Nor should we hastily pronounce this doctrine to be absurd. The
stars do appear to lie on the surface of a sphere, of which the
observer is at the centre; not only is this the aspect which the
skies present to the untechnical observer, but it is the aspect in
which the skies are presented to the most experienced astronomer of
modern days. No doubt he knows well that the stars are at the most
varied distances from him; he knows that certain stars are ten times,
or a hundred times, or a thousand times, as far as other stars.
Nevertheless, to his eye the stars appear on the surface of the
sphere, it is on that surface that his measurements of the relative
places of the stars are made; indeed, it may be said that almost all
the accurate observations in the observatory relate to the places of
the stars, not as they really are, but as they appear to be projected
on that celestial sphere whose conception we owe to the genius of
Ptolemy.
This great philosopher shows very ingeniously that the earth must be
at the centre of the sphere. He proves that, unless this were the
case, each star would not appear to move with the absolute uniformity
which does, as a matter of fact, characterise it. In all these
reasonings we cannot but have the most profound admiration for the
genius of Ptolemy, even though he had made an error so enormous in
the fundamental point of the stability of the earth.
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