Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/327

262 their density, hardness, and elasticity getting less and less; hence the wave, in whatever path, transmitted transversely, suffers continual refraction, as illustrated in Fig. 342; the general tendency being, at each parallel range to depress the wave-path, and reduce the apparent angle of emergence, the wave losing by partial reflection at every such change of direction.

Such changes of direction occur likewise, no doubt, whenever an emergent wave reaches the surface, in a path parallel or nearly so, to the axis of the mountain chain and valley; but the alternations are then much fewer, and the distances between the refracting surfaces of contact of the formations, are very much larger, and the loss, therefore, much smaller.

When the wave has emerged at the outgoing side, of a transverse mountain range, (the left-hand in Fig. 343,) owing to the curving and bending in direction, of the formations, it will emerge at some points of the outgoing flank, without any refraction, (when incident perpendicularly to the surfaces of formative contact); while at others, it will be