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EARTH EARTHQUAKE. 



cycloids round the earth. Aristarchus lived 280 B. C., 

 Hipparchus, the great astronomer of antiquity, 150 

 B. C., therefore 130 years later. At this time, all the 

 writings of Aristarchus were extant, and had the 

 Copernican system Ixrn set forth in them, Hippar- 

 chus would not have despaired of explaining the 

 motions of the planels. 'The same is true of Ptolemy, 

 in whose Almagest, the most complete work of an- 

 tiquity on astronomy, this system is not mentioned 

 in the account of Aristarchus. Every Copernicun 

 speaks of the motion of the earth, but not every one 

 who .-.peaks of the motion of the earth is a Coperni- 

 ran. Copernicus was led to the discovery of his 

 system by consideration of the complicated motion 

 of the planets, and, in the dedication of his im- 

 mortal work, De Revolutionibus Orbinm, to pope 

 Paul III., he says, that the truth ot his system is 

 proved by the motion of the planets, since their 

 successive stations and retrogradations are the 

 simple and necessary consequence of the motion 

 of tlic earth round the sun ; and we need not take 

 refuge in the complicated epicycles. Copernicus 

 did not live to see the persecutions which the Ro- 

 man Catholic priests raised against his system. They 

 began only LOO years later (about 161O), when the 

 telescope was invented, wher the moons of Jupiter 

 and the phases of Venus were discovered, and, by 

 these means, the zeal for astronomy had been highly 

 excited. Every city in Italy was then a little Athens, 

 in which the arts and sciences flourished. Galileo 

 obtained high distinction, and defended the new 

 system of the world. The Roman inquisition sum- 

 moned him before its tribunal, and he was compelled 

 to abjure this theory. (See Galileo.) The general 

 sympathy for the fate of this astronomer increased 

 the popularity of the system, and it was as violently 

 defended on one side as it was attacked on the other. 

 Among the arguments against the motion of the 

 earth, it was alleged, that a stone, falling from a 

 tower, did not fall westward of the tower, notwith- 

 standing this had advanced eastward several hundred 

 feet during the four or five seconds of the fall of the 

 stone. Copernicus had answered justly : the cause 

 of its remaining near the tower is, that it has the 

 same motion eastward, and, in falling, does not lose 

 this motion, but advances with the earth. Galileo 

 said the same, and asserted that a stone, falling from 

 the top of the mast of a vessel at full sail, falls at 

 the foot of the mast, notwithstanding the mast ad- 

 vances, perhaps, ten or more feet during the fall. 

 Gassendi tried these experiments in the harbour of 

 Marseilles, and the stones fell at the foot of the mast, 

 notwithstanding the vessel was under full sail. Gal- 

 ileo therefore maintained, that it is impossible to 

 draw any conclusions concerning the motion of the 

 earth from such experiments, since bodies would fall 

 on the earth in motion precisely the same as on 

 the earth at rest. In 1642, Galileo died. In the 

 same year, Newton was born. He proved, in 1679, 

 thj.t the opinion of Galileo was erroneous, and that 

 we certainly can try experiments on the motion of 

 the earth ; that the balls would not deviate west- 

 ward, but would fall a little eastward of the plumb- 

 line, about a half inch at the height of 300 feet. The 

 cause is this : since the top of the tower is at a 

 greater distance from the axis of the earth than its 

 base, the centrifugal force must be greater at the 

 former point than at the latter ; the ball, in falling, 

 does not lose this impulse, and, therefore, advances 

 before the plumbline, which strikes the foot of the 

 tower, since it has a less impulse eastward. This 

 hint, given by Newton, was followed by Hooke He 

 tried experiments on the motion of the earth, at a 

 height of 160 feet, and asserts that lie succeeded. 

 The academy appointed a committee, Jan. 14, 1680, 



in the presence of which he was to repeat his experi- 

 ments. Probably they were not satisfactory, since 

 they have never been mentioned in the Philosophical 

 Transactions, and were entirely forgotten. Only 

 112 years later, a young geometrician in Bologna, 

 Giiglielmini, attempted to repeat these experiments, 

 winch had been considered very difficult by astrono- 

 mers, in the lower Degli Asinelli, in that city, at a 

 height of 240 feet. After having surmounted all 

 difliciilties, he succeeded in causing the fall of sixteen 

 balls, which perceptibly deviated eastward. But 

 Guglielmini committed an error in not suspending 

 the lead every day when he tried his experiments, of 

 which he often made three or four in one night. ! le 

 did not drop the plummet until after he had finished 

 all his experiments, and, as it did not come to a per- 

 pendicular position until six months, on account of 

 stormy weather, the tower in the meantime was a 

 little bent, the point at which the plummet should 

 have fallen was altered, and his experiments were 

 lost. This happened in 1792. Benzenberg, a Ger- 

 man, performed similar experiments in 1804, in 

 Michael's tower, in Hamburg. He let fall thirty 

 balls, from the height of 235 feet : the balls deviated 

 from the perpendicular four lines eastward. But they 

 deviated, at the same time, l line southward, pro- 

 bably owing to a gentle draft of air in the tower. 

 He repeated these experiments in 1805, in a coalpit, 

 at Schlebusch, in the county of Mark, at the height 

 of 260 feet : there the balls deviated from the per- 

 pendicular five lines eastward, just as the theory of 

 the motion of the earth requires for the latitude of 

 51, but neither southward, nor northward. From 

 these experiments, Laplace calculated that the 

 chances are 8000 to 1 that the earth turns round 

 its axis. The invention of the telescope, by means 

 of which the rotation of Jupiter was soon observed, 

 but still more Newton's discovery of universal gravity, 

 and of the nature of the celestial motions, estab- 

 lished the theory of the motion of the earth ; and, in 

 modern times, no man of intelligence doubts it any 

 longer. The French general Allix, however, en- 

 deavoured to prove that the motion of the planets 

 does not depend on the law of gravitation. The flat- 

 tening of the earth (see Degree, Measurement of,) and 

 the diminution of gravity in the vicinity of the equa- 

 tor, proved by the experiments of Richers and others 

 on the motion of the pendulum in the equatorial 

 regions (see Pendulum), also give as convincing 

 proofs of the rotation of the earth, as the aberration 

 of light (q. v.) affords of the revolution of the earth 

 round the sun. Thus the human intellect has 

 triumphed over the evidences of sense, and the oppo- 

 sition of authority. 



EARTHQUAKE ; a shaking of certain parts of 

 the earth's surface, produced by causes not perceiv- 

 able by our senses. This motion occurs in very dif- 

 ferent ways, and in various degrees of violence. 

 Sometimes it is perpendicular, throwing portions of 

 the ground into the air, and making others sink. 

 Sometimes it is a horizontal, undulating motion, and 

 sometimes it appears to be of a whirling nature. 

 Sometimes it is quickly over ; sometimes continues 

 long, or recurs at intervals of weeks, days, or months. 

 At one time, it is confined within a small circle ; at 

 another, it extends for many miles. At one time, 

 it is hardly perceptible ; at another, it is so violent, 

 that it not only demolishes the works of human art, 

 but changes the appearance of the ground itself. 

 Sometimes the surface of the ground remains un- 

 broken ; sometimes it bursts open into clefts and 

 chasms ; and then occasionally appears the pheno- 

 menon of the emption of gases, and also of flames, 

 with the ejection of water, mud, and stones, as in 

 volcanic eruptions. The eruptions of proper and 



