Page:The American Cyclopædia (1879) Volume VI.djvu/367

 EARTH continued to swing in a north and south plane while the earth rotated through any consider- able angle, this tangent would continue to pass through the same point on the axis ; in other words, the plane of swing would have taken up a position intersecting its former position. This at least would be the case for all points on the earth's surface except those lying on the equator. But the plane of pendulum swing resists the influence, thus causing it really to shift its plane, and therefore this plane apparently shifts from the north and south po- sition ; this apparent shifting being obviously greater or less according as the pendulum is further from or nearer to the equator. The experiments on this plan, when carefully con- ducted, have been found to accord perfectly with theoretical anticipations based on the theory of the earth's rotation. Another proof of the earth's rotation is founded on the fact that bodies let fall from a considerable height fall slightly to the east of the point which lies directly below the point whence they had been dropped. Newton showed that this should be the case, because the point of suspension, being further from the earth's centre than the point directly beneath it, has a greater velocity on account of the earth's rotation. The experi- ment is not an easy one, for many reasons ; and it is only on the average of a great number of experiments that the tendency to easting can be established. Benzenberg in 1820 made a series of such experiments, letting 31 balls fall from a height of 235 ft., within a tower, upon a sheet of soft wax. He found the sum of deviation toward the north to be 46 -4 Paris lines, toward the south 92*6 lines, toward the east 174'5 lines, and toward the west 5O5 lines. He repeated these experiments in an abandoned coal pit at Schlebusch in Rhenish Prussia, where the fall was 262 ft. Twenty -nine balls gave the following sums of deviation : toward the north 124 lines, toward the south 103 lines, toward the east 189 lines, and toward the west 42 lines. Lastly, a long and most convincing series of experiments was carried out on the same plan by Prof. Reich in the mines of Freiberg. He dropped 106 balls to a depth of no less than 488 ft. There was a balance of southerly deviations amounting to 48'76 lines, and a balance of easterly deviations amounting to 1,093*92 lines; so that the mean deviation toward the south was but 0'46 lines, or practically inappreciable, while the mean deviation toward the east was 10'32 lines. Thus we may regard the rotation of the earth as abundantly demonstrated, indepen- dently of any evidence afforded by the celestial bodies. The various divisions of the earth's surface are described in the article GEOGRAPHY ; its structure is treated in GEOLOGY. See also PHYSICAL GEOGEAPHY. The subject may be further studied in the following works : Stef- fens, Beitrage zur innern NaturgescMcTite der Erde (Berlin, 1801) ; Ritter, Die Erdkunde im Verhaltnisse zur Natur und OescMchte des EARTHQUAKE 359 Menscken (2d ed., 19 vols., Berlin, 1822-'59), and other writings of the same author ; Stein- hauser, Neue Berechnung der Dimensionen des ErdspJiaroids (Vienna, 1858) ; Burmeister, Ge- schichte der Schopfung (Leipsic, 7th ed., 1867) ; Sandberger, Der Erdlcorper (Hanover, 1856) ; Berghaus, Was man von der Erde weiss (4 vols., Berlin, 1860) ; Figuier, La terre avant le de- luge (8vo, Paris, 1862); Hackel, NaturlicJie SchopfungsgescMchte (8vo, Berlin, 1868) ; Re- clus, La terre (2 vols., Paris, 1867-'8; Wood- ward's translation, 1871); Newton's Princi- pia; Laplace, " System of the World," Harte's translation; Humboldt, "Cosmos" (5 vols., 1844-'58); Guyot, "Earth and Man" (revised ed., Boston, 1858); Sir John F. W. Herschel, " Outlines of Astronomy " (llth ed., 1872). EARTHENWARE. See POTTERY. EARTHQUAKE, a shaking of the solid ground by more or less violent movements, produced by natural forces. Such shakings, to which every part of the world is liable, are often im- perceptible except to very sensitive instru- ments, but on the other hand are frequently productive of fearful destruction of life and property. These phenomena claim our special attention, since we must hope through them to make our next steps toward a full knowledge of the condition of the interior of our globe. After briefly considering the history of our knowledge of this subject as shown in its bib- liography, we shall recount successively a few of the remarkable earthquakes, and shall then proceed to a short summary of our present knowledge of the subject, giving first some general views on the distribution of earth- quakes, and then reviewing some of the many theories that have been broached in connec- tion with this subject; in conclusion we shall give with some minuteness the remarkable re- sults attained by Mallet and others who have lately established the science of seismology (Gr. aeta[j,6e, earthquake) upon a firm basis. Among the classical writers, Aristotle, Strabo, Seneca, Pliny, Josephus, &c., give numerous facts mixed with fanciful theories on the sub- ject of earthquakes. In the earlier works of the modern revival of knowledge, Beccaria, Bylandt, Flamsteed, Percival, Priestley, Stuke- ly, and others, have sought with but little suc- cess by observations and theories to advance our knowledge of the origin of earthquakes ; and with these we may class the memoir by Michell published in 1760. Of the works be- longing to the present age of philosophical inquiry may be mentioned, first, those that treat specially of the phenomena of individual earthquakes, such as Kant, Roche, and Pereira, on the Lisbon earthquake of 1755 ; the re- port to the academy of Naples on the great earthquake of 1783 in Calabria ; that of Pal- mieri and Scacchi on the Melfi earthquake of 1851 ; that of Volger on the earthquake of Viege, 1855 ; the report by Gilliss on his as- tronomical expedition to Chili, 1849-'52 ; and that of Mr. Mallet to the royal society at Lon-