Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/381

CHAPTER XIII.

OF THE AMPLITUDE OP THE WAVE AND THE WORK STORED UP IN IT.

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Let $\mathrm {E\ F}$ (Fig. 352) be a section vertically, at the earth's surface, $o$ the mean focal point, at the depth $o\ d$, measured
Fig. 352. upwards upon the seismic vertical $o\ \mathrm {V}$, and $d\ c$ be the amplitude of the wave, in its path of emergence at $s$, taken somewhere near $o\ \mathrm {V}$. The wave is originated by the sudden compression, of the elastic materials forming the walls of the focal cavity. Admitting the temperature, as just obtained on the commonly-assumed hypogeal increment, we have obtained a measure, of the pressure producing this compression; and if we possessed the coefficient of compression