Page:The American Cyclopædia (1879) Volume VI.djvu/371

EARTHQUAKE 363 S., and at least 100 m. E. and W. ; the point of greatest severity was apparently 30 m. S. of Santiago, though at all places visited by it it seemed to come from some point further south. This earthquake was one of the cases, extreme- ly rare in Chili, in which the origin of the dis- turbance was under the mainland, and where therefore no great sea wave was produced. In the Argentine Republic, Mendoza was over- turned in March, 1861 ; the shock was very severe, and continued from the 20th to the 23d over Buenos Ayres and the entire confederacy, and 12,000 persons are estimated to have per- ished. In the Hawaiian islands, the most se- vere earthquake ever known occurred on Feb. 19, 1871. At Honolulu it lasted 50 or 60 seconds, the motion being chiefly vertical with a N. E. and S. W. rocking movement ; a roar- ing sound that was also heard far out at sea preceded the shock, and it was noticed that vessels that lay furthest from the wharves were first struck, and afterward those close to the shore. At Lahaina the direction of the vibra- tion was S. and N. On the W. coast of Hawaii the shock was as severe as on the S. coast of Oahu ; it seemed to come from the west. The various observed phenomena point to a centre of disturbance near the centre of the circle in the circumference of which is the group of isl- ands. In the East Indies is a seat of almost perpetual volcanic and earthquake activity. In 1772, during an eruption of Papandayang, one of the loftiest volcanoes of Java, an area of 100 sq. m. was overwhelmed with ashes (not submerged under the sea), destroying about 40 villages and 3,000 inhabitants. Simul- taneously eruptions took place from two vol- canoes respectively distant 184 and 352 m. from Papandayang, although the many neighboring volcanic vents were quiet. On July 3, 1863, the city of Manila was much damaged by a violent earthquake; two systems of shocks were experienced, trending respectively in a N. to S. and E. to W. direction. The islands of Japan are subject to numerous violent dis- turbances. The earthquake of Dec. 23, 1854, which destroyed the ports of Simoda and Osaka and injured the city of Yedo, was ac- companied by a sea wave 30 ft. high, which made the destruction more complete, and then swept eastward over the Pacific ocean in a series of five or seven waves that were felt a few hours later at the Bonin islands and on the California coast, affording Bache an opportu- nity to determine approximately the average depth of the water. Registration of Earth- quakes. The observations of the nature of earthquake shocks have heretofore been gener- ally indefinite and unsatisfactory. Every dis- turbed stone or other object forms of itself a permanent record of the force and direction of the shock, but the difficulty of properly inter- preting the often complex results has led to the suggestion of a system of automatic registra- tion by means of permanent simple instruments called seismographs, of which the following are some of the principal : 1. Horizontal plates of glass, wood, or stone, strewn with sand or loose blocks of various sizes, densities, and proportions, show by the changes impressed on the positions of the movable materials the direction and force of the horizontal com- ponents of a shock. 2. Tide gauges record not only the great sea wave, but also the smaller forced waves that precede this, and therefore give the means of determining the time of the occurrence as well as other data. 3. Similarly, the self-recording mercurial ba- rometer, if sufficiently sensitive, records the time and also the force of the vertical com- ponent of the shock. 4. The delicate levels of the accurate astronomical instruments give information of the slightest change of level, and have in the hands of Wagner recorded vibrations that would otherwise have wholly escaped the senses. 5. An accidental observa- tion of Gilliss, who happened to be viewing the moon during a slight earthquake, shows that by means of a telescope sighted on ce- lestial or distant terrestrial objects we may become aware of the slightest imaginable vibrations, which may be recorded photo- graphically. 6. The telegraph as used by Gil- liss at Santiago in 1852, and by the operators in Montreal in 1871, may be used especially with a chronograph to record the times of transit of a shock as it passes several stations successively. 7. The self-recording magnet- ometers afford a very delicate record of the changes afFecting the suspended needle, and also of the effect of the shock on the magnetic condition of the globe. 8. Pendulous bodies (neither barometers nor magnetometers, but simple pendulums) have long offered a favorite mode of observing the direction of the shock, which is the same as the azimuth of the axis of the ellipse described by the pendulum in consequence of the disturbance ; the force of the shock is recorded by the extent of the arc of vibration. 9. Vertical spiral springs, from which weights are suspended or upon which they press, afford very delicate means of observing and recording the vertical compo- nent of the force. 10. The Cacciatore seis- mometer consists simply of a basin filled to the brim with mercury; at the eight points of the compass are small holes through which the liquid may be projected by the force of the earthquake shock. 11. Lament's apparatus consists of finely balanced needles, to which may be attached small mirrors throwing a re- flected beam of light into a telescope, so that the slightest movement may become visible. 12. The most complete instruments for self-regis- tration are those employed by Palmieri, Kreil, and Mallet, but the last is far more perfect than any other. Palmieri's apparatus consists of a fillet of paper drawn along uniformly, on which are made marks corresponding to the times and extent of the disturbances commu- nicated by the vertical component of the shock to certain weights hung on spiral springs ; for