he effect of true form on that
condition. For observe, if nothing more were needed than to make first a
cast of a solid form, then cut it in half, and apply the half of it to
the flat surface;--if, for instance, to carve a bas-relief of an apple,
all I had to do was to cut my sculpture of the whole apple in half, and
pin it to the wall, any ordinary trained sculptor, or even a mechanical
workman, could produce bas-relief; but the business is to carve a
_round_ thing out of _flat_ thing; to carve an apple out of a
biscuit!--to conquer, as a subtle Florentine has here conquered,[130]
his marble, so as not only to get motion into what is most rigidly
fixed, but to get boundlessness into what is most narrowly bounded; and
carve Madonna and Child, rolling clouds, flying angels, and space of
heavenly air behind all, out of a film of stone not the third of an inch
thick where it is thickest.

169. Carried, however, to such a degree of subtlety as this, and with so
ambitious and extravagant aim, bas-relief becomes a tour-de-force; and,
you know, I have just told you all tours-de-force are wrong. The true
law of bas-relief is to begin with a depth of incision proportioned
justly to the distance of the observer and the character of the subject,
and out of that rationally determined depth, neither increased for
ostentation of effect, nor diminished for ostentation of skill, to do
the utmost that will be easily visible to an observer, supposing him to
give an average human amount of attention, but not to peer into, or
critically scrutinize the work.

170. I cannot arrest you to-day by the statement of any of the laws of
sight and distance which determine the proper depth of bas-relief.
Suppose that depth fixed; then observe what a pretty problem, or,
rather, continually varying cluster of problems, will be offered to us.
You might, at first, imagine that, given what we may call our scale of
solidity, or scale of depth, the diminution from nature would be in
regular proportion, as for instance, if the real depth of your subject
be, suppose a foot, and the depth of your bas-relief an inch, then the
parts of the real subject which were six inches round the side of it
would be carved, you might imagine, at the depth of half-an-inch, and so
the whole thing mechanically reduced to scale. But not a bit of it. Here
is a Greek bas-relief of a chariot with two horses (upper figure, Plate
XXI). Your whole subject has therefore the depth of t