CHAPTER XVI.
FORM OF APERTURE
§ I. We have now, in order, examined the means of raising walls and sustaining roofs, and we have finally to consider the structure of the necessary apertures in the wall veil, the door and window; respecting which there are three main points to be considered.
1. The form of the aperture, i.e., its outline, its size, and the forms of its sides.
2. The filling of the aperture, i.e., valves and glass, and their holdings.
3. The protection of the aperture, and its appliances, i.e., canopies, porches, and balconies. We shall examine these in succession.
§ II. 1. The form of the aperture: and first of doors. We will, for the present, leave out of the question doors and gates in unroofed walls, the forms of these being very arbitrary, and confine ourselves to the consideration of doors of entrance into roofed buildings. Such doors will, for the most part, be at, or near, the base of the building; except when raised for purposes of defence, as in the old Scotch border towers, and our own Martello towers, or, as in Switzerland, to permit access in deep snow, or when stairs are carried up outside the house for convenience or magnificence. But in most cases, whether high or low, a door may be assumed to be considerably lower than the apartments or buildings into which it gives admission, and therefore to have some height of wall above it, whose weight must be carried by the heading of the door. It is clear, therefore, that the best heading must be an arch, because the strongest, and that a square-headed door must be wrong, unless under Mont-Cenisian masonry; or else, unless the top of the door be the roof of the building, as in low cottages. And a square-headed door is just so much more wrong and ugly than a connexion of main shafts by lintels, as the weight of wall above the door is likely to be greater than that above the main shafts. Thus, while I admit the Greek general forms of temple to be admirable in their kind, I think the Greek door always offensive and unmanageable.
§ III. We have it also determined by necessity, that the apertures shall be at least above a man’s height, with perpendicular sides (for sloping sides are evidently unnecessary, and even inconvenient, therefore absurd) and level threshold; and this aperture we at present suppose simply cut through the wall without any bevelling of the jambs. Such a door, wide enough for two persons to pass each other easily, and with such fillings or valves as we may hereafter find expedient, may be fit enough for any building into which entrance is required neither often, nor by many persons at a time. But when entrance and egress are constant, or required by crowds, certain further modifications must take place.
Fig. XLIII
§ IV. When entrance and egress are constant, it may be supposed that the valves will be absent or unfastened,—that people will be passing more quickly than when the entrance and egress are unfrequent, and that the square angles of the wall will be inconvenient to such quick passers through. It is evident, therefore, that what would be done in time, for themselves, by the passing multitude, should be done for them at once by the architect; and that these angles, which would be worn away by friction, should at once be bevelled off, or, as it is called, splayed, and the most contracted part of the aperture made as short as possible, so that the plan of the entrance should become as at a, Fig. XLIII.
§ V. Farther. As persons on the outside may often approach the door or depart from it, beside the building, so as to turn aside as they enter or leave the door, and therefore touch its jamb, but, on the inside, will in almost every case approach the door, or depart from it in the direct line of the entrance (people generally walking forward when they enter a hall, court, or chamber of any kind, and being forced to do so when they enter a passage), it is evident that the bevelling may be very slight on the inside, but should be large on the outside, so that the plan of the aperture should become as at b, Fig. XLIII. Farther, as the bevelled wall cannot conveniently carry an unbevelled arch, the door arch must be bevelled also, and the aperture, seen from the outside, will have somewhat the aspect of a small cavern diminishing towards the interior.
§ VI. If, however, beside frequent entrance, entrance is required for multitudes at the same time, the size of the aperture either must be increased, or other apertures must be introduced. It may, in some buildings, be optional with the architect whether he shall give many small doors, or few large ones; and in some, as theatres, amphitheatres, and other places where the crowd are apt to be impatient, many doors are by far the best arrangement of the two. Often, however, the purposes of the building, as when it is to be entered by processions, or where the crowd most usually enter in one direction, require the large single entrance; and (for here again the æsthetic and structural laws cannot be separated) the expression and harmony of the building require, in nearly every case, an entrance of largeness proportioned to the multitude which is to meet within. Nothing is more unseemly than that a great multitude should find its way out and in, as ants and wasps do, through holes; and nothing more undignified than the paltry doors of many of our English cathedrals, which look as if they were made, not for the open egress, but for the surreptitious drainage of a stagnant congregation. Besides, the expression of the church door should lead us, as far as possible, to desire at least the western entrance to be single, partly because no man of right feeling would willingly lose the idea of unity and fellowship in going up to worship, which is suggested by the vast single entrance; partly because it is at the entrance that the most serious words of the building are always addressed, by its sculptures or inscriptions, to the worshipper; and it is well, that these words should be spoken to all at once, as by one great voice, not broken up into weak repetitions over minor doors.
