Chapter VI: Front Matter (6)

The Principles of Vaulting--_continued_.

Certain practical points concerning vaulting--Ribs of early and
late vaulting--Filling in of intermediate surfaces or
cells--Methods adopted in France and England--Sexpartite
vaulting--Crypt of Glasgow Cathedral--Choir at
Lincoln--Chapter-house, Lichfield--Caudebec, Normandy--Octagonal
kitchen of the Monastery, Durham--Lady Chapel, Salisbury--Segmental
vaulting--Temple Church--Lady Chapel, St. Saviour’s,
Southwark--Westminster Abbey--Intermediate ribs--Presbytery at
Ely--Chapter-houses of Chester and Wells--Exeter
Cathedral--Cloisters, Westminster--“Liernes”--Ely
Cathedral--Chancel, Nantwich Church--Crosby Hall and Eltham
Palace--Choir at Gloucester--Winchester
Cathedral--Fan-vaulting--Cloisters at Gloucester--King’s College
Chapel, Cambridge--Divinity Schools, Oxford--Roof of Henry VII.’s
Chapel, Westminster--Ideal of its _design_.

My last lecture brought the subject of vaulting to its full _functional_ development,--that which contains all elements whose origin can be traced to the demands of utility, but none which have been introduced purely for decorative purposes. In my present lecture I must supplement what I then treated of with some cases of its application which I had not then time to detail, and then proceed to carry on my subject into its more distinctly decorative developments.

Before, however, I proceed further, it may be advantageous--though construction does not, perhaps, come within the range of lectures in this Academy, excepting so far as it exercises an influence upon form--to say a few words on certain practical points which are necessary to the full understanding, even of the artistic portion of the subject we are considering.

In the earlier forms of vaulting, the entire strength lay in the continuous arched surface, which was constructed of brick or of stone, or of rubble bonded at intervals with brick or stone; the rubble or stone being often of the cellular material called tufa, which was much used by the early builders on account of its lightness as well as the tenacity with which it united itself to the cement.

Transverse ribs were next introduced at intervals to strengthen the wider spaces; and, at a later period, the angles were similarly fortified.

These ribs, in early examples, sprang distinctly as separate arches from the impost, the vaulting passing over them (sections, Fig. 356). At a later period--even in round-arched vaulting--we find the practice coming into vogue of uniting the ribs, and even the springers of the vaulting itself, by cutting them at the base out of the same blocks of stone. We see an early specimen of this in St. Bartholomew’s Church (Fig. 357).

When the ribs became more numerous, it often occurred that five or even eight of them had to spring from one group of capitals; and at times three at least (and subsequently more) from a _single_ capital. It is clear that in such cases the three or more distinct forms could scarcely retain their separate existence, but that being united in their lower portions in a single block, their forms would, more or less, die one into another. Though we can trace this process in Norman work, it was not completely established till some time later.

It will be better understood by means of Fig. 358, in which a transverse rib, two diagonal ribs, and two wall ribs meet at their common springing line, and so intersect and unite one with another as to produce a section at the base composed of portions of them all. Now, a drawing of this group of ribs will at once show that their combined and united form must extend to some considerable height above the springing; and so far as it reaches, which is often some 8 feet or 10 feet in height, they cannot possess an individual existence (Fig. 359). To this height, then, it is customary to build the group of ribs in horizontal courses, and only to commence the radiating arch-joints where the ribs clear themselves one from another, which usually occurs at one level, though in vaults of great irregularity one rib often clears itself at a lower level than another.

In setting out the relative position of the ribs upon the common springing level, great skill and judgment are requisite, or they will clear themselves one of another so irregularly as to cause great difficulty and needless twisting in the filling in of the vaulting surface. If you set out on plan the side lines of two ribs (Fig. 360), and lay down the true position of the mouldings of _one_ of them, it is clear that, if the curvature

of both were equal, the second rib should be set out with its back line at an equal distance from the points at which the plans of the adjoining lines would intersect; for, in following the curve, both would at a given height reach a point vertically over that intersection, and so the filling in would have a proper starting-point, which would not be the case if they reached that vertical line at different heights. As, however, the diagonal rib (where the ridges are level) has to travel farther to reach a given height, its springing section has to be set _farther back_ to make it reach the vertical line over this point of intersection at an equal level with the transverse rib. The wall rib in a square vault would be similarly placed with the transverse rib; but in an oblong vault, as it would travel a _less_ distance to reach a given level, its springing section must be placed _forwarder_ than that of the transverse rib, and, of course, _greatly_ forwarder than the diagonal. This is easily adjusted by drawing the curve of the back of the rib, whose position is first determined, drawing against it the vertical line of its intersection with the next rib, and then, from the apex point of the adjoining rib, to draw its curve through the point of intersection, which will give on the springing line the distance _backward or forward_ at which the springing section of that rib should be placed (Fig. 361).

The ribs of all vaulting of early date are square and flat at the back; the vaulting, which is often very thick, passing over and resting upon their backs. In later works the ribs were usually deeper from intrados to extrados, and were notched, or as it is technically called, “rebated,” to receive the vaulting, or at least the lower part of its thickness (Fig. 362); for where the surface was not intended to be plastered, the wrought stonework was often a thin casing covered over above by a thicker mass of rough work. The curvature of the courses of wrought stone enabled them to be set without the use of continuous timber centering, and this inner facing, once finished, would itself form a substantial centering for the outer rough vault.

