SUBJECTIVE AND OBJECTIVE METHODS 



discovery. Doubtless the reasoning seemed 

 very sound and plausible to the Greeks, which, 

 starting from the assumptions that the circle is 

 the most perfect of figures, and that all motion 

 is naturally circular, proceeded to the inferences 

 that the planets move in circular orbits, and 

 that their motion is uniform. For twenty cen- 

 turies this reasoning passed unchallenged. Until 

 Kepler's time no one thought it necessary to 

 make observations and ascertain whether, as a 

 matter of fact, the planetary orbits were circu- 

 lar ; nor previous to Galileo did any one think 

 of verifying the premise that all motion is nat- 

 urally circular; nor did it occur to any one that 

 the conclusion might not inevitably follow from 

 the premise, — since the planets might, as in 

 fact they do, move in an orbit which is not the 

 natural path of motion when uninterfered with. 

 Now mark how ill it fared with this subjective 

 order of conceptions as soon as it was confronted 

 with the order of phenomena. In the first place, 

 Galileo proved, by reasoning upon direct obser- 

 vations, that all motion is naturally rectilinear 

 and not circular, — that, if you could set a body 

 moving, apart from all disturbing conditions, 

 it would go on forever in a straight line. This 

 destroyed the premise of the subjective syllo- 

 gism. Secondly, Kepler proved, by actual* ob- 

 servation, that the planets do not move in circu- 

 lar orbits, with a uniform rate of velocity ; but 



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