Page:Great Neapolitan Earthquake of 1857.djvu/447

as in Fig. 2, and jammed quite close to the plinth block at the opposite or north side. The shaft, pedestal, and plinth are socketed into each other, as shown, without cement.

A vertical plane passing through the axis of the column, &c., in a northerly and southerly direction ranges 25° E. of north. The lower edge of the pedestal is lifted more at the western than at the eastern corner of the south side, so as to infer a wave-path about 10° or 12° E. of north.

The shaft and pedestal, &c., are all of hard Apennine limestone, and the cavetto moulding above the base is 8 1/2 inches diameter only: an inference may be drawn from this as to the maximum possible velocity of shock, emergent at the angle we have found, viz., 25°, that would have left this little column unbroken at the neck formed by the cavetto. The horizontal velocity for fracture only is given by the Equation XXV.

$V={\tfrac {5}{8}}g\times {\frac {\mathrm {LD} }{a^{2}}}$;

where $\mathrm {D}$, the neck of the cavetto = 0.708 feet, $a$, the height of the column adding in the ball and iron, to the cylinder = 6.5 feet, and $\mathrm {L}$ = the length of the modulus of cohesion for the material. This will be = 225 feet, if we take the weight of a cubic foot = 160 lbs., and its cohesion at 500 lbs. per square inch (which is supported by Hodgkinson's experimental determination for marble, 551 lbs.). Then

$V=20.12\times {\frac {225\times .708}{42.25}}=75.961$ feet per second,

and

$V\sec e=75.961\times 1.103=\mathrm {V} =83.785$ feet per second;

the velocity at the emergence found, that would have just fractured the column at the cavetto.