Page:Great Neapolitan Earthquake of 1857.djvu/60

24 and also emergence, indirectly, by calculation applied to the observed conditions of the forces employed in producing fracture, overthrow, or projection.

Fissures in buildings, not overthrown, are, in fact, the sheet anchor, as respects direction of wave-path to the seismologist in the field.

The observations usually available, upon single or isolated objects, such as pillars, obelisks, vases, or statues overthrown, or others often of small size though comparatively rarer, are generally not less important, as determining direction, than those to be made upon objects of united or complex construction, or however large, such as buildings of various sorts. The latter are, however, the staple indices upon the careful observation of the injuries to which, we are mainly dependent for arriving at the directions in azimuth of shock.