116 THE STONES OF VENICE CONSTRUCTION

c and d you will roughly knock off the corners, shaded in the figure, so as to reduce the shaft to the figure described by the inside lines in A and the outside lines in B; you then proceed to smooth it, you chisel away the shaded parts in B, and leave your finished shaft of the form of the inside lines e, g, f, h.

The result of this operation will be of course that the shaft tapers faster towards the top than it does near the ground. Observe this carefully; it is a point of great future importance.

§ 5. So far of the shape of detached or block shafts. We can carry the type no farther, on merely structural considerations: let us pass to the shaft of inferior materials.

Unfortunately, in practice, this step must be soon made. It is alike difficult to obtain, transport, and raise, block shafts more than ten or twelve feet long, except in remarkable positions, and as pieces of singular magnificence. Large pillars are therefore always composed of more than one block of stone. Such pillars are either jointed like basalt columns, and composed of solid pieces of stone set one above another; or they are filled-up towers, built of small stones cemented into a mass, with more or less of regularity: Keep this distinction carefully in mind, it is of great importance: for the jointed column, every stone composing which, however thin, is (so to speak) a complete slice of the shaft, is just as strong as the block pillar of one stone, so long as no forces are brought into action upon it which would have a tendency to cause horizontal dislocation. But the pillar which is built as a filled-up tower is of course liable to fissure in any direction, if its cement give way.

But, in either case, it is evident that all constructive reason for the curved contour is at once destroyed. Far from being an easy or natural procedure, the fitting of each portion of the curve to its fellow, in the separate stones, would require painful care and considerable masonic skill; while, in the case of the filled-up tower, the curve outwards would be even unsafe; for its greatest strength (and that the more in proportion to its careless building) lies in its bark, or shell of

[Version 0.04: March 2008]