O marvellous necessity, thou with supreme reason constrainest
all efforts to be the direct result of their causes, and by a
supreme and irrevocable law every natural action obeys thee by
the shortest possible process.

Who would believe that so small a space could contain the
images of all the universe? O mighty process, what talent can
avail to penetrate a nature such as thine? What tongue will it
be that can unfold so great a wonder? Verily none. This it is
that guides the human discourse to the considering of divine
things.[1]

[Footnote 1: The sayings of Leonardo quoted in this article are taken
from _Leonardo da Vinci's Notebooks_, by E. M'Curdy. (Duckworth, 1906.)]

To Leonardo causation meant the escape from caprice; it meant a secure
relation between man and all things, in which man would gain power by
knowledge, in which every increase of knowledge would reveal to him more
and more of the supreme reason. There was no chain for him in cause and
effect, no unthinking of the will of man. Rather by knowledge man would
discover his own will and know that it was the universal will. So man
must never be afraid of knowledge. "The eye is the window of the soul."
Like Whitman he tells us always to look with the eye, and so to confound
the wisdom of ages. There is in every man's vision the power of relating
himself now and directly to reality by knowledge; and in knowing other
things he knows himself. By knowledge man changes what seemed to be a
compulsion into a harmony; he gives up his own caprice for the universal
will.

That is the religion of Leonardo, in art as in science. For him the