delicately curved lines, except where
the straight line is indispensable to their use or stability: and that
when a complete system of straight lines, throughout the form, is
necessary to that stability, as in crystals, the beauty, if any exists,
is in colour and transparency, not in form. Cut out the shape of any
crystal you like, in white wax or wood, and put it beside a white lily,
and you will feel the force of the curvature in its purity, irrespective
of added colour, or other interfering elements of beauty.

[Illustration: FIG. 34.]

Well, as curves are more beautiful than straight lines, it is necessary
to a good composition that its continuities of object, mass, or colour
should be, if possible, in curves, rather than straight lines or angular
ones. Perhaps one of the simplest and prettiest examples of a graceful
continuity of this kind is in the line traced at any moment by the corks
of a net as it is being drawn: nearly every person is more or less
attracted by the beauty of the dotted line. Now it is almost always
possible, not only to secure such a continuity in the arrangement or
boundaries of objects which, like these bridge arches or the corks of
the net, are actually connected with each other, but--and this is a
still more noble and interesting kind of continuity--among features
which appear at first entirely separate. Thus the towers of
Ehrenbreitstein, on the left, in Fig. 32., appear at first independent
of each other; but when I give their profile, on a larger scale, Fig.
35., the reader may easily perceive that there is a subtle cadence and
harmony among them. The reason of this is, that they are all bounded by
one grand curve, traced by the dotted line; out of the seven towers,
four precisely touch this curve, the others only falling back from it
here and there to keep the eye from discovering it too easily.

[Illustration: FIG. 35.]

And it is not only always _possible_ to obtain continuities of this
kind: it is, in drawing large forest or mountain forms essential to
truth. The towers of Ehrenbreitstein might or might not in reality fall
into such a curve, but assuredly the basalt rock on which they stand
did; for all mountain forms not cloven into absolute precipice, nor
covered by straight slopes of shales, are more or less governed by these
great curves, it being one of the aims of Nature in all her work to
produce them. The reader must already know this, if he has been able to
sketch at al