At a later period this outer thickness was dispensed with as a superfluous load. In all cases the hollow space against the wall behind was filled in solid to a certain height to strengthen the haunches of the vault.

The ribs now became beautifully moulded, and sometimes decorated with carving. In early works, as at St. Cross;[52] St. Peter’s, Oxford; St. Joseph’s Chapel at Glastonbury;[53] and in the aisles at Canterbury, the old Norman chevron was continued in the ribs. The meetings and intersections of the ribs at their apex were usually ornamented with bosses, and beautifully carved. These bosses assumed many varieties of form--sometimes a small rosette, or a little tuft of foliage, merely to decorate the centre of the intersection without covering the mouldings; sometimes the mouldings themselves return round a central opening, with or without foliage; sometimes a head of part of a figure was added to the last-named form in each angle, nearly at the plane of vaulting; sometimes beneath such moulded boss a disk was attached with or without foliage, as if to form a cover to the central opening; indeed, it was occasionally actually the moveable cover of such an opening. In England the usual form is a group of foliage covering the intersection, and frequently containing figure sculpture. Westminster Abbey furnishes admirable examples both of the foliated and sculptured bosses.

As regards the intermediate surfaces of the vaulting, a curious difference is found to obtain between the methods adopted in France and in England.

In France the courses of stone run parallel to the ridges, as would naturally suggest itself from the original intersecting vaults (Fig. 363); while in England they often take an irregular direction, as if suggested by placing them at right angles to an imaginary centre line of each triangular space, though really deviating much and irregularly from such a rule.

The French seem much offended by the appearance of the English system; and I remember feeling in the same way when I first saw the French method. The latter seems to throw undue pressure on the diagonal ribs, while the English mode appears to throw it more equally on _all_ the ribs; throwing it, in fact, down into the direction of their meeting-point.[54]

I will now describe a form of vaulting which, though it originated during the round-arched period, seems more properly to belong to that now under consideration. We have seen that the arches of churches were frequently arranged in _pairs_; the piers alternating in size and design. Supposing each arch to be about half the width of the nave, each _pair_ of arches would form a square on the plan; and, though such a square space may be, and often was, divided into two oblongs in the vaulting, it is equally natural to vault it as a single square. As, however, this leaves the alternate piers unrepresented in the vaulting, it became frequent to carry across from this intermediate pier a single transverse rib crossing the diagonals at their point of intersection, and between it and those diagonals to introduce oblique vaulting cells, whose ridges strike from the centres of the half-bays to the point of intersection.

Dr. Whewell, followed by Professor Willis, has given this the name of “_sexpartite_” vaulting (Fig. 364), ordinary vaulting being _quadri_partite, as having four cells. It is obvious that, in a square building of two bays on each of its sides, this may be carried out on all four sides, and thus become an _octo_partite vault (Fig. 365);[55] or, as in the aisles of Lincoln Cathedral, it may be adopted on one side only, and so be _quinque_partite (Fig. 366).

These forms of vaulting were most frequent during the transitional period; that is to say, during the latter part of the twelfth century. Thus it is used in the work of William of Sens at Canterbury, and by Bishop Hugh at Lincoln, and preparations were made for it at St. David’s. It was, however, continued at Lincoln in the great transept, and in the aisles of the nave, which are of later date; and we have an instance of it at Westminster, as late as 1250, in the Chapel of St. Faith.[56]

The same principle was applied, in a varied form, at the east end of the Priory Church at Tynemouth, where, though the bays have ordinary vaulting, the eastern wall is divided into three parts, corresponding with the windows, over which cells of vaulting are formed, converging to the intersecting point of the compartment.[57] Curiously enough, we find the same arrangement repeated a century and a quarter later in the crypt of St. Stephen’s Chapel, in the Palace of Westminster.

In the Lady Chapel at Auxerre the same idea is carried out still farther, the vaulting, square in plan, having two of its sides divided into two cells each, as on the sexpartite principle, and the other two into _three_ each, as those above referred to, making in all a _deca_partite vault (Fig. 367). If _all_ sides had the threefold division, it would have become _dodeca_partite, or a vault of twelve cells.

M. Viollet Le Duc gives a curious instance of sexpartite or septipartite vaulting united with another form (Fig. 368), for which I know no definite name, but which is itself a union of the groined vault with what I have elsewhere called the square dome.

I will describe the last-named vault by a comparison between those of two corresponding chapels near the west end of Lincoln Cathedral, to the right and left of the nave.

The two chapels are alike in plan (Figs. 369, 370),--an oblong, each side of which is divided into two arches. They only differ in that one has a central pillar and the other has none. The one is simply divided into four groined vaults on the most customary principle (Fig. 371). The other is similarly vaulted up to the line of the square, the angles of which would be represented by the four bosses of the first-named vaults; but from thence the diagonal ribs, instead of returning downwards on to a central pillar, continue to rise till they meet in the middle point of the chapel (Fig. 372). This upper portion, therefore, is the top of a square dome; and the whole vault may be described as a square dome penetrated on each side by two Welsh groined cross vaults. This combination is common in the vaulting under central towers, as at Lincoln and York; though in these cases the central portion is bounded by a strongly-marked horizontal line defining the boundary of the half-groins below, and the square dome above. In the chapel I have been describing there is no such boundary-line, but the groining compartments continue till they meet in a point at the top. This system may be carried out with any number of bays; and we have in the Chapter-house at York an instance of its application to an octagon. The plan of the vaulting there is identical (or nearly so) with that of Westminster or Salisbury, but the portion enclosed within the inner octagon, instead of turning down to the central pillar, runs up to the point at which all the arched lines would meet in the centre (Fig. 373).

