Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/348

Rh reached the range, with an angle of incidence, of 56° to 59°, passed through, therefore, with an angle of refraction of 33°, the direct wave-path having suflfered an inflection to the extent of 26°, in passing through the mountain range, and in whatever harder volcanic rocks, if any, it met with, between that and the point of observation, at the north side of the bay.

But besides these reflected and refracted waves, transmitted by the elastic material, of the roots of the range at a considerable depth below the ridge, the mountain range itself vibrated laterally, by the transverse sinuous wave, before referred to (Part II., Padula) and Part III., Chap. VI., and hence wave movements, almost precisely normal, horizontally, to the axial line, were transmitted from it. These are indicated by the observed wave-paths, at Capua, Naples, and generally all round the Bay, to the north of the range, and at La Cava, La Trinita, &c, to the south of it.

The orthogonal wave-paths, observed at Amalfi and Atrani, in a direction N. 138° east, are rather uncertain as to explanation; it is observable that they are almost precisely in the same direction as the refracted wave at Pausillipo, and it is probable they were produced, by a second series of transverse sinuous vibrations, of the axial range, produced by partial reflection of the original wave, of that order, at the free lying surfaces, of the end of the chain, at Capo di Campanella, when reached by it; and so transmitted backwards, along the chain, (like a water-wave traversing forward and back from one end to the other, of a long trough, or as the same sort of sinuous wave produced by jerking a stretched rope, returns to the hand, after it has reached the fixed and remoter end).