STONE STAIRS, those constructed of stone. When stone stairs are supported by a wall at both ends, nothing difficult can occur in the construction ; in these the inner ends of the steps may either terminate in a solid newel, or be tailed into a wall surrounding an open newel. Where elegance is not required, and where the newel does not exceed two feet six inches, the ends of the steps may be conveniently supported by a solid pillar ; but when the newel is thicker, a thin wall surrounding it would be cheaper.
In the stairs of a basement story, where there are geome trical stairs above, the steps next to the newel are generally supported upon a dwarf wall.
Stone geometrical stairs have the outer end fixed in the wall, and one of the edges of every step supported by the edge of the step below, and constructed with joggled joints, so that they cannot descend in the inclined direction of the plane, nor yet in a vertical direction ; the sally of every joint !brills an exterior obtuse angle on the lower part of the upper step, called a back rebate, and that on the upper part of the lower step, of course an interior one, and the joint formed of these sallies, is called a joggle, which may be level from the face of the risers, to about one inch within the joint. Thus is the plane of the tread of each step continued one inch within the surface of each riser, and the lower part of the joint is a na• rotv surface, perpendicular to the inclined direction, or soffit, of the stair at the end next to the newel.
In stairs constructed of most kinds of stone, the thickness of every step at the thinnest place of the end next to the newel, need not exceed two inches for steps of four feet in length, measuring from the interior angle of every step per pendicular to the rake. The thickness of steps at the interior angle should be proportioned to the length of the step : but allowing the thickness of the steps at each interior angle to be sufficient at two inches, the thickness of steps at the interior angles will be in inches half the length of the steps in feet : thus, a step of five feet long would be two inches and a half at that place.
The stone platforms of geometrical stairs, viz., the landings, half-paces, and quarter-paces, are constructed of one, two, or several stones, as they can be procured. When the platform consists of two or more stones, the first platform stone is laid upon the last step that is set, and one end is tailed in and wedged into the wall ; the next platform stone is joggled, or rebated, into one set, and the end also fixed into the wall, as that and the preceding steps are ; and thus with every stone in succession, till the platform is completed. If there is occasion for another flight of steps, the last stone of the platform becomes a spring stone for the next step, and the joint is to be joggled, as well as those of the succeeding steps, in the same manner as in the first flight. Geometrical stairs, executed in stone, depend upon the following principle : that everybody must, at least, be supported by three points placed out of a straight line, and consequently, if two edges of one body in different directions be secured to another, the two bodies will be immovable in respect to each other. This last is the case in a geometrical stair : one end of a stair stone is always tailed into the wall, and one edge either rests on the ground itself, or on the edge of the preceding stair stone, whether it be a plat or step. The stones of a platform are generally of the same thickness as those forming the steps.