond that they were convinced of the correctness of Helmholtz’ work.

Optics and visual perception. In 1851 Helmholtz invented the ophthalmoscope, the most celebrated of his inventions. He suggested that the blackness of the pupil results from the fact that the head of an observer looking at the eye of a person blocks the rays of light that would illuminate the retina. The ophthalmoscope is a device that illuminates the retina through the pupil, rendering it visible. In its modern form, constructed by H. Reute in 1852 (M’Kendrick 1899, p. 78), the ophthalmo scope enables one to look at the retina through a small opening in a reflecting plate. In 1852 Helmholtz invented the ophthalmometer, a device for measuring the radii of curvature of the anterior and posterior surfaces of the cornea and the lens. At this time Helmholtz turned to the problem of accommodation. A Dutch physiologist, Cramer, had shown that accommodation consists in an increasing curvature of the lens when the eye changes from a far point to a near point. Helmholtz, unacquainted with the work of Cramer, arrived independently at the same conclusion. Helmholtz’ new contribution to the theory of accommodation was his hypothesis about the way in which the curvature of the lens is altered. Using his anatomical knowledge, he suggested that when the fibers of the ciliary muscles contract, the tension of the lens capsule is reduced, and the lens’s own elasticity causes the anterior surface of the lens to bulge forward.

From 1851 to 1856 Helmholtz was mainly engaged in research in physiological optics. The result of this work, together with a survey of the germane literature, is presented in his monumental three-volume handbook on physiological optics (Helmholtz 1867). The handbook demonstrates Helmholtz’ mastery of the physical, mathematical, and physiological problems involved in vision and visual perception. The worth of the handbook is attested to by its continued scientific pertinence a hundred years later. Volume 1 describes the anatomy and optical properties of the eye. Volume 2 deals with problems of visual sensation. In 1852 Helmholtz undertook to test the laws of color mixture. Newton had failed to distinguish between the mixture of colored lights and of colored pigments. Thomas Young, in his famous paper of 1801, had suggested (in analogy to the mixture of pigments) that red, yellow, and blue are the three primaries from which all colors can be derived by suitable mixtures. But to his surprise, Helmholtz discovered that the combination of yellow and blue lights produces not green, as was supposed, but white. Helmholtz was the first to differentiate clearly between the addition of lights, which produces a color because of the superposition of excitations of different wave lengths stimulating the eye, and the addition of pigments, which produces a color that is a result of the wave lengths reflected by both pigments. Yellow and blue pigments when mixed give green because neither pigment absorbs green light. After clearing up the confusion between light mixtures and pigment mixtures, Helmholtz proceeded to develop a comprehensive theory of color vision. He based his theory on the extension of Müller’s law of specific nervous energies to the sense organs and on the assumption that the facts of color matching accurately mirror underlying physiological processes. Just as the difference between the sensations of light and sound depends on the kind of nerve fibers stimulated, so the sensation of color depends on the kind of nerve fiber excited in the eye. The data on color mixture, moreover, indicate that all hues except the most saturated can be obtained by suitable combinations of three primaries: red, green, and violet. Helmholtz made explicit that part of Young’s theory which dealt with nerve activity, by postulating that the nerve fibers must respond in varying degrees to all wave lengths. Hue depends on the relative frequencies of the impulses set up in the three types of fibers, brightness on the total excitation of the fibers, and saturation on the amount of white produced by fusion. He also extended the theory to account for color blindness, negative afterimages, and successive contrasts. The Young—Helmholtz theory of color vision is still widely accepted, although certain facts of color blindness and color thresholds pose difficulties for it.