The relation between the vaulting of the Chapter-houses of York and Westminster is, in fact, the same as that between the two chapels at Lincoln just described. In each case we see how similar forms may be covered over with vaulting nearly identical in plan--with or without a central pillar at pleasure.

There is a parallel case in the crypt of Glasgow Cathedral, in which the compartment is divided on three of its sides into _two_, and on the other into _three_ arches.

This crypt is a work in which the architect would appear to have revelled in self-sought perplexities, and to have solved them, one after another, with singular success.

The portion of the crypt which represents the choir overhead is really one of the most lively and amusing pieces of vaulting I know (Fig. 374). It consists of _ten_ bays; and, as the east end is necessarily divided into _two_ bays for the support of those above, nothing would have been more natural than to have placed an intermediate row of columns down the centre, dividing the whole into two ordinary ranges of vaulting. But no, the architect would have lost his fun by any such commonplace scheme, and _we_ should have lost a very pretty and instructive puzzle.

Beginning at the east end, he first cut off a space two bays long, then a second of three bays long, then a single bay, then another space of three bays, and finally a single bay at the west end; while to each of his groups of three bays, he gave a central column, and repeated the threefold division on its east and west sides. These square spaces, then, each of whose sides is divided into three, became the key-notes of his scheme, and most ingeniously and beautifully he vaulted them. The principle followed is really, however, nothing more than an adaptation of the ordinary mode of dividing a square into four smaller squares of groining, to a space whose sides are divided into _three_ instead of _two_ (A). The central square resting on the column remains unaltered, but the sides have each _three_ cells, the transverse ribs from the central column being bifurcated at their apices, and instead of going across to an opposite pillar, spread right and left to the _two_ pillars, while the main diagonal ribs remain unaltered. These are met at their apices by half-diagonals coming obliquely from the same pillars in the sides. The result is a star-like arrangement of an exceedingly pleasing, though at first sight, intricate character.

Adjoining one of these beautiful squares comes the compartment first alluded to (B). It is a very parallel case to that last described. On three sides it is the same as the Lincoln chapel, with a portion of a square dome instead of a central column (excepting only that this has the boundary-line), while the fourth side, having _three_ divisions instead of two, is dealt with precisely as has been described in the preceding case. Amongst these intricate compartments are alternated single bays, each divided transversely into three squares of ordinary groining; and the perplexity of the effect of the crypt arises not so much from the difficulty of any of the forms of vaulting, as from the constant change from one form to another, no two adjoining divisions being alike. The whole is carried out with excellent detail, and forms a most beautiful and interesting interior.

The subject of puzzles in vaulting suggests a notice of that of the choir at Lincoln, where the architect (De Noyes) seems to have put himself out of the way to make an easy matter difficult; for, instead of groining his oblong bays in the usual way, he has made each cell strike obliquely to points dividing the central ridge of the bay into three equal parts (Fig. 375); so that neither the cells nor the diagonal ribs from either side ever meet one another, but each cell is met by an intermediate or an oblique transverse rib from the opposite side. Professor Willis, in his peripatetic lecture there in 1848, called the architect “a crazy Frenchman,” it being then thought that he had been brought over by Bishop Hugh of Burgundy; but it has since been discovered that he was a member of a Norman family long settled in Lincolnshire; and the beauty of his work is such that we may well excuse this freak of eccentricity, and wish that this form of craziness was more prevalent amongst ourselves!

A curious effect is produced by carrying vaulting out accurately in a circular aisle or corridor, where it gives the diagonal ribs a twisted line, bending them out of the vertical plane. This is well seen in the apsidal aisle in the Cathedral at Bourges, both in the church itself and the crypt.

I will only notice two or three more varieties of this stage of vaulting, and those of a miscellaneous character.

The Chapter-house at Lichfield is an elongated octagon (Fig. 376), one of its sides on either hand being double the length of the others, and divided into two bays. The vaulting is a curious elongation of that of the regular octagonal chapter-house: a cell on either hand being interpolated, and the ribs all converging obliquely to the central pillar.

At Caudebec, in Normandy, we have, though of much later date, a hexagon vaulted much as our own chapter-houses, but with a pendant substituted for the central pillar, and ingeniously suspended by a long stone from a constructional vault above.

At Durham, in the octagonal kitchen of the monastery, we have a curious piece of vaulting planned with a view to a central ventilating lantern (Fig. 377). The ribs run from every corner at right angles to the side of the octagon, and consequently meet the third angle from that from which they set out, and their intersections leave an octagonal opening equal in diameter to one side of the original octagon in the centre, and this is strong enough to support the required lantern or louvre.

