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Beyond the sun and us there is darkness and so the air appears blue.
[
Footnote: Compare Vol. I, No. 301.]
8
69.
PERSPECTIVE.
It is possible to find means by which the eye shall not see remote
objects as much diminished as in natural perspective, which
diminishes them by reason of the convexity of the eye which
necessarily intersects, at its surface, the pyramid of every image
conveyed to the eye at a right angle on its spherical surface. But
by the method I here teach in the margin [9] these pyramids are
intersected at right angles close to the surface of the pupil. The
convex pupil of the eye can take in the whole of our hemisphere,
while this will show only a single star; but where many small stars
transmit their images to the surface of the pupil those stars are
extremely small; here only one star is seen but it will be large.
And so the moon will be seen larger and its spots of a more defined
form [Footnote 20 and fol.: Telescopes were not in use till a century
later. Compare No. 910 and page 136.]. You must place close to the
eye a glass filled with the water of which mention is made in number
4
of Book 113 "On natural substances" [Footnote 23: libro 113.
This is perhaps the number of a book in some library catalogue. But
09
7
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