THE KINSHIP OF LIFE. 9 



resent the divine thoughts embodied in the act of crea- 

 tion. The unity exists in the mind of the Creator. 

 He made them all, and so all bear the stamp of his 

 workmanship. He is infinite, and so they exist in in- 

 finite variety. That " material form is the cover of 

 spirit " was to Agassiz " a truth at once fundamental 

 and self-evident." Each species is, then, the material 

 form which clothes a divine idea. Homologies arise 

 not from diverging lines of descent, but from the asso- 

 ciations of divine ideas. They are the stamp of uni- 

 formity which must accompany all works of a single 

 mind, even though that mind be infinite. To trace this 

 out in Nature is for us to think again the thoughts 

 of God. 



This was Agassiz's answer, and it has the charm of 

 poetry, besides breathing the spirit of deep reverence 

 which characterized this great naturalist, to whom the 

 laboratory was not less holy than the church, and " a 

 physical fact not less sacred than a moral principle." 



It is a beautiful conception, but one which can not 

 be exactly measured or verified. All science at the bot- 

 tom -is quantitative, and whatever is true to us can be 

 reduced to measurement. We may, moreover, say if we 

 choose that the " thought of God " is not " the unchang- 

 ing species," but the law under which species are modi- 

 fied and changed. Nature is made up of changing beings 

 produced and acted upon by unchanging laws. It is the 

 mighty unseen force itself rather than the visible and 

 transitory object of its action which, in the language of 

 poetry, we may call the " thought of God." 



The progress of knowledge comes not from the 

 growth of beautiful conceptions, but from the subjec- 

 tion of all conceptions and theories to the crucial test 

 of fact. A thought which can not be put to the test of 

 human experience forms no part of science. 