The vaulting of the Lady Chapel at Salisbury is remarkable for the extraordinary slenderness of the columns which support it, being thin Purbeck marble shafts of great height, reducing the width of the chapel by cutting off a very narrow range of vaulting from either side. Somewhat similar in idea is the vaulting of the crypt beneath the Sainte Chapelle at Paris, where, to avoid the segmental vaulting which would be the natural result of its limited height, the span is reduced by a range on either side of small pillars;--in this case so near the wall as to necessitate a great amount of stilting, and the introduction of a kind of tracery beneath the transverse ribs to give abutment to the central vault.

I should, in passing, mention, that segmental vaulting is very frequent at this period, where the height is limited; and that, even where the main arches are not so, the diagonal ribs frequently assumed that form; indeed, it became necessary wherever the length of a diagonal exceeded double the height of its arch.

Taking this stage of the history of vaulting as a whole, we have peculiarly favourable opportunities of studying it here in London: possessing, as we do, excellent examples of all its most leading varieties.

In the Temple Church we have the curious circular aisle already described, being a specimen of the earliest era of true pointed-arched vaulting; while in the eastern portion, dating some forty or fifty years later, we have the most typical specimen conceivable of vaulting, all springing from a given level, and with level ridges. It is rendered the more marked in character by the division of the three ranges of vaulting by means of the pier-arches, which, coming close under the vaulting, assume the character of enlarged ribs.

Very similar to the last-named is the vaulting of the Lady Chapel of St. Saviour (or St. Mary Overie), Southwark (Fig. 378). The only striking difference being the number of spans and the absence of pier-arches, so that it assumes the form of a space divided into twelve equal and square compartments, and carried by six similar columns.

In the choir of the same church we have an excellent specimen of clerestory vaulting, with oblong compartments and stilted side-cells, worked in a manner somewhat different from the usual ploughshare system.

In the eastern half of Westminster Abbey, including the transepts, we have the vaulting of the oblong space (with ploughshare side cells), and of the square space, and of the four-sided space of all degrees of irregularity; we have apses of two dimensions, viz., the great apse of the Sanctuary and those of the radiating chapels, which are as beautiful specimens of the apse vault as can be found; we have, in the Chapter-house, the vaulted octagon, with central pillar carried out in noble proportions and with excellent detail;[58] while in the crypt below is a repetition of the same vaulting, of depressed proportions, and carried out with the severest simplicity.

We have in its inner vestibule two oblong vaults

placed side by side, one apparently the square, and the other of the narrowest proportions; and in the outer vestibule beautiful miniature vaulting, on minute columns, and with the segmental arch; while in St. Faith’s Chapel, hard by, we have an excellent example of the sexpartite vault (Figs. 379, 380). Parts of the aisles, too, are remarkable for the subdivision of their bays by transverse arches of the double orders of mouldings, giving a great nobleness and strength to their effect; and all these varieties are carried out with admirable detail and studied art.

It would lead me into too great length if I were to go into the moulding of the ribs, their combinations where grouping and intersecting one another in the springers, and the mode in which the shafts are arranged for their support. My illustrations will, however, do much to explain this. I must not omit to mention that in French buildings, and frequently in the earlier English specimens, the plans of the abaci of these shafts assume both forms and positions indicating the general section and the directions of the ribs they carry,[59] and that this is even shared by the _bases_; showing that the vaulting was the _very first_ thing thought of and designed; and that, from the very floor of the building, it influenced the general design. This was lost in England by the introduction of the circular abacus.

I have hitherto dwelt wholly upon vaulting which has none but what I have termed _functional_ ribs; that is to say, such as have a specific utility, as transverse ribs to mark the boundaries of the bays, and to strengthen the vault in its main span; diagonal ribs to fortify the angles of intersection; and wall-ribs to support the vaulting surfaces at their junction with the walls; and occasionally ridge ribs, though these more properly belong to the succeeding stage. The next stage in the history of vaulting is that in which other than merely functional ribs are made use of--intermediate ribs, in fact, to subdivide the spaces between those used during the previous period.

In square vaulting, _one_ such additional rib is more usually introduced in each space (Fig. 381). In very oblong vaults _two_, and even _three_, were often introduced in the side spaces, though only one in the middle spaces (Fig. 382). It is clear that this addition necessitates the use of ridge ribs, as, without them, the point at which the intermediate ribs meet at their apex would want abutment. So reasonable, indeed, was this motive, that we often find the ridge rib to have been omitted between the intermediate ribs and the wall ribs, because there its use ceases.

One thing which followed the use of these additional ribs was the curious serrated plan of the filling in. The oblique position of these ribs would, if the plan of the filling in remained unaltered, cause the fillet or reveal of the rib nearly to vanish on one side, and to become very wide on the other. This led them to change the plan.

On looking at the top surface of vaulting where the ribs are visible, it is at once seen that this was also necessitated by a structural cause, as without it the filling in would not rest well upon the ribs (Fig. 383).

No better specimen of this form of vaulting can be referred to than that of the presbytery at Ely, built about 1240 to 1250, and the four bays immediately to the west of the crossing in Westminster Abbey, erected by Edward I. about 1280 to 1300 (Fig. 384). The latter is the more perfect, as having level ridges; the former, curiously enough, having ridges to the side cells which rise from the intersection towards the walls. I may mention that it is very common for vaulting with intermediate ribs to have ridges rising rapidly towards the central boss.

