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D=4.718

5.816 5.488

3.449 5.600 6.365

meridional arc of 42.94". But by 337 observa- the centre; either at the summit and base of a tions

the difference of latitude appeared to be mountain, or on the surface and at a considerable 64.6", giving 11.6" as the double attraction. By depth below it. The Italian astronomers Plana complicated calculations, devised by Cavendish and Carlini, from their experiments on Mont and carried out by Dr. Hutton, the density of the Cenis, in Savoy, obtained the figures 4.950 as earth was computed to be to that of the hill as the result. Professor Airy made a similar ex17,804 : 9,933." Dr. Playfair, after carefully ex- periment at the Harton coal pit, near South amining the geological structure of the hill, Shields, in 1854. He found that a pendulum

a made the probable mean specific gravity of the vibrating seconds at the surface gained 27 secearth to be between 4.56 and 4.87. By a sim- onds per day at the depth of 1,200 feet; and ilar experiment made by Col. James, superin- he hence computed the density of the earth to tendent of the ordnance survey, at Arthur's be 6.565. Sir John Herschel (“ Outlines of Seat, the mean density of the earth has been Astronomy," 5th ed., p. 559) thus presents the found to be 5.316.-Å second method of esti- final result of the whole inquiry: "The densities mating the density of the earth is by an ex- concluded being arranged in the order of magperiment exceedingly delicate and beautiful, in nitude : which the attractive power of small spheres Schehallien experiment, by Maskelyne, calculated by of known weight is weighed and compared Playfair... with that of the earth. The principle of this Carlini, from pendulum on Mont Cenis (corrected by

Giulio).... method has also been recognized by Newton, Col. James, from attraction of Arthur's seat. in his observation that the attraction at the Reich, repetition of Cavendish experiment. surface of any sphere is directly as its radius, Cavendish, result 5.48, corrected by Mr. Baily's recombut incomparably less than its tendency to- Baily's repetition of Cavendish experiment.. ward the earth, or in other words, its weight. Airy, from pendulam in Harton coal pit....... The experiment was devised by the Rev. Mr. General mean..

5.441 Michell, who also prepared the apparatus with Mean of greatest and least.

5.639 which it was first conducted by Cavendish ("Phi- calculating on 51 as a result sufficiently aplosophical Transactions,” 1798). Two balls of proximative and convenient for memory; taking lead of about 2 inches diameter were fixed the mean diameter of the earth, considered as one at each end of a slender wooden rod 6 feet a sphere, at 7,912.41 m., and the weight of a long, which was suspended by a fine wire 40 cubic foot of water at 62.3211 lbs.; we find for, inches long attached to the centre of the rod. its solid content in cubic miles, 259,373 millions, At each extremity of a support of the length of and for its weight in tons of 2,240 lbs. avoird. the rod was placed a leaden sphere of 174 lbs. each, 5,842 trillions (=5842 x 1018).” All these weight; and the support was adjusted upon a experiments give a less density to the earth than centre exactly beneath the centre of the rod would appear to be required by the somewhat suspended above it, so that the great balls could compressible nature of its materials, and to exbe swung around and present their opposite plain this the theory of the existence of a high desides in turn to opposite sides of the smaller gree of temperature in the interior is appealed to balls. When brought near to the latter as they by some as presenting a sufficient counteracting swung at rest, protected by a glass case from influence. The probabilities of the existence of currents of air, they turned toward the large such conditions have been considered in the balls, slightly twisting the wire till its torsion article CENTRAL HEAT.—The various divisions equalled the attractive force. This observation of the earth's surface are described in the article being made through a telescope at a little dis- GEOGRAPHY; its structure is treated in GEOLOGY. tance off to avoid disturbing influences, the large See also PHYSICAL GEOGRAPHY. The subject balls were then moved round, and a similar may be further studied in the following works: measure of the movement was made on the Steffens, Beiträge zur innern Naturgeschichte other side. Cavendish after a long series of der Erde (Berlin, 1801); Ritter, Die Erdkunde trials found the attractive force equal to gbo of im Verhältnisse zur Natur und Geschichte des a grain weight, the centres of the balls being Menschen (Berlin, 17 vols., 1832-'52; not yet 8.85 inches apart, and he computed from this complete), and other writings of the same authe density of the earth to be 5.48 times that thor; Steinhuser, Neue Berechnung der Dimenof water. The experiment has been repeated sionen des Erdsphäroids (Vienna, 1858); Barby Reich of Freiberg and Baily of London, the meister, Geschichte der Schöpfung (Leipsic, 6th latter making more than 2,000 observations. ed. 1856); Sandberger, Der Erdkörper (HanReich made the density 5.44, and by a still over, 1856); Berghans, Was man von der Erde later trial ("Philosophical Magazine, March, weiss (Berlin, 1857, parts 19-23); Newton's 1853), 5.58. Baily found it 5.66. It is remark. Principia ; Laplace, « System of the World,” able that Newton should have stated in his Harte's translation ; Humboldt, “Cosmos" (5 Principia (iii. prop. 10) that the quantity of vols., 1844–58); Guyot, "Earth and Man matter in the earth is probably 5 or 6 times (revised edition, Boston, 1858); Sir John F. what it would be if all were water. Another W. Herschel, “ Outlines of Astronomy” (5th method of determining the density is by com- ed., 1858). parison of the different rates of vibration of EARTH WORM (lumbricus terrestris, Linn.), the same pendulum at different distances from an articulate animal belonging to the abranchi

