We proceed to notice the most convenient proportions of the stairs themselves as to height and breadth for their length. As to the breadth of the flights, that is compaiatively arbitrary : it should never be much less than 4 feet, so as to allow two persons to pass, except in back-staircases ; but it may be as much more as the space will permit, or the effect aimed at in the design may require. The best general, and what may bo considered standard, proportions, are 6 inches for the risers and 12 inches for the treads; though from 64 to 7 inches may be allowed for the former, and only ten for the latter, in secondary staircases. In those of a very superior kind, on the contrary, the risers do not exceed 5 or even 4 inches (less height than which last would be more fatiguing than convenient), and their treads are then made from 14 to 16 inches. The height, therefore, to the landing of the floor to bo reached being given, it is easy to calculate either how many risers of a certain number of inches will be required ; or what must be the dimensions of the risers and treads, in order to ascend within the space allowed. Supposing the first-mentioned ' height to be 14 feet, and the risers 6 inches, two risers will be equiva lent to 1 foot of ascent, and consequently twenty-eight risers will be required, or twenty-seven treads, the upper landing being the tread to the last riser. In such case, hardly less than an area of 20 by 8 feet, on the level of the upper floor, would ho sufficient for the staircase, unless there were winders instead of quarter-spaces, or of a single half apace between the two flights. The number of risers required is ascertained by reducing the given altitude of ascent to inches, and dividing it by the height of the risers : thus, taking the altitude as before (14 feet), and the risers at 5 inches, there must either be 33 risers a trifle more than 5 inches each, or 34 a trifle less. Roudelet gives the following very simple formula for calculating the dimensions of the treads and risers respectively, namely, calling 16 the riser, and t the tread, 2h+ t= 2 feet ; it is based on the principle that the ordinary length of a pace is equal to 2 feet, and that the effort exercised in lifting the leg vertically is double the effort required to move it horizontally.
Palladio, and others following him, have laid it down that the stair case ought to be seen immediately on entering a building; but it is impossible to establish any positive rule for what must depend upon particular circumstances, and this is by no means the beet general arrangement. In a public building or place where strangers go in and out without inquiry, it may be desirable that the staircase should present itself at once ; but certainly this is not the case in private mansions. On the contrary, it is in every respect better that the staircase should be kept out of view until the first vestibule has been passed through, and that it should be placed in a position as remote from the entrance into the house as the plan will admit, both in order that the approach to it may be lengthened, and that, in case it has any architectural pretensions at all, it may strike the more by not coming into view at once. At all events, only the lower part of the staircase —no more than is sufficient to indicate its situation—should he visible from the entrance, otherwise it will be inconveniently exposed ; and if there are doors to several rooms on the upper landing, persons passing from oue to the other would be seen from the hall. It is therefore a
great error to place the staircase, as is sometimes done, in the first or entrance hall of a mansion, because, in addition to the inconvenience just pointed out, such hall must be made the height of two floors, and consequently, if otherwise suitably proportioned to such height, it will be the most spacious and loftiest room, and so far be attended by a degree of effect which, instead of being afterwards increased or kept up, is greatly diminished. Such arrangement also cuts off the com munication above between the rooms on one side of the hall and those on the other, except there is a gallery or continuation of the landing carried over the entrance.
Even when kept apart from the entrance-hall or other vestibule, a staircase will always be sufficiently striking in proportion to the rest of a house, because it will produce greater architectural effect, and be loftier than the rooms themselves. We are now speaking only of what is usually termed a "grand staircase," leading up no higher than the principal floor, so that the whole of the space from the level of the landing is perfectly clear, and there are no flights leading up higher, for if there were, the space over head would appear encumbered and confused. There is in fact no part of an interior which accommodates itself more readily to architectural character and display, or which admits of greater variety of design both as to plan, section, and decora tion, than a staircase of the kind just referred to. If the house itself be not upon a very large scale, there is danger of doing here rather too much than too little. In regard to altitude .there will here always be greater magnitude than elsewhere ; if therefore corresponding magni tude of area be given to it, the staircase will overpower everything else, cause the rooms to appear small by comparison, and appear in itself too large for the house. It is therefore desirable to make the area, at least the visible area of the staircase, rather lees than more than that of any of the principal rooms. It is also rather a solecism to affect magnitude of space in other respects corresponding to that of height. While it serves as a contrast to the apartments, loftiness or excess of height, as compared with length and breadth, is as much an appropriate characteristic of a staircase as it is of a tower. Its altitude therefore from the bottom of the first flight to the ceiling, may very properly be made between two or three times the breadth. Accordingly it will be found expedient to enclose the landing, if continued quite round the staircase, not merely by a screen of columns, but in such manner as to shut it out from view, with only partial openings at intervals, in order to avoid too much spaciousness on that level, and to keep the cage of the same size from bottom to top. Of such staircase upon a large scale there is an example at Taymouth Castle, the seat of the Marquess of Breadalbane, which is about 40 feet square by 100 feet in height, with an upper corridor surrounding it, with open arches.