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thence the axes themselves are given. Thus, the circular arcwhose length is equal to the rarlius being 57-29578 degrees, if thisnumber be multiplied by 56750 toises, the measure ot a degree atthe equator, as Bouguer has stated it, the product will be the ra-dius of curvature there, or half the latus rectum of the greateraxis; and this is to half the less axis in the ratio of the less axisto the greater, that is, as 0.9953467 to I ; whence the two axes are6533820 and 6564366 toises, or 7913 and 7950 Engli-h miles; andthe differences between the two axes about 37 miles. See Ro-bertson’s Navigation, vol. ii. p. 206, &c. Suite des Mem. clel’Acad. 1718, p. 247, and Maclauriu’s Fluxions, vol. ii. book 1.chap. 14. And very nearly the same ratio is deduced from thelengths of pendulums vibrating in the same time, in different lati-tudes; provided it be again allowed, that the meridians are realellipses, or the earth a true spheroid, which, however, can only-take place in the case of an uniform gravity- in all parts of theearth. Thus, in.the new Peter»burgh-Acts, for 1788 and 1789,are accounts and calculations of experiments relative to this sub-ject, by M. krafft. These experiments were made at differenttimes and in various parts of the Russian empire. This gentle-man has collected and compared them, and drawn the properconclusions from them : thus, he infers, that the length ,r of a pen-dulum that swings seconds in any given latitude and in a tem-perature of 10 degrees of Reaumur’s thermometer, may he deter-mined by this equation: .r =439-178+ 2-321 sine % lines of aFrench toot, or x = 39-0045 + 0-206 sine 3 x, in English inches, inthe temperature of 53 of Fahrenheit’s thermometer. This ex-pression nearly agrees, not only with all the experiments made onthe pendulum in Russia , but also with tbo^e of Mr. Graham inEngland, and those of Mr. Lyons m 79° 50' north latitude, wherehe found its length to be 431-38 lines. It also shews the augment-ation of gravity from the equator to the parallel of a given lati-tude x: for, putting g- for the gravity under the equator, G for thatunder the pole, and y for that under the latitude *, M. krafft finds_?/ = (! +0 0052848 sine 2 x)g-; and therefore G = 1-0052848 g.From this proportion of gravity under different latitudes, the sameauthor infers, that, in case the earth is a homogeneous ellipsoid,its oblateness must be one 191, instead of one 230th; which oughtto be the result of this hypothesis; but on the supposition, that theearth is a heterogeneous ellipsoid, he finds its obiateness, as deduc-ed from these exjieriments, to be one 297th; which agrees withthat resulting from the measurement of some of the degrees of themeridian. This confirms an observation of M. de la Place, that ifthe hypothesis of the earth’s homogeneity be given up, then thetheory, the measurement ot degrees of latitude, and experimentswith the pendulum, all agree in their result with respect to theoblateness of the earth. See Memoires de l’Acad. 1783, p. 17.In the Philos. Trans, for 1791, p. 2..6, Mr. Dalny has given somecalculations on measured degrees of the meridian, from whence heinfers, that those degrees measured in middle latitudes, will answernearly to an ellipsoid whose axes are in the ratio ns-igned by New-ton, viz. that of 230 to 229. And as to the deviations of some ofthe others, viz. tow ards the poles and equator, he thinks they arecaused by the errors in the observed celestial ares.

Earth , the Mauneits.m of the. The notion of the magne-tism of the earth was started by Gilbert; and Boyle supposesmagnetic effluvia moved from one pole to the other. Vol. i. p.285, 299. Dr. Knight also thinks that the earth may be consider-ed as a great loadstone, whose magnetical parts are disposed in averv strong irregular manner; anti tiiat the S. pole of the earth isanalogous to the N. pole in magnets, that is, the pole by v.-hichthe magnetical sti earn enteis. lie observes, that all the phamo-inena attending the direction of the needle, in different parts of theearth, in a great measure correspond with what happens to theneedle, when placed upon a large terrella; if we make allowancesfor the different dispositions of the magnetical parts, with respectto each other, and consider the S. pole ot the earth as a N. polewith regard to magnetism. See Magnetism. See also Dr.Knight’s Attempt to demonstrate, that all the pha-nomena in na-ture may be explained by Attraction and Repulsion, prop. 87.

