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Volume  Volume1\Linear Perspective

Entry#  52. Experimental proof of the existence of the pyramid of sight (52-55).

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Perspective is a rational demonstration, confirmed by experience,

that all objects transmit their image to the eye by a pyramid of

lines.

By a pyramid of lines I understand those lines which start from the

edges of the surface of bodies, and converging from a distance, meet

in a single point; and this point, in the present instance, I will

show to be situated in the eye which is the universal judge of all

objects. By a point I mean that which cannot be divided into parts;

therefore this point, which is situated in the eye, being

indivisible, no body is seen by the eye, that is not larger than

this point. This being the case it is inevitable that the lines

which come from the object to the point must form a pyramid. And if

any man seeks to prove that the sense of sight does not reside in

this point, but rather in the black spot which is visible in the

middle of the pupil, I might reply to him that a small object could

never diminish at any distance, as it might be a grain of millet or

of oats or of some similar thing, and that object, if it were larger

than the said black  spot would never be seen as a whole; as may be

seen in the diagram below. Let _a_. be the seat of sight, _b e_ the

lines which reach the eye. Let _e d_ be the grains of millet within

these lines. You plainly see that these will never diminish by

distance, and that the body _m n_ could not be entirely covered by

it. Therefore you must confess that the eye contains within itself

one single indivisible point _a_, to which all the points converge

of the pyramid of lines starting from an object, as is shown below.

Let _a_. _b_. be the eye; in the centre of it is the point above

mentioned. If the line _e f_ is to enter as an image into so small

an opening in the eye, you must confess that the smaller object

cannot enter into what is smaller than itself unless it is

diminished, and by diminishing it must take the form of a pyramid.

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