d Lead, the World expected that the new Work should
not in this Respect fall short of the old (tho' that was but a Spit
and this a Mountain). He was therefore obliged to comply with the
Humour of the Age, (though not with ancient Example, as neither did
Bramante) and to raise another Structure over the first Cupola._"
Stephen might have said _two_ other structures. Not only did Wren wish
the interior height to be somewhat less, so as to make it more perfect
for the purpose of an auditorium, but he thought any greater exterior
height unnecessary, and would have finished off the exterior elevation
in some other way.

As matters eventuated, he raised the internal sphere so that the
disproportion with the external might be reduced. The whole dome has
three shells. (_a_) The majestic exterior visible to the eye, an
outward roof of wood covered with lead and ribbed for the sake of
ornament. (_b_) The intermediate brick cone which supports the lantern
and its accessories of 700 tons weight. This springs from the level of
the stone gallery, and rises in straight lines which converge at the
circular opening beneath the lantern. This, although seen neither from
the outside or from within, constitutes the most solid and substantial
part. Between this and the outside visible shell is an ingenious
network of beams supporting the latter, and at the base of this
network a strengthening of which the account had better be given in
Stephen's own words: "_Altho' the Dome wants not Butment, yet for
greater Caution, it is hooped with Iron in this Manner; a Chanel is
cut in the Bandage of Portland-Stone, in which is laid a double Chain
of Iron strongly linked together at every ten Feet, and the whole
Chanel filled up with Lead._"[87] (_c_) The interior dome, also of
brick. The height of this third and smallest shell reaches only to the
level of the curved lines of the fluted patterns of the exterior
shell, a difference of from fifty to sixty feet.

[Illustration: SECTION OF THE DOME.]

Since the outside cupola does not bear the heavy weight of the lantern
it has been denounced as a sham, but this is an exaggeration. It is
evident, as we look at it, that it is incapable of bearing any such
weight. Much more practical is the objection of Gwilt that the
elaborate framework of beams supporting this outside cover is certain
to decay in course of time. A third objection is that of
deception--the exterior and interior are presumed to be one a