In practice the matter has been, I suppose, regulated almost altogether by convenience, the western doors being single in small churches, while in the larger the entrances become three or five, the central door remaining always principal, in consequence of the fine sense of composition which the mediæval builders never lost. These arrangements have formed the noblest buildings in the world. Yet it is worth observing55 how perfect in its simplicity the single entrance may become, when it is treated as in the Duomo and St. Zeno of Verona, and other such early Lombard churches, having noble porches, and rich sculptures grouped around the entrance.
§ VII. However, whether the entrances be single, triple, or manifold, it is a constant law that one shall be principal, and all shall be of size in some degree proportioned to that of the building. And this size is, of course, chiefly to be expressed in width, that being the only useful dimension in a door (except for pageantry, chairing of bishops and waving of banners, and other such vanities, not, I hope, after this century, much to be regarded in the building of Christian temples); but though the width is the only necessary dimension, it is well to increase the height also in some proportion to it, in order that there may be less weight of wall above, resting on the increased span of the arch. This is, however, so much the necessary result of the broad curve of the arch itself, that there is no structural necessity of elevating the jamb; and I believe that beautiful entrances might be made of every span of arch, retaining the jamb at a little more than a man’s height, until the sweep of the curves became so vast that the small vertical line became a part of them, and one entered into the temple as under a great rainbow.
§ VIII. On the other hand, the jamb may be elevated indefinitely, so that the increasing entrance retains at least the proportion of width it had originally; say 4 ft. by 7 ft. 5 in. But a less proportion of width than this has always a meagre, inhospitable, and ungainly look except in military architecture, where the narrowness of the entrance is necessary, and its height adds to its grandeur, as between the entrance towers of our British castles. This law however, observe, applies only to true doors, not to the arches of porches, which may be of any proportion, as of any number, being in fact intercolumniations, not doors; as in the noble example of the west front of Peterborough, which, in spite of the destructive absurdity of its central arch being the narrowest, would still, if the paltry porter’s lodge, or gatehouse, or turnpike, or whatever it is, were knocked out of the middle of it, be the noblest west front in England.
§ IX. Further, and finally. In proportion to the height and size of the building, and therefore to the size of its doors, will be the thickness of its walls, especially at the foundation, that is to say, beside the doors; and also in proportion to the numbers of a crowd will be the unruliness and pressure of it. Hence, partly in necessity and partly in prudence, the splaying or chamfering of the jamb of the larger door will be deepened, and, if possible, made at a larger angle for the large door than for the small one; so that the large door will always be encompassed by a visible breadth of jamb proportioned to its own magnitude. The decorative value of this feature we shall see hereafter.
§ X. The second kind of apertures we have to examine are those of windows.
Window apertures are mainly of two kinds; those for outlook, and those for inlet of light, many being for both purposes, and either purpose, or both, combined in military architecture with those of offence and defence. But all window apertures, as compared with door apertures, have almost infinite licence of form and size: they may be of any shape, from the slit or cross slit to the circle;56 of any size, from the loophole of the castle to the pillars of light of the cathedral apse. Yet, according to their place and purpose, one or two laws of fitness hold respecting them, which let us examine in the two classes of windows successively, but without reference to military architecture, which here, as before, we may dismiss as a subject of separate science, only noticing that windows, like all other features, are always delightful, if not beautiful, when their position and shape have indeed been thus necessarily determined, and that many of their most picturesque forms have resulted from the requirements of war. We should also find in military architecture the typical forms of the two classes of outlet and inlet windows in their utmost development; the greatest sweep of sight and range of shot on the one hand, and the fullest entry of light and air on the other, being constantly required at the smallest possible apertures. Our business, however, is to reason out the laws for ourselves, not to take the examples as we find them.
§ XI. 1. Outlook apertures. For these no general outline is determinable by the necessities or inconveniences of outlooking, except only that the bottom or sill of the windows, at whatever height, should be horizontal, for the convenience of leaning on it, or standing on it if the window be to the ground. The form of the upper part of the window is quite immaterial, for all windows allow a greater range of sight when they are approached than that of the eye itself: it is the approachability of the window, that is to say, the annihilation of the thickness of the wall, which is the real point to be attended to. If, therefore, the aperture be inaccessible, or so small that the thickness of the wall cannot be entered, the wall is to be bevelled57 on the outside, so as to increase the range of sight as far as possible; if the aperture can be entered, then bevelled from the point to which entrance is possible. The bevelling will, if possible, be in every direction, that is to say, upwards at the top, outwards at the sides, and downwards at the bottom, but essentially downwards; the earth and the doings upon it being the chief object in outlook windows, except of observatories; and where the object is a distinct and special view downwards, it will be of advantage to shelter the eye as far as possible from the rays of light coming from above, and the head of the window may be left horizontal, or even the whole aperture sloped outwards, as the slit in a letter-box is inwards.
