hat faculty to the retina to which we owe not merely the idea of light,
but the existence of it; for light is to be defined only as the
sensation produced in the eye of an animal, under given conditions;
those same conditions being, to a stone, only warmth or chemical
influence, but not light. And that power of seeing, and the other
various personalities and authorities of the animal body, in pleasure
and pain, have never, hitherto, been, I do not say, explained, but in
any wise touched or approached by scientific discovery. Some of the
conditions of mere external animal form and of muscular vitality have
been shown; but for the most part that is true, even of external form,
which I wrote six years ago. "You may always stand by Form against
Force. To a painter, the essential character of anything is the form of
it, and the philosophers cannot touch that. They come and tell you, for
instance, that there is as much heat, or motion, or calorific energy (or
whatever else they like to call it), in a tea-kettle, as in a
gier-eagle. Very good: that is so; and it is very interesting. It
requires just as much heat as will boil the kettle, to take the
gier-eagle up to his nest, and as much more to bring him down again on a
hare or a partridge. But we painters, acknowledging the equality and
similarity of the kettle and the bird in all scientific respects,
attach, for our part, our principal interest to the difference in their
forms. For us, the primarily cognisable facts, in the two things, are,
that the kettle has a spout, and the eagle a beak; the one a lid on its
back, the other a pair of wings; not to speak of the distinction also of
volition, which the philosophers may properly call merely a form or mode
of force--but, then to an artist, the form or mode is the gist of the
business."

100. As you will find that it is, not to the artist only, but to all of
us. The laws under which matter is collected and constructed are the
same throughout the universe: the substance so collected, whether for
the making of the eagle, or the worm, may be analyzed into gaseous
identity; a diffusive vital force, apparently so closely related to
mechanically measurable heat as to admit the conception of its being
itself mechanically measurable, and unchanging in total quantity, ebbs
and flows alike through the limbs of men, and the fibres of insects.
But, above all this, and ruling every grotesque or degraded accident of
this, are two laws of bea