any movement of translation as it is devoid of rotation. Thus it was
that Ptolemy convinced himself that the stability of the earth, as it
appeared to the ordinary senses, had a rational philosophical
foundation.

Not unfrequently it is the lot of the philosophers to contend against
the doctrines of the vulgar, but when it happens, as in the case of
Ptolemy's researches, that the doctrines of the vulgar are
corroborated by philosophical investigation which bear the stamp of
the highest authority, it is not to be wondered at that such
doctrines should be deemed well-nigh impregnable. In this way we
may, perhaps, account for the remarkable fact that the theories of
Ptolemy held unchallenged sway over the human intellect for the vast
period already mentioned.

Up to the present we have been speaking only of those primary motions
of the heavens, by which the whole sphere appeared to revolve once
every twenty-four hours. We have now to discuss the remarkable
theories by which Ptolemy endeavoured to account for the monthly
movement of the moon, for the annual movement of the sun, and for the
periodic movements of the planets which had gained for them the
titles of the wandering stars.

Possessed with the idea that these movements must be circular, or
must be capable, directly or indirectly, of being explained by
circular movements, it seemed obvious to Ptolemy, as indeed it had
done to previous astronomers, that the track of the moon through the
stars was a circle of which the earth is the centre. A similar
movement with a yearly period must also be attributed to the sun, for
the changes in the positions of the constellations in accordance with