But not alone the gradation of their quality arranges the local-sign feelings in a scale. Our _movements_ arrange them also in a time-scale. Whenever a stimulus passes from point _a_ of the skin or retina to point _f_, it awakens the local-sign feelings in the perfectly definite time-order _abcdef_. It cannot excite _f_ until _cde_ 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 _f_, without there clinging to it faint reverberations of the various time-orders of transition in which, throughout past experience, it has been aroused. To the local sign _a_ there clings the tinge or tone, the penumbra or fringe, of the transition _bcd_. To _f_, 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 _f_ 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 psychologists who set little store by local signs and great store by movements in explaining space-perception, would have a perfectly definite time-order, due to motion, by which to account for the definite order of positions that appears when sensitive spots are excited all at once. Without, however, the preliminary admission of the 'ultimate fact' that this collective excitement shall feel like a _line_ and nothing else, it can never be explained why the new order should needs be an order of _positions_, and not of merely ideal serial rank. We shall hereafter have any amount of opportunity to observe how thoroughgoing is the participation of motion in all our spatial measurements. Whether the local signs have their respective qualities evenly graduated or not, the feelings of transition must be set down as among the _veræ causæ_ in localization. But the gradation of the local signs is hardly to be doubted; so we may believe ourselves really to possess two sets of reasons for localizing any point we may happen to distinguish from out the midst of any line or any larger space. [168] M. Binet (Revue Philosophique, Sept. 1880, page 291) says we judge them locally different as soon as their sensations differ enough for us to distinguish them as qualitatively different when successively excited. This is not strictly true. Skin-sensations, different enough to be discriminated when _successive_, may still fuse locally if excited both at once.