# Page:Great Neapolitan Earthquake of 1857.djvu/296

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WAVE-PATH FROM FISSURES.

The fissures that are most instructive, are those in the external quoins, those on the soffits of the arching, and at the junction of the cross walls between the rooms (or cells) and the external walls.

The fissures resulting from the shock of December last are readily distinguishable from those of 1851. The walls have been all limewashed more than once, in the interval of time between, so that the former fissures are filled and obscured, those of December last, new, clean, and empty. The largest fissures are open 0.3 to 0.5 inch in 10 feet. They are wider, larger, and more numerous on the S. and E. wings. The width of similarly circumstanced fissures on the E. and S. wings are on the average of eleven pairs as 7 : 6.5. The angle ${\displaystyle (\theta )}$ made by the path of the wave with the east flank wall, therefore, was

 ${\displaystyle \mathrm {Tan} \,{\theta }={\frac {6.5}{7}}=.93}$ nearly,

or ${\displaystyle \theta =43^{\circ }}$, but the building is ordinal 23° W. of N., adding this, we have the azimuth of the wave-path at Eboli = ${\displaystyle 43^{\circ }+23^{\circ }=66^{\circ }}$ W. of N.

None of the photographs (Figs. 124, 125, 126, Coll. Roy. Soc.), were taken sufficiently near, unfortunately, to show with distinctness any external fissures in this building, nor to show the S. W. angle at all. Referring to the block plan and elevation (Fig. 127), however, some large fissures in the external walls of the projecting buildings over the terrace, and, generally, in that portion of the structure, give an angle of slope with the vertical = ${\displaystyle 15^{\circ }}$ to ${\displaystyle 16^{\circ }}$, and allowing for the change due to the ordinal of the building, indicate an angle of emergence for the wave-path ${\displaystyle e=18^{\circ }}$ from the E.

The church was the only other building I could find at