“Here is a vast nave (completed except the extreme west end by about the year 1196), so admirably roofed with stone that the work has lasted intact for seven hundred years, and will probably, if not wantonly injured, last for centuries to come. These vaults are sexpartite.... The diagonal ribs are round-arched, while the transverse and longitudinal ribs are pointed. The intermediate transverse ribs are, however, pointed but slightly; and to bring their crowns up to the level of the intersections of the diagonals they are considerably stilted. The crowns of the main transverse ribs are a little lower than those of the diagonals, and those of the longitudinals are lower still. The vaults have, therefore, a distinctly domical form. These various adjustments, by greater or less pointing, stilting, and even by the retention of the round arch where it will serve best, exhibit the flexibility of the Gothic system in an interesting and instructive manner.” Mr. Moore, after some further details, continues:--“In the vaults of Paris, as in all Gothic vaults, the shells consist of successive courses of masonry which are slightly arched from rib to rib over each triangular cell. The beds of these successive courses are not parallel, but are variously inclined according as the mason found necessary or convenient in developing the concave and winding surfaces engendered by the forms and positions of the ribs to which they had to be accommodated. These courses of masonry have here in Paris, as they have in most Gothic vaults, a considerable inclination near the springing from the longitudinal rib upward toward the diagonal, and they become gradually more level as they approach the crown of the vault, where they are more nearly parallel. But perfectly parallel they can hardly ever be, since each course forms a portion of a surface that is concaved in all directions.” Mr. Moore adds that in the earliest and finest Gothic vaultings this masonry is composed of small stones perfectly faced and closely jointed; and the vaulting of Paris, especially that of the choir, is a model of careful and finished workmanship. [Illustration: _Photo_] [_Ed. Hautecœur, Paris._ THE NAVE: SOUTH ARCADE.]