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, 