The best windows for outlook are, of course, oriels and bow windows, but these are not to be considered under the head of apertures merely; they are either balconies roofed and glazed, and to be considered under the head of external appliances, or they are each a story of an external semi-tower, having true aperture windows on each side of it.
§ XII. 2. Inlet windows. These windows may, of course, be of any shape and size whatever, according to the other necessities of the building, and the quantity and direction of light desired, their purpose being now to throw it in streams on particular lines or spots; now to diffuse it everywhere; sometimes to introduce it in broad masses, tempered in strength, as in the cathedral colored window; sometimes in starry showers of scattered brilliancy, like the apertures in the roof of an Arabian bath; perhaps the most beautiful of all forms being the rose, which has in it the unity of both characters, and sympathy with that of the source of light itself. It is noticeable, however, that while both the circle and pointed oval are beautiful window forms, it would be very painful to cut either of them in half and connect them by vertical lines, as in Fig. XLIV. The reason is, I believe, that so treated, the upper arch is not considered as connected with the lower, and forming an entire figure, but as the ordinary arch roof of the aperture, and the lower arch as an arch floor, equally unnecessary and unnatural. Also, the elliptical oval is generally an unsatisfactory form, because it gives the idea of useless trouble in building it, though it occurs quaintly and pleasantly in the former windows of France: I believe it is also objectionable because it has an indeterminate, slippery look, like that of a bubble rising through a fluid. It, and all elongated forms, are still more objectionable placed horizontally, because this is the weakest position they can structurally have; that is to say, less light is admitted, with greater loss of strength to the building, than by any other form. If admissible anywhere, it is for the sake of variety at the top of the building, as the flat parallelogram sometimes not ungracefully in Italian Renaissance.
Fig. XLIV.
§ XIII. The question of bevelling becomes a little more complicated in the inlet than the outlook window, because the mass or quantity of light admitted is often of more consequence than its direction, and often vice versâ; and the outlook window is supposed to be approachable, which is far from being always the case with windows for light, so that the bevelling which in the outlook window is chiefly to open range of sight, is in the inlet a means not only of admitting the light in greater quantity, but of directing it to the spot on which it is to fall. But, in general, the bevelling of the one window will reverse that of the other; for, first, no natural light will strike on the inlet window from beneath, unless reflected light, which is (I believe) injurious to the health and the sight; and thus, while in the outlook window the outside bevel downwards is essential, in the inlet it would be useless: and the sill is to be flat, if the window be on a level with the spot it is to light; and sloped downwards within, if above it. Again, as the brightest rays of light are the steepest, the outside bevel upwards is as essential in the roof of the inlet as it was of small importance in that of the outlook window.
§ XIV. On the horizontal section the aperture will expand internally, a somewhat larger number of rays being thus reflected from the jambs; and the aperture being thus the smallest possible outside, this is the favorite military form of inlet window, always found in magnificent development in the thick walls of mediæval castles and convents. Its effect is tranquil, but cheerless and dungeon-like in its fullest development, owing to the limitation of the range of sight in the outlook, which, if the window be unapproachable, reduces it to a mere point of light. A modified condition of it, with some combination of the outlook form, is probably the best for domestic buildings in general (which, however, in modern architecture, are unhappily so thin walled, that the outline of the jambs becomes a matter almost of indifference), it being generally noticeable that the depth of recess which I have observed to be essential to nobility of external effect has also a certain dignity of expression, as appearing to be intended rather to admit light to persons quietly occupied in their homes, than to stimulate or favor the curiosity of idleness.
CHAPTER XVII.
FILLING OF APERTURE
§ I. Thus far we have been concerned with the outline only of the aperture: we were next, it will be remembered, to consider the necessary modes of filling it with valves in the case of the door, or with glass or tracery in that of the window.
1. Fillings of doors. We concluded, in the previous Chapter, that doors in buildings of any importance or size should have headings in the form of an arch. This is, however, the most inconvenient form we could choose, as respects the fitting of the valves of the doorway; for the arch-shaped head of the valves not only requires considerable nicety in fitting to the arch, but adds largely to the weight of the door,—a double disadvantage, straining the hinges and making it cumbersome in opening. And this inconvenience is so much perceived by the eye, that a door valve with a pointed head is always a disagreeable object. It becomes, therefore, a matter of true necessity so to arrange the doorway as to admit of its being fitted with rectangular valves.
