Page:Great Neapolitan Earthquake of 1857.djvu/197

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Before concluding this section, it remains to assign the values of the coefficient L for practical use. It consists of two factors: the tenacity or resistance to rupture, by a force suddenly applied; and the specific gr .vity of the mass fractured off, by direct pull from an unit of section. When a direct force, producing fracture by extension, is gradually applied to any prism, whose length and section are both unity, the work necessary to produce the rupture is W = P t ............ ( .) P being the static load gradually applied, and 1 the amount of extension of the body on the unit of length at the' limit of rupture. But if P be applied at once (suddenly), then 2 W = P l, the accumulated work, is P twice that necessary for fracture, or -= the force, whose tension suddenl t aIriolied, as by an earthquake shock, shall rupture the prism. This force we suppose applied by the weight of a prism of the material fractured, whose base is the unit of section fractured; or being the specific gravity P L=�8 = .........