Page:Great Neapolitan Earthquake of 1857.djvu/179

6th. In the case of a solid parallelopiped with two adherent wedges, overturned round the free or external arris.

This form is that frequently occurring, as thrown from the ends of rectangular buildings, and described in treating of fissures, the end wall being the parallelopiped, and the wedges the adherent portions of masonry, fractured from the side walls.

The general and exact treatment of this case involves expressions too complex for practical use. The case should never be appealed to for deciding the value of $\mathrm {V}$, unless the magnitude of the parallelopiped be large, in proportion to that of the wedges, the lower angle of the latter small, and not very unequal at the two ends of the parallelopiped, and the thickness of the walls $\beta$, small in proportion to the height $\alpha$. In that case a sufficiently near approximation is readily made.

Referring to Fig. 98, let the mass of the two wedges

be determined, and reduced to a parallelopiped, two of whose sides shall be equal to $\alpha$ and $\gamma$, these being the