§ II. Now, in determining the form of the aperture, we supposed the jamb of the door to be of the utmost height required for entrance. The extra height of the arch is unnecessary as an opening, the arch being required for its strength only, not for its elevation. There is, therefore, no reason why it should not be barred across by a horizontal lintel, into which the valves may be fitted, and the triangular or semicircular arched space above the lintel may then be permanently closed, as we choose, either with bars, or glass, or stone.
This is the form of all good doors, without exception, over the whole world and in all ages, and no other can ever be invented.
§ III. In the simplest doors the cross lintel is of wood only, and glass or bars occupy the space above, a very frequent form in Venice. In more elaborate doors the cross lintel is of stone, and the filling sometimes of brick, sometimes of stone, very often a grand single stone being used to close the entire space: the space thus filled is called the Tympanum. In large doors the cross lintel is too long to bear the great incumbent weight of this stone filling without support; it is, therefore, carried by a pier in the centre; and two valves are used, fitted to the rectangular spaces on each side of the pier. In the most elaborate examples of this condition, each of these secondary doorways has an arch heading, a cross lintel, and a triangular filling or tympanum of its own, all subordinated to the main arch above.
§ IV. 2. Fillings of windows.
When windows are large, and to be filled with glass, the sheet of glass, however constructed, whether of large panes or small fragments, requires the support of bars of some kind, either of wood, metal, or stone. Wood is inapplicable on a large scale, owing to its destructibility; very fit for door-valves, which can be easily refitted, and in which weight would be an inconvenience, but very unfit for window-bars, which, if they decayed, might let the whole window be blown in before their decay was observed, and in which weight would be an advantage, as offering more resistance to the wind.
Iron is, however, fit for window-bars, and there seems no constructive reason why we should not have iron traceries, as well as iron pillars, iron churches, and iron steeples. But I have, in the “Seven Lamps,” given reasons for not considering such structures as architecture at all.
The window-bars must, therefore, be of stone, and of stone only.
§ V. The purpose of the window being always to let in as much light, and command as much view, as possible, these bars of stone are to be made as slender and as few as they can be, consistently with their due strength.
Fig. XLV.
Let it be required to support the breadth of glass, a, b, Fig. XLV. The tendency of the glass sustaining any force, as of wind from without, is to bend into an arch inwards, in the dotted line, and break in the centre. It is to be supported, therefore, by the bar put in its centre, c.
But this central bar, c, may not be enough, and the spaces a c, c b, may still need support. The next step will be to put two bars instead of one, and divide the window into three spaces as at d.
But this may still not be enough, and the window may need three bars. Now the greatest stress is always on the centre of the window. If the three bars are equal in strength, as at e, the central bar is either too slight for its work, or the lateral bars too thick for theirs. Therefore, we must slightly increase the thickness of the central bar, and diminish that of the lateral ones, so as to obtain the arrangement at f h. If the window enlarge farther, each of the spaces f g, g h, is treated as the original space a b, and we have the groups of bars k and l.
So that, whatever the shape of the window, whatever the direction and number of the bars, there are to be central or main bars; second bars subordinated to them; third bars subordinated to the second, and so on to the number required. This is called the subordination of tracery, a system delightful to the eye and mind, owing to its anatomical framing and unity, and to its expression of the laws of good government in all fragile and unstable things. All tracery, therefore, which is not subordinated, is barbarous, in so far as this part of its structure is concerned.
§ VI. The next question will be the direction of the bars. The reader will understand at once, without any laborious proof, that a given area of glass, supported by its edges, is stronger in its resistance to violence when it is arranged in a long strip or band than in a square; and that, therefore, glass is generally to be arranged, especially in windows on a large scale, in oblong areas: and if the bars so dividing it be placed horizontally, they will have less power of supporting themselves, and will need to be thicker in consequence, than if placed vertically. As far, therefore, as the form of the window permits, they are to be vertical.
§ VII. But even when so placed, they cannot be trusted to support themselves beyond a certain height, but will need cross bars to steady them. Cross bars of stone are, therefore, to be introduced at necessary intervals, not to divide the glass, but to support the upright stone bars. The glass is always to be divided longitudinally as far as possible, and the upright bars which divide it supported at proper intervals. However high the window, it is almost impossible that it should require more than two cross bars.
§ VIII. It may sometimes happen that when tall windows are placed very close to each other for the sake of more light, the masonry between them may stand in need, or at least be the better of, some additional support. The cross bars of the windows may then be thickened, in order to bond the intermediate piers more strongly together, and if this thickness appear ungainly, it may be modified by decoration.