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ate division of the class of annelids. (See ANNE- but Dr. Williams (in his “Report on the British LIDA, for the characters of the class.) This well- Annelida" to the British association, in 1851) known worm has a long, cylindrical, contractile considers them as utero ovaria. The lumbrici rebody, divided into many apparent rings (some- produce by sexual organs; their eggs are sphertimes 150) by transverse wrinklings; the inter- ical and present nothing remarkable; both sexes nal surface of the muscular envelope sends off are united in the same individual. During the annular septa, dividing the cavity of the body breeding season, from 6 to 9 of the segments into as many chambers as there are segments, (from the 26th to the 37th, as generally dethe partitions having openings which allow the scribed) are developed into a kind of collar, passage of the contents of the general cavity from nearly surrounding the body, by which these one chamber to the others. Each segmentis pro. animals seize each other during coition; its comvided with setæ or bristles, beginning at the 14th ponent glandular follicles secrete a whitish viscid ring from the head, 4 on each side, united in pairs, Auid, probably used for the formation of their forming 8 longitudinal rows, of which 4 are lat- cocoons or egg-cases. According to Dufour, eral and 4 inferior; they are short and rough, and these cocoons have a long narrow neck, each, in are used as fulcra during creeping or climbing in the large species, containing from 1 to 6 eggs ; the ground. The sense of touch is very acute, the statement of Montègre that the young are as is shown by the quickness with which they born alive seems to be confirmed by the observaretire into the ground when touched, or at the tions of Dr. Williams (op. cit.), who says that jar produced by an approaching footstep; the they escape from the egg before leaving the sense is believed to be most acute toward the body of the parent; these conflicting opinions head, especially in the 1st segment. The eyes have been reconciled by some authors by calling are wanting. The mouth is near the anterior these animals ovo-viviparous, producing their extremity of the body, without teeth, with 2 young sometimes completely formed, and at somewhat prominent lips; the pharynx is simple; others surrounded by their egg-like envelope; short, and muscular, the oesophagus narrow, thé it is probable that, like the leech, most lumbrici stomach very muscular, and the intestine short, lay oviferous capsules, fringed at the ends, in straight, constricted by the muscular septa, and which the young are developed without underopening at the posterior extremity of the body. going metamorphosis. It seems certain from The blood is red, and the circulation is complete the experiments of Dufour (Annales des sciences and closed; the several pairs of simple trans- naturelles, t. v. p. 17, and t. xiv.p. 216, 1st series) verse canals, situated above the stomach, whose that the earth worm reproduces by means of pulsations may be distinctly seen, may be con- eggs; he describes them as an inch in length, sidered the heart. The dorsal vessel lies upon of a corneo-membranous consistence, deposited the intestinal canal enveloped in the hepatic tis- in the earth at a depth of from 6 inches to 6 sue. The blood, though red, is quite different feet, in localities where the soil is neither inunfrom that of the vertebrates; according to Sie dated nor too dry, isolated, and each egg conbold, it contains colorless, spherical, unequal-siz- taining 1 or 2 young. In this case the eggs cannot ed granular globules; these,

