Page:Great Neapolitan Earthquake of 1857.djvu/172



pass at once to the second class of seismometric determinants—viz., those derivable from the overturning or projection of objects by the shock; i.e. by the velocity impressed upon them by the wave itself, and in the direction, of its line of transit, or contrary to it; taking in also, such work of fracture, as may occur in detaching them from their contacts.

And here, as the conditions of observation are very simple, being limited chiefly, to the accurate measurements of two ordinates and an azimuth, and to some considerations as to the forms of the bodies, and of their points of attachment, and to the mutual relations of these, we may avoid that prolix detail, which wss unavoidable in treating of the deductions, as to direction from fissures and fractures.

From what has been already stated as to the effects of inertia in masses exposed to shock, it is obvious that any