Volume 3 deals with problems of space perception and object perception. Central to Helmholtz’ theory of space and object perception is his doctrine of unconscious inference. Helmholtz argued in his inaugural lecture at Köonigsberg in 1852 that the law of specific nerve energies implies that sensations serve only as the signs of external objects. That is, sensations tell us as much about the real nature of external phenomena as the name of a man tells us about the man. Accordingly, perceptual experience involves a construction on the part of the observer. A problem of great concern for Helmholtz was to determine what in the nature of perceptual experience is innate and what is derived from experience. He asserted that what in the perceptual image can be modified by experience must itself be considered a product of experience ([1867] 1924-1925, vol. 3, p. 13). Applying this criterion, he concluded that the only innate properties are the intensity and the quality of a sensation. Thus, conscious experience consists initially of a mass of sight, sound, taste, and smell sensations, each differentiated only with respect to quality and intensity. How does one come to experience coherent objects ordered in space and time? The answer lies in the distinction between sensation and perception. Perception involves a two-stage process: (1) sensation and (2) unconscious inference. Sensations are the immediate products of stimulating sense organs and associated neural systems. Unconscious inference is a central reasoning-like process which utilizes the information provided by sensation to infer the properties of external objects and events. Thus, perception is not simply an aggregate of sensations. Perception goes beyond the sensations provided by the receptor organs and entails a judgment about the environment. The unconscious judgments in perception are automatic and irresistible. The knowledge gained in perception, based on sensations and the memory of sensations, is a knowledge of acquaintance (kennen). In contrast, the conscious judgments in thought are flexible and deliberate, and the knowledge gained, based on concepts, is a knowledge of awareness (wissen). For Helmholtz these differences, however, are only superficial. Both the unconscious judgments in perception and the conscious judgments in thought involve the same mental operations and have the same logical status ([1853-1870] 1962, pp. 178-181). The view that perception inherently involves a judgment has played an important role in psychological theory.

Acoustics. In 1855 Helmholtz was appointed professor of anatomy and physiology at Bonn, where he remained until 1858, when he became professor of physiology at Heidelberg. While still immersed in the preparation of his Physiological Optics Helmholtz had decided to write a similar work on acoustics. In 1856 he reported the discovery of summation tones. These tones, whose frequencies are the sum of two input frequencies, are generated because of the nonlinear response of structures in the external ear. In 1857 Helmholtz formulated his well-known theory of vowel quality. Differences between vowel sounds arise because the mouth cavity when shaped for different vowels serves as an adjustable resonator which differentially strengthens the harmonic components of the fundamental voice tone. Papers quickly followed on sound production, tone quality, harmony, and the musical scales. In 1862 Helmholtz’ classic work, On the Sensations of Tone, appeared. This book brings together his many experimental and historical studies in acoustics and music theory. The aim of the work is to provide connecting links between the fields of physical acoustics, physiological acoustics, and music. The most famous of Helmholtz’ contributions to audition is his theory of pitch perception. Applying the law of specific nerve energies to the ear, Helmholtz suggested that there exist specific fibers in the inner ear that respond by resonance to the different frequencies. Each fiber excites its own nerve so that the neural impulses transmitted to the brain correspond to the component frequencies of a sound wave. Thus, the resonance theory of pitch provides an explanation of Ohm’s law which asserts that it is possible to hear the simple harmonic components into which a complex sound may be analyzed. Although such a simple resonance theory is no longer ten able, experiments have demonstrated that a locus of maximum vibration which changes with sound frequency does occur on the basilar membrane in the way Helmholtz suggested. Helmholtz extended his theory of pitch to providean account of timbre, dissonance, consonance, and melody. Timbre de pends upon the relative intensities of the harmonics present, dissonance on the beats generated when two frequencies affect overlapping segments of the basilar membrane, consonance and melody on the identity of harmonics produced by simultaneous tones or a succession of tones. Helmholtz’ views on the musical relationships have been much discussed and criticized but are still relevant today.

Aesthetics . Since his early student days, Helmholtz had been concerned with problems of aesthetic significance. Although science and art differ in their methods, he believed them to be intimately connected because both seek to acquaint us with reality (Koenigsberger [1902-1903] 1906, p. 172). While the scientist expresses truth by means of abstract concepts, the artist expresses truth by means of images. Since art has a cognitive function, the articulation of meanings that cannot be conveyed by words, it must conform to the laws governing human intelligence. The function of the scientist is not, however, to instruct the artist. This is essentially impossible since neither the artist nor the observer is consciously aware of the laws on whose fulfillment beauty depends ([1862] 1954, p. 366). Rather, the function of the scientist is to provide the artist with the information which may aid him in his artistic invention. The artist can succeed in his work only when he is aware of the subtle relations present within a phenomenon and of their effects upon an observer (Koenigsberger [1902-1903] 1906, p. 106). In a lecture on anatomy and sculpture delivered in 1848, Helmholtz considered the methods and benefits of teaching anatomy to artists (ibid., pp. 51-57), and in a lecture on optics and painting, Helmholtz ([1853-1870] 1962, pp. 250-286) discussed the complex problems faced by the painter who seeks to produce an accurate representation of the forms, sizes, distances, and illuminations of objects in a scene. To cope successfully with these problems, the artist must translate rather than copy nature, taking into careful consideration the operation of the sensory system. For Helmholtz the relations between art and science are particularly clear and striking in music. Musical composition depends more on the immediate sensations than is the case with the other arts, like sculpture, in which the object represented has a much greater importance ([1862] 1954, p. 3). Part 3 of the Sensations of Tone deals with the agreeableness of different chords, the formation of scales, and the elementary rules of musical composition. Helmholtz cautioned that the history of music shows that the construction of scales and musical composition is by no means determined by the properties of the ear but depends on artistic invention and aesthetic principles which change with time (ibid., p. 235).

