ABSTRACTION. 197 



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 circum 

 stance of material poles, or fixed points in the body itself, in 

 which points this opposition of properties seemed to be 

 inherent. The first comparison and abstraction had led only 

 to this conception of poles ; and if anything corresponding to 

 that conception had existed in the phenomena of chemistry or 

 optics, the difficulty now justly considered so great, would have 

 been extremely small. The obscurity rose from the fact, that 

 the polarities in chemistry and optics were distinct species, 

 though of the same genus, with the polarities in electricity 

 and magnetism : and that in order to assimilate the pheno 

 mena to one another, it was necessary to compare a polarity 

 without poles, such for instance as is exemplified in the polari 

 zation of light, and the polarity with (apparent) poles, which 

 we see in the magnet ; and to recognise 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 labours and more or less sagacious suggestions of many 

 superior minds. 



The conceptions, then, which we employ for the colligation 

 and methodization 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 imply that it is not often a very difficult thing to 

 perform this process of abstraction 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 



