For instance, he attributes the use of the cusp or 'redent', in its more complex forms, to the necessity, or convenience, of diminishing the space of glass which the tracery grasps; and he attributes the reductions of the mouldings in the tracery bar, under portions of one section, to the greater facility thus obtained by the architect in directing his workmen. The plan of a window once given, and the moulding-section,—all is said, thinks M. Viollet le Duc. Very convenient indeed, for modern architects who have commission on the cost. But certainly not necessary, and perhaps even ^convenient, to Niccola Pisano, who is himself his workman, and cuts his own traceries, with his apron loaded with dust.
155. Again, the redent—the 'tooth within tooth' of a French tracery—may be necessary, to bite its glass. But the cusp, cuspis, spiny or spearlike point of a thirteenth century illumination is not in the least necessary to transfix the parchment. Yet do you suppose that the structural convenience of the redent entirely effaces from the mind of the designer the æsthetic characters which he seeks in the cusp? If you could for an instant imagine this, you
