Page:Mind (Old Series) Volume 12.djvu/534

THE PEBCEPTION OF SPACE. (IV.) 521 Helmholtz might have retorted (had not the retort been as fatal to the uniformity of his own principle as to Wundt's) that if the muscle-explanation, were true, it ought not to give rise to just the opposite illusions in the skin. We saw on p. 7 that subdivided spaces appear shorter than empty ones upon the skin. To the instances there given, add this : Divide a line on paper into equal halves, puncture the extremities, and make punctures all along one of the halves ; then, with the finger-tip on the opposite side of the paper, follow the line of punctures ; the empty half will seem much longer than the punctured half. This seems to bring things back to unanalysable laws, by reason of which our feeling of size is determined differently in the skin and in the retina, even when the objective conditions are the same. Hering's explanation of Zollner's figure is to be found in Hermann's Handb. d. Pliysiologie, iii. 1, p. 579. Lipps * gives another reason why lines cutting another line make the latter seem to bend away from them more than is really the case. If, he says, we draw (Fig. 14) the line pm upon the line ab, and follow the latter with our eye, we shall, on reaching the point m, tend for a moment to slip off ab and to follow mp, without distinctly realising that we are not still on the main line. This makes us feel as if the remainder mb of the main line were bent a little away from its original direction. The illusion is apparent in the shape of a seeming Fig. 14 a/- 771' approach of the ends b, b, of the two main lines. This to my mind would be a more satisfactory explanation of this class of illusions than any of those given by previous authors, were it not again for what happens in the skin. 1 Grundtatsachen des Seelenlebens, pp. 526-30. 34