Quatrefages says, are properly be called cocoons, as the young undergo not part of the blood, but belong to the fluid of no metamorphosis in them; this would be the the general cavity; the latter maintains that the mode of reproduction usually noticed in the class; coloring matter is in simple solution. There is no in the branchiate annelids it is stated by good obapparent external organ of respiration, and the servers that some are born alive and mature, and peculiar canals in the abdominal cavity are re- others of the same species are developed from garded by some as internal branchiæ or aquifer- eggs deposited in a gelatinous covering ; so that ous vessels. The structure of these organs is little there is no anomaly in the mode of reproduction understood; but in all genera of the division there described by Dr. Williams, and there would seem are at the commencement of the intestine very no necessity for maintaining that the viviparous tortuous canals, opening generally on the ven- mode of reproduction rested on mistaken obsertral surface; these canals are lined with ciliæ, vations, or that the excluded worms in these which have an undulatory movement always in cases are entozoa, which, it is well known, are one direction; they never contain air, according very common in the earth worm. Still, the to Siebold, but circulate an aqueous respiratory subject is much in need of a thorough revision, fluid by means of the ciliæ; even the terrestrial Earth worms live in moist earth, in which they earth worms can live only in damp earth, from make galleries in all directions, swallowing the which they obtain the necessary aqueous fluid. earth as they proceed; their food is principally In the lumbricus these canals are surrounded by soft and decaying vegetables, as may be proved a distinct vascular net-work; they appear to by any one who chooses to watch a garden walk end in loops, and their external orifices have not by the light of a lantern on a damp evening, been satisfactorily ascertained. The most prob- when they may be seen creeping out of their able opinion is that the respiration is carried holes, elongating their first tactile segment, feelon principally by the general integument, and ing in all directions for food, and, seizing any suitpartly by the vascular system on the walls of the able substance with their projected proboscis, intestine; the ciliated canals described by Siebold retiring backward into the ground; their conaro believed by Quatrefages to be organs for the stant presence wherever there is decaying vegesecretion of the mucus which invests the body; table matter proves that their food is principally derived from such substances; they also, as which they could not have reached without Montègre observed, will feed upon animal mat- climbing perpendicularly. In their movements ters; it seems more reasonable to believe, with they display great muscular force, each seta De Blainville, that they swallow earth for the being moved by its appropriate system of muspurpose of making progress in their galleries, cles;

Dr. Williams says that these setw, with than that they do this to extract humus or any their fine hair-like appendages, will actually peneother nutritious substance from it. They seek trate a deal board, and that the path of a worm each other chiefly at night and in the latter part on such a polished surface will show under the of spring, though some species have been noticed microscope 4 series of minute perforations. This together at all times of the day, and during all would hardly explain their ascending perpendicthe warm months; it is well known that they ular surfaces, especially when of glass or similar are most abundant on the surface of the ground impenetrable material; in such cases, which are during and after nocturnal rains. It has long incontestable, they must retain their bold by been believed that this animal possesses & means of the tenacious mucus with which their remarkable power of reproducing parts lost by skin is covered. There is no question that accident or design, even to the extent of form- many species have been confounded under L. ing perfect individuals from separated portions; terrestris (Linn.). The largest European species the experiments of Dugès prove that very im- is called L. gigas, and is 18 inches long, and as portant parts may be reproduced, and it may large as the little finger; other common and easily be believed that in a worm divided into smaller species are L. anatomicus and L. tratwo, the anterior portion might produce an pezoides. Whether all the American species anus by the simple contraction of the wound; are distinct or not has not been sufficiently but that the posterior portion should be able to demonstrated; there are certainly some species reproduce cerebral ganglia, mouth, stomach, described peculiar to this country, but probacardiac and sexual organs, cannot be admitted; bly the L. terrestris is common to both hemithe anterior may survive a long time, but the spheres. The history and habits of this composterior division gradually dries up and dies. monest of animals, trodden under foot by every. Dr. Williams, after attending to the experi- body, show how creatures apparently the best ments of Bonnet, Spallanzani, and others, to known may give rise to the most contradictory which Prof. Owen gives assent, says: “On the opinions among naturalists, and how a come authority of hundreds of observations, labo- plete study of the most insignificant worm may riously repeated at every season of the year, illustrate some of the highest problems of ani. the author of this report can declare with de- mal physiology.—Those who wish to pursue this liberate firmness, that there is not one word subject into its details are referred to the writof truth in the above statement." In 1853 ings of Dufour, Dugès, Milne-Edwards, BlanchMr. Newport exhibited before the Linnean so- ard, and especially Quatrefages in the Annales ciety of London 3 specimens of earth worms, des sciences naturelles since 1828; to the article one of which was living, in which more than “Annelids,” in the “Cyclopædia of Anatomy

