Fig. 133, square in general outline, has its edges softened by roll mouldings, and the profile is further developed by curving the line from the roll out to the soffit. This curve is struck from a centre which is obtained by letting fall a vertical line from the centre of the roll to its circumference, as shown in the figure. The line from the roll to the upright face of the arch is also inclined to that face instead of being at right angles with it, as it usually was in early profiles, and thus the flat surfaces are greatly lessened, and the effect of the whole is materially lightened.
The diagonal ribs were at first of a different profile. In the apse of Morienval they were simple three-quarter rounds, as at a, Fig. 134. In St. Denis the form was changed to that shown at b in the same figure; while at
FIG. 134.
Senlis this form was made more pleasing, and the rib was at the same time made stronger, by bringing the curves together in a more acute point, and by separating the two members of the rib by a sunk fillet, as at c. A defect[1] which resulted from the association of this form of the diagonal with the form a, Fig. 133, of the transverse rib, as at St. Denis, was that the round member of the one was heavier than the round members of the other. Whereas, for good proportion—since the diagonals are lighter than the transverse ribs,—it ought to be just the other way, or certainly the rounds of the transverse rib ought to be at least equal in the magnitude to the round of the diagonal.
At Paris this defect was avoided by giving the same profile—that of a, Fig. 133—to both diagonals and transverse ribs. The round mouldings of the smaller ribs were thus naturally made smaller than those of the larger ones, and
- ↑ See Viollet-le-Duc, s.v. Profil, p. 506.
