Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/404

Rh Saponara, to be the same as that determined (from unexceptionable data) at Viscolione, in the Plain, only a mile away, it would give the velocity of oscillation of the hill itself of Saponara

but Viscolione was on the deep clays of the Piano, Saponara upon the bare limestone rock. The velocity of the wave of shock, therefore, should be taken, from the nearest station also on rock, which was Tramutola, and which would give the velocity of oscillation $$= 15.267 - 14.765 = 0.862$$ feet per second. Tramutola itself, however, as already stated, had possibly a small surface oscillation; and if we suppose it to have been as much as the last deduced, at Saponara, the final seismic wave velocities will come out, for Tramutola 13·903 feet per second, and for Saponara, the velocity of oscillation of its "colline," = 1·724 feet per second.

These low velocities of the wave of shock, now for the first time brought within the domain of figures, will, I doubt not, be received with much surprise by most physical geologists. The impression has been universal, from which I was not myself exempt at the period of publication of my first Report ('Reports Brit. Assoc. 1850'), that the velocity of the wave itself, if not as great as its velocity of transit, was, at any rate, very great; and no attempt had been made to correct this fancy, by appeal to observation and to mechanics. It was with quite the same surprise, however, that the low velocity of transit, first indicated by my own experimental determinations by means of gunpowder explosions, was received by physicists, who, twelve years ago, imagined, (myself included,) that the transit rate must be found about that, which theory

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