Page:Great Neapolitan Earthquake of 1857.djvu/105

Rh outwards. This mostly happens from quoins of stability disproportionate to the rest of the building, and unfits it for seismometry.

When the force of shock of an abnormal wave is sufficient to cause prostration of the walls, they almost always fall outwards, and the debris is found as in Fig. 40, $$a$$ to $$b$$ being the direction of the wave.



When the building is rectangular, and the abnormal wave in the direction $$a$$ to $$b$$, Fig. 41, arrives first at one of the long side walls, making an angle of 45° less, with the end walls, the latter are generally fissured vertically at$$n n$$, but the long side walls are also bowed, or possibly prostrated; the greatest amount of curvature being at $$c$$ and $$c'$$, and the fissures taking the hollow curved forms, seen in the elevation of the wall $$g f$$, the central fissures, being secondary or sub-fissures, dependent upon the bowing.

This form of building is difficult to obtain the abnormal angle from, with correctness, and those more nearly square should be sought for.

The remarks that have been made apply to cardinal and ordinal buildings alike, the former, when presented, being by far the best, however, for observation.