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their knowledge was very imperfect. An early treatise on refraction, in nine books, was written by J. Baptista Porta; but Kepler was the first who elucidated this subject in any great degree, having demonstrated the properties of spherical lenses very accurately, in a treatise published anno 1611. After Kepler, Galileo introduced the doctrine into his Letters; as also an Examination of the Preface of Johannes Pena upon Euclid's Optics, concerning the use of Optics in astronomy. Des Cartes also wrote a treatise on Dioptrics, commonly annexed to his Principles of Philosophy, one of his best works: in which the true doctrine of vision is more distinctly explained than by any former writer, and in which is contained the law of refraction, discovered by Snell, though the name of the inventor is suppressed. Here are also laid down the properties of elliptical and hyperbolical lenses, with the practice of grinding glasses. Dr. Barrow has treated on Dioptrics in a brief but very elegant manner, in his Optical Lectures, read at Cambridge. There are also Huygens's Dioptrics, an excellent work of its kind. Molyneux's Dioptrics, a heavy and dull work. Hartsocker's Essai de Dioptrique, Cherubin's Dioptrique Oculaire, et De Vision Parfaite, David Gregory's Elements of Dioptrics, Traber's Nervus Opticus, and Zahn's Oculus Artificialis Teledioptricus. Dr. Smith's Optics is a complete work of its kind. Wolfius's Dioptrics are contained in his Elementa Matheseos Universalis. Harris's Optics, Bouguer's Optics, and the second volume of Hauy's Natural Philosophy, may also be advantageously consulted. The Treatise on Optics, and the Optical Lectures of Newton, contain an account of inestimable experiments and reasonings in this science: and Mr. Dollond's discovery of achromatic glasses, by which colors are obviated in refracting telescopes, has been of great importance to this branch of optics. See OPTICS.

DIORTHO'SIS, n.s. Gr. dioplwois, of diopoow to make straight. A chirurgical operation, by which crooked or distorted members are restored to their primitive and regular shape.

DIOSCOREA, in botany, a genus of the hexandria order and diœcia class of plants; natural order eleventh, sarmentaceæ. Male CAL. sexpartite: COR. none. Female CAL. Sexpartite : STYL. three: CAPS. trilocular and compressed; and there are two membranaceous seeds. There are fifteen species, of which the only remarkable one is the D. bulbifera, or the yam. It has triangular winged stalks, which trail upon the ground, extend far, and frequently put out roots from their joints as they lie upon the ground, by which the plants are multiplied. The roots are eaten by the inhabitants of both the Indies; and, in the West India islands, make the greatest part of the negroes' food. The plant is supposed to have been brought from the East to the West Indies; for it has never been observed to grow wild in any part of America; but, in the island of Ceylon, and on the coast of Malabar, it grows in the woods, and there are in those places many different species. It is propagated by cutting the root in pieces, observing to preserve an eye in each, as in planting pota

toes. One plant will produce three or four large roots. The skin of these roots is pretty thick, rough, unequal, covered with many stringy fibres or filaments, and of a violet color, approaching to black. The inside is white and of the consistence of red beet. It resembles the potatoe in its mealiness, but is of a closer texture. When raw, the yams are viscous and clammy; when roasted, or boiled, they afford very nourishing food; and are often preferred to bread by the inhabitants of the West Indies, on account of their lightness and facility of digestion. When first dug out of the ground, the roots are placed in the sun to dry; after which, they are either put in sand, dry garrets, or casks; where, if kept from moisture, they may be preserved whole years without being spoiled or diminished in their goodness. The root commonly weighs two or three pounds; though some yams have been found upwards of twenty pounds weight.

DIOSCORIDES, a physician of Anazarba, in Cilicia, who lived in the reign of Nero. He was originally a soldier; but afterwards he applied himself to study, and wrote a book upon Medicinal Herbs. See BOTANY.

DIOSCURI, in antiquity, a name given to Castor and Pollux, as Kovoot, the children, Atog, of Jupiter. They are often borne on the medals of the Roman consuls, and generally appear, as in the annexed diagram, on horse-back, armed with spears, and with helmets surmounted with stars.

FPAETVS

ROMA

DIOSCURIA, dioσkovpia, in antiquity, a festival in honor of Castor and Pollux. It was observed by the Cyreneans, but more especially by the people of Sparta, the birth-place of these heroes. The solemnity was full of mirth, being at a time wherein they shared plentifully of the gifts of Bacchus, and diverted themselves with sports, of which wrestling matches made a part.

