THE PEKCEPTION OF SPACE. (IV.) 543 reproduces the idea of its associates in regular order, and its idea is similarly reproduced by any one of them with the order reversed. Out of the fusion of these two contrasted repro- ductions comes the form of space 1 Heaven knows how. The obvious objection is that mere serial order is a genus, and space-order a very peculiar species of that genus ; and that, if the terms of reversible series became by that fact coexistent terms in space, the musical scale, the degrees of warmth and cold, and all other ideally graded series ought to appear to us in the shape of extended corporeal aggre- gates, which they notoriously do not, though we may of course symbolise their order by a spatial scheme. W. Volk- mann, the Herbartian, takes the bull here by the horns, and says the musical scale is spatially extended, though he admits that its space does not belong to the real world. 2 I am unacquainted with any other Herbartian so bold. To Lotze we owe the much-used term ' Local-sign '. He insisted that space could not emigrate directly into the mind from without, but must be reconstructed by the soul ; and he seemed to think that the first reconstructions of it by the soul must be super-sensational. But why may not sensations themselves be the soul's original spatial recon- stractive acts, upon which, of course, other acts of further reconstruction may ensue ? Wundt has all his life devoted himself to the elaboration of a space-theory, of which the neatest and most final expression is to be found in his Logik (i. 457-60). He says : " In the eye, space-perception has certain constant peculiarities which prove that no single optical sensation by itself possesses the extensive form, but that everywhere in our perception of space heterogeneous feelings combine. If we simply suppose that luminous sensations per se feel extensive, our supposition is shattered by that influence of movement in vision, which is so clearly to be traced in many normal errors in the measurement of the field of view. If we assume on the other hand that the movements and their feelings are alone possessed of the extensive quality, we make an unjustified hypothesis, for the phenomena compel us, it is true, to accord an influence to movement, but give us no right to call the retinal sensations indifferent, for there are no visual ideas without retinal sensations. If then we wish rigorously to express the given facts, we can ascribe a spatial constitution only to combinations of retinal sensa- tions with those of movement." Thus Wundt, dividing theories into " nativistic " and " genetic," calls his own a genetic theory. To distinguish it l Psychol. als Wissenschaft, 113.
- Lehrbuch d. Psychol, 2te Auflage, Bd. ii. p. 66. Volkmann's 5th
Chapter contains a really precious collection of historical notices concern- ing space-perception-theories.
