Féré’s experiments, he says, “agree perfectly, in showing that pleasurable sensations are accompanied by an increase of energy, and disagreeable ones by a diminution. The sensation of pleasure resolves itself, therefore, into a feeling of power, that of displeasure into a feeling of impotence. We have thus reached the material demonstration of the theoretic ideas propounded by Bain, Darwin, Spencer, Dumont, and others.”[61] I may remind the reader that Féré has applied his dynamometric researches to all kinds of sensations: to smell, to taste, to vision modified by glasses of the principal colours of the spectrum, red giving a dynamometric pressure of 42, which progressively descends to 20-17 for violet. For auditory sensations, he finds that the dynamic equivalent is in proportion to the amplitude and number of the vibrations. The same results are found to follow motion, the movements of the upper or lower limb exercising a dynamogenic influence on the corresponding member. Still further: an excitation _imperceptible to the consciousness_, a latent perception, determines a dynamic effect just as much as a conscious impression. Suggested hallucinations, agreeable or the reverse, are equally accompanied by an increase or diminution of pressure on the dynamometer. Footnote 61: Féré, _Sensation et Mouvement_, p. 64. This work is to be consulted for the details of the experiments about to be summarised. If the formula, “diminution of vital energy,” of which we have found that melancholia is an extreme instance, can give rise to no ambiguity, this is not the case with the opposite formula; and certain authors have, for this reason, thought—and rightly so—that it ought to be stated in precise terms. Pleasure corresponds to an increase of activity; but if we understand by this expression a large quantity of work done, the pleasure would result from a _diminution_ of the potential energy of the organism, as Léon Dumont has pointed out—_i.e._, from an impoverishment, which is contradicted by experience. We must therefore understand this increase of activity in the sense that the work done does not expend more energy than the nutritive actions; or, to employ Grant Allen’s formula, “Pleasure is the concomitant of the healthy action of any or all of the organs or members supplied with afferent cerebro-spinal nerves, to an extent not exceeding the ordinary powers of reparation possessed by the system.”[62] Footnote 62: _Physiological Æsthetics_, p. 21. This point has been well discussed by Lehmann (_op. cit._, pp. 205-208).