[Illustration: FIG. 37.]
A. There is, first, a steady change through the whole line, from less to
more curvature, or more to less, so that _no_ part of the line is a
segment of a circle, or can be drawn by compasses in any way whatever.
Thus, in Fig. 36, _a_ is a bad curve because it is part of a circle, and
is therefore monotonous throughout; but _b_ is a good curve, because it
continually changes its direction as it proceeds.
[Illustration: FIG. 38.]
The _first_ difference between good and bad drawing of tree boughs
consists in observance of this fact. Thus, when I put leaves on the line
_b_, as in Fig. 37, you can immediately feel the springiness of
character dependent on the changefulness of the curve. You may put
leaves on the other line for yourself, but you will find you cannot make
a right tree spray of it. For _all_ tree boughs, large or small, as well
as all noble natural lines whatsoever, agree in this character; and it
is a point of primal necessity that your eye should always seize and
your hand trace it. Here are two more portions of good curves, with
leaves put on them at the extremities instead of the flanks, Fig. 38;
and two showing the arrangement of masses of foliage seen a little
farther off, Fig. 39, which you may in like manner amuse yourself by
turning into segments of circles--you will see with what result. I hope
however you have beside you, by this time, many good studies of tree
boughs carefully made, in which you may study variations of curvature in
their most complicated and lovely forms.[59]
[Illustration: FIG. 39.]
[Illustration: FIG. 40.]
209. B. Not only does every good curve vary in general tendency, but it
is modulated, as it proceeds, by myriads of subordinate curves. Thus the
outlines of a tree trunk are never as at _a_, Fig. 40, but as at _b_. So
also in waves, clouds, and all other nobly formed masses. Thus another
essential difference between good and bad drawing, or good and bad
sculpture, depends on the quantity and refinement of minor curvatures
carried, by good work, into the great lines. Strictly speaking, however,
this is not variation in large curves, but composition of large curves
out of small ones; it is an increase in the quantity of the beautiful
element, but not a change in its nature.