[Illustration: FIG. 88.--Banqueting House, Whitehall, “The upper windowe of y^e Modell,” by Inigo Jones.] It has already been pointed out how the mullioned window was gradually altered by the introduction of a wider light surmounted by an arch (Fig. 66), or by the introduction of an elliptical light (Fig. 70). But the mullioned window in any form was out of place in a truly classic design. Jones has an early drawing of 1616 in which he makes use of it, as well as of other Jacobean features, but it is doubtful whether any executed work of his can show a stone mullioned window. The type employed in the Banqueting House is that which he favoured, and it is probable that a drawing entitled “The upper windowe of y^e modell” (Fig. 88) is a sketch by him for the windows in the upper story of this building. By comparing this sketch with that of the Banqueting House (Fig. 36) the similarity will be apparent. Jones, like Webb after him, was a student of Serlio, and he has a sheet of sketches of windows taken from Serlio with notes of his own appended. He and Webb do not seem to have concerned themselves with the filling of the window space, all they troubled about was the proportion and embellishment of the main opening. Yet the filling is of considerable interest. Mullioned windows were filled with lead lights, which only required glass of small size. Their successors, where the main opening was large, appear to have been filled with wooden frames having mullions and transoms of the same material, which reduced the actual openings to a size suitable for glazing in the old way. Later on the lead which held the glass was replaced by thick wooden bars holding glass of a larger size. But the opening part of all these windows was a casement, that is a framework (generally of iron) which was hung at the side and opened like a door. Then, from somewhere--but nobody knows exactly whence or when--came the ingenious sliding sash, which was hung with cords and counterbalanced by concealed weights, so that it could be moved up and down. This was really a remarkable change, although we are so accustomed to sash-windows as to take them for granted as part of the universal scheme of things. Their effect on the architectural treatment of windows was of the first importance. They made mullions impossible, they compelled window spaces to be of large size, and these large spaces necessarily influenced the design. They also rendered small bay-windows impossible, as well as large bay-windows with a narrow canted side. They practically put an end to any attempt at modified versions of the Jacobean style, but they were excellently adapted to the larger, plainer, and more regular classic. Considering the effect they had on design it is to be regretted that we know nothing of their origin, or the date of their introduction. At present only one authenticated instance of their use can be cited before the time of William III.