Page:Great Neapolitan Earthquake of 1857.djvu/91

Rh fissures only be produced, those at $$a$$ will be wider than those at $$b$$, as was before stated; or if the impressed movement be capable of more than this, the end wall $$a$$ will be prostrated; and that $$b$$ may stand, but fissured from the side walls, or with still greater violence, it, too, may be thrown forwards in the same direction as that of the wave transit, but to a less horizontal distance.

Were the building in Figs. 21-23 square in plane, instead of rectangular, it will readily be conceived that precisely the same phenomena must succeed to a normal wave, whose path should be orthogonal to one in the direction $$a...b$$ or in $$s...t$$.

If, however, the building be rectangular, and with the sides $$ce$$ and $$hk$$ of considerable absolute length, and largely exceeding that of the ends, and the path of a normal wave be through them in the direction $$a...b$$ (Fig. 28), it then rarely happens that fissures occur, or occur alone near the quoins.



The wave, as before, passes from $$a$$ towards $$b$$, and the side wall $$ce$$, as before, moves by inertia in the contrary