he ground that the motions of the sun and moon were not
known with sufficient accuracy. It is possible that with better data he
might have made much more progress. He was in no hurry to publish
anything, perhaps on account of possible opposition. Certainly Luther,
with his obstinate conviction of the verbal accuracy of the Scriptures,
rejected as mere folly the idea of a moving earth, and Melanchthon
thought such opinions should be prohibited, but Rheticus, a professor at
the Protestant University of Wittenberg and an enthusiastic pupil of
Copernicus, urged publication, and undertook to see the work through the
press. This, however, he was unable to complete and another Lutheran,
Osiander, to whom he entrusted it, wrote a preface, with the apparent
intention of disarming opposition, in which he stated that the
principles laid down were only abstract hypotheses convenient for
purposes of calculation. This unauthorised interpolation may have had
its share in postponing the prohibition of the book by the Church of
Rome.

According to Copernicus the earth is only a planet like the others, and
not even the biggest one, while the sun is the most important body in
the system, and the stars probably too far away for any motion of the
earth to affect their apparent places. The earth in fact is very small
in comparison with the distance of the stars, as evidenced by the fact
that an observer anywhere on the earth appears to be in the middle of
the universe. He shows that the revolution of the earth will account for
the seasons, and for the stationary points and retrograde motions of the
planets. He corrects definitely the order of the planets outwards from
the sun, a matter which had been in dispute. A notable defect is due to
the idea that a body can only revolve about another body or a point, as
if rigidly connected with it, so that, in order to keep the earth's axis
in a constant direction in space, he has to invent a third motion. His
discussion of precession, which he rightly attributes to a slow motion
of the earth's axis, is marred by the idea that the precession is
variable. With all its defects, partly due to reliance on bad
observations, the work showed a great advance in the interpretation of
the motions of the planets; and his determinations of the periods both
in relation to the earth and to the stars were adopted by Reinhold,
Professor of Astronomy at Wittenberg, for the new Prutenic or Prussian
Tables, which were t