324 PERSONAL PREPARATION FOR RESEARCH. 



co-operate in promoting the collection of observations in 

 other sciences, as thay already have to some extent in 

 magnetism, astronomy, meteorology, &c. 



CHAPTER XXXV. 



USE OF THE POWER OF COMPARISON IN SCIENTIFIC 

 RESEARCH. 



COMPARISON is one of the fundamental actions and powers 

 of the intellect, and is the mental faculty by means of 

 which we distinguish and discriminate likeness and differ- 

 ence, and are thereby enabled to unite similar ideas, and 

 separate dissimilar ones, and form simple judgments. The 

 human mind can detect similarities in nature, because 

 they impress upon it similar sensations ; it also detects 

 differences, because they impart to it different sensations. 

 It can also, by means of the memory, retain and repro- 

 duce, in an imperfect way, the similar and different im- 

 pressions it has experienced. But there are innumerable 

 similarities and differences which do not directly affect 

 our senses or perceptive abilities, and which can only be 

 detected by the aid of the reasoning power. 



Experience is the original source of the basis of intellect. 

 The ultimate basis of comparison is sensation. This pro- 

 duces impressions and ideas, without which comparison is 

 unable to operate, because it has no materials to act upon. 

 The sensations, impressions, and ideas may be produced 

 either by external causes, by memory, or by the action 

 of the brain and mind. 



Comparison is a compound form of the simple act of 



