Ernst Heinrich Weber
(b. Wittenberg, Germany, 24 June 1795; d. Leipzig, Germany, 26 January 1878). anatomy, physiology, psychophysics.
Weber was the oldest of the three Weber brothers who throughout their lives were closely linked in their scientific activity. Their greatest achievement lay in applying the modern exact methods of mathematical physics to the study of the functioning of various systems of higher animals and man. The leader in this endeavor, Ernst very early drew the attention of the physicist Wilhelm Eduard to the problems of the mechanics of circulation and later influenced the orientation of Eduard Friedrich toward theoretical medicine, helping him to obtain a post at the Leipzig medical school and to remain there as his close collaborator. Eduard was subsequently stimulated and helped by Wilhelm in the study of muscle mechanics.
Their father, Michael Weber, was professor of theology at Wittenberg from 1789 and later — after the fall of the city, a Napoleonic stronghold, in 1814 and the evacuation of the university—at Halle. Ernst, the third of his thirteen children, had been greatly influenced by Ernst Chladni, who of ten visited the family and excited the boys’s interest in physics as a basis of all natural sciences Weber attended secondary school in Meissen, where he acquired an excellent knowledge of Latin. In 1811 he began his medical studies at Wittenberg, but the war soon forced him to leave for Leipzig. He received the M.D. in 1815 from the University of Wittenberg, then temporarily evacuated to Schmiedeberg, with a dissertation on comparative anatomy. He could not, however, remain there because the university had no facilities for his anatomical work and its status was uncertain. At Leipzig, Weber became assistant at the medical clinic run by J. C. Clarus, qualified as docent in 1817 with a work on the comparative anatomy of the nervus sympathicus, and the following year became extraordinary professor of comparative anatomy. In 1821 he was nominated to the chair of human anatomy, which in 1840 was joined with physiology. In 1865 he gave up physiology and supported the appointment of Carl Ludwig, who established an independent physiological insitute that attracted many foreign students. In 1871 Weber retired from the chair of anatomy.
Weber began with research in anatomy and discovered several important structures, some of which still bear his name—for instance, Weber’s ossicles, which form a chain of small bones on each side of the air bladder, and the ear atrium of some fishes (the Weberian apparatus). This work marked the beginning of a series of comparative embryological and paleontological studies that led to the discovery of the intermediary stages between the primitive structures of the splanchnocranium and the middle ear auditory ossicles of mammals—a brilliant step in demonstrating the links between isolated facts and continuity in the evolution of structure and function. Weber’s injection of the ducts of certain glands showed that their finest branches end blindly in the acini and have no direct communication with the surrounding small blood vessels, as had been supposed despite earlier finidings by Malpighi (1686). It proved definitively that the digestive juices are specific products of glands, formed from the material brought by the blood, not just separated from the blood plasma. This finding opened up a new field of physiological and chemical research Weber’s wide experience in both research and teaching enabled him to write a revised edition of G. F. Hildebrandt’s Handbuch der Anatomie. Its first part, Allgemeine Anatomie, entirely rewritten, became a valuable source of information because Weber carefully separated facts from theory and was not satisfied with merely describing structures; rather , he added what was known of their physical properties and chemical composition, as well as an appraisal of their significance. He was convinced that a knowledge of many conditions, not simply anatomical structure, was necessary for understanding the phenomena of life. The disadvantage of Weber’s revised edition was that it was completed before the advance brought about by the subsequent development of microsopic research and by the cell theory. He also revised J. C. Rosenmullerüller’s Handbuch der Anatomie (1840).
In 1821, assisted by his brother Wilhelm,—then only seventeen years old and preparing for his university entrance examination—Weber began a long physical study of the flow and the progress of waves in fluids, particularly in elastic tubes. In their Wellenlehre (1825) they formulated the basic laws of hydrodynamics and were the first to apply that branch of physics to the circulation of the blood. Ernst studied—at first with Wilhemm, a precocious genius—the mechanical properties of the arteries, describing them as the would a technical device, the effect of elasticity transforming the pulsatile movement of the blood in the large arteries in to a continuous flow into the small ones (18274). He also showed that the pulse is a wave in the arteries caused by the heart action and that its propagation—calculated from the delay of pulsation in a more distant artery—is much faster than the flow of the blood (1834) and that besides dilatation due to the pressure inside an elastic tube, blood vessels also change their diameter under the influence of nerves on the muscle wall (1831). He summarized his findings, the theory of waves in elastic tubes, and they laws of the movement of blood in the vessels in 1850.
Weber also demonstrated the resistance of the capillary bed, the importance of the blood volume, and its influence on the movement and distribution of the blood in the body. His work laid the base for the exact analysis of the movement of fluids in elastic tubes; and although the blood circulation has subsequently been subjected to a thorough research, Weber’s work, with some additions but no substantial changes, has remained its foundation.
