UNIVERSITY 



THE AIM AND ACHIEVEMENTS OF SCIENTIFIC METHOD. 57 



famous demonstration that the orbit of Mars instead of being 

 a circle, as the prepossession in favour of " perfection " had 

 hitherto compelled him to suppose, is actually an ellipse of 

 which the sun occupies one focus. It will interest us more to 

 attend to the remarkable change in his whole attitude towards 

 the Objective upon which I have already remarked. We find ^ 

 the evidences of this change most prominent in the introduc- 

 tion' and the later chapters of the treatise. Ce n'est que le 

 premier pas qid write, and when Keppler has once been com- 

 pelled to seek the secondary construction that is to make the 

 primary facts intelligible in a disinterested study of those facts 

 themselves in their quantitative determination, he travels fast 

 towards a characteristically " modern " point of view. Since 

 the planets no longer move in circles they must resign with 

 these the crystal spheres in which since the days of Plato they 

 have been " quiring to the young-eyed cherubim." These 

 destroyed, what is to guide a planet's motion ? The anima 

 mundi remains, it is true, and Keppler, like his great con- 

 temporary Gilbert, finds nothing objectionable in the concep- 

 tion. He had, in fact, used the admitted existence of the 

 anima mundi as an argument against the Ptolemaic orbits, 

 inviting his readers to pity the condition of the distracted world- 

 souls who in that complicated system "ad tarn multa respicere 

 jubentur ut plane tarn duobus permixtis motibus invehant ! "* 

 Similar considerations seem to deter Keppler from assigning 

 to the anima mundi the perpetual solution of the mathematical 

 difficulties incidental to following an elliptical path round an 

 eccentric, sun. He looks elsewhere for a means of, at least, 

 lightening the world-soul's burden and finds what he wants 

 within the Objective itself in a new conception of the sun as 

 fans motus. This conception has not been reached without 

 external suggestion, and when we meet the phrase orbs virtutis ' 

 tractoria we are left in no doubt as to the source of that 



* Introd., p. 149 (Vol. 3 of Frisch's ed.). 