§ IX. We have thus arrived at the idea of a vertical frame work of subordinated bars, supported by cross bars at the necessary intervals, and the only remaining question is the method of insertion into the aperture. Whatever its form, if we merely let the ends of the bars into the voussoirs of its heading, the least settlement of the masonry would distort the arch, or push up some of its voussoirs, or break the window bars, or push them aside. Evidently our object should be to connect the window bars among themselves, so framing them together that they may give the utmost possible degree of support to the whole window head in case of any settlement. But we know how to do this already: our window bars are nothing but small shafts. Capital them; throw small arches across between the smaller bars, large arches over them between the larger bars, one comprehensive arch over the whole, or else a horizontal lintel, if the window have a flat head; and we have a complete system of mutual support, independent of the aperture head, and yet assisting to sustain it, if need be. But we want the spandrils of this arch system to be themselves as light, and to let as much light through them, as possible: and we know already how to pierce them (Chap. XII. § VII.). We pierce them with circles; and we have, if the circles are small and the stonework strong, the traceries of Giotto and the Pisan school; if the circles are as large as possible and the bars slender, those which I have already figured and described as the only perfect traceries of the Northern Gothic.58 The varieties of their design arise partly from the different size of window and consequent number of bars; partly from the different heights of their pointed arches, as well as the various positions of the window head in relation to the roof, rendering one or another arrangement better for dividing the light, and partly from æsthetic and expressional requirements, which, within certain limits, may be allowed a very important influence: for the strength of the bars is ordinarily so much greater than is absolutely necessary, that some portion of it may be gracefully sacrificed to the attainment of variety in the plans of tracery—a variety which, even within its severest limits, is perfectly endless; more especially in the pointed arch, the proportion of the tracery being in the round arch necessarily more fixed.
§ X. The circular window furnishes an exception to the common law, that the bars shall be vertical through the greater part of their length: for if they were so, they could neither have secure perpendicular footing, nor secure heading, their thrust being perpendicular to the curve of the voussoirs only in the centre of the window; therefore, a small circle, like the axle of a wheel, is put into the centre of the window, large enough to give footing to the necessary number of radiating bars; and the bars are arranged as spokes, being all of course properly capitaled and arch-headed. This is the best form of tracery for circular windows, naturally enough called wheel windows when so filled.
§ XI. Now, I wish the reader especially to observe that we have arrived at these forms of perfect Gothic tracery without the smallest reference to any practice of any school, or to any law of authority whatever. They are forms having essentially nothing whatever to do either with Goths or Greeks. They are eternal forms, based on laws of gravity and cohesion; and no better, nor any others so good, will ever be invented, so long as the present laws of gravity and cohesion subsist.
§ XII. It does not at all follow that this group of forms owes its origin to any such course of reasoning as that which has now led us to it. On the contrary, there is not the smallest doubt that tracery began, partly, in the grouping of windows together (subsequently enclosed within a large arch59), and partly in the fantastic penetrations of a single slab of stones under the arch, as the circle in Plate V. above. The perfect form seems to have been accidentally struck in passing from experiment on the one side, to affectation on the other; and it was so far from ever becoming systematised, that I am aware of no type of tracery for which a less decided preference is shown in the buildings in which it exists. The early pierced traceries are multitudinous and perfect in their kind,—the late Flamboyant, luxuriant in detail, and lavish in quantity,—but the perfect forms exist in comparatively few churches, generally in portions of the church only, and are always connected, and that closely, either with the massy forms out of which they have emerged, or with the enervated types into which they are instantly to degenerate.
§ XIII. Nor indeed are we to look upon them as in all points superior to the more ancient examples. We have above conducted our reasoning entirely on the supposition that a single aperture is given, which it is the object to fill with glass, diminishing the power of the light as little as possible. But there are many cases, as in triforium and cloister lights, in which glazing is not required; in which, therefore, the bars, if there be any, must have some more important function than that of merely holding glass, and in which their actual use is to give steadiness and tone, as it were, to the arches and walls above and beside them; or to give the idea of protection to those who pass along the triforium, and of seclusion to those who walk in the cloister. Much thicker shafts, and more massy arches, may be properly employed in work of this kind; and many groups of such tracery will be found resolvable into true colonnades, with the arches in pairs, or in triple or quadruple groups, and with small rosettes pierced above them for light. All this is just as right in its place, as the glass tracery is in its own function, and often much more grand. But the same indulgence is not to be shown to the affectations which succeeded the developed forms. Of these there are three principal conditions: the Flamboyant of France, the Stump tracery of Germany, and the Perpendicular of England.