1458

THEORY AND PRACTICE OF ENGINEERING.

Book II.

mould 17 de and 18, of the vertical face, which will give its greatest height, and that of itshorizontal bed 12 18, 17 18, representing the extrados on the plan, which gives its greatestlength. Having then faced the stone, square with the bed, the mould is placed on it, todraw the head of the voussoir and that of the extrados ; on this tracing we may cut the twojoints, these moulds giving their double obliquity ; it is only necessary to find the two otherlines, which should terminate them at the intrados, and on the side of the sloping face ; this isdone by cutting the second face with the bevel of the obtuse angle, which the surface of theextrados forms with the talus of the wall; the head mould, 12, 13, ed is then applied tofinish the tracing of the voussoir; this process may be applied to the others. The deve-lopment is seen below, as well as the key in perspective.

.v.-v-v

BULL’s-EYE.

ELEVATION.

Fig. 2609.

Wmk\

Fig. 2610.

Fig. 2606.

PLAN.

F»g- 2606-

Fig. 2611.

MOULD.

MOniD oy VERTICAL PACB.

Fig. 2607,

'/ DEVELOPMENT,

DEVELOPMENT.

Fig. 2613;

CONICAL VAULT DOUBLY SKEWED

Fig. 2608. KEY,