o what he
can for the assistance of his faithful and valued counsellor.
Copernicus yielded to the request, and the counsellor began to improve
shortly after his arrival. At the end of some weeks the Duke wrote
again to the canons of the cathedral asking that the leave of absence
granted to Copernicus should be extended in order to enable him to
complete the cure which had been so happily begun. In this second
letter the Duke talks of Copernicus as a {31} most skilful and learned
physician. At the end of the month there is a third letter from the
Duke, in which he thanks all the canons of the cathedral for their
goodness in having granted the desired permission, and he adds that he
shall ever feel under obligations "for the assistance rendered by that
very worthy and excellent physician, Nicholas Copernicus, a doctor who
is deserving of all honor." Not long afterward, when Copernicus's book
on astronomy was published, a copy of it was sent to the Duke, and he
replied that he was deeply grateful for it, and that he should always
preserve it as a souvenir of the most learned and gentlest of men.

There are a number of notes on the art of medicine made by Copernicus
in the books of the cathedral library at Frauenburg. They serve to
show how faithful a student he was, and to a certain extent give an
idea of the independent habit of mind which he brought to the
investigation of medicine as well as to the study of astronomy.
Unfortunately, these have not as yet found an editor; but it is to be
hoped that we shall soon know more of the medical thinking of a man
over whose mind tradition, in the unworthier sense of that word,
exercised so little influence.

In 1530 Copernicus wrote a short prelude to the longer work on
astronomy which he was to publish later. The propositions contained in
this work show how far he had advanced on the road to his ultimate
discovery. After a few words of introduction, the following seven
axioms are laid down:--

{32}

1. The celestial spheres and their orbits have not a single center.

2. The center of the earth is not the center of the universe, but only
the center of gravity and of the moon's orbit.

3. The planes of the orbits lie around the sun, which may be
considered as the center of the universe.

4. The distance from the earth to the sun compared with that from the
earth to the fixed stars is extremely small.

5. The daily motion of the heavenly sphere is apparent that is, it is