of the anterior part of the body had been and Physiology;" to the report of Dr. Williams, restored, smaller in diameter and with shorter above quoted ; and to Siebold's “Comparative segments than the anterior portion; and he says Anatomy," with its amplo references to the that it is not uncommon to find specimens with best works. parts similarly restored. Though generally a EARTHENWARE. See POTTERY. despised creature, and occasionally marring the EARTHQUAKE. In every part of the world beauty of the garden walks by little hillocks of the surface is subject to be shaken at times earth, they not only do not injure vegetation, by movements taking place in the interior and but are really useful in permitting air and water transmitted somewhat like a wave to distant to penetrate the ground through the channels regions. No country escapes these visitations, which they pierce in every direction, manuring but in volcanic districts they occur more frethe fields, and throwing up fine dirt around the quently than elsewhere; and commencing in roots of grass; a field in which no worms exist these, they have been known to pass beneath can be safely put down as of little value to the sea and land, from one hemisphere to another, agriculturist; they are most active in spring, till full į of the entire surface of the globe has when most needed, and retire during winter been more or less disturbed by the movement. deep into the ground; according to Mr. Darwin, Such was the great earthquake of the year 1755, they perform under ground that which the known as that of Lisbon, which will be described plough and the spade do on the surface, and below. Some countries are so subject to these have covered a field manured with marl, in the disturbances that the habitations of the peocourse of 80 years, with a bed of earth 13 ple are built low, with broad bases and subinches thick. Worms also furnish food for stantial walls, with particular referenco to their birds, moles, frogs, and other small animals, and stability against the shocks. This is the case are used as bait for many kinds of fish. The throughout Central America, and in Chili, Peru, rapid ascent and descent of worms in the ground &c. Taking into account the whole surface of are easily understood from the action of their the earth, there is probably not a day that passes numerous setæ ; they have often been seen high without the occurrence somewhere of a sensible up on perpendicular surfaces, and in situations disturbance of this kind, and hardly a month without one or more worthy of note. The same pour down in torrents at times, or in places in countries have continued to be frequently visited which they are usually of rare occurrence. Imby earthquakes from remote periods. Calabria, mediately before the shocks occur, the air is the southern extremity of Italy, has been re- generally very still, while the surface of the peatedly devastated since its early settlement ocean or lakes is unusually disturbed. A sound by the Greek colonists, and, together with the then breaks upon the stillness like distant thunneighboring island of Sicily, has been the scene der, or like a carriage rumbling afar off upon a of some of the most terrible earthquakes on rough pavement; or it may break at once with record. From Feb. 1783, to the end of the year an awful explosion, as when the peal and the 1786, a period of nearly 4 years, this country flash come together from every part of the was almost constantly disturbed. No fewer than cloud in wbich one is enveloped ; at the same 949 shocks were experienced in the first of these time the ground is shaken and lifted upward, or years, of which 501 were shocks of the first de- thrown forward, as by the passage of an irregree of force. Lyell observes that these convul- sistible wave beneath it. The shocks may be sions were not remarkable above many others repeated several times in quick succession, or for their duration, violence, or extent, but great recur after long intervals; the movements may importance is given to them from the minute. be so great as to rend the surface into chasms, ness of the observations of men competent to and these may open and shut again, or remain in collect and describe with accuracy the physical fissures of the width of a few feet or yards, and facts which throw light on