All the seismographs that have hitherto been employed have two grave disadvantages: they are either too simple, so that their indications are valueless, or too complicated, so that their high cost and delicacy, and the difficulty of mounting them and keeping them in order, tend to prevent them from being generally used.
Seismology will not be able to make any serious progress until it has at its disposal very certain and very numerous data as to telluric movements registered at a large number of points at once by accurate instruments. I have endeavored to construct a simple apparatus capable of automatically registering such facts as it is most necessary to know in scientific researches on the movements of the earth. After numerous experiments I believe that I have succeeded in solving this delicate problem, since my apparatus, put to the test of experience, has given me satisfactory results. I have consequently decided to submit it to the approval of men of science.
My seismograph is capable of registering (1) vertical shocks, (2) horizontal ones, (3) the order in which all the shocks manifest themselves, (4) their direction, and (5) the hour of the first movement.
The apparatus is represented in the accompanying cut. The horizontal shocks are indicated by the front portion of the system, and the vertical ones by the back portion. The hour of the first shock is indicated as follows: The elastic strip of steel, C, is fixed by one of its extremities to a stationary support, d. When, as a consequence of a vertical motion, the free extremity of this strip oscillates, the leaden ball, x, drops into the tube, c, and, on reaching the bottom of this, acts by its shock upon a cord, i, which actuates the pendulum of a clock that has previously been stopped at 12. The other strip, B, is very similar to the one just described, but, instead of carrying a ball, it holds a small metallic cylinder, u, so balanced that a vertical shock in an upward direction causes it to drop forward into the anterior half of the tube to the left. A second vertical shock in a downward direction causes it to drop into the other half. The cylinder, u, and the ball, x, are regulated in their positions by means of screws affixed to a stationary support.
The portion of the apparatus designed to register horizontal (undulatory) motions consists of four vertical pendulums, z z z z, each of which is capable of moving in but one direction, since, in the other, it rests against a fixed column.
Telluric waves, according to modern observations, almost invariably in every region follow two directions that cross each other at right angles. When the seismograph has been arranged according to such directions, no matter from what part the first horizontal shock comes, one of the four pendulums will be set in motion. If, after the first undulation in one direction, another occurs in the opposite, the pendulum facing the first will in its turn begin to move; and if other undulations make themselves felt in diametrically opposite directions, the other pendulums will begin to act. These pendulums, in their motion, carry along the appendages, e e e e, which are so arranged as to fall in the center of the marble or iron table, one upon another, and thus show the order according to which the telluric waves manifested themselves. The part of the apparatus that records vertical shocks has a winch, r, which falls at the same place when the lead ball drops.
The apparatus as a whole may be inclosed in a case. When it is desired to employ it, it should be mounted in a cellar, while the clock that is connected with it can be located in one of the upper stories of the house. - F. Cordenons, in La Nature.