1628

THEORY AND PRACTICE OF ENGINEERING.

Boox II.

Chapel, in which there is evidently some improvement ; but at the time of its constructionperfect knowledge on this subject had not been attained. In a catenarian chain formed oflinks of equal length, every side is a tangent to the curve, and the direction of each link isat right angles to it, acting in a direction perpendicular to the line it forms in the cate-naria ; and hence its useful application to the science of construction. It is quite clear thatwherever the curve passes through the section of a building, stability is obtained; andwhere it does not, it is doubtful: certainly the best application of flying buttresses isthat which can be tested by this principle.

The main arches of theroof abut against the outerbuttresses, and spring from acluster of mouldings set rounda circular pier ; the situationof the small columns and hol-lows which decorate it beingdetermined by the crossingof equilateral triangles. Theribs of each severy abut inthe centre upon a circle 3 feet6 inches in diameter, formedof two stones, and indicatedby No. 1.: in the middle is amortise-hole 9 inches square;

No. 2. is in width 17 inchesin the widest part; No. 3. is2 feet 2 inches; No. 4., 3 feet8 inches; No. 5., the same ;

No. 6., 3 feet 3 inches; No. 7.

4 feet 3 inches; No. 8., thesame; No. 9., 3 feet 2 inches,and No. 10., which abutsagainst the outer wall, 4 feet.

By a reference to the planon fig. 3044., it will be un-derstood how the severalrings of voussoirs which com-pose the quarter of the para-bolic conoid abut and arelocked one into the other : theconstruction of this vault issomewhat similar to thatadopted by Soufflet at theChurch of St. Genevieve atParis , although his mannerof applying it materiallydiffers.

The buttress in the presentexample has an area of 56 feet,

Fig. 3043.

Fig. 3042. king’s college chapel : ribs of vault.

equal to that of the piers, to which it is attached; or the two piers and buttresses togetherhave an area of 224 feet: it is curious to find that of the 336 feet before given to thepoints of support, one-sixth should be applied to the piers, one-sixth to the buttresses,and the other portion to the walls between ; for 55 ft. 6 in. x 6 = 336 feet—the area of thepoints of support taken on both sides ; so equally are the parts even distributed.

When the Normans first used flying buttresses, as at the Cathedral at Chartres , theAbbaye aux Hommes at Caen , and several other buildings, they abutted them against theordinary outside wall; but it was soon discovered that a greater resistance was necessary tooppose the thrust, and prevent the abutments from yielding. Salisbury Cathedral wasprobably one of the earliest where flying buttresses were used; and the opinion of SirChristopher Wren is worthy of quoting upon this subject, as it applies more particularlyto the first constructed, and not so immediately to those erected in the fourteenth orfifteenth centuries. “ Almost all the cathedrals of the Gothic form are weak and defectivem the poise of the vault of the aisles; as for the vaults of the nave, they are on both sidesequally supported and propped up from spreading by the bowes or flying buttresses, whichrise from the outward walls of the aisles: but for the vaults of the aisles, they are indeedsupported on the outside by the buttresses ; but inwardly, they have no other stay but thepillars themselves, which, as they are usually proportioned, if they stood alone, without theweight above, could not resist the spreading of the aisles one minute : true, indeed, thegrea oad above of the walls and vaulting of the nave should seem to confine the pillars