Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/103

The total horizontal velocity of both fracture and overthrow, is therefore

$V_{f}+V_{t}=4.61+6.665=11.275\ \mathrm {feet\ per\ second} =V$,

and not greater, as the two surfaces of the fracture lay close together, at the angle of rotation. The angle of emergence here, however, as will immediately be shown, is $e=23^{\circ }7'$, and hence the total velocity of the wave

$\mathrm {V} =V,\sec e=12.255$ feet per second;

a sensible though apparently not very large reduction in velocity from that ascertained for points much nearer the focus.

In passing along the streets I noticed that several of the lamp irons had been shaken down from the walls. They consisted of wrought-iron arms, extending horizontally about 8 feet from the faces of the walls, with three spur braces or stays, also of iron, two above and one beneath: all being spiked into the mortar joints, and carrying a lantern for an oil light. The chuck that would be required to dislodge these, must have been pretty sharp: they would scarcely warrant calculation, however.

The house of Don Dominico Antonio Burso, stands upon the old town walls to the north side, (under $b$, Photog. No. 302, Coll. Roy. Soc.,) between the two old semi-cylindric towers. It is on a free-lying brow, of the slope to the north, and is considerably fissured, and the north walls have gone out. It gives a wave-path 119° 15' E. of north. The towers rather indicate a wave-path, from the south due north.