e.g., in the case of light, an increase from a stimulus of intensity 1 to one of intensity 100, 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), in order to produce a sensation perceptibly greater we must add not 1 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 sensations form an arithmetical, those of the stimuli form a geometrical, series; the change in sensation is proportional to the relative change of the stimulus.  Sensations of tone show the same proportion (3:4) 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 intensity is just perceptible is 100:101).  In addition to the investigations on the threshold of difference there are others on the threshold of stimulation (the point at which a sensation becomes just perceptible), on attention, on methods of measurement, on errors, etc.  Moreover, Fechner does not fail to connect his psycho-physics, the presuppositions and results of which have recently been questioned in several quarters,[2] 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 material basis), nay, that they are the same essence, only seen from different sides.  Body is the (manifold) phenomenon for others, while spirit is the (unitary) self-phenomenon, in which, however, the inner aspect is the truer one.  That which appears to us as the external world of matter, is nothing but a universal consciousness which overlaps and influences our individual consciousness.  This is Spinozism idealistically interpreted.  In aesthetics Fechner shows himself an extreme representative of the principle of association.

[Footnote 1:  Fechner teaches:  The sensation increases and diminishes in proportion to the logarithm of the stimulus and of the psycho-physical nervous activity, the latter being directly proportional to the external stimulus.  Others, on the contrary, find a direct dependence between nervous activity and sensation, and a logarithmic proportion between the external stimulus and the nervous activity.]