IO SPACE AND GEOMETRY.
estimate with considerable exactness the thickness of a plate that we grasp in the dark with the forefinger and thumb of our hand; and we may do the same tolerably well also by touching the upper surface with the finger of one hand and the lower with the finger of the other. Haptic space, or the space of touch, has as little in common with metric space as has the space of vision. Like the latter, it also is anisotropic and non-homogeneous. The cardinal directions of the organism, "forwards and backwards," "upwards and downwards," "right and left/' are in both physiological spaces alike non-equivalent.
SENSE OF SPACE DEPENDENT ON BIOLOGICAL FUNCTION.
The fact that our sense of space is not developed at points where it can have no biological function, should not be a cause of special astonishment to us. What purpose could it serve to be informed concerning the location of internal organs over the functions of which we have no control ? Thus, our sense of space does not extend to any great distance into the interior of the nostrils. We cannot tell whether we perceive scents introduced by one of a pair of pipettes, at the right or at the left. (E. H. Weber, loc. tit., p. 126.) On the other hand, tactual sensibility; in the case of the ear, according to Weber, extends as far as the tympanum, and enables us to determine whether the louder of two sound-