Q. How is the equilateral arch formed and described?
A. From two segments of a circle; the centres of it have a radius or line equal to the breadth of the arch, and it may be described from an equilateral triangle. (fig. 6.)
Q. How is the obtuse-angled arch formed and described?
A. Like the foregoing, it is formed from two segments of a circle, and the centres of it have a radius shorter than the breadth of the arch; it is described from an obtuse-angled triangle. (fig. 7.)
Q. During what period were these pointed arches in use?
A. They were all gradually introduced in the twelfth century, and continued during the thirteenth century; after which the lancet arch appears to have been generally discarded, though the other two prevailed till a much later period.
Q. What are the different kinds of complex pointed arches?
A. Those commonly called the Ogee, or contrasted arch; and the Tudor arch.
Q. How is the ogee, or contrasted arch, formed and described?