It would be tedious, however, to go again through many of the facts recorded in Part II., by pointing out their relations in this respect. They will best be studied, the principles once understood being kept in view, and with the Maps A and B, and Zannoni's great map before the reader.
3rd. Increment of effect, reduplication of shock, and change in the directions of wave-path are produced, locally and abruptly, by dispersive and reflected waves, passed out, along with, or before, or after, the direct wave, from closely adjacent mountain flanks, not transverse, or but obliquely so, to the principal wave-path of the locality.
Of this the most striking examples occur at Potenza, situated, as will be remarked, in a basin-like hollow, with mountain ranges, separated from it and from each other, inflected in various directions close round it. Besides the main shock of the direct wave in the path north, 87·30° E., it was shaken by subordinate shocks, reflected from the flanks of these surrounding mountains, in paths in every azimuth round the horizon.
So also, the chain of cities extending from Melfi south to Atella, not only received the main shock in their respective wave-paths, but as will be seen marked (Map A) had various other wave-paths in different azimuths, yet all pointing out reflected waves, from the east flank of that chain of the Apennines which branching out at St. Fele, ends in Monte Vulture. Montemurro is another remarkable case, where, standing surrounded by a crescent of mountains to the north and west, it will be observed that, besides the main wave-path north 142° E., it is marked with several
2A2
