Its greatest advantage was the ease with which any required width could be combined with any required height. With this power of adaptation the architect was at liberty to indulge in all the wildness of the most exuberant fancy, hardly controlled by any constructive necessities of the work he was carrying out. Whether this was really an advantage or not, is not quite clear. A tighter rein on the fancy of the designer would certainly have produced a purer and severer style, though we might have been deprived of some of those picturesque effects which charm so much in Gothic cathedrals, especially when their abruptness is softened by time and hallowed by associations. We must, however, in judging of the style, be careful to guard ourselves against fettering our judgment by such associations. There is nothing in all this that might not have been as easily applied to round as to pointed arches, and indeed it would certainly have been so applied, had any of the round-arched styles arrived at maturity. Far more important than the introduction of the pointed arch was the invention of painted glass, which is really the important formative principle of Gothic architecture; so much so, that there would be more meaning in the name, if it were called the “_painted-glass style_,” instead of the pointed-arch style. In all the earlier attempts at a pointed style, which have been alluded to in the preceding pages, the pointed arch was confined to the vaults, pier arches, and merely constructive parts, while the decorative parts, especially the windows and doorways, were still round-headed. The windows were small, and at considerable distances, a very small surface of openings filled with plain white glass being sufficient to admit all the light that was required for the purposes of the building, while more would have destroyed the effect by that garish white light that is now so offensive in most of our great cathedrals. As soon, however, as painted glass was introduced, the state of affairs was altered: the windows were first enlarged to such an extent as was thought possible without endangering the safety of the painted glass, with the imperfect means of supporting it then known.[35] All circular plans were abandoned, and polygonal apses and chapels of the chevet introduced; and lastly, the windows being made to occupy as nearly as was possible the whole of each face of these polygonal apses, the lines of the upper part of the window came internally into such close contact with the lines of the vault, that it was almost impossible to avoid making them correspond the one with the other. Thus the windows took the pointed form already adopted for constructive reasons in the vaults. This became even more necessary when the fashion was introduced of grouping two or three simple windows together so as to form one; and when those portions of wall which separated these windows one from the other had become