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OBSERVATIONS ON VAULTS.

Vaults rising from walls are of two kinds. Theone, by which the space covered is partly enclosed,as in cylindrical and cylindroidal vaulting. The other,whereby the whole space covered is enclosed, as inpyramidal, conical, and domical vaults.

Vaults , springing from pillars or piers, are of fivedifferent kinds, and the space covered may be openon all the sides : as, 1st, Groined Vaults ; 2d, PendentVaults; 3d, Groined Rib Vaults ; 4th, Rib Vaults byribs of the same curvature; and, 5th, Rib PendentVaults.

Fig. 1. Cylindrical . Fig. 2. Pyramidal. Fig. 3.Conical . Fig. 4. 15. 16. and 17- Domical Vaults.Fig. 5. and 6. Groined Vaults . Fig. J. 8. 9. 10. 11.12. 13. and 14. Pendent Vaults. Fig. 1$. and 19.Groined Rib Vaults. Fig. 20. 21. and 22. RibVaults by ribs of the same curvature. Fig. 23. and24. Pendent Rib Vaults.

Each class of vaulting will admit of infinite variety,according to the curve by which the vault may begenerated.

The generation of cylindrical and cylindroidal,domical by hemispheres, or hemispheroids, pyramidaland conical vaults, is obvious.

Groined vaults are generated by the crossing ofcylindrical or cylindroidal vaults of the same height.The lines of intersection are called groins, and arecurves elongated from the curve of the crossingvaults, in proportion to the diagonals of the plan overwhich they are vertical. A groined vault may alsobe conceived to be composed of parts of a concavepyramid inverted, (Fig. 5. and 6.) The forms ofpendent vaults are generated by cylindrical or cylin-droidal vaults crossing other vaults of greater height,or by plain (Fig. 14.) cylindrical or cylindroidal