EACH DISCOVERY DEPENDENT UPON PREVIOUS ONES. 183 



The chronological order of discovery is from the easy to 

 the difficult, from the less complex and abstract to the 

 more so, from the evident to the obscure. To an infinite 

 mind all things are equally easy of comprehension, and 

 therefore one truth is not essentially more difficult to 

 understand than another ; but the human mind, by means 

 of which all our discoveries are made, is extremely finite, 

 and the degree of ease or difficulty of our discovering new 

 truths depends upon the extent of that power. All our 

 knowledge of nature is based upon and derived from ex- 

 perience obtained through the medium of our senses and 

 perceptive powers. The mind can perceive dynamical 

 phenomena more readily than statical ones, because they 

 exhibit motion, which excites additional senses. It can 

 detect large things more easily than small ones, because 

 they produce a greater effect upon our perceptive faculties ; 

 hence motions of masses are sooner discovered than those 

 of molecules. It can unravel less complex phenomena with 

 greater ease than more complex ones, because the latter 

 require a greater variety and number of mental opera- 

 tions; hence discovery in biology follows that in the 

 physical and chemical sciences. We usually discover a 

 qualitative fact and then its quantitative variation, but if 

 the former is more abstruse, we discover it by the aid of 

 previous knowledge of the latter ; thus we already know 

 the quantitative proportions in which the various forces 

 are converted into each other, but we do not yet know the 

 more abstruse qualitative truth, viz., the mode or way in 

 which that change is effected in any case. 



Future research is as wide as the universe of existence 

 and thought, and boundless as the universal perigon of 

 truth ; and as the relation of the sciences to the human 

 mind determines the order of development of different 

 subjects, all things cannot be evolved at once, but only in 



