Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/559

Rh Rise height in inches. Tread breadth in inches. 10 .. Rise height in inches. STAIRS.] The construction of stairs is generally considered the highest department of the art of joinery. The principal object to be attended to is that the stairs should afford a safe and easy communication between floors at different levels. The strength of a stair ought to be apparent as well as real, in order that those who ascend it may feel conscious of safety. To make the communication safe, it should be guarded by a railing of proper height and strength ; in order that it may be easy, the rise and width (or tread) of the steps should be regular and justly propor tioned to each other, with convenient landings ; there should be no winding stsps, and the top of the rail should be of a convenient height for the hand. The first person that attempted to fix the relation between the height and width of a step, upon correct principles, was, we believe, Blondel, in his Cours d Architecture. His formula is applicable to very large buildings, but not to ordinary dwellings. Mr Ashpitel, who investigated the subject at length, gives the following rules for buildings of seven different classes : Tread breadth in inches. 12 Hi!.!..... .. .&quot;. .....::;! 5| 94 6| 11 6 9 7 104 61 These dimensions give angles of ascent varying from 24 to 37. Of course the projection of the nosing is not reckoned. Hawksley s patent treads for staircases to public thorough fares are composed of iron frames, in which small blocks of wood, placed the end way of the grain, are so secured as to present to the foot a roughened surface. They appear to be durable, and to admit of easy renewal of the wood when worn or injured. The forms of staircases are various, commencing with a straight flight, which should only be used to a low story. In towns, where space cannot be allowed for convenient forms, they are often made triangular, circular, or elliptical, with winding steps, or are made of a mixed form, with straight sides and circular ends. In large mansions, and in other situations where convenience and beauty are the chief objects of attention, winding steps are never intro duced when it is possible to avoid them. Good stairs, therefore, require less geometrical skill than those of an inferior character. The best architectural effect is produced by rectangular staircases, with ornamented railing and newels. In Gothic structures scarcely any other kind can be adopted with propriety for a principal staircase. Modern architecture admits of greater latitude in this respect, the end of the staircase being sometimes circular, and the hand-rail continued, beginning from either a scroll or a newel. When a rectangular staircase has a continued rail, it is necessary that it should be curved so as to change gradually from a level to an inclined direction. This curvature is called the ramp of the rail. The plan of a staircase of this kind is represented by ABCDinfig. 101; and fig. 103 shows a section of it, supposing it to be cut through at ab, on the plan. The hand-rail is supposed to begin with a newel at ^ the bottom, and the form of the cap of the newel ought to be determined so that it will mitre with the hand-rail. Let II in fifr. FlG - 101. Plan of Rectangular 102 be the section of the hand-rail, and a b the radius of the newel; then the form of the cap may be traced at 497 C. The sections of hand-rails are of various shapes ; some of the most common ones are too small ; a hand-rail should never be less than would require a square of which the side is 24- inches to circumscribe it. For the level landings of a stair case the height of the top of the hand-rail should never be more than about 40 inches, and in any part of the FIG. 102. Section of Hand-Bail and Newel. inclined rail the height of its upper side above the middle of the width of the step should be 40 inches, less the rise of one step when measured in a vertical direction. To describe the ramps, let r s in fig. 103 be a vertical line drawn through the middle of the width of the step ; set r u equal to r s, and draw u t at right angles with the back of the rail, cutting the horizontal line st in t ; then from the point t, as a centre, describe the curve of the rail. When there is a contrary flexure, as in the case before us, the T FIG. 103. Section for Construction of Kamps. method of describing the lesser curve is the same. The hand-rail of a stair generally begins with a scroll, and the first step of the stair is generally finished with what is called a curtail, a form corresponding closely to the scroll. There are a great variety of geometrical spirals; but as they all finish on a point, and as all architectural scrolls and volutes finish on a circle or eye, the usual mathematical scrolls are inapplicable. The earliest spiral adapted to architecture was that of De Lorme. Since his time several systems have been invented, particularly that Fig. 106. FIGS. 104 to 106 illustrate the construction of the Ionic Volute. of Goldmann ; the best is that derived from the Ionic volute (fig. 104). The height, eye, and number of revolutions of the IV -63