Chap. XXIV.

MASONRY.

1429

Fig. 2434.

Fig. 2436.

4J

Fig. 2438.

OBLIQUE CONICALVAULT.

Fig. 2439. SPHEROIDAL VAULT.

Fig. 2436. CYLINDRICAL VAULT. Fjg. 2437. CONICAL VAULT.

Cylindrical Vaults have theirvoussoirs always parallel to theiraxis, whatever their curvature orituation: oblique or inclinedvaults of this description shouldhave their courses of voussoirssimilarly arranged.

Cornea/ Vaults have their coursesinclined towards the point of thecone, whether they form a part ofan entire, or the frustum of acone; taking care in the formercase to avoid the too great acute-ness of the voussoirs by making thepoint or trompillon of a single stone.

"When the conical vault is of asize which renders the lower vous-soirs too thin, its length must bedivided into several parts ; so thatif the great circle be divided into8 voussoirs, and the length of thearch into 4 parts, the second partshould be divided into 5 voussoirs,the third into 3, and the fourth beconstructed of a single piece:these slices must be comprisedbetween surfaces perpendicularwith that of the cone, by cutting offany irregularity in the first row.

Spherical Vaults consist of hori-zontal courses of concentric ringsplaced upon each other : when therows of voussoirs form squares onthe plan, or other plane figures,as triangles, pentagons, &c., theyare difficult of construction andnot so solid, especially at the anglesof the polygons; nor does this ar-rangement effect so firm a tie aswhen the voussoirs are arranged inhorizontal rows.

When the vaults are composedof several parts the rows of vous-soirs should be disposed as theywould be in the vaults originatingthem ; thus in the figures composed of parts of cylindrical vaults uuiting in the centre, therows of voussoirs are parallel to those axes.

4 y 3

Fig. 2440.

Fig. 2441.