Before going further, I will, to prevent mistake, give the names of the
parts of a groined compartment (Fig. 349). The main ribs from wall to
wall are called by us _transverse ribs_; by the French, _arcs
doubleaux_. Those which pass from angle to angle, intersecting in the
middle, we call _diagonal ribs_; the French, _arcs ogives_. Those which
adhere to the wall, we call _wall ribs_; the French, _formerets_. If
there is a rib or moulding along the apex, we call it a _ridge rib_; the
French, a _lierne_. The latter, however, does not exist in early
examples. Other features appear as we proceed, but I limit my first list
to the simpler forms of vaulting. The French names are found in the
treatise of Philibert de l’Orme, a work of the sixteenth century;
whether they have been traditionally kept up I do not know, but they are
now universally adopted by French writers on the subject.
I will just go over our leading cases, already treated of, showing the
changes effected in them by the use of the pointed arch.
In the square groined space with level ridges there was no alteration
excepting in the form of the arch, and in the more finished mouldings
made use of. The diagonal ribs often took the form of a round arch, but
this depended wholly on the proportions of the surrounding pointed
arches.
As the diagonals were not formed by elliptical curves, it followed that
the vaulting surfaces were not portions of cylinders, and that an error
had to be thrown into them. In fact, they were filled in from rib to rib
without any view to purely geometrical forms.
When the pointed arch is applied to an oblong compartment, or to the
sides of a polygonal apse, its advantage becomes more manifest; for the
power of making the narrow arches against the walls as high as we please
wholly removes the difficulty which we encountered while limited to the
round arch, and that without the _necessity_ of stilting, though the
convenience which the last-named method offered for the introduction of
windows still led to its frequent use.
The irregular compartments of an apsidal aisle ceased now to present
difficulties, as all their arches could be made of equal height.
It is curious that, while we have in London two specimens of such aisles
in the round-arched style (those in the Tower of London and St.
Bartholomew’s), so have we also two in the pointed arched style, and
those very different indeed in their treatment. The aisle round the apse
of Westminster Abbey has compartments enormously wider on one side than
on the other, and this is met simply by the varied proportions of the
arches (Fig. 350); while that surrounding the round portion of the
Temple Church[51] has double as many compartments as there are pillars
in the arcade, and, consequently, behind every arch of the great arcade
is a groined compartment which is nearly square, while behind every
pillar is one of a triangular plan, vaulted in a peculiar manner from
its corners without any ribs between the transverse ribs.
The vaulting of a polygon with a central pillar assumed now a form of
exquisite beauty. Its two special types in its simpler form are the
Chapter-houses at Salisbury and Westminster,--truly a _par nobile
fratrum_,--and claiming special attention as showing the extraordinary
beauty attained by the use of ribbed vaulting united with the pointed
arch.
[Illustration: Fig. 350.--Westminster Abbey. Vaulting of Aisle round
Apse.]
[Illustration: Fig. 351.]
[Illustration: Fig. 352.]