The use of these additional ribs became, from the latter part of the thirteenth century, rather the rule than the exception.

I may mention early specimens of it at Chester, both in the Chapter-house (Fig. 385) and in the Lady Chapel, the latter with raised ridges; but in each the addition being only in the side cells. The Chapter-house at Wells has the intermediate ribs added throughout to those of the more normal examples at Westminster and Salisbury, giving its vaulting a peculiarly full and rich, though rather crowded, effect. Bosses are usually introduced at all points of meeting, adding greatly to the richness of the whole.

Though I have called these ribs _non-functional_, such is the case only in a limited sense, for, though not necessary, they nevertheless do their work: they divide and strengthen the vaulting spaces, and tend to do away with the necessity (if such may be supposed to exist) for any great thickness of filling in. They form, in fact, a stone framework or centering, with frequent supports on which the vaulting permanently rests. Nearly the whole of Exeter Cathedral is groined in this manner, and excellent specimens, though of rather late date, may be seen in the west and south walks of the cloisters of Westminster Abbey, and in the two vestibules through which the cloister is approached. These have the advantage of close proximity to the eye, which enables one to study them with facility.

The next step in the history of vaulting may be said to be wholly decorative in its motive. It is the addition of short cross ribs between those already described, and arranged in patterns, such as stars, etc., round the central bosses, adding much to the complexity and ornamental character of the vault, and making a farther increase to the number of the bosses.

Wonderful skill is often evinced in the arrangement of these patterns, which, traversing the changing planes or surfaces of the vaulting, produce in the perspective an extraordinary diversity of effect. These ribs have received from Professor Willis the name of “Liernes,” a term given by Philibert de l’Orme to the ridge-ribs (perhaps in common with these), but, as we are short of an English name for these cross-ribs, it comes in conveniently to our aid. The term means, I believe, in carpentry, a short joist or rail, serving as a tie to steady other timbers, which is very appropriate to its use (real or apparent) in vaulting.

We have a few excellent specimens of this class of vaulting in London; more particularly that of St. Stephen’s crypt, and of a bay of the cloisters opposite the entrance to the Chapter-house, both erected in the first half of the fourteenth century.

In the former, both the intermediate ribs and the liernes are very subservient in size to the main ribs; which gives an excellent effect: indeed, I know of no work more studious in design and detail than that piece of vaulting.

The vaulting of three bays of the eastern limb of Ely Cathedral, built by Alan de Walsingham at about the same period, is also of excellent design, as is that of the chancel of Nantwich Church in Cheshire.

I am imitating the last-named to a certain extent in timber in the vaulting of the nave of Chester Cathedral, where, though the springers exist, the vaulting has never been completed.

Liernes are not placed at right angles to the surface of the vaulting, but in a vertical plane; perhaps from the facility it affords for setting them out on the ground plan.

We find the same cause regulating the geometrical system adopted for setting out the stones forming the bosses, which had also to contain a short piece of the impinging ribs. Professor Willis, in his admirable papers on vaulting, gives in minute detail the method adopted, showing that, to facilitate the operation, they made the upper surface of the boss-stone _horizontal_, to serve as a sort of drawing-board on which to draw the plan of the intersecting ribs. I have tested this in several instances. In the western part of the nave at Westminster, there being no outer thickness of stone vaulting, the boss-stones appear, and their surfaces are horizontal. On sweeping away the accumulation of dust and rubbish which covers them, I found, sure enough, the centre and side lines of all the ribs carefully drawn upon them.

In the lierne vaulting at Ely, though there has been an outer thickness of stonework, it was cleared away in the last century for the sake of lightness, so that the boss-stones, once concealed, are now visible. On clearing them from obstructions, I again found, as at Westminster, the lines of the ribs (here much more complex), carefully set out upon the top of the stones. Each of these little stone tables, in fact, has drawn out upon it the bit of the full-size plan of the vaulting which its surface would contain.

The lierne vaulting, though commencing as early as the first quarter of the fourteenth century, was so popular as to be continued throughout the remaining periods of Gothic architecture, used side by side, and often in union with other and later systems. The same was naturally the case with ordinary rib vaulting, so that in later times we have at least _three_ systems used contemporaneously.

I know of no specimens of lierne vaulting more charming than what we see in the oriels of the halls of Crosby Hall (Fig. 386), and Eltham Palace (Fig. 387), two sister works, unquestionably the work of the same architect, in the reign of Edward IV. They are of different plans. The one consists of five sides of an octagon, the other of a double square. The latter is on the system I have mentioned as having its central compartment raised like a square dome, to allow of the passage of the arch by which it opens into the hall. Both are carried out with the depressed arch belonging to their late period, and are treated with exquisite care and taste.

At Gloucester, in the choir, and Winchester, in the nave, this manner of vaulting assumes a very peculiar form; the side cells falling in at a low level, as what are called “_Welsh_” groins, leaving a width of barrel-vault above, which is richly decorated by surface ribs and liernes.