geological questions. extending to unknown depths; smoke and flames The details that have been recorded of the are occasionally sent forth from them during the earthquakes in the countries bordering on the continuance of the earthquake, even if the reMediterranean would make this region appear gion be not volcanic. Torrents of water are more subject to them than any other part of the ejected from these chasms, and springs of water globe; but had any other volcanic region been are often forced by the convulsion into new outsettled during the same periods by a population sets and directions. Objects upon the surface, as of the same degree of civilization, it is probable dwellings, trees, and animals, are engulfed in that the records of the two would not have ma- che chasms; and by subsidence of the surface, terially differed in this respect. Among the ear- large trees, mountains even, and whole cities are liest accounts of earthquakes of particular inter- swallowed up. Occurring as they most frequently est is that which resulted in the destruction of do along the seaboard, the water is observed comHerculaneum and Pompeii in the year 63, which monly to retire to some distance, leaving the har. was 16 years previous to the time when those bors dry, and then to return in a great wave of cities were buried in the ashes from Vesuvius. many feet in height, which sweeps every thing The ancient city of Antioch in Syria was almost before it. This may occur by the progress of destroyed in the year 115, at the time of the the great wave, the recession being occasioned visit of the emperor Trajan, who was himself in the same way as the similar movement upon hurt. In 458 it was again visited by an earth- a small scale noticed along the shore as a steamquake, and in 626 occurred the most disastrous boat approaches it, the water first receding, and one of which any record has been preserved. then returning in a great wave; or it may be Gibbon states that 250,000 pe ns are said to owing to a tract being uplifted in the sea at have perished at this time, a conflux of stran- some distance, toward which the waters would gers to the festival of the Ascension swelling first be drawn from every direction, and immethe multitudes belonging to the city. “His- diately after be propelled back with redoubled tory," he remarks, " will distinguish the pe- force. Of all the calamities to which man is riods in which these calamitous events have exposed, there are none of so fearful a character been rare or frequent, and will observe that as earthquakes; none involve such terrible and this fever of the earth raged with uncommon devastating destruction to life and property. violence during the reign of Justinian. Each There are none of the approach of which he year is marked by the ropetition of earthquakes is less forewarned, and none against which he of such duration that Constantinople has been can take fewer precautions. The very mysteshaken above 40 days; of such extent that the riousness of the danger oppresses him with tershock has been communicated to the whole ror. He is ignorant in what form it is most surface of the globe, or at least of the Roman imminent, or in what direction to seek a way empire.”—The approach of earthquakes is her- of escape. Of modern earthquakes, that of alded by several premonitory symptoms of an Lisbon, in 1755, and that of New Madrid, Mo., unmistakable character. The air appears to be in 1811, present some of the most interesting affected in some respect, perhaps in its electric details. That of Chili, in 1822, is interesting condition, and the brute animals show a sensi- for the permanent elevation of the country betiveness to this by uttering cries of distress and tween the Andes and the coast which attended running wildly about. Men sometimes are af- it. The area thus raised has been estimated to fected with dizziness, and a sensation like sea- equal fully 100,000 square miles, and the height sickness. The atmosphere is often hazy for of the elevation to vary from 2 to 7 feet. Lines months, and the sun seen through it appears red of sea beaches at higher levels and further inand fiery. The weather suddenly changes from land indicate the previous lifting up of the same fierce gusts of wind to dead calms, and rains region at different times along the same lines.