DIOSMA, African spiræa, a genus of the monogynia order and pentandria class of plants: COR. pentapetalous; nectarium crown-shaped, above the germen: CAPS. five, coalited: SEEDS hooded. There are nine species, of which the most remarkable are,

1. D. hirsuta, with narrow hairy leaves; a very handsome shrub, growing to the height of five or six feet. The stalks are of a fine coral color, the leaves come out alternately on every side of the branches; the flowers are produced in small clusters at the end of the shoots, and are of a white color. They are succeeded by starry seed-vessels, having five corners; in each of which corners is a cell, containing one smooth, shining, oblong, black seed; these seed-vessels abound with a resin which emits a grateful scent, as does also the whole plant.

2. D. oppositifolia, with leaves in the form of a cross. It rises to the height of three or four feet; the branches are slender, and produced, from the stem very irregularly; the flowers are produced at the ends of the branches, between the leaves; the plants continue long in flower, and make a fine appearance, intermixed with other exotics in the open air.

DIOS NOMBRE DE, a town of Mexico, on the road from the mines of Sombrerete to Durango. It contains 6800 inhabitants.

DIOSZEGH, a large market town of Hungary, in the county of Bihar, thirty miles S.S. W of Zathmar.

DIOSPOLITES Nomos, a division of Thebais, or the Higher Egypt, to distinguish it from another of the Lower Egypt, or the Delta; south of the Nomos Thinites, on the west side of the Nile.

DIOSPYROS, the Indian date-plum, a genus of the diœcia order and polygamia class of plants; natural order eighteenth, bicornes. CAL. hermaphrodite and quadrifid: coR. urceolated and quadrifid; STAM. eight: STYL. quadrifid: BERRY octospermous. There are two species, viz.

1. D. lotus, which is supposed to be a native of Africa, from whence it was transplanted into several parts of Italy, and also into the south of France. The fruit of this tree is supposed to be the lotus with which Ulysses and his companions were said to have been enchanted, and which made those who eat of it forget their country and relations. In the warm parts of Europe this tree grows to the height of thirty feet.

2. D. Virginiana, pinshamin, persimon, or pichumon pluin, is a native of America, but particularly of Virginia and Carolina. The seeds of this sort have been frequently imported into Britain, and the trees are common in many nurseries about London. It rises to twelve or fourteen feet; but generally divides into many irregular trunks near the ground, so that it is very rare to see a handsome tree of this sort. Though plenty of fruit is produced on these trees, it never comes to perfection in this country. In America the inhabitants preserve the fruit till it is rotten, as is practised with medlars in England, when they are esteemed very pleasant. Both species are propagated by seeds, and the plants require to be treated tenderly while young; but when theyare grown up, they resist the greatest cold of this country. DIP, v.a., v. n. & n. s. ) Goth. doppen; Sax. DIP'CHICK, n.s. dopen; Dutch doopene; Teut. tauffen; Hindoo duba, from Gr. CUTTW. To imnierse; put into a liquid; wet; and, figuratively, to be deeply involved in any affair, and to engage as a pledge. As a neuter verb to sink; enter; immerge: as a substantive it is applied by miners to the direction of coalshafts and minerals (see p. 268), and by scientific men to the depression of a part of the horizon, the needle of the compass, &c. Dip-chick the example explains.

Who, dipping all his faults in their affection, Work like the spring that turneth wood to stone, Convert his gyves to graces. Shakspeare. Dipchick is so named of his diving and littleness. Carcw.

And though not mortal, yet a cold shuddering

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The persons to be baptised may be dipped in water; and such an immersion or dipping ought to be made thrice, according to the canon. Ayliffe's Parergon.

Crowd round her baths, and, bending o'er the side,

Unclasped their sandals, and their zones untied, Dip with gay fear the shuddering foot undressed, And quick retract it to the fringed vest. Darwin. In nautical observations it is necessary to know the depression or dip of the sea, to correct the apparent altitude of an observed object.

DIPET'ALOUS. adj. Having two flower leaves.

Dr. A. Recs.

Δις and πεταλον.