That at Gloucester is a work of extraordinary magnificence. Its great specialty lies in its having two sets of diagonal ribs (Fig. 388), the one on the ordinary system, the other comprising two bays each, and by their intersection defining the position of the “_Welsh_” groins. Thus the whole of the ordinary diagonal ribs, and half of the others, become mere ornamented mouldings on the surface of the barrel-vault, while to them is added a vast network of liernes, cutting it into an infinity of panels, whose angles are marked by a perfect army of carved bosses. The same was imitated at a later period in the Lady Chapel.

In many cases, as in the western portals at Winchester, the upper portion of the groining assumes forms in which the lines of the true ribs seem almost forgotten. This is done to a very vicious extent in the choir at Wells. I may mention, as a late example of this manner of vaulting, an exquisitely beautiful chamber adjoining the cloister at Windsor.

During this period two practices crept into use, to which it is not easy to assign precise dates, but which worked great changes in the art of vaulting. The one is the use--especially at first for diagonal ribs--of a curve drawn from two centres, which gradually brought down the arches to excessively low proportions. The other practice was the use of portions of the same curve for several, or even all, of the ribs, either throughout their height, or at least for their lower part. The first-named custom was very natural in cases where the height of the vaults was limited by circumstances, as in St. Stephen’s crypt. The diagonal ribs here were struck from three centres to the double rib, and in the next ribs from two to each single rib, and were also slightly segmental; that is to say, that they made an angle with the vertical line. They may be said to be a sort of imitation of the ellipse, as also is the case with the diagonals in the vaulting of the south and west cloisters at Westminster.

The other practice (_i.e._ the repetition of the same curve for different ribs) is very curious and important in its results. It influenced in an extraordinary degree the _plan_ of the vaulting at its intermediate heights. Professor Willis has called special attention to these half-height plans, as a matter of much importance to the effect.

If vaulting were carried out on perfect theoretical principles, and with the level ridge, these plans would be _rectangular_. The mere substitution of circular curves, unless made a little segmental, softens the angle of the square, while any modification of these curves produces its effect, one way or another, on this half-height plan. Professor Willis has illustrated this in a very interesting manner from the variations found in the cloisters at Norwich; a work generally of uniform design, but which, having been carried out at several different periods, the habits of the masons had undergone changes which produced very curious effects in this respect.

I may mention that where the ribs are of the same curve the ridges cannot be level; but that the use of the two-centred curve enabled them to repeat the same curve, for the springers, but slightly to change it above by varying the position of the centre, from which the upper part of the curve is struck, so as to make the ridges level where it was desired.

This tendency to the repetition of the same curve led to the development of a most remarkable variety in vaulting, which especially characterised its later history in this country. I allude to that extraordinary form known as _Fan_ vaulting.

It is self-evident that if a number of ribs of equal curvature spring at equal angles from a single pillar, the plan of the vault at any level will be a circle or a portion of a circle; and that they may be bounded at the level of their apex, or at any other level, by a circular moulding, forming the whole into a figure which I have had occasion to mention as having been generated at a very different date and from another cause, in the Norman vaulting of the circular Chapter-house at Worcester,[60] a figure which I have defined as a concave-sided conoid, and likened to the flower of a convolvulus.

Now, the vaulting of any space, if set out in square compartments, and having ribs of similar curvature and at equal distances, may be formed into a number of portions of this figure by merely drawing semicircles and quadrants, as the case may be, from apex to apex of the surrounding arches (Fig. 389).

A remainder of the ordinary vaulting, with rising ridges, exists, however, above this extemporised fan, and the whole has to be dealt with artistically on a system suited to the new form.

The general idea of such treatment of a fan or conoid may be said to be parallel to that of a circular or rose window. The ribs are viewed as radiating mullions, and are made to multiply in number as the circle expands, and usually to terminate round the outer boundary with a series of tracery forms like the heads of two-light windows. A good rose-window of late date, if imagined to be elastic, and drawn out from its centre into a conoidal form, would make a good compartment of fan groining; or a groining fan compressed into a plane would make a good rose-window. The interstices between the fans are filled up in various ways; either by circles of somewhat similar design, which sometimes drop down in little pendent fans, like stalactites from the roof of a cavern; or with a number of circles fitted together; or by continuing the diagonal ribs to their intersection with the ridges, and filling in the triangular spaces with tracery.

It is not, however, essential that the compartments so dealt with should be _square_ in plan. If _oblong_, the semicircles or quadrants are drawn from the apex of the narrower and lower arches; and from the same centres portions of circles are drawn from the apex of the wider and higher arches, assuming the form of an additional or outer zone of a rose-window, and intersecting on the line of the cross ridges, and thus forming a portion cut out of a great fan (Fig. 390). Or the roof may be described as being formed of very large fans intersecting one another. Such is the famous roof of King’s College Chapel, at Cambridge, but the frustums of fans are there bisected by vast transverse ribs, which were, no doubt, required for strength, owing to the great scale of the vaulting (Fig. 391).

The earliest instance which is known of fan vaulting is in the cloisters at Gloucester, dating from the beginning of the fifteenth century; indeed, Professor Willis thinks the invention due to a school of masons there. It, contrary to the usual practice, is formed with simple arches, instead of four centres. Each fan has but the transverse and wall ribs at its springing. At the next stage it forms the diagonal, then two intermediate ribs, and finally four more on each side of the transverse rib, and ends in little two-light window-like heads, while the space above is filled with four large cusped arches, and as many pear-shaped figures (Fig. 392).

