ides of the clerestory windows. He set to work
something in this way. After satisfying himself that he had hit on a
better plan than the plain cylindrical or the cross-vaulting of the
Romans, or the other forms of intersecting vaults, he seems to have
taken a hemisphere as a plan to work upon, and fixed his imaginary
centre about the level of the top of the triforium. In the great
square western severy of the nave this was easier, but the other
severies are oblong. Here he stretched his sections out, so as to
include the clerestory windows and their much-needed light. The usual
way of expressing this is to say that the vault is intersected across
by an elliptic cylinder. The wreaths, garlands, and festoons, and the
various conventional patterns with which the edges and surfaces of the
various parts of the vaulting is adorned cannot be estimated from the
pavement. We may add here that the pendentives were purposely
constructed of "_sound Brick invested with Stucco of Cockle-shell
lime_," and not of Portland stone, for further ornament if
required.[95] So are the circular sections.

The nave is connected with the dome by the space between the great
piers or walls of more than 30 feet in length. These piers are also
broader at their ends than those which support the arcading, the
latter covering a square of about 10 feet. The greater massiveness is
owing to their assistance being required in supporting the dome. They
have large pilasters at the angles, and their coffered wagon
vaulting, adorned with geometrical patterns, is very striking.

=The Nave Aisles.=--We will first point out an unnoticed feature in
the great piers at either end. Their inner faces as seen from the
aisles have recesses or niches for the reception of monuments, and
other recesses are generally found in the wall opposite. At the west
of the aisles there are eight of these altogether, just behind the
coupled columns. They are repeated in all the great piers leading to
the dome, but although of sufficient height to permit of the
introduction of life-sized effigies, still remain unoccupied. The
coupled columns are repeated at the entrances to the chapels. At both
ends the perspective is narrowed; at the west by the chapels, at the
east by the breadth of the great piers. The windows stand in recesses
which are segments of circles. Their sides are made to represent piers
with concave surfaces. These latter carry an entablature from which
spring the round