Page:Great Neapolitan Earthquake of 1857.djvu/121

Rh greater range, each distinct story of the building acquires a separate momentum of its own, in virtue of the weight and attachment to the walls, of the floors and objects upon them. All the fractures tend therefore to separate and close again, as the wave makes its transit; and the several masses, moving horizontally at the same time, with a rotation alternate and increasing as it ascends the building, the replacements do not often coincide with the displacements, and in a few seconds the stability of the walls may be so far destroyed, that the whole falls to the ground in ruin the most complete. Fissures running horizontally or nearly so from the quoins are not unfrequently observable where the emergence is very steep or nearly vertical, examples of which may be observed at both sides of the N.W. wall of the church of Pertosa (Photog. No. 25, page 42).

With vertical or nearly vertical emergence also, gravity acting with inertia, in the first semiphase of the wave, upon the masses of masonry situated directly above doorways, windows, and other such apertures, their tendency to come down is great; and hence, not only are vertical fissures formed over such openings, but they are open widest at bottom, one of which will be remarked breaking across the stone lintel over the west door of Pertosa church (Photog. No. 25), but diagonal fissures crossing the piers between windows, where there are doors or other opes beneath, in a lower story, of which examples occur in the Palazzo Palmieri at Polla and will be observed in the Photogs. 178 and 180, Part II.

It is upon the heavy Italian roofs and floors, however, already described, that the most instant and formidable