es is also requisite; and such knowledge not being
usually possessed, grave mechanical mistakes are frequently made. Take
an instance. For the stability of a figure it is needful that the
perpendicular from the centre of gravity--"the line of direction," as it
is called--should fall within the base of support; and hence it happens,
that when a man assumes the attitude known as "standing at ease," in
which one leg is straightened and the other relaxed, the line of
direction falls within the foot of the straightened leg. But sculptors
unfamiliar with the theory of equilibrium, not uncommonly so represent
this attitude, that the line of direction falls midway between the feet.
Ignorance of the law of momentum leads to analogous blunders: as witness
the admired Discobolus, which, as it is posed, must inevitably fall
forward the moment the quoit is delivered.

In painting, the necessity for scientific information, empirical if not
rational, is still more conspicuous. What gives the grotesqueness of
Chinese pictures, unless their utter disregard of the laws of
appearances--their absurd linear perspective, and their want of aerial
perspective? In what are the drawings of a child so faulty, if not in a
similar absence of truth--an absence arising, in great part, from
ignorance of the way in which the aspects of things vary with the
conditions? Do but remember the books and lectures by which students are
instructed; or consider the criticisms of Ruskin; or look at the doings
of the Pre-Raffaelites; and you will see that progress in painting
implies increasing knowledge of how effects in Nature are produced. The
most diligent observation, if unaided by science, fails to preserve from
error. Every painter will endorse the assertion that unless it is known
what appearances must exist under given circumstances, they often will
not be perceived; and to know what appearances must exist, is, in so
far, to understand the science of appearances. From want of science Mr.
J. Lewis, careful painter as he is, casts the shadow of a lattice-window
in sharply-defined lines upon an opposite wall; which he would not have
done, had he been familiar with the phenomena of penumbrae. From want of
science, Mr. Rosetti, catching sight of a peculiar iridescence displayed
by certain hairy surfaces under particular lights (an iridescence caused
by the diffraction of light in passing the hairs), commits the error of
showing this iridescence on surfaces and