indow could be drawn with the
compasses, and a curve of contrary flexure rarely occurred. In the
latest half of that period flowing lines are introduced into the
tracery, and very much alter its character (Fig. 20). The cusping
throughout is bolder than in the E. E. period.

[Illustration: FIG. 20.--ROSE WINDOW FROM THE TRANSEPT OF LINCOLN
CATHEDRAL. (1342-1347.)]

In perpendicular windows spaces of enormous size are occupied by the
mullions and tracery. Horizontal bars, called transoms, are now for
the first time introduced, and the upright bars or mullions form with
them a kind of stone grating; but below each transom a series of small
stone arches forms heads to the lights below that transom, and a minor
mullion often springs from the head of each of these arches, so that
as the window increases in height, the number of its lights increases.
The character of the cusping changed again, the cusps becoming
club-headed in their form (Fig. 21).

[Illustration: FIG. 21.--PERPENDICULAR WINDOW.]

Arches in the great arcades of churches, or in the smaller arcades of
cloisters, or used as decorations to the surface of the walls, were
made acute, obtuse, or segmental, to suit the duty they had to
perform; but when there was nothing to dictate any special shape, the
arch of the E. E. period was by preference acute[18] and of lofty
proportions, and that of the Dec. less lofty, and its head equilateral
(_i.e._ described so that if the ends of the base of an equilateral
triangle touch the two points from which it springs, the apex of the
angle shall touch the point of the arch). In the Perp. period the four
centred depressed arch, sometimes called the Tudor arch, was
introduced, and though it did not entirely supersede the equilateral
arch, yet its employment became at last all but universal, and it is
one of the especially characteristic features of the Tudor period.

_Roofs and Vaults._

The external and the internal covering of a building are very often
not the same; the outer covering is then usually called a roof--the
other, a vault or ceiling. In not a few Gothic buildings, however,
they were the same; such buildings had what are known as open
roofs--_i.e._ roofs in which the whole of the timber framing of which
they are constructed is open to view from the interior right up to the
tiles or lead. Very few open roofs of E. E. character are now
remaining, but a good many parish churches retain roofs of the De