Epistemology . Helmholtz’ interest in sensory physiology naturally led him to the problems of epistemology. Following the English tradition, he appealed to psychology for an understanding of epistemology. He argued that a knowledge of the sensory mechanisms is necessary for determining the status of objects. In a letter to Carl Ludwig, in 1855, Helmholtz wrote, “I believe that philosophy will only be reinstated when it turns with zeal and energy to the investigation of epistemological processes and of scientific methods…. Most essential of all in this critical investigation is the exact knowledge of the processes of sense-perception” (Koenigsberger [1902-1903] 1906, p. 139). Kant had established 12 categories of a priori concepts. These represented the operation of inherent characteristics of the mind, which condition experience and do not arise from experience. Examples of a priori concepts are space and time, the geometrical axioms, and the law of causality. Helmholtz first questioned the correctness of Kant’s position concerning the inherent nature of space. He concluded that the experience of an ordered space is not innate but is derived from movements of the eye and body ([1853-1870] 1962, p. 156). Helmholtz’ empirical theory of perception led him to an empirical theory of cognition. In 1866 he turned to the epistemology of mathematics. He undertook to show that the geometric axioms are also the products of experience and that they depend upon the notion of congruence, which is based upon mechanical movements and is itself acquired through experience. Thus, the axioms of geometry are not innate but have their origin in an individual’s experience with objects and with the space in which he lives. To show that the axioms of Euclidean geometry are not examples of a priori intuitions, Helmholtz independently developed Riemannian non-Euclidean geometry. In 1888 Helmholtz tried to show that the axioms of arithmetic can also be derived from experience. He accepted only the law of causality as a priori and transcendental and asserted that all thought presupposes the law of causation, which is therefore not derivable from experience (Koenigsberger [1902-1903] 1906, p. 142). For example, the law of causation underlies the unconscious inference by which we pass from sensation to perception, since this process assumes the existence of external objects that cause our sensations. Whether the mechanism of unconscious inference is itself innate or is derived from experience, Helmholtz left as an open question (ibid., p. 110).

In 1871 Helmholtz became professor of physics in Berlin. He spent the last years of his life primarily in physical research. He was concerned with experiments in electrodynamics, physical optics, meteorological physics, and the physical significance of the principle of least action. Helmholtz also encouraged Heinrich Hertz, perhaps his most famous student, who verified Maxwell’s theory by producing electromagnetic waves. In 1887 the Physical-Technical Institute was founded in Berlin, with Helmholtz as director. In 1893 he visited the Chicago World’s Columbian Exposition and toured the United States and Canada. While returning home, he fell down the ship’s stairs and suffered a concussion and severe loss of blood. He recovered, but those who saw him reported that he tired easily and found it difficult to work. In July 1894 he suffered a cerebral hemorrhage and died in September of that year.

Jacob Beck

[See alsoHearing; Perception, article onDepth perception; Psychophysics; Vision, especially the article onColor Vision and Color Blindness.]

WORKS BY HELMHOLTZ

(1853–1870) 1962 Popular Scientific Lectures. New York: Dover. ? First published in German.

(1862) 1954 On the Sensations of Tone as a Physiological Basis for the Theory of Music, New York: Dover. ? First published as Die Lehre von den Tonempfindungen als physiologische Grundlage fiir die Theorie der Musih.

(1867) 1924-1925 Helmholtz’s Treatise on Physiological Optics. Edited by James P. C. Southall. 3 vols. New York: The Optical Society of America. ? Translated from the third German edition.