All the minutest parts of the image intersect each other without
interfering with each other. To prove this let _r_ be one of the
sides of the hole, opposite to which let _s_ be the eye which sees
the lower end _o_ of the line _n o_. The other extremity cannot
transmit its image to the eye _s_ as it has to strike the end _r_
and it is the same with regard to _m_ at the middle of the line. The
case is the same with the upper extremity _n_ and the eye _u_. And
if the end _n_ is red the eye _u_ on that side of the holes will not
see the green colour of _o_, but only the red of _n_ according to
the 7th of this where it is said: Every form projects images from
itself by the shortest line, which necessarily is a straight line,
&c.
[Footnote: 13. This probably refers to the diagram given under No.
66.]
271.