movements of which earthquakes are but incidents have been given but passing notice.
The instruments used in the study of earthquakes are of much interest. The seismograph (q.v.) automatically records the time, violence, and duration of exceedingly slight tremors. In some localities slight tremors have been found to be of daily occurrence, while in no part of the world are they altogether lacking. So delicate are these instruments that the pressure of a hand against a stone column on which they rest will instantly cause a variation of the pointer; the sag in the heart of a city during the heavy traffic hours of the day and the sag of valleys between hills during heavy rainfall are indicated. The centre of disturbance of any earthquake shock may be quickly located by comparing the records of time and violence of the shock in different observatories passed by the wave in its course, and then with a globe and pair of compasses determining the point from which a wave would reach all of these observatories at the times recorded. Also by connecting points of simultaneous arrival of the wave, a coseismal curve may be drawn; perpendiculars erected upon chords of this curve will pass through the epicentrum. This determination of the locus of an earthquake is of much economic importance.
Among memorable earthquakes of recent times may be noted that of Lisbon, November 1, 1755, which left the city a heap of ruins, destroyed 60,000 lives, and was felt from the Madeiras to Britain: that in Calabria in 1783; that which destroyed Caracas in 1812; that which destroyed Aleppo in 1822; that at Mount Ararat in 1840; those at Brusa. Asia Minor, in 1855: Naples, 1857: at Quito, 1859; Mendoza, Argentina, South America, 1860; Manila. 1863; in Peru, 1868; Manila. 1880; Valparaiso, 1880; Ischia. 1883; the earthquake phenomena accompanying the volcanic eruption of Krakatoa. 1883; Colchester, and the eastern counties of England, 1884 ; Malaga and Granada, 1884 and 1885: Charleston, 1886: Japan. 1891; Chilpancingo. Mexico, 1892; and Quczallenango. Ouatemala. 1902.
Bibliography. Reports of British Association Committee on Earthquakes ( London, 1850, 1852, 1854, 1858, 1801): Transactions of the Seismological Society of Japan (Yokohama, 1880-90): Mallet, Dynamics of Earthquakes," in Transactions of the Royal Irish Academy (Dublin, 1846); Mallet, The Great Neapolitan Earthquake of 1857 (London, 1802); Ewing, "Earthquake Measurement," in Memoirs of the Science Department of the University of Tokio, No. 9 (Tokio, 1883) : Whitney. "The Owens Valley Earthquake." in Overland Monthly, vol. ix. (San Francisco, 1872) : Dutton, "The Charleston Earthquake of August 31, 1886," in Ninth Annual Report, United States Geological Survey (Washington. 1889) ; Milné, Earthquakes and Other Earth Movements ( New York, 1886); Humboldt, Cosmos (London. 1805), and Travels (London. 1840) ; Fouqué, Les tremblements de terre (Paris, 1888).
EARTHS. The oxides of a number of elements whichi are not easily reduced to a metallic state. The alchemists applied the term in general to bodies that were insoluble or only slightly soluble in water, and not changed by heat. With the establishment of modern chemistry by Lavoisier, the earths, which had been regarded as elements, became recognized as compounds. The earths are widely disseminated throughout the mineral kingdom. The term "alkaline earths' is applied to the oxides of barium, calcium, and strontium, and sometimes to that of nutgnesium.
EARTHSHINE. The reflection from the moon of the light cast upon her by the earth, particularly noticeable on clear nights at the time of new moon, when sometimes the whole surface of the moon can be seen in ashy-colored light.
EARTH-SNAKE. See Shieldtail.
EARTH-STAR (translation of Neo-Lat. Geaster, from Gk.(
Greek characters), ge, earth + EARTHWORM. astēr, star).
A genus of puffballs which, at the time of
spore-dispersion, open in a star-like form. Before the period of spore-dispersion the earth-star has a rounded or pear-shape form, seldom
more than two inches in diameter. When the
spores are ripe the outer leathery layer of the
skin, or periderm. splits radially from the central apex into a number of triangular segments,
which expand like the petals of a flower to assume a star like arrangement and then become
strongly reflexed. In certain species, particularly in Geaster hygrometricus, this periderm is
very sensitive to humidity and dryness, with the
result that the plant expands during moist periods and closes up during dry ones. Earth-stars
are found in nearly all parts of the world, some
species being restricted to particular regions,
while others are cosmopolitan. In America they
are quite commom in pastures and open woodlands. See Basidomycetes and Fungi.
EARTH- WOLF. A name for the "Aard-Wolf," in The New International Encyclopædia, New York: Dodd, Mead and Co. (1905) (q.v.).
EARTHWORKS, Military. Shelter trenches made by soldiers in the field to protect them- sehes from the fire of the enemy. There are many forms of earthworks, for which see {{NIE link|Fortifi-cations; Redoubt; Trench.
EARTHWORM. The popuhir name for worms of the family Lumbricidæ. especially the common Lumbricus terrestris and Allobophora fœtida. They belong to the oligochætous section of the chætopod annelids, and are widely distributed in temperate and tropical lands.
Habits. Like most other oligochætes, earthworms are subterranean in their habits, and appear above the surface only under unusual conditions, such as excessive rain, which floods their undergroud burrows and forces them to the surface to avoid drowning. They also come to the surface to feed and to throw out their 'castings;' but this is almost wholly at night, and although they have no eyes or light-detecting organs, they seem to avoid the light. Earthworms are often seen in great numbers upon sidewalks, steps, and paved streets after a wet night or a hard rain, and they are often reported to have actually 'rained down,' Such cases, however, are easily explained by the fact that the worms crawl about actively in their attempt to get out of the water, and even climb up comparatively smooth surfaces, and as the hard surface of the sidewalk or roadway prevents their reentering the earth when daylight returns, they are all left exposed to view. Although naturally somewhat sluggish, these worms can burrow with considerable speed, especially in light soil. The burrowing is accomplished not only by fore-
