etc., as great as the vibrational number of the given motion";[1] Ohm's analysis of the "periodic motions perceived by the human ear,"[2] and Wheatstone's stereoscope united to demonstrate that the psychical and the physical stand in close connection.
Finally, Young's color-theory, with its three primary colors—red, green and violet—paved the way for a passage from physical to physiological considerations; for it led to the hypothesis of "specific energies" in the nerve-fibers.
Ere we pass to the epoch-making transformations of last century, two movements, discredited in many ways it is true, yet of importance as preparatory, demand recognition. It may surprise us to find that they are phrenology and physiognomy. Gall and Spurzheim, both physicians, substituted for the descriptive and introspective faculty-psychology an anatomical scheme parallel essentially in result. They concluded that the faculties can be localized in definite portions of the brain, and that these, in turn, can be traced by reference to the surface formation of the skull. Phrenology created wide-spread interest early in the nineteenth century—witness George Combe (1828) in Edinburgh, who, it may be interesting to relate, received a call to the chair of philosophy in the University of Michigan, or Caldwell and Godman in this country. Through a long series of fluctuating fortunes their suggestions became effective finally as elements in a scientific physiological psychology when Broca (1861) located the brain-center of speech; and, ever since, thanks to the labors of Hughlings Jackson, Ferrier, Golz, Hitzig and many others, this has provided an important sphere of study to physiological psychology.
In similar fashion, the observations, opinions and speculations of Lavatar, in his "Physiognomische Fragmente" (1772), produced a furore; elicited Sir Charles Bell's famous "Essay on the Anatomy of Expression" (1806), with its theory of the relation between intellectual power and the facial angle; and, at last, attained complete scientific consecration in Darwin's masterly book, "Expressions of the Emotions in Man and Animals" (1872).[3] Thus positive error and misleading half-truth sometimes serve to state problems which, otherwise, might have failed to gain hearing. One may conclude fairly, then, that questions about the relation of body to mind were in the air throughout the entire course of the eighteenth century and, at its close, had begun to become clamant.
III
At this juncture philosophical activity assumed unprecedented proportions and left a solid deposit destined to a constructive influence
