Wundt also attempted to apply his methods to the field of anthropology. His Volkerpsychologie was a monumental work. Language, religion and custom were the three aspects of primitive tribal life which he studied. To these three he applied the method of analysis, tracing the concrete forms to their origins in gesture and vocal sounds, imagery and habit. But Wundt's excursion into this field was less fruitful than it would have been if he had pos sessed a direct knowledge of anthropology.
Helmholtz.—The middle of the nineteenth century was a time when a variety of new movements began to influence the course of psychological thought. Before considering them it is necessary to mention the important contributions made by Her mann Helmholtz (1821-94). Helmholtz was professor of physiol ogy in the earlier part of his career and later (1871) became professor of physics. From his early days he was in contact with the idealistic philosophy of Germany and this remained throughout his life an influence which drew him toward the problems of per ception. As Helmholtz had a gift for making instruments, he was equipped in a most extraordinary way for the particular work which he undertook. His main contributions were contained in two great works. The work entitled Die Lehre von den Tot! empfindungen: Physiologisclte Grundlage fur die Theorie der Musik (1873), was a complete study of sound, both as regards its produc tion, the physiological mechanism of hearing and the character of perceptions. The other work, Handbuch der physiologischen Optik (1859), was equally comprehensive in its treatment of vision. In the analysis of sound Helmholtz explained the nature of overtones and the consequent "colour" or distinctive character which different instruments give to the same tone. Physics, physiology and psychology were brought together in the treat ment of this subject and the result remains one of the great exam ples of experimental analysis. In the field of vision Helmholtz was the first to appreciate the work done by Thomas Young. In 18o1 Young suggested that sensations of different colours depend on different frequencies of the vibrations and that there were three primary colours, red, yellow and blue. Experiments by Wollaston caused him to change this list, putting violet for blue.
The subject seems to have attracted little attention till Helmholtz took it up. A rival theory existed which goes back to the time of Aristotle and rests on the actual description of visual experiences. It had been revived by Goethe in his Farbenlehre and was dis tinguished by the fact that black and white were included in the list of colours. Goethe was interested in the work of J. E. Purkinje (1819) on subjective visual experiences, and also enter tained a peculiar dislike for the work of Newton. Purkinje is re membered as the observer of the "Purkinje phenomenon," which is the fact that as the intensity of light decreases the colours with short wave lengths (green, blue) are more visible than the others. The Young-Helmholtz theory was based on the physical analysis of light rather than the immediate experiences and therefore omitted black and white, which may be regarded as degrees of brightness. Since the days of Helmholtz the theories of hearing and vision have been developed in many different directions. In 1879 James expressed doubts about the finality of the explanation of hearing, and work done by Rutherford, Rayleigh, Ewald and others must be taken into consideration in judging its merits. In the case of vision new factors have been introduced. Hering (1874) proposed an explanation which involved the idea of chemical changes in the retina and four primary colours related to four substances in which the changes take place. The explana tion of after-images has been a complicating factor and the pos sibility that the rods and cones of the retina are the most impor tant factors gives the whole question another aspect. The work of Max Schultze (1866), Parinaud (La Vision, 1898) and von Kries (1894), together with the suggestions of Wundt, McDougall and the more radical views of Ladd-Franklin, would claim attention in a complete history of this subject. The original work of Helm holtz has been reissued in 3 vols. (Eng. trans. 1924) and this edition contains accounts of later work. But whatever changes may be necessitated by the progress of science, the achievements of Helmholtz will remain immensely significant for the historical development of psychology.