Stone Stairs.—The principal object in erecting a stairway' must neces sarily be the securing of a safe and easy communication between floors at different levels, and, that those who ascend it may feel conscious of safety, the strength of the stair should be directly- apparent as well as substantial. To render the communication perfectly secure, it should also be guarded by a railing of appropriate height and strength.
Ratio of all stairs the correct ratio of the gradient—that is, the proper relative proportion between the height of the step (riser) and the breadth (tread)—must become a principal consideration where ease of ascent is of importance. It is claimed that the first attempt to fix this rela tion upon correct principles was made by Blonde} in his Coors a" Architec ture. His formula, hoi.vever, was applicable only to large buildings,.and no. t suitable to ordinary dwellings. The absolute measures of the riser and tread must necessarily depend upon the aim and design of the stair way, the riser varying from 5/, to 7X inches and the tread from 9 to 13 inches; so that the larger tread accompanies the smaller riser, and vice versa. The ratio of the gradient may be formed from the rule that two risers and one tread taken together should measure 24 inches. In this measurement it should be remarked that the tread is to be measured hori zontally from face to face of risers.
Classes of to the different positions and uses in tended in the edifice, stairways nmst be distinguished into classes, such as principal and back stairs and outside flights (perrons). In material they may be constructed of cut stone, such as sandstone, marble, granite, etc., or of brick in different forms and modes of construction.
The Forms of Stairways are various, beginning with the simplest or straight line, but diversified, according to the necessary adaptation to space and convenience, into triangular, circular, or elliptical, with winding steps, or of mixed forms with straight sides and circular ends. Straig-ht line stairs, in which every step of the tread is the same throughout the entire length, may consist of several runs or flights. To the latter belong the so-called " double stairs," in which the two flights rise symmetrically to one bead, or landing-place.
Stairs of Cul Stone are constructed either as saddled or geometrical stairs. In the former the steps are built for about inches on either side into the stair walls or arches, which should be at least one brick in thickness; in the latter the steps are walled in for about 12 inches only, lying free at the other end. Furthermore, a mutual foundation of about one inch is given to the steps throughout their whole length, with the intention of obtaining; a more even distribution of pressure. Figures 17 to 20 (p. 1) exhibit different forms of principal stairs saddled, while Figure 21 shows the perron, which is richly constructed in crit stone, likewise sad dled.
stair seen in Figure 17 is an example of the simple straight-line stair on a g,rand scale; it is in the Library at Munich, built by Gartner. Halfway in its length will be seen a so-called podest, or landing-place.
18, from a private house in Berlin, shows an elegantly-constructed broken-line stairway with three arms; light is obtained from a skylight. A triple-flight stair of this kind has two landing-places, which will be square if the flights are built of the same width.
19 gives an example of a double stairway with three flights, the upper two of which have the same direc tion, while the lower one—not entirely visible in the Fignre—is common to both. As the part at the uppermost step of a stairway is called the "stair-head," in contradistinction to the entrance at the lower step, the illustration may be said to give an example of a double-headed stair.
2o—our last example of grand stairways in cut stone—represents a large winding stair in the early Renaissance style in a French castle. In cases like this, if the inner solid or hollow part (stair-spindle or centre-post) be not too small in diameter, the stair will by no means be inconvenient; but the same breadth must be given to the steps in the half-length that rectangular steps have in the whole leng,th.
In all the above examples the staircase—that is to say, the space in which the stair is placed—is elegantly, and even superbly, finished.