OF CONSCIOUSNESS AND INTELLECT. 7 



intellect to do with the developement of the human 

 fetus, or the fetus in a fowl's egg? not more, 

 surely, than with the developement of the seeds of 

 a plant. Let us first endeavour to refer to their 

 ultimate causes 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 consciousness, 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 mag- 

 netism 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 man- 

 ner, 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 con- 

 ception could not have been formed in all its clear- 

 ness 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. 



