MULLION (by some supposed to be a corruption of munnion, from the Latin munio, to defend or strengthen), a term in Gothio architec ture applied to the upright bars, or stone shafts, dividing the general aperture of a window into secondary openings, which are again in Per pendicular or Third Pointed windows frequently subdivided vertically by a similar shaft crossing the mullions horizontally, and therefore called a transom ; whereby the whole space beneath the head of a window (supposing it to be an arched one) is formed into a series of panels in which the glass is fixed, and which are sometimes technically distinguished as lights or days. Except in very small windows not exceeding in width one such light or compartment, mullions invariably occur in Gothic windows, being in fact absolutely necessary when no other mode of glazing was practised than that of small panes act in lead, because without some kind of strengthening or support, either by stone or metal rods, a spacious surface of the kind would be damaged by a strong wind, whereas each division becomes a separate window of no greater width than a single small one : consequently the number of the mullions depends upon the width of the window. Two-mullioned and three-mullioned windows aro the most usual in ecclesiastical archi tecture, except for the large east or west windows in churches, or windows of nearly equal dimensions in other buildings. In these they
are frequently very inumerous ; that, for instance, in the facade of York Cathedral is divided into eight lights or compartments by seven mul limn, while that above the entrance to Westminster Dail has eight mullions. Again, the former of these is untraniomcd, but the other is transomed, being divided in its height to the spring of the arch into two tiers of arch-headed compartments ; it also affords an instance of what is by no means uncommon in third pointed buildings of principal and eubordinate mullions, being divided by two larger mullions into three leading compartments, each of which contains three smaller ones. The lesser or simple mullions, sometimes described as those of the first order, consist of the mouldings which run into and form the cusps, where the heads of the compartments are foiled; while the larger ones have additional mouldings. In explanation of this we may refer to the window from Kirton Church, at col. 443, GOTHIC ARCHITEC TURE, where the centre mullion is larger and composed of more mouldings than the other two, which have only those that form the cusps. As far as they go, the other specimens of windows given in that article will further exemplify the subject of mullions, and nerve to render it evident that unless windows were so divided it would bo impossible that their heads should be filled up with tracery.