SUBJECTIVE AND OBJECTIVE METHODS 



the need of a new search in order to account for 

 such residuum. The old conclusion, that plan- 

 etary motion is circular and uniform because 

 motion is naturally circular and uniform, left no 

 unexplained residual phenomenon. As an ex- 

 planation it was complete, though utterly false. 

 If asked whyxki^ planets move in circles with a 

 uniform velocity, the ancients might have re- 

 plied, and in fact did reply, that it is because 

 their motion is uninterfered with. On the other 

 hand Kepler's theorem, that planetary motion 

 is elliptical and rhythmically accelerated and 

 retarded, although motion is naturally rectilinear 

 and uniform, left an unexplained residual phe- 

 nomenon. As an explanation it was true, but 

 it was incomplete. When asked why the planets 

 do not move in straight lines with uniform 

 velocity, Kepler recognized a difficulty which 

 must be explained, and which he tried to solve. 

 In his perplexity he had recourse to the sub- 

 jective method, and suggested that the planets 

 were perhaps living animals moved by their own 

 volitions, or else that, as many of the Christian 

 Fathers thought, they were controlled in their 

 movements by presiding archangels. Could we 

 read all the unwritten annals of that time, we 

 should doubtless find that many educated per- 

 sons rejected Kepler's discoveries on account of 

 this unexplained residuum ; attaching a higher 

 value to the mutual congruity of a set of con- 

 i6i 



