Page:Mind (New Series) Volume 8.djvu/103

 T. LIPPS, Eaumaesthetik u. geometrisch-optische Tduschungen. 89 former in the Zeitschrift fur Psych., etc., Bd. xvii., pp. 383 ff., and a reply by the latter in Bd. xviii., pp. 404 ff., which reaches me while revising this notice for the press. Some of the figures in the book are not convincing, and particularly in the elabo- rate discussion of divided distances in cc. xxix.-xxxvi., which Dr. Lipps tells us he had not originally intended to print. But this may depend on the particular selection of figures which as he says may not be equally convincing to every person. Just because of this if for no other reason one would think actual meas- urements such as those made by Messrs. Heymans, Thiery and others would be so useful. Dr. Lipps has deliberately in his experiments abstained from such measurements, but the reason as explained in his recent article (p. 425) that the force which the ideas of tendencies possess and their relative effects upon us cannot be measured does not seem very good, for it assumes the truth of the theory. But without questioning the completeness of verification by experience, one may still, on more general grounds, remain uncon- vinced that the theory gives the primary reason of the illusions while believing at the same time that it contains an important result. I will explain my difficulty. The general theory that the illusions are illusions of judgment would not of itself cause any hesitation, for by allowing that these judgments are so immediate as to appear part of the perception the author separates them from explicit judgments. But the fuller account which Dr. Lipps gives in his recent article of how the illusion arises, causes me much difficulty. It appears now that the primary seat of the illusion is not the illusory figure itself, but the ideal standard with which it is compared. Thus, in the Miiller-Lyer illusion, the line B with outward appendages seems bigger than the simple line A, because A when in idea juxtaposed to B seems smaller. In other words, we see B bigger because it really is seen bigger than our idea of A. I confess I had previously misunderstood the meaning of the process from the book. According to this then A shrinks in idea because its compression is not relieved as B's is. I find it hard to see how this applies to the case of deflection. But in any case I observe, (1) granted that the retinal image of B undergoes no alteration, there seems to be no greater essential difficulty in supposing the seen B to be modified in perception than to suppose the imagined A to be modified in a definite direction by the addition of a fresh idea, as it must be if the force interpretation holds ; (2) the content of this elaborate process still has to be taken up ' immediately ' into the perception of B. And (3) the account seems to agree ill with my subjective experience. If I first draw the line A and then add even on one side only the oblique appendages, I find the line, to use famous words, 'a-swellin' wisibly under my eyes '. I find it hard to believe that it is only my idea of the original A which has shrunk. At the same time I have in my eyes the very marked experience of movement.