So far we have dealt with the space of sight; but there is also a =space of touch=; and we have next to ask _whether the perception of distance can be couched in terms of touch alone_. Our appeal lies to those who are born blind. Observations show that, in their case, the direct perception of solidity, of plasticity, is rare and fleeting; it arises, perhaps, when they clasp a child to their breast, or when they have been trained by long manipulation to distinguish objects of various shapes and sizes; it does not form a permanent item of their mental furniture. The blind _behave as if_ they perceived distance; they avoid obstacles,—near obstacles by the pressure or temperature of the air reflected back upon their face, and remote obstacles by sounds; they can be taught geometry, and they measure objective distances by pacing; but the meaning of distance seems always to remain abstract, very much as the meaning of light and colour must remain abstract; there is no realising perception of distance. The brain mechanism which is ready to act at once at the behest of sight thus seems to be lacking where touch alone is present; even the perception of crude volume, of depth, has to be built up afresh by the individual. _The blind live mainly in a world of sounds_; touch is employed, as a rule, only for special and limited purposes, such as dressing, reading, handicraft; and their world is therefore not pervasively spatial, like the world of the seeing. Go back now, for a moment, to the objection raised on p. 124! We have, as a matter of fact, been led to the belief that =the meaning of depth is carried, in the last resort, by a brain-habit=. But how differently does this sentence read before and after the discussion! You have learned something of the difficulties of the study of perception; you see why it is necessary to look at perception historically, developmentally; you have been taken behind the obvious visual cues to the perception itself; you have seen how the kinæsthetic sensations and the binocular picture may be made the subject of experiment. Even the bare outline that the narrow compass of the present book allows should convince you that the objection was duly answered.