Page:Philosophical Review Volume 2.djvu/89

Rh and intensively they are (1) homonomous, (2) heteronomous. Sub-forms of both the latter types are the (in algebraic sense) positive and negative after-sensations. This use of 'positive' and 'negative' is certainly correct; but the words are already employed, in psychological optics, in two different senses, and it seems unnecessary to add a third. The temporal division is one which, at least in optics, it will be difficult to carry through.

Stimuli are classified as immediate (induction current), mediate (light- and sound-waves) and — both (mechanical, thermal, electrical). Here again the reader is, I think, rendered a little impatient by the novel terminology; so very little is won by it.

The doctrine of specific energies — which culminated in Donders' phrase, that by exchange of nerves we should hear the lightning and see the thunder — is discussed at length. The specific energy of a nerve is its capacity of definite reaction to any kind of stimulus. Dr. Dessoir weighs the facts alleged in all sense-departments, and finds them wanting. But, besides the lack of supporting facts, there is a series of theoretical objections to the doctrine; and the authors of these (Helmholtz, Wundt, Stumpf) are passed in review. As regards the seat of the determination of sensation-quality, a position is taken up which pretty closely resembles that of Wundt. The author concludes, with commendable carefulness, as follows: Every sense-apparatus has a specific excitation, every cortical area a specific function. Even this leaves the question open: How many of each are there?

Perceptions are in certain cases externalized (thunder-clap) and excentrically projected (contact-sensations). The key to these phenomena is given by introspection and dynamometry. Sensations are externalized when they are attended by insignificant (locally limited) muscular work; projected when they greatly (widely) strengthen the muscular force. There has been a tendency of late to apotheosize the muscle-sense; and I confess myself a sceptic. Has the attendant phenomenon