1440

THEORY AND PRACTICE OF ENGINEERING.

Book IT*

the vault: in the accompanying diagram a semicircular vault is penetrated at right anglesby one of a less diameter. AHU is the form of the void or opening determined by theintersection of perpendiculars dropped from the joints of both the arches. The develop-ment of the soffite or intrados of the lesser arch is of that portion of the arch comprisedbetween the right line pq on the plan, and the curved line A Ii 15 forming the arris of thevoid or opening. the upper stone, in isometrical perspective, shows the key of the arch

Fig. 2519.

Fig. 2521.

Fig. 2522. Fig. 2523.

where the smaller arch intersects ; the voussoir underneath is the next in succession, and thelower one that of the springing : it is apparent by tracing the various lines, which partscorrespond in plan and section, and the letters also indicate the position of the stones, as

well as their development.

A similar Vault intersected by another in an oblique Direction . — The same method ofsetting out is applied to this kind; the stone in isometrical perspective is the springingstone at MTN. The development shows the portion of the arch comprised between thecorresponding letters'on the plan.