The limits of my lecture will not permit me to follow up this part of my subject as its importance demands; and my means of producing illustrations (for which I have heartily to thank several zealous and talented gentlemen engaged in my office, as well as one of my sons) have exhausted themselves before this laborious phase is reached.

I have already referred to the Gloucester cloisters and King’s College Chapel.

The central compartment or crossing of St. George’s, Windsor, is a most magnificent treatment of an oblong space. The aisles of the same chapel, with the smaller chapels adjoining, are charming examples, as are the aisles and small chapels of Henry VII.’s Chapel, and the cloisters of St. Stephen’s, Westminster. Bath Abbey and Sherborne Minster are thus vaulted, and a whole century later, appearing long after date, comes the beautiful ceiling of the staircase to the hall at Christ Church, Oxford (Fig. 393), a square space groined on a central pillar (Fig. 394).

In the construction of the vaulting of these later periods, we have a curious instance of the manner in which extremes meet. In the earliest specimens of vaulting, all the strength lies in the vaulting surface itself. As time went on, ribs were introduced, one after another, to strengthen and support it, till at length they amounted to a permanent framework of stone, centering on which the vaulting surface lay.

Now, at length, time has its revenge, and the extreme multiplication of ribs led to the loss of their uses; the whole, or nearly the whole, being cut out of the same blocks with the panels; and thus the original system was reverted to; the vaulting surface becoming again the entire structure, and the ribs and panels simply cut as ornaments out of its substance.

The most remarkable production of the fan system of vaulting is the gorgeous central roof of Henry VII.’s Chapel, a work in which ingenuity, perplexity, and beauty are united in the most wonderful manner which can be conceived.

Though it stands quite alone in point of intricacy and magnificence, it is not the first instance of the use of the peculiar system on which it is founded. How Fuller could have attributed its origin to the foreign studies of the King and Bishop Fox, it is difficult to conceive; for, not only is fan groining itself a purely English invention, but the special system of _this_ roof has, so far as I know, only English prototypes.

The earliest of these is the vaulting of the Divinity School at Oxford,[61] finished about 1480. This was subsequently imitated, though with the loss of its leading principle, in the choir of the Cathedral (then the Church of St. Fridewide’s Convent in the same city), a work which, though popularly attributed to Wolsey, is probably of earlier date.

I have often looked in vain for the leading principle on which this wonderful work was designed. Its _construction_ is plain enough; the difficulty is the ideal of its _design_. Like everything, however, which is founded on reason, its idea once perceived, it becomes perfectly simple, and one then only wonders where the difficulty lay.

It was simply as follows:--First imagine, for argument’s sake, that the architect had intended to divide his space into three spans--a wide and two narrow ones--like the Lady Chapel at Salisbury, or the crypt of the Sainte Chapelle at Paris, supporting the vaulting on ranges of thin pillars (Fig. 395). The setting out of the divisions was about the following. The whole span being divided into five parts, two were given to the width of a bay, one to the imaginary aisle, and three to the central span. The vaulting of the aisles, then, would be in oblongs of double their width _set lengthway_ of the building, and the central span in oblongs half as long again as their width _set crossway_ to the building.

Let us apply to each the rule I have already laid down for the fan vaulting of oblongs. Beginning with the ideal aisles, from the pillars and responds and centres draw the lower circles of the fans reaching the apex of the _narrower_ arches, and the upper circles reaching the apex of the _wider_ arch (Fig. 396). This gives us an oblong fan vault in its most normal form.

Then do precisely the same with the wider or central span, and our space is covered with oblong fan vaulting of the most usual kind. Now, as the lower arch of the central span is identical with the higher arch of the side spans, it follows that the fans in the sides (or aisles) are continued and completed in the central vault, the lower arch of the small vault being also continued round to complete the design. The decoration of the smaller fans then is in _two_ stages, and that of the larger ones in _three_; but, the design of both being continuous, the one is only an extension of the other.

Had the architect stopped here, no system of vaulting, on the fan principle, or space so divided, could be more systematic or more simple in its ideal.

He had no thought, however, of stopping at so commonplace a stage, and his pillars were designed only to do their work on paper, and then to be erased. The columns were omitted, and their places supplied by pendants; but, as such a roof could not stand for a moment, something must be done to supply the support which the pillars would have afforded.

This was effected by the introduction of strong transverse arches crossing the whole chapel, and springing much lower than the vaulting (Fig. 397). These crossed the narrower spans, striking arbitrarily into their fans, and uniting themselves with the central vaulting. The pendants are not to be looked upon as constructionally interfering with these transverse arches, as they become, in fact, part of them, and the arches may be supposed to pass through them in an imaginary line, so that, as in the case of the Lady Chapel at Caudebec, the pendant is in reality a voussoir, the greater portion of which hangs down below the face of the vaulting; the small arches upwards towards the wall help to strengthen and weight the transverse arches at their weakest part.

Begun 1445. Finished about 1480.]

In the Divinity Schools (Fig. 398) these great arches show themselves throughout as the supports of the otherwise helpless vault; in Henry VII.’s Chapel they are visible only in the side vaults, which are strutted up from them with strong tracery, but their upper portions penetrate the central vault, and become concealed from view.

