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352 restricted action, as exemplified at St. Arsenio, St. Pietro, and Diano. Indeed, anything that tends to solution or diminution, of continuity between a given extent of surface, and the media at the side whence the wave advances to it, acts pro tanto in this way. It must have been the observation of this fact, upon its great scale, but without any clue to its real cause, that gave rise to the ancient belief, which still holds its ground in the minds of the Italians; that caverns or deep pits, wells, or even large vaults, or other hollow substructures, produce more or less immunity from earthquake. Thus Pliny mentions, that the Capitol of ancient Rome, was saved from the effects of earthquake, by the catacombs.

At the passage of each such elevation, a portion of the wave is extinguished, as respects its direct path, and places situated upon the flanks of the slopes, remote from the seismic vertical, receive the effects of the shock with increased energy. Places in the plain beyond these, in the direction of the wave movement, receive its effects with reduced energy.

Places upon the flanks of the slopes, nearest to the seismic vertical, receive the effects of the shock with reduced energy, and in wave-paths differing much, from the direct ones from the focus, and extremely variable in direction, at different near points of surface.

Those in the plains between the elevations perceive the directions of shock most nearly in the original wave-paths, mixed with waves of apparently steeper emergence, the nearer they are situated to the bases of the flanks remote