Another great contribution to the physiology of the blood circulation was the startling discovery by Eduard and Ernst Weber that electrical stimulation of some parts of the brain or of the peripheral end of the vagus nerve slows the action of the heart and can even bring it to a standstill (1845). It was the first instance of nerve action causing inhibition of an autonomic activity, rather than exciting it. It became an important milestone in the evolution of physiology not only for its significance to the circulation but also because its discovery brought to light a hitherto unknown but essential kind of nerve action. The ensuing chain of investigations showed that inhibition is a common phenomenon in the central nervous system and that an adequate balance between excitation and inhibition is indispensable for its normal function.
About 1826 Weber began a long series of remarkable systematic studies of sensory functions, especially of the “lower senses,” which had hitherto been one of the most neglected areas of physiology. Physiologists had studied mainly the problems of vision and hearing, which seemed more interesting and promising. In his studies of other physiological problems Weber, a distinguished anatomist,usually followed function in close relation to structure. In this field, however, their was no anatomical basis because the skin, muscle, and visceral receptors were not discovered until later (Meissner, 1852; Krause, 1860). Nonetheless, his physical approach and attempts to determine quantitative relations of the stimulus to its effect, sensation, led to remarkable results despite the very simple methods used in his observations and experiments. An important feature of Weber’s examinations and comparisons was the use of the notion of threshold (although this term was not actually used). He was well aware of the significance of its exactly determined values for estimating and comparing the performance of the skin and other sensory organs. A markedly greater ability to distinguish two very slightly different weights when they are lifted from, rather than when placed on, the hand, is explained by the special muscle sense. Examining the sense of touch in great detail, especially the local sense and differential threshold with a compass, Weber determined the characteristics of sensations of pressure and of temperature—positive (warm) and negative (cold)—and stressed the role of adaptation and local differences. Thus he gave sensory physiology a new orientation toward quantitative approach and methods, bringing into prominence both facts (mostly his own findings) and problems. He not only systematically collected facts but also drew rational conduction about the physiological bases of the observed phenomena He assumed isolated conduction in nerve fibers and formulated theories of projection and objectification. The division of each nerve fiber into a small circle of nerve endings was the background of local discrimination and of differences in its limen as determined by a compass.
In using his physical considerations as the basis for examining the differential thresholds of skin and muscle sensations, Weber found that two sensations are just noticeably different as long as the ratio between the strengths in each pair of stimuli remains constant. For instance, the smallest appreciable difference between two weights or lengths (usually called “just noticeable difference” or “Weber fraction”) is a constant fraction of the weights themselves, approximately 1/30 (a just discriminable increment of intensity).
It was supposed that Weber’s law was generally valid, but many discussions and criticisms led to the more moderate view that for most modalities it applies only over a limited range of intensities. Nevertheless, Fechner, assuming that discriminable increments are equal units of sensation, derived the formula
S = K log I + C,
where intensity of sensation (S) is a linear function of the logarithm of intensity of the stimulus (I) and K and C are constants. Fechner’;s derivation has been criticized mainly because the stimulus—a physical factor—can easily be measured, while sensation—a subjective impression—cannot be expressed in physical terms. Quantitative comparisons became possible, however, when modern electrophysiological methods made it possible to follow the response of single sensory fibers—that is, the frequency of the messages from a single receptor. Over a certain range of intensities, it is indeed a linear function of the logarithm of the stimulus, as has been shown for the muscle spindle by B. H. Matthews and for the Limulus eye by H. K. Hartline and C. H. Graham. It cannot be stated whether it is fitting for the response of all forms of sense organs, but it seems that Fechner’s equation corresponds to a fundamental feature of sense organ behavior.
Weber was the first to draw the attention of physiologists to the skin as the seat of differentiated sense organs directed toward the external world, like other sensory organs, in contrast with the common sensibility (Gemeingefühl) directed toward our own body. His research had many philosophical implications and a great impact on further studies of skin senses and some general problems of sensation by physiologists and psychologists. He began a very fruitful period in the research on senses and is rightly considered as one of the founders of psychophysics. His work on tactile sensations has become classic.
I. Original Works. A partial list of Weber’;s writings was published in Almanach der K. Akademie der Wissenschaften in Wien, 2 (1852), 203–211; and, more recently, by P. M. Dawson (see below), 110–113. They include Anatomia comparata nervi sympathici (Leipzing, 1817); De aure et auditu hominis et animalium (Leipzing, 1820); Wellenlehre, auf Experimenten be gründet (Leipzing, 1825), written with Eduard Weber; Zusätze zur Lehre von Bau and Verrichtungen der Geschlechtsorgane (Leipzig, 1846); “Tastsinn and Gemeingefühl,” in R. Wagner, Handwörterbuch der Physiologie, III, pt. 2 (Brunswick, 1846, repr. separately 1851), also Ostwalds Klassiker der Exakten Wissenschaften no. 149 (Leipzing, 1905); Ueber die Anwendung der Wellenlehre auf die Lehre vom Kreislauf des Blutes und insbesondere auf die Pulslehre (Leipzing, 1850); and “Ueber den Raumsinn und die Empfindungskreise in der Haut und im Auge,” in Berichte über die Verhandlungen der K. Sächsischen Gesellschaft der Wissenschaften, Math.-phys. KI. (1852), 85–164, his chief paper on projection and the theory of circles.