DIPHT HONG, n. s. Fr. diphthongue; Ital. and Span. diftongo; Lat. diphthongus; Gr. digoyyos, from dis, double, and pooyyn, a sound.

ous

We see how many disputes the simple and ambiguand now it has begot the mistake concerning diphnature of vowels created among grammarians, thongs; all that are properly so are syllables, and not diphthongs, as is intended to be signined by that word. Holder's Elements of Speech.

of their being two syllables, and the objection is gone. Make a diphthong of the second eta and iota, instead Pope.

DIPHTHONGS are distinguished by some authat regard the ear; but a more accurate distincthors into those that regard the eye, and those tion was long ago made by that eminent grammarian, Mr. Ruddiman, into proper and improper. A third class, however, seems to exist in the English language, which may be styled wherein only one of the vowels is sounded, the neutral. 1. Improper diphthongs, are those other being sunk; as we and œ in the Latin, and ea, ei, eo, ie, ou, oe, ue, and ui, in the English language. The Latins pronounced the two vowels in their diphthongs ae or æ, oe or c, much as we do; only that the one was heard much weaker than the other, though the division was made with all the delicacy imaginable. Neutral diphthongs are those combinations of vowels, wherein either a new sound, different from that of both, takes place, or neither of them is sounded; for instance, the sound of eo in people, is quite different from that of eo in jeo

2.

To be baptized, is to be dipped in water; metapho- pardy, or of either of the vowels separate; and rically, to be plunged in afflictions.

Poole's Continuators.

the apparent diphthong, or diphthong of the eye, as others style it, ue, in rogue, vogue, &c.

is sunk altogether. Among the former of these classes may be ranked ee and oo, wherein the original sound of the vowels, instead of being lengthened, like that of aa, is changed to that of i and u. The diphthong oe, in shoe, also belongs to this class, with many others. 3. Proper diphthongs, are such as include the sound of both the component vowels, though still in one syllable; such as au, eu, and ei, in Latin; and ai, au, ay, eu, ey, oi, and ou, in English.

DIPLOE, n. s. The inner plate or lamina

of the skull.

DIPLOE, in anatomy, the soft meditullium, or medullary substance, which lies between the two lamina of the bones of the cranium.

DIPLOMA, n. s. Fr. diplome; from Gr. dirua. See the article following.

In 1728 he received from Edinburgh and Aberdeen an unsolicited diploma. Academical honours would have more value, if they were always bestowed with equal judgment. Johnson's Life of Watts.

DIPLOMA is peculiarly used for an instrument' or licence, given by colleges, societies, &c., to clergymen or physicians, to exercise their respective professions, after passing examination, and being admitted to a degree.

DIPLOMATICS, the science of diplomas, or of ancient literary monuments, public documents, &c. It does not, however, nor can it, absolutely extend its researches to antiquity; but is chiefly confined to the middle age, and the first centuries of modern times. For though the ancients were accustomed to reduce their contracts and treaties into writing, yet they graved them on tables, or covered them over with wax, or brass, copper, stone, or wood, &c. And all that in the first ages were not traced on brass or marble, have perished by the length of time, and the destructive events, that have taken place. The word diploma signifies, properly, à letter, or epistle, folded in the middle, and not open. But, in more modern times, the title has been given to all ancient epistles, letters, literary monuments, and public documents, and to all those pieces of writing which the ancients called syngrapha, chirographa, codicilli, &c. In the middle age, and in the diplomas themselves, these writings are called literæ, præcepta, placita, chartæ indiculæ, sigilla, and bullæ; as also panchartæ, pantochartæ, tractoriæ, descriptiones, &c. The originals of these pieces are named exemplaria, or autographa, chartæ authenticæ, originalia, &c.; and the copies, apographa, copiæ, particulæ, &c. The collections that have been made of them, are called chartariæ and chartu 'æ. The place where these papers and documents were kept, the ancients named scrinia, tabularium, or ærarium, words that were derived from the tables of brass, and, according to the Greek idiom, archeium, or archivum. To understand the nature of these ancient papers, diplomas, and MSS., and to distinguish the authentic from the counterfeit, it is necessary to observe, that the paper of the ancients came from Egypt, and was formed of thin leaves, or membranes, taken from the branches of a tree named Papyrus, or Biblum