The same system is carried into the apse (Fig. 399), and that with the most surprising skill. The apse is supposed to be a portion of an entire octagon, with an aisle supported by eight small columns, of which two are lost by its conjunction with the straight part of the chapel. These columns being converted into pendants, the structural arches supply, as before described, the support demanded, but in this case they converge to the central part of the octagon.

The treatment of this point in detail cannot intelligibly be described in words. It is, perhaps, the most consummately skilled piece of designing to be found in the whole range of Mediæval vaulting.

I have now completed my running (and all too rapid) sketch of the arched and vaulted systems of Mediæval architecture, though purposely leaving to another occasion the subject of domes. The limits of three lectures have only sufficed to give a somewhat cursory glance at its salient points, leaving the treasures of its detail to be searched out by the zealous student.

No subject in the whole history of architecture is so remarkable, or would more richly repay the investigator. I commend it to your individual study, and will only add that our own country is more rich in the variety of its vaulting than any other, and that London is especially well supplied with objects of study, containing, as it does, excellent examples of nearly every variety of vaulting, from the stern severity of the work of King Edward the Confessor in the substructures of his monastic buildings at Westminster, to that gorgeous and astonishing work which I have just been describing, and of which we may boldly assert (whatever may be our individual preferences), that _the world does not contain its equal_.

LECTURE XVI.

The Dome.

Non-existence of the Dome in our old English architecture--Highly
developed forms in France, Germany, and Italy, contemporary with
our great Mediæval edifices--Suggestions for its introduction into
our revived and redeveloped Neo-mediæval style--So-called Tomb of
Agamemnon at Mycenæ--The Pantheon--Temple of Minerva Medica--Torre
dei Schiavi--Temples of Vesta at Rome and Tivoli--Temple of Jupiter
in Diocletian’s Palace, Spalatro--Tomb of St.
Constantia--Baptistery at Nocera--Baptistery at Ravenna--Important
domical development--“Pendentive Domes”--Early
specimens--Pendentive domes the special characteristic of the
Byzantine style--How this originated--Further domical
developments--Cathedral at Florence--Churches of SS. Sergius and
Bacchus, the Apostles, and St. Sophia, Constantinople.

It has been my lot to deliver my lectures from this chair in groups so very detached from one another, as to render it impossible for my hearers to follow them as a continuous series. In spite, however, of this disadvantage, I purpose to make my present lecture form a natural sequence to the last which I had the pleasure of delivering three years ago.

My last course was on arched construction, and my last lectures were on vaulting. My present one will carry on the same subject into its culminating development--THE DOME.

Strongly as my tendencies towards our own Mediæval architecture draw me towards the modes of vaulting which prevail in our own ancient buildings, and which formed the subject of my later lectures, I am bound to admit that the noblest of all forms by which a space can be covered is the dome; and, much more than this, that of all architectural forms it is the most sublime and the most poetic, and is susceptible of, and demands, the highest artistic treatment. I deplore, therefore, its non-existence in our old English architecture.

This regret, however, is diminished by the abundant evidence we possess that the dome, though absent from English buildings, was by no means held to be alien from the contemporary architecture of neighbouring countries, inasmuch as we possess it in highly developed forms over a large part of France, in Germany, and in Italy, erected at the same periods with many of our great Mediæval edifices.

If, then, I am departing from the line I had been taking in tracing out the history of old English architecture, I am not only supplying a hiatus in that history, but I trust that I may be able to offer suggestions for a more practical object--the supplying of that hiatus in our revived and redeveloped Neo-mediæval style.

In a former lecture, after defining a vault as the covering of a rectilinear space produced by the motion of an arch parallel to itself, I defined a dome as the covering of a circular space produced by the revolution of an arch round its central vertical axis. It follows that, if the arch so revolving is semicircular, the resulting dome is a hemisphere.

The revolving arch may, however, be of any form which an arch can assume. It may be elliptical, parabolic, hyperbolic, cycloidal; or it may be a pointed, a horse-shoe, or an ogee arch. Any one of these, or other forms of arch revolving on its centre, will generate a dome of its own sectional form. The _plan_, too, in spite of my definition, need not be a circle; it may be an ellipse, or of other forms.

I will not at this stage admit of square-planned, polygonal, or other straight-sided domes, because it may be doubted whether they are genuine domes at all, or whether they are not figures resulting from the intersection of a certain number of ordinary vaults. Anyhow, these are not generated by the revolution of an arch, so that if they are domes, my definition is at fault.

Simple, however, as is the hemispherical dome, it does not appear to have been historically the primeval type; for, strange to say, the earliest known domes assume, in section, the form of a lofty pointed arch. I refer specially to that of the supposed tomb of Agamemnon at Mycenæ, and also to some portrayed on the Assyrian sculptures.

These would hardly come within the range of this lecture, were it not so curious a fact that the earliest form of the dome foreshadows the very use to which I would now especially desire to accommodate it.

It is easy to perceive why the pointed arch was adopted in these primeval domes. They were not built with radiating joints, but in overhanging courses; and it will readily be seen on comparing their sections, that for this mode of construction the pointed arch is much more favourable than the circular; while, as soon as ever the radiating system was adopted, the semicircle at once became the simplest and most obvious section.