xl SCIENCE PROGRESS. 



difference. The interpretation of the law may detain us for a moment, as the question it 

 raises is still under discussion. Three interpretations are possible: (i) physiological, (2) 

 psychological, (3) psycho-physical. Wundt himself subscribes to the second, i.e., holds that 

 the disproportion between increment of stimulus and increment of sensation takes place on 

 psychological ground, between thesensificatory brain-charge, or internal stimulus, and the sensa- 

 tion. Delboeuf and others maintain that it is physiological, i.e., that the internal stimulus is 

 already a logarithmic function of the external objective stimulus, and that sensation increases in 

 direct proportion with it. Confirmation of this from the physiological side appears in the recent 

 observations of A. D. Waller [Brain, 1895, "Points relating to the Weber-Fechner Law, 

 Retina ; Muscle ; Nerve ") on muscle and retina, where, assuming the electrical signs of physico- 

 chemical action recorded by galvanometer photographs to represent the sensificatory changes 

 consequent on excitation of living matter, he finds that the internal change is always a loga- 

 rithmic function of the external stimulus ; the curves agree with the classical Weber-Fechner 

 curve. (Wundt gives an excellent summary of the arguments on either side, up to 1893, in the 

 fourth edition of his Grundzuge d. physiol. Psychologie, i. , 390, where the position is much more 

 clearly stated than in the work before us. ) 



In the absence of physiological evidence as to the relation of external to internal stimulus, 

 Wundt had interpreted the Weber-Fechner Law by the psychological Principle of Relativity, 

 finding "in the law of the logarithmic relation of sensation to stimulus a mathematical ex- 

 pression for a psychological process of universal validity ". And under this principle he marshals 

 all the remaining phenomena of sensation quantitatively apprehended, whether as regards 

 intensity, or degree of quality. In our sense experience, we never deal with an isolated magni- 

 tude — there is always a process of comparison between the sum of previous experience, i.e., 

 former sensations, and the individual sensation of the moment. This principle is applied to 

 the analysis of the several senses — sight and hearing being more fully treated. The physical 

 data in either case are lucidly presented, and will be valuable to the student who has not had 

 access to the general literature of the subject. The section on Contrast Phenomena opens up 

 the Helmholtz-Hering controversy, viz., whether contrast colours are due to subjective error of 

 judgment, or to direct physiological interference with one another. Wundt prefers to denote 

 the process underlying contrast as one of " associative contrast " ; " contrast " there must be, 

 on the principle of relativity, but "judgment" in his estimation belongs to a different category 

 (cf. recent discussion in Pfliiger s Archiv, xxxvii., xxxix. , xl., xli., etc.). 



How are Ideas built up from these sensational elements? Wundt next develops his 

 theory of sense-perception by spatial localisation, analyses the mental processes of association 

 in the several senses, and connects the separate elements of an association into a single idea. 



Every sensation, when of sufficient intensity, and not inhibited by opposing influences, is 

 followed by a muscular movement. Such movements we term reflex, and these reflexes 

 gradually become purposive and definite {e.g., light-stimuli at first excite merely irregular 

 movements. After a time these take on a definite form, and serve a definite purpose; the eye 

 moves in such a way as to bring the image of the stimulating light upon the yellow spot, — and 

 if the light moves to and fro within the field of vision, the eye follows it with a continuous 

 movement). The reflex thus controlled, and made to serve a definite purpose by the 

 sensations inseparable from the movement itself, muscle-sensations being here singled 

 out as illustrative. This brings us to another of the disputed questions in current 

 psychology. Are the muscle-sensations (sense of effort, muscular sense) peripheral only, con- 

 fined to muscle, skin, etc., or is there also central motor innervation? Here Wundt ex- 

 presses himself with no reservation : our sensations of movement are by no means dependent 

 solely upon the external or internal work performed by the muscles, but are influenced also 

 by the intensity of the impulse to movement proceeding from the central organ in which the 

 motor nerves originate. (This controversy, and the evidence deduced from the study of fatigue, 

 the after-effect, and presumably correspondent of, muscular action, are admirably summed up 

 in the Physiol. Psychologie, i., 426-434.) Leaving the question of the origin of sensations of 

 muscular effort, Wundt finds pathological support of his conclusion that our recognition of the 

 position of an object is normally based upon the sensation of effort attending the movement of 

 the sensory organ to the object. For when muscular movements have been disorganised by 

 paralysis, or other disturbances, there is often more or less complete re-adaptation to the new 

 physiological conditions. So that if the power of localisation may be gained afresh after a 

 transformation of the whole system of muscle-sensations we may assume that, when sense- 

 perception in general was in process of development, the establishment of a relation between 

 muscle-sensations, and the place from which an external stimulus operates, was a matter of 

 slow and Gradual evolution. 



