Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/312

Rh lines parallel to and over it, are at levels respectively of 1000 feet English above it, and above each other, and the seismic vertical, is the strong perpendicular black line. All observed stations, to the eastward of the meridian passing through the seismic vertical, are arranged to the right of the latter, and at their respective radial surface distances from it, and all the stations to the westward of the same meridian in the same way, arranged to the left hand of the seismic vertical; and all at the nearest approximation to their true levels above the sea.

In No. 1, the two fine lines drawn from each station, are those of the least and greatest emergences there observed, while in No. 2 the mean depths along the seismic vertical taken from each pair, (or for each station,) are deduced and plotted, as also shown by the fine lines, which form, with the horizon, the angles of mean depths; and, finally, from all the latter is deduced, the general mean focal depth or that point which represents the mean depth of the centre of effort, or mean of all the partial foci.