Stone Stairs. When stairs are support ed by a wall at both ends, nothing diffi cult can occur in the construction ; in this the inner ends of the steps may ei ther terminate into a solid newal, or be tailed into a wall surrounding an open newal. Where elegance is not required, and where the newal does not exceed two feet six inches, the ends of the steps may be conveniently supported by a solid pillar ; but when the newal is thicker, a thin wall surrounding the newal would be cheaper. In the stairs of a stink story, where there is a geometrical stair above, the steps next to the newal are generally supported upon a dwarf wall. Geome trical 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 sally-formed oirits; so that they cannot descend in the inclined direction of the stair, not yet in a vertical direction ; the upper sally of every step forms an interior obtuse an gle, called a back rebate, and the lower, of course, an exterior one ; and the joint formed of these sallies is called a joggle. The upper part of the joint may be level from the face of the risers, to about one inch within the joint.
This is the plane of the tread of each step, continued one inch within the sur face of each riser ; the lower part of the joint is a narrow surface, perpendicular to the rake of the stair, at the end next to the newal. In stairs constructed of most kinds of stone, the thickness of eve ry step, at the thinnest place of the end Bext to the newal, has no occasion to ex ceed two inches, for steps of four feet in length, that is, by measuring from the in terior angle of every step perpendicular to the rake.
The thickness of steps at.the interior angle should be proportioned to the length of the step ; but allowing that the thickness of the steps at each interior an gle is sufficient at two inches, then will the thickness of the steps at the interior angles be half the number of inches that the length of the steps has in feet ; thus a step five feet long would be two inches and a half at that place.
The stone platform of geometrical stairs, viz. the landing half spaces, and quarter spaces, are constructed of one, two, or several stones, according to the difficulty of procuring them. When the platform consists of two or more stones, the first platform stone is laid upon the last step that is set, and the one end wedged in the wall : the next platform stone is joggled, or rebated, into the one next set, and the end again fixed in the wall, as that and the preceding steps are, and every stone in succession, till the platform is completed. If there is occa sion for another flight of steps, the last platform becomes a spring stone for the next step ; the joint is to be joggled, as well as all the succeeding steps, in the same manner as the first flight. Geome
trical stairs, executed in stone, depend on the following principle : that every body must at least be supported by three points, placed out of a straight line, and, consequently, if two edges of a body in different directions be secured to ano ther, the two bodies will be immoveable 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 the stair stone be a plat or step. The stones forming a plat form are generally of the same thickness as those forming the steps.
Roofs. Roof is that part of a building raised upon the walls,and extending over all the parts of the interior, which con sists not only of the covering or exterior part, hut of all the necessary supports of that part, for protecting its contents from inclement seasons. There are many forms of roofs, the most simple of which is that which has only one plane, and is called a shed roof; but the form which has always been, and still continues to be, in most general use, wherever the nature of climate requires it to be raised, is that, the vertical section of which consists of two sloping sides, is consequently trian gular, and called a span or pediment roof.
Here it will be proper to say some thing of the changes of inclination or pitch which have prevailed in this simple form, among different nations, from time to time, arising as well from the nature of the climate as the caprice of the people, and as transmitted down to the present age. The ancient Egyptians, Babyloni ans, and Persians, as well as other eastern nations, and also the present inhabitants of those climates where rain seldom ap pears, make their roofs quite flat. The ancient Greeks, perceiving the inconve nience of this, raised them in the middle, with a gentle inclination towards the sides; the height from the middle to the level of the walls not exceeding one ninth or one-eight part of the span ; as may he seen by many ancient temples still remaining in that country. The Ro mans made the height from one-fifth to two.ninth parts of the span. After the decline of the Roman empire, high pitch ed roofs began to he in general request all over Europe, and the vertical section of that which most generally prevailed seems to have been an equilateral trian gle, which was considered as the standard. In Germany, this has been remarkable from very remote antiquity, as appears from Vitruvius : the equilateral pitch, and that of a higher one, appears to have continued as long as pointed architecture preiailed.