the picture of it is inverted. This is illustrated by conceiving a blind
man who, holding in his hands two sticks that cross each other, doth with
them touch the extremities of an object, placed in a perpendicular
situation. It is certain this man will judge that to be the upper part of
the object which he touches with the stick held in the undermost hand,
and that to be the lower part of the object which he touches with the
stick in his uppermost hand. This is the common explication of the erect
appearance of objects, which is generally received and acquiesced in,
being (as Mr. Molyneux tells us [Diopt. par. 2. c. 7. P. 289.]) 'allowed
by all men as satisfactory'.

90. But this account to me does not seem in any degree true. Did I
perceive those impulses, decussations, and directions of the rays of
light in like manner as hath been set forth, then indeed it would not be
altogether void of probability. And there might be some pretence for the
comparison of the blind man and his cross sticks. But the case is far
otherwise. I know very well that I perceive no such thing. And of
consequence I cannot thereby make an estimate of the situation of
objects. I appeal to anyone's experience, whether he be conscious to
himself that he thinks on the intersection made by the radious [SIC]
pencils, or pursues the impulses they give in right lines, whenever he
perceives by sight the position of any object? To me it seems evident
that crossing and tracing of the rays is never thought on by children,
idiots, or in truth by any other, save only those who have applied
themselves to the study of optics. And for the mind to judge of the
situation of objects by those things without perceiving them, or to
perceive them without knowing it, is equally beyond my comprehension. 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: