Page:Great Neapolitan Earthquake of 1857.djvu/168

120 emerges so nearly vertical that its horizontal elements are those mainly effective in dislocation, and produce only fissures by resolution, where there are piers and window apertures horizontal ones, as in Fig. 92.



Stone staircases, the steps of which are bedded into the walls, often produce most complicated effects, both by primary and secondary fracture, and, as objects for deductive information, should usually be avoided.

The choice of buildings best suited for observation in an earthquake region, will have been discerned from what has been stated, though much must always depend upon the observational power and sharpness of the observer, and something upon prior experience (acquirable, however, in a very few days' work). Buildings of the simplest character, large, well-built, not too much injured, and cardinal, are the most important points.

There are many detached objects the observation of which can afford valuable results, in reference to the path of the wave and the direction of its transit, besides the dislocations of the shell of buildings; such as the swing of lamps or candelabra, of hung pictures, &c., and of twisted objects, such as vases, obelisks, &c., which, however, do not demand detailed consideration in this place. Several examples occur in Part II.