OF CONSCIOUSNESS AND INTELLECT. 7 



those phenomena of life which are not psychological ; 

 and let us beware of drawing conclusions before we 

 have a groundwork. We know exactly the mechanism 

 of the eye ; but neither anatomy nor chemistry will 

 ever explain how the rays of light act on conscious- 

 ness, so as to produce vision. Natural science has 

 fixed limits which cannot be passed ; and it must always 

 be borne in mind that, with all our discoveries, we shall 

 never know what light, electricity, and magnetism are in 

 their essence, because, even of those things which are 

 material, the human intellect has only conceptions. 

 We can ascertain, however, the laws which regulate 

 their motion and rest, because these are manifested in 

 phenomena. In like manner, the laws of vitality, and 

 of all that disturbs, promotes, or alters it, may certainly 

 be discovered, although we shall never learn what life 

 is. Thus, the discovery of the laws of gravitation and 

 of the planetary motions led to an entirely new concep- 

 tion of the cause of these phenomena. This concep- 

 tion could not have been formed in all its clearness 

 without a knowledge of the phenomena out of which it 

 was evolved ; for, considered by itself, gravity, like 

 light to one born blind, is a mere word, devoid of 

 meaning. 



The modern science of physiology has left the track 

 of Aristotle. To the eternal advantage of science, and 

 to the benefit of mankind, it no longer invents a horror 

 vacui, a quinta essentia^ in order to furnish credulous 

 hearers with solutions and explanations of phenomena, 



