This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol5", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
The simplest type of Gothic window is undoubtedly the lancet, being, as the name implies, long and narrow, the head being formed of two arcs meeting at a point more or less acute. An example is given in Fig. 159. This type may be either employed singly or grouped. In the latter case it is usual to carry the central window to a greater elevation than the outer ones.
A somewhat more elaborate type is shown in Fig. 160, wherein the window is composed of two lancets with a mullion dividing them, and united under one main arch. The space between the small arches and the main arch is composed of plain masonry pierced with a quatrefoil. This type of tracery is called "plate tracery." The plans drawn to a large scale in Fig. 161 show how the jams, abacus, and arch moulds are superimposed over one another, and also how the mouldings are worked out of the various stones.
In this case a quatrefoil is shown above the lancets and filling in the blank over their junction, the whole being surmounted and enclosed by an arch with hood-mould.
It will be noticed how carefully the joints are arranged so as to avoid the mitres, provide true bedding, and allow the stones to be cut out of square blocks with little waste or labour.
A further elaboration of the above, and one that will naturally strike the observant mind, is reached by cutting away the plane faces yet left to form tracery, as in Fig. 161.
Many types of tracery will commend themselves to the student by a careful study of the many examples of mediaeval architecture to be met with in England.
In tracery of a more ornate character use is made of cusping to a great extent, the plain lancet shape being replaced by a trefoil head, as in Figs. 161, 162, and 163.
These several examples are given in order to illustrate the principles of jointing better than can be done by description. The separate arch rings are kept distinct, and the tracery joints are all cut to radiate to centres, as well as to meet the requirements mentioned above.
In windows of more than two mullions the traceried heads are often of an apparently much more complicated design.
This complication will resolve itself into a simple matter on further study, as all properly constituted heads are laid out on true geometrical principles. It should therefore be the aim of the architect to so set out his design as to base it in some combination of plain geometrical figures as a groundwork, and to fill in and elaborate the details to suit the foundation thus laid down.
Pursuing the subject of elaborate detail in tracery, we next arrive at the type in which the curved lines of the design are intersected by continuations of the mullions, or by what may be termed subsidiary mullions. Such a type is found illustrated in Fig. 164, which is a large scale elevation of the chancel window in Tooting Wesleyan Chapel, designed by Mr. J. S. Gibson, F.R.I.B.A. Here the centre mullions are carried upwards above the general springing line, and in the upper segments the space between is again divided by a short mullion surmounted by tracery. The outer mullions are only partially carried up, but on the other hand the spaces are subdivided over the cusped ogee arches, and the apices of the arches are continued up as mullions closely interweaved with elaborate tracery.
A similar class of window, but of more flowing lines, is given in Fig. 157, where it constitutes the gable window of the same church. In this instance the two centre mullions only rise above the springing line, and the space between is subdivided by a small mullion over the cusped arch, the sides being of the flowing or curvilinear type of window.
In cases where windows are pierced in thick walls a very fine effect can be arranged by the introduction of interior tracery, preferably with a larger opening (by splaying the space between the outer and inner tracery). This inner window would be unglazed, the outer being the window proper, and glazed. Its face would be kept somewhat near the main face of the external wall.
It is usual in such cases to elaborate the internal tracery to a somewhat greater extent than the external. Mullions with columns, caps, and bases are frequently introduced.
There is another feature deserving of mention in this class of work, and that is the apparent as well as actual additional strength resulting in the use of the two sets of traceried windows.
A plan of a window of this type will be seen in Fig. 165.
Circular windows and those of elaborate tracery, denominated rose windows, are suitable for gable ends.
As their names imply, they are of circular shape, and may be either filled in with plate tracery with radiating mullions (whence the term "wheel" windows), or with elaborate tracery, when they are distinguished by the name of " rose " windows.
The simple varieties are usually plain circles with trefoils, quatrefoils, or cinquefoils, and their corresponding cusps inserted therein as ornament. The inner portion of the wall is usually splayed, and the sills also, to afford the greatest diffusion of light possible. The heads of the openings may be either circular, following the same sweep as the upper portion of the window, or may be pointed (see Fig. 166).