s life。 He himself tells us that he had even questioned whether it were not better for him to confine himself to such verbal teaching； following thus the example of Pythagoras。 Just as his life was drawing to a close； he decided to pursue the opposite course； and the first copy of his work is said to have been placed in his hands as he lay on his deathbed。 The violent opposition which the new system met from ecclesiastical sources led subsequent commentators to suppose that Copernicus had delayed publication of his work through fear of the church authorities。 There seems； however； to be no direct evidence for this opinion。 It has been thought significant that Copernicus addressed his work to the pope。 It is； of course； quite conceivable that the aged astronomer might wish by this means to demonstrate that he wrote in no spirit of hostility to the church。 His address to the pope might have been considered as a desirable shield precisely because the author recognized that his work must needs meet with ecclesiastical criticism。 Be that as it may； Copernicus was removed by death from the danger of attack； and it remained for his disciples of a later generation to run the gauntlet of criticism and suffer the charges of heresy。 The work of Copernicus； published thus in the year 1543 at Nuremberg； bears the title De Orbium Coelestium Revolutionibus。 It is not necessary to go into details as to the cosmological system which Copernicus advocated； since it is familiar to every one。 In a word； he supposed the sun to be the centre of all the planetary motions； the earth taking its place among the other planets； the list of which； as known at that time； comprised Mercury； Venus； the Earth； Mars； Jupiter； and Saturn。 The fixed stars were alleged to be stationary； and it was necessary to suppose that they are almost infinitely distant； inasmuch as they showed to the observers of that time no parallax； that is to say； they preserved the same apparent position when viewed from the opposite points of the earth's orbit。 But let us allow Copernicus to speak for himself regarding his system； His exposition is full of interest。 We quote first the introduction just referred to； in which appeal is made directly to the pope。 〃I can well believe； most holy father； that certain people； when they hear of my attributing motion to the earth in these books of mine； will at once declare that such an opinion ought to be rejected。 Now； my own theories do not please me so much as not to consider what others may judge of them。 Accordingly； when I began to reflect upon what those persons who accept the stability of the earth； as confirmed by the opinion of many centuries； would say when I claimed that the earth moves； I hesitated for a long time as to whether I should publish that which I have written to demonstrate its motion； or whether it would not be better to follow the example of the Pythagoreans； who used to hand down the secrets of philosophy to their relatives and friends only in oral form。 As I well considered all this； I was almost impelled to put the finished work wholly aside； through the scorn I had reason to anticipate on account of the newness and apparent contrariness to reason of my theory。 〃My friends； however； dissuaded me from such a course and admonished me that I ought to publish my book； which had lain concealed in my possession not only nine years； but already into four times the ninth year。 Not a few other distinguished and very learned men asked me to do the same thing； and told me that I ought not； on account of my anxiety； to delay any longer in consecrating my work to the general service of mathematicians。 〃But your holiness will perhaps not so much wonder that I have dared to bring the results of my night labors to the light of day； after having taken so much care in elaborating them； but is waiting instead to hear how it entered my mind to imagine that the earth moved； contrary to the accepted opinion of mathematiciansnay； almost contrary to ordinary human understanding。 Therefore I will not conceal from your holiness that what moved me to consider another way of reckoning the motions of the heavenly bodies was nothing else than the fact that the mathematicians do not agree with one another in their investigations。 In the first place； they are so uncertain about the motions of the sun and moon that they cannot find out the length of a full year。 In the second place； they apply neither the same laws of cause and effect； in determining the motions of the sun and moon and of the five planets； nor the same proofs。 Some employ only concentric circles； others use eccentric and epicyclic ones； with which； however； they do not fully attain the desired end。 They could not even discover nor compute the main thingnamely； the form of the universe and the symmetry of its parts。 It was with them as if some should； from different places； take hands； feet； head； and other parts of the body； which； although very beautiful； were not drawn in their proper relations； and； without making them in any way correspond； should construct a monster instead of a human being。 〃Accordingly； when I had long reflected on this uncertainty of mathematical tradition； I took the trouble to read again the books of all the philosophers I could get hold of； to see if some one of them had not once believed that there were other motions of the heavenly bodies。 First I found in Cicero that Niceties had believed in the motion of the earth。 Afterwards I found in Plutarch； likewise； that some others had held the same opinion。 This induced me also to begin to consider the movability of the earth； and； although the theory appeared contrary to reason； I did so because I knew that others before me had been allowed to assume rotary movements at will； in order to explain the phenomena of these celestial bodies。 I was of the opinion that I； too； might be permitted to see whether； by presupposing motion in the earth； more reliable conclusions than hitherto reached could not be discovered for the rotary motions of the spheres。 And thus； acting on the hypothesis of the motion which； in the following book； I ascribe to the earth； and by long and continued observations； I have finally discovered that if the motion of the other planets be carried over to the relation of the earth and this is made the basis for the rotation of every star； not only will the phenomena of the planets be explained thereby； but also the laws and the size of the stars； all their spheres and the heavens themselves will appear so harmoniously connected that nothing could be changed in any part of them without confusion in the remaining parts and in the whole universe。 I do not doubt that clever and learned men will agree with me if they are willing fully to comprehend and to consider the proofs which I advance in the book before us。 In order； however； that both the learned and the unlearned may see that I fear no man's judgment； I wanted to dedicate these； my night labors； to your holiness； rather than to any one else； because you； even in this remote corner of the earth where I live； are held to be the greatest in dignity of station and in love for all sciences and for mathematics； so that you； through your position and judgment； can easily suppress the bites of slanderers； although the proverb says that there is no remedy against the bite of calumny。〃
In chapter X。 of book I。； 〃On the Order of the Spheres；〃 occurs a more detailed presentation of the system； as follows： 〃That which Martianus Capella； and a few other Latins； very well knew； appears to me extremely noteworthy。 He believed that Venus and Mercury revolve about the sun as their centre and that they cannot go farther away from it than the circles of their orbits permit； since they do not revolve about the earth like the other planets。 According to this theory； then； Mercury's orbit would be included within that of Venus； which is more than twice as great； and would find room enough within it for its revolution。 〃If； acting upon this supposition； we connect Saturn； Jupiter； and Mars with the same centre； keeping in mind the greater extent of their orbits； which include the earth's sphere besides those of Mercury and Venus； we cannot fail to see the explanation of the regular order of their motions。 He is certain that Saturn； Jupiter； and Mars are always nearest the earth when they rise in the eveningthat is； when they appear over against the sun； or the earth stands between them and the sunbut that they are farthest from the earth when they set in the eveningthat is； when we have the sun between them and the earth。 This proves sufficiently that their centre belongs to the sun and is the same about which the orbits of Venus and Mercury circle。 Since； however； all have one centre； it is necessary for the space intervening between the orbits of Venus and Mars to include the earth with her accompanying moon and all that is beneath the moon； for the moon； which stands unquestionably nearest the earth； can in no way be separated from her； especially as there is sufficient room for the moon in the aforesaid space。 Hence we do not hesitate to claim that the whole system； which includes the moon with the earth for its centre； makes the round of that great circle between t