We farther find, that sixteen others, exclusive of all the preceding, fall within a concentric circle of 2½ geographical miles' radius, and outside of the last of one mile radius, namely—
|
Senarchia |
Tricarico |
And outside of this again, there are found twelve wave-paths, all converging within a concentric circle of five miles' radius, and whose divergences are accountable for.
Reside all these, we have the separate system of reflection, &c., of Salerno to Naples, &c.
Now it has been shown p. 18 (Part I.), that the point of intersection upon the surface, of any two wave-paths, is geometrically sufficient, to fix the position of the seismic vertical. Here we have sixteen, or eight pairs, (any one of which may be taken indifferently as intersecting with any other,) all passing through the same point, or within 500 yards around it. If therefore, we were to put out of view all the others, the evidence from these alone is irresistible, that we have obtained the real position, of the place upon the earth's surface, vertically above that one beneath, whence the shock emanated.
The focal centre of impulse, in nature, it will be remem-
