Page:Great Neapolitan Earthquake of 1857.djvu/193

Rh gravity above the base of fracture, as in the preceding equations, $$f$$ or $$f'$$ of Fig. 104, and Equations XII., XIII., &c., &c., in which   and $$a$$, as before, the distance of the centre of gravity from the axes of inceptive rotation, we have  The sign $$+$$ applying to the first semiphase, and that $$-$$ to the second semiphase of the wave.

Substituting for $$k^2$$ its value, and also for $$a$$,  we obtain  Rh