ABSTRACTION. 457 



pared the results that followed from his different guesses, with the obser- 

 vations of Tycho Brahe; but the merit was very small 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 destined to 

 create light and order out of darkness and confusion has to be sought for 

 among the very phenomena which it afterward serves to arrange. Why, 

 according to Dr. Whewell himself, did the ancients fail in discovering the 

 laws of mechanics, that is, of equilibrium and of the communication of mo- 

 tion ? Because they had not, or at least had not clearly, the ideas or con- 

 ceptions of pressure and resistance, momentum, and uniform and accelera- 

 ting force. And whence could they have obtained these ideas except from 

 the very facts of equilibrium and motion ? The tardy development of sev- 

 eral of the physical sciences, for example, of optics, electricity, magnetism, 

 and the higher generalizations of chemistry, he 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 opposite 

 properties in opposite directions? The thing was superficially manifest 

 only in two cases, those of the magnet and of electrified bodies ; and there 

 the conception was encumbered with the circumstance of material poles, 

 or fixed points in the body itself, in which points this opposition of proper- 

 ties seemed to be inherent. The first comparison and abstraction had led 

 only to this conception of poles ; and if any thing corresponding to that con- 

 ception had existed in the phenomena of chemistry or optics, the difficulty 

 now justly considered so great, would have been extremely small. The ob- 

 scurity arose from the fact, that the polarities in chemistry and optics Avere 

 distinct species, though of the same genus, with the polarities in electricity 

 and magnetism ; and that in order to assimilate the phenomena to one anoth- 

 er, it was necessary to compare a polarity without poles, such for instance as 

 is exemplified in the polarization of light, and the polarity with (apparent) 

 poles, Avhich we see in the magnet; and to recognize that these polarities, 

 while different in many other respects, agree in the one character which is 

 expressed by the phrase, opposite properties in opposite directions. From 

 the result of such a comparison it was that the minds of scientific men 

 formed this new general conception ; between which, and the first confused 

 feeling of an analogy between some of the phenomena of light and those of 

 electricity and magnetism, there is a long interval, filled up by the labors 

 and more or less sagacious suggestions of many superior minds. 



The conceptions, then, which we employ for the colligation and methodi- 

 zation of facts, do not develop themselves from within, but are impressed 

 upon the mind from without ; they are never obtained otherwise than by 

 way of comparison and abstraction, and, in the most important and the 

 most numerous cases, are evolved by abstraction from the very phenomena 

 which it is their office to colligate. I am far, however, from wishing to im- 

 ply that it is not often a very difficult thing to perform this process of ab- 

 straction well, or that the success of an inductive operation does not, in many 

 cases, principally depend on the skill with which we perform it. Bacon 

 :was quite justified in designating as one of the principal obstacles to good 



