. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. EARTHQUAKE PHENOMENA. 419 city, that (in the absence of better means) shall give the horizontal velocity of shock within a norrow limit of error. Let there be constructed two similar sets of right cylinders—say, each set six to twelve in number—all of equal height (a) and of the same sort of material, but varying in diameter in each set, with a uniform decrement from the greatest to the least. Convenient dimensions for earthquake observatio
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. EARTHQUAKE PHENOMENA. 419 city, that (in the absence of better means) shall give the horizontal velocity of shock within a norrow limit of error. Let there be constructed two similar sets of right cylinders—say, each set six to twelve in number—all of equal height (a) and of the same sort of material, but varying in diameter in each set, with a uniform decrement from the greatest to the least. Convenient dimensions for earthquake observations of mean inten- sity will be such that the cylinder of largest diamete^ shall have its altitude equal to three diameters, or b =z -'7 and that the cylinder of Q least diameter shall have its diameter one-third of that of the greatest one, or 6 = q. Any number of cylinders of intermediate diameters Fig. 6. X6. may be interpolated between, and the greater the number thie-more- accurate the instrument becomes. A series of six to ten in each set will, however, be sufficient for any purpose. For observation of shocks of extreme violence, larger diameters in proportion to- altitude should be chosen for all the cylinders. The material of the cylinders is not important—cast-iron, stone,. pottery, or other substances at hand—whose arrisses will not crumble- away by being overthrown—may be used; but no material will be found more convenient than some hard heavy seasoned wood, of uni- form substance, straight grain, and equable specific gravity, from which the cylinders can be formed in the lathe, and their bases brought perfectly square to the axes with facility. Upon any horizontal and solid floor let two planks be placed, as in, fig. G, with their directions in length respectively lying N. and S. and, E. and W., each plank to be about three inches in* thickness, and in width equal to the diameter of the largest cylinder, and its Please note that these images are ex
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