ABSTRACTION. 217 



site properties in opposite directions ? The thing was 

 superficially manifest only in two cases, those of the 

 magnet, and of electrified bodies j" and there the con- 

 ception was encumbered with the circumstance 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 any- 

 thing corresponding to that conception had existed in 

 the phenomena of chemistry or optics, the difficulty 

 which Mr. Whewell justly considers as so great, would 

 have been extremely small. The obscurity arose 

 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 phenomena to one 

 another, it was necessary to compare a polarity 

 without poles, such for instance as is exemplified 

 in the polarization of light, and the polarity with 

 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 direc- 

 tions. From the result of such a comparison it was 

 that the minds of scientific men formed this new gene- 

 ral 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 other- 

 wise than by way of comparison and abstraction, and, 



