described from two centres, and the complex pointed arch described from four centres.

Q. What are the different kinds of simple pointed arches?

A. The Lancet, or acute-pointed arch; the Equilateral pointed arch; and the Obtuse-angled pointed arch.

Q. How is the lancet arch formed and described?

A. It is formed of two segments of a circle, and its centres have a radius or line longer than the breadth of the arch, and may be described from an acute-angled triangle. (fig. 5.).

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?

A. It is formed of four segments of a circle, and is described from four centres, two placed within the arch on a level with the spring, and two placed on the exterior of the arch, and level with the apex or point (fig. 8); each side is composed of a double curve, the lowermost convex and the uppermost concave.

Q. When was the ogee arch introduced, and how long did it prevail?

A. It was introduced early in the fourteenth century, and continued till the close of the fifteenth century.

Q. How is the Tudor arch described?

A. From four centres; two on a level with the spring, and two at a distance from it, and below. (fig. 9.)

Q. When was the Tudor arch introduced, and why is it so called?

A. It was introduced about the middle of the fifteenth century, or perhaps earlier, but became most prevalent during the reigns of Henry the Seventh and Henry the Eighth, under the Tudor dynasty, from which it derives its name.