VOL. VI.-46

722

A depression of the land was occasioned in the wave like the swellings of the sea, and occaisland of Jamaica in 1692, when Port Royal, the sionally break into fissures. This lasted for 15 capital, was carried down, with the greater part minutes, during which chimneys were shaken of the buildings in the city, beneath the surface down and houses disjointed. The sea roared of the water. A thousand acres or more thus with the unusual commotion, and with the sank in less than one minute, the sea rolling in rumbling of the earth the noise was more apand driving the vessels in the harbor over the palling than that of the loudest thunder. Water tops of the houses. A similar catastrophe oc- spouts burst forth, and springs opened, which curred on a much more gigantic scale in the continue to flow to this day. As the moveisland of Java in 1772, when Papandayang, then ment passed beneath the ocean, it was felt by one of the loftiest of the volcanoes of this region, several ships, the impression being like that was in action ; an area suddenly sank down, produced by striking upon rocks. The motion including the mountain of 15 m. long and 6 is described as undulatory, and proceeding at m. broad, carrying with it 40 villages, and de- the rate of about 20 m. a minute. — The earth. stroying 2,957 of the inhabitants. The great quake of New Madrid, below St. Louis, on the earthquake of Lisbon commenced on Nov. 1, Mississippi, in 1811, is the most important that 1755. The rumbling sound below the sur- has occurred in this country of which we have face was immediately followed by the shock, any record. Humboldt remarks that it prewhich threw down the principal portion of the sents one of the few examples of the incessant city. In the short space of 6 minutes it is be- quaking of the ground for several successive lieved that 60,000 persons perished. The sea months, far from any volcano. Over an extent retired, leaving the bar dry, and returned in of country 300 m. in length, from the mouth of a great wave 50 feet or more in height. The the Ohio to that of the St. Francis, the ground mountains around were shaken with great vio- rose and sank in great undulations, and lakes lence, and were even rent and thrown in frag- were formed, and were again drained. The surments into the valleys below. Multitudes of face burst open in fissures, from which mud and people sought safety from the falling buildings water were thrown as high as the tops of the by crowding upon the marble quay, which had trees. The direction of these fissures was genjust been constructed at great expense. It sud- erally from the N. E. toward the S. W., and the denly sank with them like a ship foundering at inhabitants, noticing this, felled the tallest trees sea; but when the waters closed over the place no at right angles to this line, and stationing themfragments of the wreck, none of the boats and selves upon them, thus escaped being engulfed. vessels near by that were drawn into the whirl- Flint, the geographer, observed hundreds of pool, and not one of the thousands of bodies car- these chasms 7 years after this catastrophe; ried down, reappeared upon the surface. Over and Lyell, who visited the same region in the spot the water stood 600 feet deep; and be- 1846, noticed many, which then appeared like neath this, locked in the fissured rocks, in chasms artificial trenches, which might be traced for of unknown depth, lie the relics of what was more than half a mile. They were generally the life and wealth of this portion of the earth's parallel, and varied, according to his measuresurface in the middle of the 18th century. ments, from 10° to 45° W. of N. The country These rocks are the clayey and other compara- is still called the "sunk country," and its extively soft strata of the tertiary formation. tent, along the White Water and its tributaWhen in some future epoch they are raised ries, is 70 to 80 m. N. and S., and 30 m. E. and again to the surface by a convulsion of the same W. During the continuance of these convul. nature with that which engulfed them, the sions the inhabitants distinguished 2 classes of vestiges they contain may reappear, converted earthquakes, those in which the movement was in part or wholly into stone, like fossils en- vertical, and those in which it was horizontal; tombed when the strata were deposited. The the latter were regarded as far more desolating portion of the surface of the earth that was than the former. They continued until the deshaken by this earthquake was estimated by struction of the city of Caracas, which took Humboldt as equal to 4 times the extent of Eu- place March 26, 1812. One evening, about this rope. The shock was felt in the Alps and on time, is described by the inhabitants of New the coast of Sweden. In Germany the thermal Madrid as brilliant and cloudless, during which springs of Töplitz disappeared for a time, and the western sky was a continued glare of vivid again burst forth, deluging the region around flashes of lightning, and peals of thunder were with ochre-stained waters. The waters of the incessantly heard, proceeding apparently, as did lakes in Scotland, as Loch Lomond especially, the flashes

, from below the horizon. In the rose suddenly more than 2 feet, and then sub- destruction of Caracas, the whole city, with its sided below their usual level. On the shores splendid churches, was in an instant a heap of of Barbados, Martinique, and Antigua, the ruins, under which about 12,000 of its inhabittide suddenly rose 20 feet, and the sea was ants were buried.–Fissures are occasionally met of inky blackness. Even the distant waters with in different parts of the country wbich ex. of Lake Ontario were strangely agitated, and tend through the solid rock to a great depth, the shock was sensibly felt along the coast of and which were without doubt produced by Massachusetts. In Deane's “History of Scit- earthqnakes of some unknown period. A reuate" it is stated that the earth was seen to markable chasm of this nature may be followed

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