same nerve always originates the same sensation. "Müller's law of the specific energies marks an advance of the greatest importance. . . and is, in a certain sense, the empirical exposition of the theoretical discussion of Kant on the nature of the intellectual process in the human mind."[1] Of course, Müller's views drew criticism,[2] but for us now the point is that they started activity which, bit by bit, built physiological psychology into a science.
Fortunate in his disciples—Brücke, Helmholtz, du Bois Reymond, Ludwig, Czermak, Donders (most teachers would forego all personal glory gladly to obtain such human material)—Müller enjoyed luck in the contemporary course of events. For a science more developed and surer of itself than physiology was about to join forces with the newer branch. Magnus, his Berlin colleague in physics, became the focal point of a movement to which Mitscherlich, Liebig, Ohm, F. Neumann, and the brothers Weber all contributed, the first and last notably. The sobering drill of hard, experimental fact gained its recognition here. Or, as we say in philosophy, the prose of Kant was added to the romance of Schelling. For physiological psychology the steadying influence came most by way of Ernst Heinrich Weber, of Leipzig (17951878). Weber, with his younger brothers, Wilhelm and Eduard, worked from the first along distinctively modern lines. The speculative thought, prevalent in his youth, seems to have passed over his head. Exact experimental methods came naturally, as it were, to him and to his brothers. From early life they employed mechanical and mathematical analyses in dealing with physical, physiological and psychological phenomena. Kunze, Fechner's nephew and biographer, goes so far as to say, "they were among the first to raise the study of nature among Germans to the eminence occupied by the philosophers and discoveries of the Latin races."[3] Their first joint research is typical of this. In the "Wellenslehre auf Experimente begründet" they add to Chladni's acoustic theory a parallel account for light, which leads substantially to the inference of an elastic ether. Prior to this Weber had published researches on the "Comparative Anatomy of the Sympathetic Nerves" (1817) and "On the Ear and Hearing in Men and Animals" (1827). His psychological contributions appeared in Wagner's "Handwörterbuch der Physiologie," Vol. III., part 2 (1831), and in the "Archiv für anatomische Physiologie" (1835). The classical paper, "Tastsinn und Gemeingefühl," was printed in the former and published separately in 1851. Weber here applied the method of least observable differences to sensations of pressure and to the measurement of lines by the eye. These experiments resulted in
