Page:Mind (Old Series) Volume 12.djvu/220

 THE PERCEPTION OF SPACE. (ll.) 207 it is, a still longer intervening continuum must be sensible, with the feeling lodged at its end. But how, when the space between the brain and the point of projection has no nerves (which is the case with spaces beyond the body's limits), is it to be felt as an intervening continuum at all ? Simply by forming with the mass of sensitive tissue and surface beyond which it extends a new object for some other sense. Suppose the cane held in my right hand and its point pressed against the wall. I can, by paying attention, feel the whole solidity of my arm, the sensations in its joints as they move, and the pressure of the fingers upon the cane. But I also feel the wall where the cane touches it a yard away from my hand. Now this yard forms with the arm a common object, either for the exploring motion of my left hand (which may pass first down the right arm, and then down the cane it holds, by a combination of continuous movements) ; or for the skin of the body and leg, against the length of which both arm and cane may be applied. 1 This common objectivity of arm and cane gives the space of the projection as a whole, the first of those three factors which we saw extradition to involve. The next factor is the particular kind of sensation to be extradited. This can be nothing else than the feeling of the hardness or softness of the wall as it would affect our exploring hand. The similarity of the cane's actual pressure to this ideal pressure makes it seem as if the actual feeling of the hand had migrated into a new place. Most probing and palpating instruments are rigid, and communicate without alteration the feeling the hand itself would receive if it took the place of their farther extremity. Finally, the last factor is the precise distance within the total depth at which the sensation shall be lodged. In the case of the rigid stick this offers no difficulty. Easy experiences teach us that the cane's tip is the point from which diverge all the pressures it exerts upon our hand. Thither accordingly we send our image of the resisting thing we feel. When the cane is flexible, its own changes of shape become important, and we lodge the feeling of resistance partly in its tip, partly along its whole length. If we move the cane's tip through the air, instead of letting it touch the wall, all we need do is to multiply our hand-movement sensations by a certain factor corresponding to the cane's length. This gives us the distinct image of a large path traversed by the tip. This 1 Again I omit all mention of the eye, so as to account for the blind man.