Add
to this that the explaining the manner of vision by the example of cross
sticks and hunting for the object along the axes of the radious pencils,
doth suppose the proper objects of sight to be perceived at a distance
from us, contrary to what hath been demonstrated.
91. It remains, therefore, that we look for some other explication of
this difficulty: and I believe it not impossible to find one, provided we
examine it to the bottom, and carefully distinguish between the ideas of
sight and touch; which cannot be too oft inculcated in treating of
vision: but more especially throughout the consideration of this affair
we ought to carry that distinction in our thoughts: for that from want of
a right understanding thereof the difficulty of explaining erect vision
seems chiefly to arise.
92. In order to disentangle our minds from whatever prejudices we may
entertain with relation to the subject in hand, nothing seems more
apposite than the taking into our thoughts the case of one born blind,
and afterwards, when grown up, made to see. And though, perhaps, it may
not be an easy task to divest ourselves entirely of the experience
received from sight, so as to be able to put our thoughts exactly in the
posture of such a one's, we must, nevertheless, as far as possible,
endeavour to frame true conceptions of what might reasonably be supposed
to pass in his mind.
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