CHAPTER X.
OF THE REITERATION OF THE SHOCK, EXPERIENCED IN SOME LOCALITIES, AND OF ITS CAUSE.
The earthquake of December 16, 1857, consisted, irrespective of tremulous movements, such as those last discussed, of two shocks: the first and more powerful of the two, was felt over the whole area disturbed; the second, which occurred about an hour after the first, was less powerful, however, and limited in its seismal area to a much smaller region than the former.
These two, however, appear to have been, distinct earthquakes, due to separate originating impulses, though from a common originating point, only following each other, with but a brief interval of time; but in some places, as recorded a second shock of considerable intensity, was felt following the first, in rapid succession. In every instance, this second appears to have been a reflected shock, the first, the direct one, and the two difiered often very considerably, in wave-path.
The conditions conducing these, will be best explained further on, in treating of the disturbing efiects, of local position, &c., upon the shock. In the case of Naples itself, where a distinct moment of pause, was observed, after the
