54 THE AIM AND ACHIEVEMENTS OF SCIENTIFIC METHOD. 



little later Leibniz corrects the deficiencies of this principle, 

 pointing out that Descartes had neglected to observe that the 

 direction as well as the quantity of " force " (momentum) is 

 conserved. Our interest fastens on his further remark that if 

 Descartes had noticed the fact, " he would have fallen into my 

 System of Pre-established Harmony." * 



18. 



But for the illustrations most suitable to my purpose I 

 must direct your attention to the writings of Keppler ; for the 

 student who picks his way discreetly through Frisch's monu- 

 mental editionf of the Omnia Opera of that heroic astronomer, 

 will gain as his reward a vivid idea of how profoundly the 

 whole " situation " in which Objective facts are actually central 

 is determined by the character of what I have already called 

 the "embroidery"; and will, moreover, catch sight of the 

 human spirit at the precise moment of one of its most interest- 

 ing metamorphoses. 



Keppler begins (in the My sternum Cosmographicum, 1596) 

 as an enthusiastic young convert to the heliocentric doctrine 

 of Copernicus. He defends the new theory on the ground 

 of its superior simplicity, not, bien entendu, its simplicity as 

 a description of the facts, but its real and meritorious simplicity 

 as an actual creative plan. 



" Amat [Natura] simplicitatem : amat unitatem. Nunquam 

 in ipsa quicquam otiosum aut superfluum extitit ; at saepius 

 una res multis ab ilia destinatur effectibus." J One form of 

 orbit, then, should be expected to suffice for all the planets, 

 instead of the deplorably diverse orbits of the Ptolemaic system. 

 In the spirit thus indicated he proceeds to determine the reasons 

 why the solar system could not but be precisely as it is. First 

 we learn why a combination of curves and linear distances (from 



* Leibniz, Jfonodologie, 80 ; ThJodice'e, 61. 



t Keppler, Omnia Opera, ed. Frisch, Frankfort, 1858-71. 



t Cap. I, p. 113 (Vol. I. of Frisch's ed.). 



