VAULT, VAULTING. The continuation of an arched covering over a conaiderable surface is commonly spoken of in the Arts under the name of vaulting ; and occasionally the word vault is applied to the actual assemblage of voussoirs of an arch, in contradistinction to the haunches, spandrils, or other supplementary parts. Both of these eignifleations may be retained without inconvenience, because they express conditions it may often be necessary to refer to in practice, and for which it is desirable to possess names.
There is little to be added to what has been already said under Anon and Balms, with respect to the mechanical principles of vaulting, excepting that in the case of Intersecting arches it may be desirable occasionally to form the lines of intersection by arched ribs, springing from the respective abutments, but even in this case the resolution of the thrust must ultimately be the same, in principle, as in any ordinary arch. It is customary in practical works on architecture and engineer ing, to class the various descriptions of vaults as follows :-1, Waggon headed and semicircular vaults ; 2, Domical vaults ; 3, Pointed arched vaults; 4, Grained arches, which in their turn may be made to peas through numberless modifications, according to the positions assigned to the various ribs, pillars, or points of support. It Is in the latter form of vaulting that the fan tracery so much admired in Gothic archi tecture occurs ; and the skill with which the mediteval architects con centrated the strength of the vaulting In the ribs, whilst they reduced the thickness of the spandril filling, enabled them to secure effects of the most elaborate and pictorial character. In the simple square groin the ribs near the wall, and those at the intersection of the arches, perform the office of supporting the vaulting ; in the more ornate fan tracery, other ribs are introduced, so as to form, on plan, a star of four points, or the primitive arches may rise to different heights, either ultimately meeting by intersection, or truncated in the middle of the space. Polygonal spaces were covered in the mediaeval period either by means of a series of fan-shaped ribs, starting from arches applied against the external wall, and from a central column, as in the cases of many of our chapter-houses, or by grained arches spanning the whole space between the walls ; or by pendentive roofs, when the internal dimensions are not very great. Excellent examples of the first of
these systems of vaulting over polygonal buildings are to be found at Winchester, Salisbury, Wells, Lincoln, fie.; of the second, at Durham, York, &c..; and of the third at Caudebec. In many of Sir C. Wreu's churches, the system of grained vaulting has been applied with as much boldness and artistio success as in the aildings of the mediaeval arebi tecta ; but the compulsory use of the semicircular arch in the Italian architecture, rendered the intersections of the side vaults with the principal ones less susceptible of ornamental decoration than is the ease with the diagonal ribs of the preceding style. The vaulting of St. Paul's, and of St. Peter's at Rome, may be referred to as illustrations of the most effective specimens of this mode of construction as applied to modern cathedrals. It must not be forgotten, however, that tho ancient Romans had proved themselves to be perfectly able to overcome all the practical difficulties of vaulting ; and the ruins of the palaces of Nero and of Diocletian, the reservoirs of Possilippo and of Constantinople, and the great church of Sta. Sophia may be cited as illustrations of the various solutions they had discovered of the problem of vaulting large areas.
It may be advisable to call attention to the mode of vaulting adopted in some parts of the London Docks, in which the space covered is vaulted by means of grained arches of brickwork, of elliptical form, springing from granite pillars. In cases where the vaults are intended to store combustible goods of great value, there are such manifest advantages in the use of the granite pillars, instead of east-iron ones, that, writing under the impressions produced by the fearful misfortune of June 22nd, 1861, the author may be pardoned for dwelling on this detail of fire-proof construction.
(Ware, Tracts on Vaults and Bridges ; Willis, Architecture of the Middle Ages ; Owilt's Ereer/optedia of Architecture ; 1Londelet, L'Art de Bdtir, &a., &e.)