Page:Great Neapolitan Earthquake of 1857.djvu/95

Rh diagonally in the direction $$ad$$ through the side walls, fracture occurs in jagged lines in directions perpendicular to $$ad$$, the wave-path. The fissures at the end $$c$$, therefore, commencing at top, very near the internal angles of the quoins, run down in the direction $$pk$$, making an angle with the plumb line of the wall $$c$$ (before disturbance) $$cpk = hia$$ = the angle of emergence.



The portions of the side walls detached with the ends grow wider as they approach the base. They therefore make the end wall $$c$$ too rigid, to turn round upon or near its base, as in the former case (Fig. 21), to admit of the fissure $$pk$$ opening; hence a cross fracture occurs somewhere below one-third the height of the wall $$c$$, as at $$n$$, which frees the mass and admits of its movement. This cross fracture may take any direction downwards from $$n$$ towards $$t$$, dependent upon the nature of the masonry, &c., and the mass $$c$$ chiefly turns over, to the extent of opening of the fissure, round the joint at $$t$$, or may partly slip upon