So tremendous was the revolution in human knowledge implied by this
discovery, that we can well imagine how Ptolemy, dazzled as it were
by the fame which had so justly accrued to him, failed to make one
further step. Had he made that step, it would have emancipated the
human intellect from the bondage of fourteen centuries of servitude
to a wholly monstrous notion of this earth's importance in the scheme
of the heavens. The obvious fact that the sun, the moon, and the
stars rose day by day, moved across the sky in a glorious
never-ending procession, and duly set when their appointed courses
had been run, demanded some explanation. The circumstance that the
fixed stars preserved their mutual distances from year to year, and
from age to age, appeared to Ptolemy to prove that the sphere which
contained those stars, and on whose surface they were believed by him
to be fixed, revolved completely around the earth once every day. He
would thus account for all the phenomena of rising and setting
consistently with the supposition that our globe was stationary.
Probably this supposition must have appeared monstrous, even to
Ptolemy. He knew that the earth was a gigantic object, but, large as
it may have been, he knew that it was only a particle in comparison
with the celestial sphere, yet he apparently believed, and certainly
succeeded in persuading other men to believe, that the celestial
sphere did actually perform these movements.

Ptolemy was an excellent geometer. He knew that the rising and the
setting of the sun, the moon, and the myriad stars, could have been
accounted for in a different way. If the earth turned round
uniformly once a day while poised at the centre of the sphere of the
heavens, all the phenomena of rising and setting could be completely
explained. This is, indeed, obvious after a moment's reflection.
Consider yourself to be standing on the earth at the centre of the