Page:Great Neapolitan Earthquake of 1857.djvu/533

The horizontal velocity for fracture from the equation

$V={\frac {2}{3}}g\times {\frac {bL}{a^{2}}}$ is therefore

$V=5.48$ feet per second.

The horizontal velocity for overthrow after fracture from the equation

$V^{2}={\frac {4}{3}}g\times {\sqrt {a^{2}+b^{2}}}\times ({\frac {1-\cos {\theta }}{\cos ^{2}{\theta }}})$

$\theta$ being 22° 40′, $a$ = 7 feet, $b$ = 3 feet, is $V$ = 5.14 feet per second:

The total horizontal velocity for fracture and overthrow is therefore

$V=5.48+5.14=10.62$ feet per second:

but $e$ = 16° 25′ assumed the same as at Sarconi; therefore

$\mathrm {V} =10.62\times \sec e=11.04$ feet per second,

the actual velocity of the wave in its direct path. This result—deduced from two similar blocks of masonry, of the simplest and best form, natural seismometers in fact, and coinciding so closely with previous and distant determinations—affords a strong confirmation of the correctness of the explanation given, of the nature of the higher velocity that overthrew Saponara, close to which, but down on the level of the plain, we see thus the wave has its ordinary velocity.

I pursued my way towards Montemurro, where I hoped to rest.

At 4 miles S.E. of Saponara, under Spinosa, on the level of the bed of the Agri, at 3^h 15^m Nap. time, the barometer read 29.11 inches, thermo. 42° gives the height above the sea = 649.1 feet.