Ægyptiacum, and which were pasted one over the other with the slime of the Nile, and were pressed and polished with a pumice stone. This paper was very scarce; and it was of various qualities, forms, and prices, which they distinguished by the names of charta hieratica, luria, augusta, amphitheatrica, saitica, tanirica, emporetica, &c. They cut it into square leaves, which they pasted one to the other, in order to make rolls of them; from whence an entire book was called volumen, from volvendo; and the leaves of which it consisted, paginæ. Sometimes, also, they pasted the leaves all together by one of their extremities, as is now practised in binding; by this method they formed the back of a book, and these the learned called codices. They rolled the volume round a stick, which they named umbilicus; and the two ends which came out beyond the paper, cornua. The title, written on parchment, in purple characters, was joined to the last sheet, and served it as a cover. They made use of all sorts of strings or ribands, and even sometimes of locks, to close the book; sometimes, also, it was put into a case It is easy for those, who apply themselves to this study, to distinguish the parchment of the ancients from that of the moderns, as well as their ink and various exterior characters; but that which best distinguishes the original from the counterfeit, is the writing or character itself; which is, in most cases, very distinctly different from one century to another. There are two works which furnish the best lights on this matter, and which may serve as sure guides in judging of what are called ancient diplomas. The one is the celebrated Treatise on the Diplomatic, by F. Mabillon; and the other, the first volume of the Chronicon Gotvicense. We shall here only add, that all the diplomas are written in Latin, and consequently the letters and characters have a resemblance to each other; but there are certain strokes of the pen which distinguish not only the ages, but also the different nations; as the writings of the Lombards, French, Saxons, &c. The letters in the diplomas are usually longer, and not so strong as those of MSS. There has been also introduced a kind of court hand, of a very disproportionate length, and the letters of which are called, Exiles litteræ, crispa ac protractiores. The first line of the diploma, the signature of the sovereign, that of the chancellor, notary, &c., are usually written in this character. The signature of the diploma consists either of the sign of the cross, or of a monogram, or cipher, composed of the letters of the names of those who subscribed it. The initial letters of the name, and sometimes also the titles, were placed about this cross. By degrees, the custom changed, and they invented other marks. They sometimes added also the date and epoch of the signature, the feasts of the church, the days of the kalendar, &c. The successive corruption of the Latin language, the style, and orthography of each age, as well as their different titles and forms; the abbreviations, accentuations, and punctuation, and the various methods of writing the diphthongs; all these matters united, form so many characters and marks, by which the authenticity of a diploma

is to be known. The seal annexed to a diploma was anciently of white wax, and artfully imprinted on the parchment itself. It was afterwards pendent from the paper, and enclosed in a box or case, which they called bulla. There are some also that are stamped on metal, and even on pure gold.

DIPONDIUS, a coin, of very little value, mentioned by St Luke, xii. 6. Our translation of the passage is, Are not five sparrows sold for two farthings? In St. Matthew, x. 29, it runs, Are not two sparrows sold for a farthing? The Greek has assarion instead of as, which some say was worth half an as, i. e. four French deniers and one-eighth; and, according to others, two deniers and five-sixteenths. Dipondius seems rather to signify half an as-Calmet. Dr. Arbuthnot, however, says, that this coin was at first libralis, or of a pound weight; and, even when diminished, it retained the name of libella; so that dipondius denotes two asses.

DIPPEL (John Conrad), a German physician, born at Darmstadt in 1672. He studied theology at Giessen, and afterwards read medical lectures at Strasburgh, but took his doctor's degree at Leyden in 1711. He was much addicted to the study of alchemy, and, among other secrets, pretended to have discovered the philosopher's stone. After rambling from place to place, he at last settled at Hamburgh; but having used some indiscreet freedoms with the administration of Denmark, he was given up to the government of that country, by whom he was sentenced to perpetual imprisonment in the island of Bornholm. He, however, obtained his liberty at the end of seven years; and about the same time was invited to Sweden, to attend the king, who was dangerously ill, but through the influence of the clergy, whom he had ridiculed, he was obliged to leave the kingdom in 1727. He afterwards went to Germany, and in 1733 gave out publicly that he should not die till 1808, but next year he was found dead in his bed. He denied the inspiration of the Scriptures, and wrote a number of wild enthusiastic books, under the name of Christianus Democritus. His works were published in 5 vols. 4to. 1747. We are indebted to him for the discovery of the Prussian blue, and he invented a useful oil, which is called after him.

