172 THE STONES OF VENICE CONSTRUCTION

§ 18. Now, in the arches h, i, k, a slight modification has been made in the form of the central piece, in order that it may continue the curve of the cusp. This modification is not to be given to it in practice without considerable nicety of workmanship; and some curious results took place in Venice from this difficulty.

At l (Plate 3) is the shape of the Venetian side stone, with its cusp detached from the arch. Nothing can possibly be better or more graceful, or have the weight better disposed in order to cause it to nod forwards against the keystone, as above explained, Chap. X. § 2, where I developed the whole system of the arch from three pieces, in order that the reader might now clearly see the use of the weight of the cusp.

Now a Venetian Gothic palace has usually at least three storeys; with perhaps ten or twelve windows in each storey, and this on two or three of its sides, requiring altogether some hundred to a hundred and fifty side pieces.

I have no doubt, from observation of the way the windows are set together, that the side pieces were carved in pairs, like hooks, of which the keystones were to be the eyes; that these side pieces were ordered by the architect in the gross, and were used by him sometimes for wider, sometimes for narrower windows; bevelling the two ends as required, fitting in keystones as he best could, and now and then varying the arrangement by turning the side pieces upside down.

There are various conveniences in this way of working, one of the principal being that the side pieces with their cusps were always cut to their complete form, and that no part of the cusp was carried out into the keystone, which followed the curve of the outer arch itself. The ornaments of the cusp might thus be worked without any troublesome reference to the rest of the arch.

§ 19. Now let us take a pair of side pieces, made to order, like that at l, and see what we can make of them. We will try to fit them first with a keystone which continues the

[Version 0.04: March 2008]