Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/319

254 physical features of the shaken country, are shown. Upon this map the observed directions alone of wave-path at each station, are marked with their azimuths in figures, the protraction of the wave-paths themselves to their intersection about the seismic vertical being reserved to the Map A only, and marked thereon in red lines.

The more important applications of the Map B will occur further on, when referring to the effects of physical configuration of surface, upon the forms of the isoseismals, &c. On both Maps A and B, all the towns that were affected by the system of reflected and refracted waves only, are distinguished thus .....

On examining the forms, of these closed curves, it will be perceived that they are very far from circular, or symmetrical, or similar to each other; and that the seismic vertical, is very far from being situated in the centre of figure, with respect to any of them. In fact, viewing each isoseismal line as an irregular ellipse, the vertical through the centre of effort, is very nearly in one of the foci. This is, however, probably quite an accidental circumstance, as very many conditions, and those of great complexity, but chiefly comprehended under the one expression, "want of homogeneity of medium, and of uniformity of surface," have concurred to produce the figures found. The operation of these distorting forces, which will be presently considered, proves how wide away from the truth, are those beautifully regular, circles and ellipses, by which Johnston, Berghaus, and, indeed, all previous describers of earthquakes, have limited the supposed fields of their action.

The superficial areas, within the several coseismal curves as thus laid down on Maps A, B, and C are as follow:—