Page:Great Neapolitan Earthquake of 1857.djvu/93

Rh outwards, than they do to the wall $$hk$$, being forced inwards, the quoin stones bonded into both wails finding a better fulcrum in the transverse resistance of the end walls in the latter case. The wall $$ce$$ in some degree resembles a beam merely supported at the two ends, while that $$hk$$ is partially in the condition of one encastré at both ends, both being subjected to transverse strains; and accordingly the latter usually presents the characteristic curve of double curvature when looked at in plan upon top, as in Fig. 29.

The difference in result is practically not great, but sufficient generally, to cause the side wall first moved by the wave, to have a greater curvature than the opposite one, both being more or less fractured. When the shock is of sufficient force, however, the wall $$ce$$ is quite overthrown, falling outwards, and tearing away from the end portions, in an irregular, sloping, and hollow curve, following along the joints, so that the detached mass is in the form in the section in line $$ss$$ looking towards $$ce$$. This seldom happens, when the wall $$hk$$ is devoid of intermediate support, without its being more or less prostrated likewise. This form of fracture is seen in two of the walls in the Photog. (No. 30) of overthrown houses at Polla, though unfortunately somewhat masked by the effects of the falling walls having been in this instance precipitated upon and against others. 2