216 OPERATIONS SUBSIDIARY TO INDUCTION. 



the case of a set of phenomena which the whole 

 scientific world are engaged in attempting to connect. 

 The honour, in Kepler's case, was that of the accurate, 

 patient, and toilsome calculations by which he com- 

 pared the results that followed from his different 

 guesses, with the observations of Tycho Brahe ; but 

 the merit was very smaU of guessing an ellipse : the 

 only wonder is that men had not guessed it before. 

 nor could they have failed to do so if there had not 

 existed an obstinate a priori prejudice that the 

 heavenly bodies must move, if not in a circle, in some 

 combination of circles. 



The really difficult cases are those in which the 

 conception, that is to create light arid order out of 

 darkness and confusion, has to be sought for among 

 the very phenomena which it afterwards serves to 

 arrange. Why, according to Mr. Whewell himself, 

 did the ancients fail in discovering the laws of 

 mechanics, that is, of equilibrium and of the commu- 

 nication of motion ? Because they had not, or at 

 least had not clearly, the ideas or conceptions, of 

 pressure and resistance, momentum, and uniform and 

 accelerating force. And whence could they have 

 obtained these ideas, except from the very facts of 

 equilibrium and motion ? The tardy developement of 

 several of the physical sciences, for example of optics, 

 electricity, magnetism, and the higher generalizations 

 of chemistry, Mr. Whewell ascribes to the fact that 

 mankind had not yet possessed themselves of the Idea 

 of Polarity, that is, the idea of opposite properties in 

 opposite directions. But what was there to suggest 

 such an idea, until, by a separate examination of several 

 of these different branches of knowledge, it was shown 

 that the facts of each of them did present, in some 

 instances at least, the curious phenomenon of oppo- 



