limiting geometrical line, with the laterally salient
portions of sculpture. This, I repeat, is the primal construction of
good bas-relief, implying, first, perfect protection to its surface from
any transverse blow, and a geometrically limited space to be occupied by
the design, into which it shall pleasantly (and as you shall ultimately
see, ingeniously,) contract itself: implying, secondly, a determined
depth of projection, which it shall rarely reach, and never exceed: and
implying, finally, the production of the whole piece with the least
possible labor of chisel and loss of stone.

166. And these, which are the first, are very nearly the last
constructive laws of sculpture. You will be surprised to find how much
they include, and how much of minor propriety in treatment their
observance involves.

In a very interesting essay on the architecture of the Parthenon, by the
professor of architecture of the Ecole Polytechnique, M. Emile Boutmy,
you will find it noticed that the Greeks do not usually weaken, by
carving, the constructive masses of their building; but put their chief
sculpture in the empty spaces between the triglyphs, or beneath the
roof. This is true; but in so doing, they merely build their panel
instead of carving it; they accept no less than the Goths, the laws of
recess and limitation, as being vital to the safety and dignity of their
design; and their noblest recumbent statues are, constructively, the
fillings of the acute extremity of a panel in the form of an obtusely
summitted triangle.

167. In gradual descent from that severest type, you will find that an
immense quantity of sculpture of all times and styles may be generally
embraced under the notion of a mass hewn out of, or, at least, placed
in, a panel or recess, deepening, it may be, into a niche; the sculpture
being always designed with reference to its position in such recess;
and, therefore, to the effect of the building out of which the recess is
hewn.

But, for the sake of simplifying our inquiry, I will at first suppose no
surrounding protective ledge to exist, and that the area of stone we
have to deal with is simply a flat slab, extant from a flat surface
depressed all round it.

168. A _flat_ slab, observe. The flatness of surface is essential to the
problem of bas-relief. The lateral limit of the panel may, or may not,
be required; but the vertical limit of surface _must_ be expressed; and
the art of bas-relief is to give t