I. The practical duties of buildings are twofold.
They have either (1), to hold and protect something; or (2), to place or carry something.
1. Architecture of Protection. This is architecture intended to protect men or their possessions from violence of any kind, whether of men or of the elements. It will include all churches, houses, and treasuries; fortresses, fences, and ramparts; the architecture of the hut and sheepfold; of the palace and the citadel: of the dyke, breakwater, and sea-wall. And the protection, when of living creatures, is to be understood as including commodiousness and comfort of habitation, wherever these are possible under the given circumstances.
2. Architecture of Position. This is architecture intended to carry men or things to some certain places, or to hold them there. This will include all bridges, aqueducts, and road architecture; light-houses, which have to hold light in appointed places; chimneys to carry smoke or direct currents of air; staircases; towers, which are to be watched from or cried from, as in mosques, or to hold bells, or to place men in positions of offence, as ancient moveable attacking towers, and most fortress towers.
II. Protective architecture has to do one or all of three things: to wall a space, to roof it, and to give access to it, of 48 persons, light, and air; and it is therefore to be considered under the three divisions of walls, roofs, and apertures.
We will take, first, a short, general view of the connection of these members, and then examine them in detail: endeavoring always to keep the simplicity of our first arrangement in view; for protective architecture has indeed no other members than these, unless flooring and paving be considered architecture, which it is only when the flooring is also a roof; the laying of the stones or timbers for footing being pavior’s or carpenter’s work, rather than architect’s; and, at all events, work respecting the well or ill doing of which we shall hardly find much difference of opinion, except in points of �sthetics. We shall therefore concern ourselves only with the construction of walls, roofs, and apertures.
III. 1. Walls.—A wall is an even and united fence, whether of wood, earth, stone, or metal. When meant for purposes of mere partition or enclosure, it remains a wall proper: but it has generally also to sustain a certain vertical or lateral pressure, for which its strength is at first increased by some general addition to its thickness; but if the pressure becomes very great, it is gathered up into piers to resist vertical pressure, and supported by buttresses to resist lateral pressure.
If its functions of partition or enclosure are continued, together with that of resisting vertical pressure, it remains as a wall veil between the piers into which it has been partly gathered; but if it is required only to resist the vertical or roof pressure, it is gathered up into piers altogether, loses its wall character, and becomes a group or line of piers.
On the other hand, if the lateral pressure be slight, it may retain its character of a wall, being supported against the pressure by buttresses at intervals; but if the lateral pressure be very great, it is supported against such pressure by a continuous buttress, loses its wall character, and becomes a dyke or rampart.
IV. We shall have therefore (A) first to get a general idea of a wall, and of right construction of walls; then (B) to see 49 how this wall is gathered into piers; and to get a general idea of piers and the right construction of piers; then (C) to see how a wall is supported by buttresses, and to get a general idea of buttresses and the right construction of buttresses. This is surely very simple, and it is all we shall have to do with walls and their divisions.
V. 2. Roofs.—A roof is the covering of a space, narrow or wide. It will be most conveniently studied by first considering the forms in which it may be carried over a narrow space, and then expanding these on a wide plan; only there is some difficulty here in the nomenclature, for an arched roof over a narrow space has (I believe) no name, except that which belongs properly to the piece of stone or wood composing such a roof, namely, lintel. But the reader will have no difficulty in understanding that he is first to consider roofs on the section only, thinking how best to construct a narrow bar or slice of them, of whatever form; as, for instance, x, y, or z, over the plan or area a, Fig. I. Having done this, let him 50 imagine these several divisions, first moved along (or set side by side) over a rectangle, b, Fig. I., and then revolved round a point (or crossed at it) over a polygon, c, or circle, d, and he will have every form of simple roof: the arched section giving successively the vaulted roof and dome, and the gabled section giving the gabled roof and spire.
As we go farther into the subject, we shall only have to add one or two forms to the sections here given, in order to embrace all the uncombined roofs in existence; and we shall not trouble the reader with many questions respecting cross-vaulting, and other modes of their combination.
VI. Now, it also happens, from its place in buildings, that the sectional roof over a narrow space will need to be considered before we come to the expanded roof over a broad one. For when a wall has been gathered, as above explained, into piers, that it may better bear vertical pressure, it is generally necessary that it should be expanded again at the top into a continuous wall before it carries the true roof. Arches or lintels are, therefore, thrown from pier to pier, and a level preparation for carrying the real roof is made above them. After we have examined the structure of piers, therefore, we shall have to see how lintels or arches are thrown from pier to pier, and the whole prepared for the superincumbent roof; this arrangement being universal in all good architecture prepared for vertical pressures: and we shall then examine the condition of the great roof itself. And because the structure of the roof very often introduces certain lateral pressures which have much to do with the placing of buttresses, it will be well to do all this before we examine the nature of buttresses, and, therefore, between parts (B) and (C) of the above plan, IV. So now we shall have to study: (A) the construction of walls; (B) that of piers; (C) that of lintels or arches prepared for roofing; (D) that of roofs proper; and (E) that of buttresses.
VII. 3. Apertures.—There must either be intervals between the piers, of which intervals the character will be determined by that of the piers themselves, or else doors or windows in the walls proper. And, respecting doors or windows, 51 we have to determine three things: first, the proper shape of the entire aperture; secondly, the way in which it is to be filled with valves or glass; and thirdly, the modes of protecting it on the outside, and fitting appliances of convenience to it, as porches or balconies. And this will be our division F; and if the reader will have the patience to go through these six heads, which include every possible feature of protective architecture, and to consider the simple necessities and fitnesses of each, I will answer for it, he shall never confound good architecture with bad any more. For, as to architecture of position, a great part of it involves necessities of construction with which the spectator cannot become generally acquainted, and of the compliance with which he is therefore never expected to judge,—as in chimneys, light-houses, &c.: and the other forms of it are so closely connected with those of protective architecture, that a few words in Chap. XIX. respecting staircases and towers, will contain all with which the reader need be troubled on the subject.