87.—Designs for Window Headsdetails

133. Designs for Window Heads.—All thse designs for window heads were worked out on simple geometrical combinations, as shown in Fig. 87, which is a window with six days, or openings, divided in two groups of three each by means of pointed arches shown at b a c and c d e, over which a circle is struck, with its center at o, whose diameter is equal to half the width of teh window, and its circumference is divided into twelve parts, as shown at 1, 2, 3, 4, etc. Within each of these parts, small circles, tangent to one another and to the circumference of the great circle, are described, and form the generating elements of the interior design.

This example is given with the contruction lines simply to show how these details are geometrically worked out. All the elements of the design can be located and executed by means of a pair of compasses and a straightedge, without any other device to lay off measurements. (p. 102)