THE PERCEPTION OF SPACE. (l.) 29

of the quality in question. It must divide the series into two parts, unless indeed it have a maximum or minimum of the quality, when it either begins or ends it. Such an ideal series of local-signs in the mind is, however, not yet identical with the feeling of a line in space. Touch a dozen points on the skin successively, and there seems no necessary reason why the notion of a definite line should emerge, even though we be strongly aware of a gradation of quality among the touches. We may of course symbolically arrange them in a line in our thought, but we can always distinguish between a line symbolically thought and a line directly felt. But note now the peculiarity of the nerve-processes of all these local-signs : though they may give no line when excited successively, when excited together they do give the actual sensation of a line in space. The sum of them is the neural process of that line ; the sum of their feelings is the feeling of that line ; and if we begin to single out particular feelings from the mass, and notice them by their rank in the scale, it is impossible to see how this rank can appear except as an actual fixed space-position sensibly felt as a bit of the total line. The scale itself appearing as a line, rank in it must appear as a definite part of the line. If the seven notes of an octave, when heard together, appeared to the sense of hearing as an outspread line of sound which it is needless to say they do not why then no one note could be discri- minated without being localised, according to its pitch, in the line, either as one of its extremities or as some part between. 1 1 But not alone the gradation of their quality arranges the local-sign feelings in a scale. Our movements arrange them also in a tfime-scale. Whenever a stimulus passes from point a of the skin or retina to point /, it awakens the local-sign feelings in the perfectly definite time-order abcdef. It cannot excite / until ode have been successively aroused. The feeling c sometimes is preceded by ab, sometimes followed by ba, according to the movement's direction ; the result of it all being that we never feel either a, c or /, without there clinging to it faint reverberations of the various time-orders of transition in which, throughout past experi- ence, it has been aroused. To the local-sign a there clings the tinge or tone, the penumbra or fringe, of the transition bed. To /, to c, there cling quite different tones. Once admit the principle that a feeling may be tinged by the reproductive consciousness of an habitual transition, even when the transition is not made, and it seems entirely natural to admit that, if the transition be habitually in the order abcdef, and if a, c and /be felt separately at all, a will be felt with an essential earliness, f with an essential lateness, and that c will fall between. Thus those psycholo- gists who set little store by local-signs and great store by movements in explaining space-perception, would have a perfectly definite time-order out of which to account for the definite order of positions that appears when sensitive spots are excited all at once. Without, however, the preliminary