DIPPING, among miners, signifies the interruption, or breaking off the veins of ore; an accident that gives them a great deal of trouble before they can discover the ore again. A great part of the skill of the miners consists in the understanding of this dipping of the veins. In Cornwall they have this general rule to guide them in this respect: most of their tin-loads, which run from east to west, constantly dip towards the north. Sometimes they underlie; that is, they slope down towards the north three feet in height perpendicular. This must carefully be observed by the miners, that they may exactly know where to make their air-shafts when occasion requires; yet, in the higher mountains of Dartmaer, there are some considerable loads which run north and south; these always underlie towards the east. Four or five loads may run nearly parallel to each ther in the same hill;

and yet, which is rare, they may meet all together in one hatch, as it were a knot, and so separate again, and keep their former distances.

The DIPPING NEEDLE, or INCLINATORY NEEDLE, is defined, by Dr. Hutton, ‘a magnetical needle, so hung, as that, instead of playing horizontally, and pointing out N. and S., one end dips or inclines to the horizon, and the other points to a certain degree of elevation above it. It is used for observing the quantity of inclination towards the earth assumed by the magnetic needle. The inventor of the dipping needle was Robert Norman, a compass-maker, at Ratcliffe, about 1580. This is not only testified by his own account, in his New Attractive, but also by Mr. Whiston, Dr. Gilbert, Mr. William Burrowes, Mr. Henry Bond, and other writers of that period. The occasion of the discovery he himself relates, viz. that it being his custom to finish, and haug the needles of his compasses, before he touched them, he always found that, immediately after the touch, the N. point would dip or decline downwards, pointing in a direction under the horizon; so that, to balance the needle again, he was always forced to put a piece of wax on the S. end, as a counterpoise. The constancy of this effect led him at length to observe the precise quantity of the dip, or to measure the greatest angle which the needle would make with the horizon. This, in 1576, he found at London to be 71° 50.

It is not quite certain, however, whether the dip varies, as well as the horizontal direction, in the same place. Mr. Graham made many experiments with the dipping needle in 1723, and found the dip between 74° and 75°. Mr. Nairne, in 1772, found it somewhat above 72°. And, by many observations made since that time at the Royal Society, the medium quantity is 721°. The trifling difference between the first observations of Norman, and the last of Mr. Nairne and the Royal Society, has led some philosophers to the opinion that the dip is unalterable; and yet it may be difficult to account for the great difference between these and Mr. Graham's numbers, considering the well-known accuracy of that ingenious gentleman. Philosophical Transactions, vol. xlv. p. 279; vol. lxii. p. 476; vol. xix. lxx. lxxi. From a comparison of Mr. Gilpin's observations of the dip in August, 1805, when he found it 70° 20′, with those of Mr. Cavendish, in 1775, its annual decrease, on a mean, appears to have been 4-3′; and its progressive annual decrease, on a mean, in the above-mentioned period of thirty years, to have been 1·4′. It is certain, from many experiments and observations, that the dip is different in different latitudes, and that it increases in going northward. It appears from a table of observations, made with a marine dipping needle of Mr. Nairne's, in a voyage towards the north pole in 1773, that

in lat. 60° 18′ the dip was 75° 0', in lat. 70° 45′ the dip was 77° 52′, in lat. 80° 12′ the dip was 81° 52′, and in lat. 80° 27' the dip was 82° 24'. See Phipps's Voyage, p. 122. See also the Observations of Mr. Hutchins, made in Hudson's Bay and Straits, Philosophical Transactions, vol. lxv. p. 129. Messrs Burrowes, Gilbert, Ridley,

