ticed respecting the
means by which height is attained in buildings of various plans, and
the expediency and methods of superimposition of one story or tier of
architecture above another.

Sec. III. For, in the preceding inquiry, I have always supposed either
that a single shaft would reach to the top of the building, or that the
farther height required might be added in plain wall above the heads of
the arches; whereas it may often be rather expedient to complete the
entire lower series of arches, or finish the lower wall, with a bold
string course or cornice, and build another series of shafts, or another
wall, on the top of it.

Sec. IV. This superimposition is seen in its simplest form in the interior
shafts of a Greek temple; and it has been largely used in nearly all
countries where buildings have been meant for real service. Outcry has
often been raised against it, but the thing is so sternly necessary that
it has always forced itself into acceptance; and it would, therefore, be
merely losing time to refute the arguments of those who have attempted
its disparagement. Thus far, however, they have reason on their side,
that if a building can be kept in one grand mass, without sacrificing
either its visible or real adaptation to its objects, it is not well to
divide it into stories until it has reached proportions too large to be
justly measured by the eye. It ought then to be divided in order to mark
its bulk; and decorative divisions are often possible, which rather
increase than destroy the expression of general unity.

Sec. V. Superimposition, wisely practised, is of two kinds, directly
contrary to each other, of weight on lightness, and of lightness on
weight; while the superimposition of weight on weight, or lightness on
lightness, is nearly always wrong.

1. Weight on lightness: I do not say weight on _weakness_. The
superimposition of the human body on its limbs I call weight on
lightness: the superimposition of the branches on a tree trunk I call
lightness on weight: in both cases the support is fully adequate to the
work, the form of support being regulated by the differences of
requirement. Nothing in architecture is half so painful as the apparent
want of sufficient support when the weight above is visibly passive:
for all buildings are not passive; some seem to rise by their own
strength, or float by their own buoyancy; a dome requires no visibility
of support, one fancies it supported by the air. B