hich he wished to impose on it, than when the vault was regarded and
built as an intersection of surfaces. There was still one difficulty,
however, one slight failure both practical and theoretical in the
vault architecture, which for a long time much exercised the minds of
the builders. The ribs of the vaulting being all of unequal length,
they had to assume different curves almost immediately on rising from
the impost; and as the mouldings of the ribs have to be run into each
other ("mitered" is the technical term) on the impost, there not being
room to receive them all separately, it was almost impossible to get
them to make their divergence from each other in a completely
symmetrical manner; the shorter ribs with the quicker curves parted
from each other at a lower point than the larger ones, and the
"miters" occurred at unequal heights. The effort to get over this
unsatisfactory and irregular junction of the ribs at the springing was
made first by setting back the feet of the shorter ribs on the impost
capping, somewhat in the rear of the feet of the larger ribs, so as to
throw their parting point higher up; but this also was only a
makeshift, which it was hoped the eye would pass over; and in fact it
is rarely noticeable except to those who know about it and look for
it. Still the defect was there, and was not got over until the idea
occurred of making all the ribs of the same curvature and the same
length, and intercepting them all by a circle at the apex of the
vault, as shown in Figs. 106, 107; the space between the circles at
the apex of the vault being practically a nearly flat surface or
_plafond_ held in its place by the arches surrounding it; though, for
effect, it is often treated otherwise in external appearance, being
decorated by pendants giving a reversed curve at this point, but which
of course are only ornamental features hung from the roof. If we look
again at Fig. 104, we shall see that this was a very natural
transition after all, for the arrangement of the ribs and vaulting
surfaces in that example is manifestly suggestive of a form radiating
round the central point of springing, though it only suggests that,
and does not completely realize it. But here came a further and very
curious change in the method of building the vault, for as the ribs
were made more numerous, for richness of effect, in this form of
vaulting, it was discovered that it was much easier to build the whole
as a solid face of