Weber’s papers were published mainly in Deutsches Archiv für die Physiologie and Meckel’s Archiv für Anatomie and Physiologie (1820-1828), Müller’s Archiv für Anatomie, Physiologie und wissenschaftliche medizin (1835-1846), and Berichte über die Verhandlungen der K. Sächsichen Gesellschaft der Wissenschaften zu Leipzig (1846—1850). Dissertations written under his guindance were collected in Annotationes anatomicae et physiologicae (Programata collecta), 2 fascs. (Leip-zing, 1827-1834, 1836-1848), both reed. (1851) with fasc. 3, containing several of his own important papers.
II. Secondary Literature. An appreciation of Weber’s scientific achievement is C. Ludwig, Rede zum Gedächtniss an Ernst Heinrich Weber (Leipzig, 1878). A fairly detailed account in English is P. M. Dawson, “The Life and Work of Ernest Heinrich Weber,” in Phi Beta Pi Quarterly, 25 (1928), 86–116. With regard to the importance and impact of his work, papers on Weber are rather scarce. See also Ursula Bueck-Rich, Ernst Heinrich Weber (1795-1878) und der Anfang einer Physiologie der Hautsinne (inaug. diss., Zurich. 1970); H. E. Hoff, “The History of Vagal Inhibition,” in Bulletin of the History of Medicine, 8 (1940), 461–496; P. Hoffmann, “Ernst Heinrich Weber’s Annotationes anatomicae et physiologicae,” in Medizinische Klinik, 30 (1934), 1250. There are many references to Weber’s works on sensory physiology in E. G. Boring, A History of Experimental Psychology, 2nd ed. (New York, 1950); and Sensation and Perception in the History of Experimental Psychology New York, 1942).
Weber, Ernst Heinrich
Weber, Ernst Heinrich
Ernst Heinrich Weber (1795-1878), German anatomist and physiologist, is best known for his work in sensory physiology. Weber’s law, later generalized by Gustav Theodor Fechner and now known as the Weber-Fechner law, is recognized as one of the most significant of the early attempts to quantify the relation between stimulus and sensation and, consequently, as a forerunner of modern psychophysics.
Weber was born in Wittenberg, the eldest of three brothers who achieved distinction in the sciences. Most of his academic life was spent in Leipzig, where he was professor of anatomy from 1818, and of physiology from 1840.
Weber’s law asserts that a just-noticeable difference in the intensity of a sensation corresponds to an increase or decrease in the intensity of a stimulus by a constant fraction of its original intensity. What is called the Weber fraction or Weber ratio is thus ΔR/R, where R is the stimulus and ΔR is the minimal stimulus increment or decrement. It was thought at first that this fraction might prove to be constant throughout the intensity range of each modality, and that a specific constant could be found for each sense and even for such functions as spatial and temporal discrimination. Although Weber’s own experiments and those of his successors have failed to confirm the universality of the law, and Fechner’s reformulation has proved to be misleading, the experiments themselves represented a major contribution to sensory physiology. Weber’s most important publication, “Der Tastsinn und das Gemeingefuhl” (1846), was judged by E. B. Titchener (1901-1905) to be “the foundation stone of experimental psychology.”
Weber’s researches took him into virtually every field of sensory physiology, including vision, audition, and olfaction, as well as touch; into the physiology of blood circulation; and, in collaboration with his brothers, into related areas of physics. His most enduring interest, however, was in touch. “Der Tastsinn” reports exhaustive observations on the sensitivity to stimulation of the various parts of the body, internal as well as superficial, with speculations as to the neural basis of sensation and as to the ways in which simple sensations form the basis for the perception of external objects. Weber demonstrated the two-point threshold, measured it at various locations on his own body, and developed a neurological theory to account for it. There are, he found, “sensory circles” which represent small regions of common innervation, each of which has its own distinctive characteristics, and which provide the basis for tactual localization. In addition to the familiar modalities of sensation, Weber recognized the Gemeingefuhl (–common sensibility”—not to be confused with the sensus communis). By this he meant the complex of sensory experiences which we apprehend as states of ourselves rather than as properties of objects. The Gemeingefuhl has significant components of pressure, temperature, muscular sensation, and especially pain, but Weber considered it sufficiently distinctive to warrant its being classified separately. With the recent revival of interest in the body percept, Weber’s conception of the Gemeingefühl may acquire new significance.
Robert B. MacLeod
1820 De aure et auditu hominis et animalium. Leipzig: Fleischer.
1834 Annotationes anatomicae et physiologicae. Fasc. 1: De pulsu, resorptione, auditu et tactu. Leipzig: Koehler.
1846 Der Tastsinn und das Gemeingefühl. Volume 3, pages 481-588 in Rudolph Wagner, Handwbrterbuch der Physiologie. Brunswick (Germany): Vieweg.
Boring, Edwin G. (1929) 1950 A History of Experimental Psychology. 2d ed. New York: Appleton.
Titchener, Edward B. 1901-1905 Experimental Psychology: A Manual of Laboratory Practice. 2 vols. New York and London: Macmillan. → Volume 1: Qualitative Experiments. Volume 2: Quantitative Experiments, 2 parts.