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 an effect of the rotary motion of the earth upon it axis. 6. The apparent motions of the moon and of the sun are so different because of the effect produced by the motion of the earth. 7. The movements of the earth account for the apparent retrograde motion and other irregularities of the movements of the planets. It is enough to assume that the earth alone moves, in order to explain all the other movements observed in the heavens. It is no wonder that one of his bishop-friends, Frisio, writing to another bishop-friend, Dantisco, said: "If Copernicus succeeds in demonstrating the truth of his thesis--and we may well consider that he will from this prelude--he will give us a new heaven and a new earth." This shorter exposition of Copernicus's views was found in manuscript in the imperial library in Vienna only about a quarter of a century ago. {33} It is mentioned by Tycho Brahe in one of his works on astronomy in which he reviews the various contemporary advances made in the knowledge of the heavens.