Bond, &c. endeavoured to apply this discovery of the dip to the finding of the latitude; and Bond first proposed finding the longitude by it; but for want of observations and experiments, he could not conduct his reasoning to any length. Mr. Whiston, being furnished with the farther observations of colonel Windham, Dr. Halley, Mr. Pound, Mr. Cunningham, M. Noel, M. Feuille, and his own, made great improvements in the doctrine and use of the dipping needle, brought it to more certain rules, and endeavoured to find the longitude by it. For this purpose, he observes: 1. That the true tendency of the N. or S. end of every magnetic needle is not to that point of the horizon to which the horizontal needle points, but towards another directly under it, in the same vertical, and in different degrees under it, in different ages, and at different places. 2. That the power by which the horizontal needle is governed, and all our navigation usually directed, it is proved, is only one quarter of the power by which the dipping needle is moved; which should render the latter by far the more effectual and accurate instrument. 3. That a dipping needle of a foot long will plainly show an alteration of the angle of inclination, in these parts of the world, in one-eighth of a degree, or seven and a half geographical miles; and a needle of four feet, in two or three miles; i. e. supposing these distances taken along, or near a meridian. 4. A dipping needle four feet long, in these parts of the world, will show an equal alteration along a parallel, as another of a foot long will show along a meridian, i. e. that will, with equal exactness, show the longitude, as this the latitude. This depends on the position of the lines of equal dip, in these parts of the world, which, it is found, do lie about 14° or 15° from the parallels. Hence he argues, that as we can have needles of five, six, seven, eight, or more feet long, which will move with strength sufficient for exact observation; and since microscopes may be applied for viewing the smallest divisions of degrees on the limb of the instrument, it is evident that the longitude at land may thus be found to be less than four miles. And as there have been many observations made at sea with the same instrument by Noel, Feuille, &c., which have determined the dip usually within a degree, sometimes within a half, or one-third of a degree, and this with small needles of five or six, or, at the most, nine inches long; it is inferred that the longitude may be found even at sea, within less than one-eighth of a degree.

The phenomena of the dipping needle are:That about the equatorial parts of the earth it remains in an horizontal position, but depresses one end as we recede from these; the north end, if we go towards the north, and the south end, if we proceed towards the south pole. The farther north or south that we go, the inclination becomes the greater; but there is no place of the globe hitherto discovered where it points directly downwards, though it is supposed that it would do so in some part of it very near the pole. Its inclination is likewise found to vary very considerably at different times in different places of the earth, and by some changes of situation, in such a manner as must appear at first sight very unac

countable. Of all those who have attempted the investigation of this obscure subject, none have been more successful than M. Cavallo, who, in his Treatise on Magnetism, has given particular attention to all the phenomena, and accounts for them upon plain and rational principles, in the following manner :-The dip of the magnetical needle, in general, may be understood from the following easy experiment: Lay an oblong magnet horizontally upon a table, and over it suspend another smaller magnet (a sewing needle to which the magnetic virtue has been communicated will answer the purpose), in such a manner as to remain in an horizontal position when not disturbed by another magnet. Now, if this last small magnet or sewing needle, suspended by the middle, be brought just over the middle of the large one, it will turn itself in such a manner that the south pole of the small magnet will point towards the north pole of the large one; and if at an equal distance from both, will remain in an horizontal position. But if we move it nearer to one of the poles than the other, it will be readily understood that the corresponding end of the needle will be attracted by the pole to which it approaches, and of consequence inclined downwards; the contrary end being proportionably elevated. It is likewise evident, that this inclination will be greater or less according to the distance at which the small magnet is placed from the pole of the large one; the attraction of the nearest pole having always the greatest effect upon it. And it is equally plain that, when brought directly over one of the poles of the large magnet, it will turn its own contrary one directly towards it, and thus lie exactly in the axis of the large one. The application of this experiment to the phenomena of the dipping needle is obvious, as nothing more is requisite for solving the whole mystery, than to suppose the earth itself to be the large magnet, and the magnetic needle, or any other magnetic body, the small magnet in the experiments: for admitting that the north pole of the earth possesses a south magnetism, and that the opposite pole is possessed of a north magnetical polarity; it appears, and the theory is confirmed by experiment, that when a magnet is suspended properly in the equatorial parts of the world, it must remain in an horizontal position; but when removed nearer to one of the poles, it must incline one of its extremities, viz. that which is possessed of the contrary magnetic polarity; and that this inclination must increase in proportion as the magnet or magnetic needle recedes from the equator of the earth; and, lastly, when brought exactly upon either of the poles of the earth, it must stand perpendicular to the ground, or in the same direction with the axis of the earth. The only difficulty in this explanation arises from the attributing a south magnetism to the north pole of the earth; but by this our author means only that its magnetism is contrary to that end of the magnetic needle which turns towards it; and in the same sense it must be understood, that the south pole of the earth has a north magnetic polarity. If the extremities of the axis of the earth, or the poles about which it performs its diurnal revolution, coincided with its magnetic poles, or even if the magnetic poles

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