Mem.: That I must first show the distance of the sun from the earth;
and, by means of a ray passing through a small hole into a dark
chamber, detect its real size; and besides this, by means of the
aqueous sphere calculate the size of the globe ...

Here it will be shown, that when the sun is in the meridian of our
hemisphere [Footnote 10: _Antipodi orientali cogli occidentali_. The
word _Antipodes_ does not here bear its literal sense, but--as we
may infer from the simultaneous reference to inhabitants of the
North and South-- is used as meaning men living at a distance of 90
degrees from the zenith of the rational horizon of each observer.],
the antipodes to the East and to the West, alike, and at the same
time, see the sun mirrored in their waters; and the same is equally
true of the arctic and antarctic poles, if indeed they are
inhabited.

How to prove that the earth is a planet (865-867).