NICOLAUS COPERNICUS 13 



mint was founded, and also had a high reputation in medicine. 

 Copernicus was a contemporary of Luther. He did not 

 join the reformers, but always took a tolerant attitude to- 

 wards them, even when in danger of coming thereby into 

 conflict with his ecclesiastical superiors. Copernicus spent 

 thirty-six years upon his famous work De Revolutionibus 

 orbium coelestium, up till nearly the time of his death. He 

 started from the wish to calculate the motion over the heavens 

 of the sun, moon and planets, in a simple and trustworthy 

 manner. As foundation he took the traditional knowledge 

 and views which at that time were to be found in the thirteen 

 books of the Almagest. The compiler of this, Ptolemy (70- 

 147 A.D.), took his main data from Hipparchus, whose ob- 

 servations were of high quality, and in so far Copernicus was 

 well equipped. But in the Almagest the earth is assumed to 

 be at rest, which at that time also was regarded as beyond 

 a doubt. But Copernicus could not succeed, on the basis 

 of this assumption, in calculating satisfactorily the motion 

 of the heavenly bodies as actually observed from the time 

 of Hipparchus up to his own time; the many circles and 

 epicycles which had to be assumed as the path of all bodies 

 moving around the earth became extremely complicated, and 

 the complication became greater and greater as Copernicus 

 attempted to bring the actual observations into his calcula- 

 tions. For example, the orbits had to be assumed as arranged 

 eccentrically about the earth, which resulted in the abolition 

 of the fundamental idea, that of the central position of the 

 earth. On the other hand, everything became quite simple 

 and comprehensible as soon as Copernicus tried abandoning 

 this fundamental idea completely, allowing the earth to re- 

 volve around the sun like the planets, and also to turn once 

 daily upon an axis which remained always parallel to itself. 

 From the point of observation of an inhabitant of the earth 

 regarded as moving in this manner, the actually observed 

 positions and motions of the other planets resulted in a simple 



