Page:Great Neapolitan Earthquake of 1857.djvu/107



now proceed to the fourth of our classes of waves, namely, the subabnormal, or the wave whose direction of transit, is diagonally in both an horizontal and a vertical plane, passing through the building; a wave which is at once abnormal and emergent.

On referring to Figs. 43 and 44 the general character of the dislocation produced by such will be evident.



The wave emergent in the direction $$a$$ to $$b$$ dislodges the portions of the quoin $$c$$, which it first reaches by inertia, during the time of the first semi-vibration, and those of the diagonally opposite quoin, are thrown forward and often projected out of place also, by inertia in the time of the second half vibration. As explained for the abnormal