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 for practical use.

It consists of two factors: the tenacity or resistance to rupture, by a force suddenly applied; and the specific gravity 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

being the static load gradually applied, and the amount of extension of the body on the unit of length at the limit of rupture. But if be applied at once (suddenly), then , the accumulated work, is twice that necessary for fracture, or the force, whose tension suddenly applied, 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