326 PERSONAL PREPARATION FOE RESEARCH. 



either compare two things or ideas immediately together, 

 or through the medium of others. It may be either 

 qualitative, i.e. as to matters of fact, or quantitative, as in 

 cases of degree or amount ; it may also be either perfect 

 or imperfect, complete or incomplete. Like all the other 

 mental powers, it may be voluntary or automatic, and act 

 either consciously or unconsciously. 



Kealities are often very different from appearances ; 

 many phenomena which are essentially the same often 

 exhibit no likeness, except to those who are disciplined 

 in looking beneath the surface of things, and in detecting 

 fundamental truths. By the progress of science the 

 most apparently remote phenomena are not unfrequently 

 brought together, and shown to be due to the same cause, 

 and apparently similar ones are shown to be essentially 

 different. The same action taking place in different 

 substances, or in widely different degrees in the same 

 substance, not unfrequently looks like a totally different 

 one ; for instance, the rusting of iron and its vivid com- 

 bustion in oxygen are essentially the same, but to persons 

 in general they appear to have no resemblance. Many 

 phenomena are essentially different which appear alike ; for 

 example, the electric attraction of a pith ball and the 

 magnetic attraction of iron look much alike, but are widely 

 diverse. As phenomena which were apparently different 

 have been shown to be similar, so also will some of those 

 which we now consider to be unlike, probably be found in 

 future times to be alike ; and some of those which we 

 consider to be similar be found to be different. At pre- 

 sent, in nearly all chemical treatises, it is said that the 

 products of chemical action are entirely different in pro- 

 perties from their constituents ; but the real truth pro- 

 bably is, that the properties altered are not the most 

 essential ones. 



