needs to be added to our
definition of its form, with respect to a part of its decoration, which
rises out of that construction. We have seen that the first condition of
its form is, that it shall have pointed arches. When Gothic is perfect,
therefore, it will follow that the pointed arches must be built in the
strongest possible manner.

[Illustration: Fig. XV.]

Now, if the reader will look back to Chapter XI. of Vol. I., he will
find the subject of the masonry of the pointed arch discussed at length,
and the conclusion deduced, that of all possible forms of the pointed
arch (a certain weight of material being given), that generically
represented at _e_, Fig. XV., is the strongest. In fact, the reader can
see in a moment that the weakness of the pointed arch is in its flanks,
and that by merely thickening them gradually at this point all chance of
fracture is removed. Or, perhaps, more simply still:--Suppose a gable
built of stone, as at _a_, and pressed upon from without by a weight in
the direction of the arrow, clearly it would be liable to fall in, as at
_b_. To prevent this, we make a pointed arch of it, as at _c_; and now
it cannot fall inwards, but if pressed upon from above may give way
outwards, as at _d_. But at last we build as at _e_, and now it can
neither fall out nor in.

Sec. XCIV. The forms of arch thus obtained, with a pointed projection
called a cusp on each side, must for ever be delightful to the human
mind, as being expressive of the utmost strength and permanency
obtainable with a given mass of material. But it was not by any such
process of reasoning, nor with any reference to laws of construction,
that the cusp was originally invented. It is merely the special
application to the arch of the great ornamental system of FOLIATION; or
the adaptation of the forms of leafage which has been above insisted
upon as the principal characteristic of Gothic Naturalism. This love of
foliage was exactly proportioned, in its intensity, to the increase of
strength in the Gothic spirit: in the Southern Gothic it is _soft_
leafage that is most loved; in the Northern _thorny_ leafage. And if we
take up any Northern illuminated manuscript of the great Gothic time, we
shall find every one of its leaf ornaments surrounded by a thorny
structure laid round it in gold or in color; sometimes apparently copied
faithfully from the prickly developement of the root of the leaf in the
thistle, running along the stems and