6o4 NEW SYSTEMS. SO that, e. g., in the case of light, an increase from a stimu* Ills of intensity i to one of intensity lOO, gives just the same increase in the intensity of the sensation as an increase from a stimulus of intensity 2 (or 3) to a stimulus of 200 (or 300) — is much more generally valid than its discoverer supposed ; it holds good for all the senses. In the case of the pressure sense of the skin, with an original weight of 15 grams (laid upon the hand when at rest and supported), ill order to produce a sensation perceptibly greater we must add not i gram, but 5, and with an original weight of 30 grams, not 5, but 10. Equal additions to the weights are not enough to produce a sensation of pressure whose intensity shall render it capable of being distinguished with certainty, but the greater the original weights the larger the increments must be; while the intensities of the sensa- tions form an arithmetical, those of the stimuli form a geo- metrical, series ; the change in sensation is proportional to the relative change of the stimulus. Sensations of tone show the same proportion (3 14) as those of pressure; the sensibility of the muscle sense is finer (when weights are raised the proportion is 15 : 16), as also that of vision (the relative brightness of two lights whose difference of inten- sity is just perceptible is 100 : loi). In addition to the investigations on the threshold of difference there are others on the threshold of stimulation (the point at which a sen- sation becomes just perceptible), on attention, on methods of measurement, on errors, etc. Moreover, Fechner does not fail to connect his psycho-physics, the presupposi- tions and results of which have recently been questioned in several quarters,* with his metaphysical conclusions. Both are pervaded by the fundamental view that body and spirit belong together (consequently that everything is endowed with a soul, and that nothing is without a contrary, find a direct dependence between nervous activity and sensation, and a logarithmic proportion between the external stimulus and the nervous activity.
- So by Helmholtz ; Hering {Feckners psychophysisches Gesetz, 1875) ; P.
Langer {Grundlagen der Psychophysik, 1876) ; G. E. MUller in G5ttingen (^Ztir Grundlegung der Psychophysik, 1878) ; F. A. MuUer {Das Axiom der Psycho- physik, 1882) ; A. Elsas {Ueber die Psychophysik, 1886) ; O. Liebmann {Aphor. ismen zur Psychologic, Zeitschrift fiir Philosophic, vol. ci. — Wundt has pub-
