considerations Copernicus deduced the important fact that the stars
and the other celestial bodies must all be vast objects. He was thus
enabled to put the question in such a form that it could hardly
receive any answer but the correct one. Which is it more rational to
suppose, that the earth should turn round on its axis once in
twenty-four hours, or that thousands of mighty stars should circle
round the earth in the same time, many of them having to describe
circles many thousands of times greater in circumference than the
circuit of the earth at the equator? The obvious answer pressed upon
Copernicus with so much force that he was compelled to reject
Ptolemy's theory of the stationary earth, and to attribute the
diurnal rotation of the heavens to the revolution of the earth on its
axis.

Once this tremendous step had been taken, the great difficulties
which beset the monstrous conception of the celestial sphere
vanished, for the stars need no longer be regarded as situated at
equal distances from the earth. Copernicus saw that they might lie
at the most varied degrees of remoteness, some being hundreds or
thousands of times farther away than others. The complicated
structure of the celestial sphere as a material object disappeared
altogether; it remained only as a geometrical conception, whereon we
find it convenient to indicate the places of the stars. Once the
Copernican doctrine had been fully set forth, it was impossible for
anyone, who had both the inclination and the capacity to understand
it, to withhold acceptance of its truth. The doctrine of a
stationary earth had gone for ever.

Copernicus having established a theory of the celestial movements
which deliberately set aside the stability of the earth, it seemed