Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/160

Rh horizontally, and square to the face of the wall, would have fractured and overthrown it.

The wave-path, however, was oblique in azimuth to the wall, $$i$$ being = 25°, upon the data preceding; and we may take the emergence here at about 15° $$= e$$, from other determinations, whence we obtain, for the total velocity, in the path of the wave, that would have prostrated the wall,

feet per second; on the supposition that the wall had received no support from the bank of earth to the south; which, however, did prop it sensibly at one end, as the vertical fracturing due to torsion, seen in the photograph, proves.

A velocity in the path of the wave, greater than 11·564 feet per second, therefore, would have been required for its overthrow; and it was not overthrown, but was upon the verge of it, being out of plumb nearly three feet. The actual velocity of shock to which it was exposed, therefore, was very little below, 11·564 feet per second; but we already have found from the thrown rock at Monticchio, that the velocity there = 11·757 feet per second, which harmonizes closely.

The Syndico, had a large silver pocket-watch, which on the night of the earthquake, hung by its ring upon a nail, driven horizontally, in a north and south direction, upon the south side, of a wall of his chamber running east and west. The nail projected about 3 inches from the face of the wall, and the watch was hanging so from it, that the back of the case, was in contact with the wall. He happened to have his eyes upon the watch very nearly at