of entrance, which gives to every arch, pointed and round, throughout the
roof, a different spring from its neighbours.

The vaulting ribs have the simplest of all profiles--that of a
chamfered beam. I call it simpler than even that of a square beam; for
in barking a log you cheaply get your chamfer, and nobody cares whether
the level is alike on each side: but you must take a larger tree, and
use much more work to get a square. And it is the same with stone.

And this profile is--fix the conditions of it, therefore, in your
mind,--venerable in the history of mankind as the origin of all Gothic
tracery-mouldings; venerable in the history of the Christian Church as
that of the roof ribs, both of the lower church of Assisi, bearing the
scroll of the precepts of St. Francis, and here at Florence, bearing
the scroll of the faith of St. Dominic. If you cut it out in paper, and
cut the corners off farther and farther, at every cut, you will produce
a sharper profile of rib, connected in architectural use with
differently treated styles. But the entirely venerable form is the
massive one in which the angle of the beam is merely, as it were,
secured and completed in stability by removing its too sharp edge.

Well, the vaulting ribs, as in Giotto's vault, then, have here, under
their painting, this rude profile: but do not suppose the vaults are
simply the shells cast over them. Look how the ornamental borders fall
on the capitals! The plaster receives all sorts of indescribably
accommodating shapes--the painter contracting and stopping his design
upon it as it happens to be convenient. You can't measure anything; you
can't exhaust; you can't grasp,--except one simple ruling idea, which a
child can grasp, if it is interested and intelligent: namely, that the
room has four sides with four tales told upon them; and the roof four