1869.] Geometry in Arching. 653 which the bracket and cantilever are so much in use amongst architects as this. And, such is their intrinsic value, as features in design, as well as supports, that there is no prospect whatever of their dropping into disuse. To them we owe the great superiority of effect of our domestic architecture over that of other nations ; and, so long as wood continues to be plentiful, the skill of our carpenters will always be in requisition with respect to them. Therefore, it be- comes a necessity for the young practi- tioner to be, not alone informed as to what is and has been the practice in the formation of these very useful as well as ornamental appendages, but to seek and study out new outlines of shape, and fresh ideas of beauty, to make them all that they are capable of being made. GEOMETRY IN ARCHING. THERE is a wide divergence of opinion, with regard to the nativity and paternity of the Arch. Who de- vised this cunning and most useful fea- ture in Architecture, or where it had its birth, are alike tantalizing questions, to the archaeologist. We claim a right to our opinion ; and will freely give it in favor of Etruria, of which country Tar- quin, King of Rome, was a native, and, as he used the arch in the formation of the cloaca maxima, or main sewer, of that city, and employed Etrurian work- men, for the purpose, the presumption is very strong, that Tarquin's native land is entitled to the honor. As to the claims of Egypt and of Greece, they may find adherents, amongst theorists ; but practical minds know too well, that Rome has done more to cultivate the various properties of the arch, than all the world besides ; and that, as there remains, to this day, the greatest speci- men of its earliest construction, in that cloaca maxima, built by Etrurian hands, under a Roman king, who was himself an Etrurian, we may decide accordingly. But, whatever was its origin, its vast utility in building is unquestionable. The predominance, in Grecian con- struction, of straight lines, gave way to the arch, which led to the rapid expan- sion of design in Architecture, that found new forms, from the ideas of the various peoples, whose incursions into Roman territory, gave fresh impetus to invention, by blending their conceptions with those they found in their plunder- ing incursions. Thus the Romanesque, the Moorish, and the several forms of Gothic had their origin. We will now proceed to describe those forms, and the mode of outlining them, by means of their respective centres ; first premising, that the several stones of which an arch is composed are termed voussoirs, or arch stones, the uppermost one of which, as it serves to lock the arch together, as it were, is called the keystone. The lowest stone in each side is entitled the springer, as it is from these points the arch takes its rise. The highest point in an arch is known as the crown, and is often called the ver- tex, this latter in pointed architecture only. The springing line is the lowest part of the arch, between which and the crown, or vertex, the solid space is termed the haunch or flank. The under, or concave, surface is denominated the intrados ; the upper, or convex, the ex- trados. The supports are called either piers, or springing walls; and likewise abut- ments, but this last term is more applied to the arch of a bridge or viaduct. That part, at the springing line, on which the arch rests is known as the impost, and the span is the width of the two opposite imposts from each other.
