seismometer

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A detecting device that receives seismic impulses.

Century Dictionary and Cyclopedia

1. n. An instrument by the aid of which the data are obtained for the scientific study of earthquake phenomena. The forms of instruments used for this purpose are varied, and more or less complicated, in accordance with the wishes and means of the observer. A common bowl partly filled with a viscid fluid, like molasses, which, on being thrown by the earthquake-wave against the side of the bowl, leaves a visible record of the event, is one of the simplest forms of seismometer which have been proposed, as giving a rude approximation to the direction of the horizontal element of the wave. Another simple form of seismometer consists of two sets of cylinders, each set numbering from six to twelve, and the individual cylinders in each uniformly decreasing in size. These are placed on end, one set at right angles to the other, on plates resting on a hard horizontal floor, surrounded by a bed of dry sand, in which the cylinders when overthrown will rest, exactly in the position originally given by the shock. This instrument is theoretically capable of giving the velocity of the horizontal component of the shock, its surface-direction in azimuth, or the direction of the horizontal component of the seismic wave, and also the direction of translation of the wave. In practice, however, the results given by this simple and inexpensive apparatus have not been found satisfactory. The seismometer now most generally used in large observatories, or those where accurate work is expected, involves Zöllner's horizontal pendulum, the use of which was proposed many years ago, but which was put into the present practical form by Messrs. Ewing and Gray. The group of instruments constituting the seismometer of Prof. J. A. Ewing is arranged to give a complete record of every particular of the earthquake movement, by resolving it into three rectangular components—one vertical and two horizontal—and registering these by three distinct pointers on a sheet of smoked glass which is made to revolve uniformly by clockwork, the clock being started by an arrangement similar to that of the Palmieri seismoscope. To this is added another clock which gives the date of the shock and the interval which has elapsed since it took place. Another and simpler form of seismometer designed by Mr. Ewing, and called the “duplex-pendulum seismograph,” does not show the vertical element of the disturbance, nor exhibit anything of the relation of time to displacement; but it is in other respects satisfactory in its performance. Of this latter form, fifteen sets were in use in Japan in 1886, and others were being made for other countries. Compare seismograph, and see cut under seismoscope.
2. n. In technical usage, the tendency is to restrict the application of the term “seismometer” to instruments of such high character that from the records or indications they give the actual motion of the ground may be inferred or worked out. Many instruments are sensitive to the vibrations of the ground, but their indications or records are very far from being exact measures of the disturbing influences. The Bosch-Omori and the Marvin seismographs while not absolutely perfect are scismometers, but, at the same time, they are seismographs, simply because they produce written records. The use of the term “seismo-scope” is restricted to instruments that simply indicate the existence of seismic influences, without either measuring or recoding them.

Wiktionary

1. n. geology A device used by seismologists to detect and measure seismic waves and therefore locate earthquakes etc; a seismograph

GNU Webster's 1913

1. n. (Physics) An instrument for measuring the direction, duration, and force of earthquakes and like concussions.