Earth , Magnitude of the. See Geography and Astro-nomy.

Earth , the Structure of. The substances of which theearth is composed, are neither disposed in a regular series, accord-ing to their specific gravities, nor yet thrown together in total dis-order, as it by accident or chance. Human industry lias hitherto

been able to penetrate but a very little way into the bowels of theearth, and we can but know little of its interior parts. The depthof the earth, from the surface to the centre, is nearly four thousandmiles; and yet the deepest mine in Europe , that at Colteberg, inHungary , is not more than one thousand yards deep; “the greatest,depth, therefore,” says an excellent writer, “ to w hich avarice hasever yet penetrated, may- be compared to the puncture made inthe body of an elephant, by the proboscis of a gnat.” See Geo-logy.

Earths, in chemistry, every bodv which possesses the follow-ing properties is so denominated. 1. Insoluble in water, or nearlyso; or at least becoming insoluble when combined with carbonicacid. 2. Little or no taste or smell; especially when combinedwith carbonic acid. 3. EixedT'incondHi'tibie , and incapable, whilepure of being altered by- the lire. 4. A specific gravity not ex-ceeding 4.9. 5. When pure, capable of assuming the i’orm of a

white powder. 6. Not altered whc-n heated with combustibles.The earths at present known, are nine in nlimber, namely,

1. Barytes. 6. Yttria.

2. Strontium 7. Glucina.

3. Lime. 8. Zirconia.

4. Magnesia. 9. Silica.

5. Alumina.

W hich see under their respective names. Every one of the abovecharacteristics is not, perhaps, rigorously applicable to each ofthese bodies; but all of them possess a sufficient number of com-mon properties to render it useful to arrange them under one class.The discoveries which the illustrious professor, Mr. Davy, haslately made respecting the composition of the alkalies, led him tosuspect that the earths are similar compounds; and from accurateexperiments which he has made, it seems exceedingly probablethat the earths are compo- ed of oxygen, and a metallic base.

EARTH NUTS, or GROUN1) NUTS. See Arachis.

Earth Nuts, or Pig Nuts. See Bunium.

Earth Pucf.kons. See Puceron.

EARlilQUAKE, a sudden and violent concussion of theearth, generally accompanied with strange noises under ground, orin the air; oiten destroying whole cities at once, throwing downrocks, altering the course of rivers, and producing the most terri-ble devastations. Though there is hardly any country known, inwhich shocks of an earthquake have not at some time or otln /been felt, vet there are some much more subject to them thanothers. Northern countries, in general, are less subject to earth-quakes than those situated near the equator, or in the southern la-titudes; but this does not hold universally. T he islands of Japan ,w hich are situated pretty far north, are nevertheless exceedinglyliable to these dreadful convulsions. Islands, in general, are alsomore subject to them than continents; but neither does this holdwithout exceptions. Particular parts of continents, and particularislands, are more subject to them than others lying in the neigh-bourhood, and differing little from them in external appearance.Portugal is more subject to earthquakes than Spain , and the lattermuch more than France; Mexico and Peru more than the othercountries of America, and Jamaica more than the other Caribbeeislands. Earthquakes are frequent, though not often violent, inItaly; but in Sicily they are often terribly destructive. AsiaMinor has been remarkably subject to them from the remotest an-tiquity ; and the city of Antioch in particular has suffered morefrom earthquakes than any other in that country. The same phe-nomena are said also to occur very frequently in the extremities ofAsia , even in very high latitudes. Although no natural pha-nome-non is more caleulated to impress the human mind with terror,and consequently to he well remembered and taken notice of,than an earthquake; yet the philosophy of them is but lately ar-rived at any degree ot perfection; and even at tills day, the his-tory of earthquakes is very incomplete. The destruction occa-sioned by them engrosses the mind too much to admit of philoso-phical speculations at the time they happen: the same thing pre-vents the attentive consideration of the alterations, that take place-in the atmosphere after the earlhquake is over, and which mightprobably throw some light on the causes which produced it; andthe suddenness of its coming on prevents an exact attention to thoseslight appearances in the earth or air, which, il'carefully observed,might serve as warnings to avoid the destruction. From the ob-servations that have been made, however, the follow ing pha’no-menu may be deduced, and reckoned pretty certain. 1. Where

there