ed and built up
out of the data of action is also well illustrated in the case of the
blind, and to this also M. Villey devotes an interesting chapter under
the title _La conquete des representations spatiales_.

This is effected in their case by the high development of what we must
call active touch. Just as we distinguish between hearing and listening,
between seeing and looking, so must we distinguish between touching and
_palpation_.

Mere passive touch gives a certain amount of information, but
comparatively little. It is necessary to _explore_; that is what is done
in active touch--palpation--of different degrees.

The sensitiveness of the skin varies at different places from the tongue
downwards. Palpation by the fingers marks a further stage. The blind
also, we are told, largely employ the feet in walking as a source of
locative data.

To the concepts reached by such palpation with the hand, M. Villey gives
the name of Manual Space. In this connection he thinks it necessary to
distinguish between synthetic touch and analytic touch--the former
resulting from the simultaneous application of different parts of the
hand on the surface of a body, the latter that which we owe to the
movements of our fingers when having only one point of contact with the
object the fingers follow its contour. Various examples of the delicacy
of the information thus obtainable are given. Following two straight
lines with the thumb and index respectively, a blind man can acquire by
practice a sensibility so complete as to enable him to detect the
slightest divergence from parallelism.

The analysis passes on from the data of Space manual to those of Space
brachial; then to the information derived from walking and other
movements of the lower limbs, and then to the co-ordination of the
information derived from the sensations of hearing, which is necessarily
very important to the blind.

The conclusion of the whole matter is that our principal spatial ideas
are common alike to the blind and the vident. Both can be taught and are
taught the same geometry. Both understand one another in the
description of spatial conditions. The common element cannot possibly be
supplied either by the data of visual sensation which the blind do not
possess, or by the data of passive tactual sensation which the vident
hardly ever employ. _Une etendue commune se retrouverait a la fois dans
les donnees de la vue et dans celles du toucher._ The common ele