Maeterlinck

uppermost subdivision of the Cretaceous system in Belgium. It is a soft, almost tufaceous limestone, and is full of fossils, especially of Bryozoa.

Maeterlinck, MAURICE (1862), Belgian dramatist and essayist, was born at Ghent. His thought has been greatly influenced by Novalis and Emerson. His first volume, consisting of verse, with the title Serres Chaudes, appeared in 1889, and was followed by Douze Chansons (1897). He has also written dramas-La Princesse Maleine (1889), Les Aveugles and L'Intruse (1890), Les Sept Princesses (1891), Pelléas et Mélisande (1892), Alladine et Palamides, Intérieur, and La Mort de Tintagiles (1894), Aglavaine et Sélysette (1896), Sœur Béatrice and Ardiane et Barbe Bleue (1901), Monna Vanna (1902), and Joyzelle (1903). His other works include a translation from the Flemish of Van Ruysbroeck, entitled L'Ornement des Noces Spirituelles (1891); a translation from Novalis (1895); two volumes of philosophical essays, Le Trésor des Humbles (1896) and La Sagesse et la Destinée (1898); La Vie des Abeilles (1901); and Le

Maurice Maeterlinck.

(Photo by C. Gerschel, Paris.)

Temple Enseveli. Several of these works have been excellently translated into English by Sutro, notably the remarkable La Vie des Abeilles, as The Life of the Bee (1902). Maeterlinck's dramas are not dramas of action but of thought, but he makes a very real drama of the mind, painting human nature in vivid colors. His plays are pervaded by melancholy, his characters suggesting a vain struggle in the inexorable web of fate. An edition of his dramas, translated by Richard

518

Hovey, was published in 1896, and a translation of Monna Vanna, by William Winter, was presented in New York City in 1905.

Mæviad. See BAVIAD.

Mafeking, tn., Bechuanaland, British S. Africa, 200 m. N. of Kimberley, on the Cape TownBulawayo Ry. It was ineffectually besieged by the Boers from Oct. 11, 1899, to May 18, 1900. Pop. of dist. (1904) 21,436.

Maffei, FRANCESCO SCIPIONE, COUNT (1675-1755), Italian writer, was born at Verona. His tragedy, Merope (1714; Eng. version by Ayres, 1740), is generally regarded as having brought about the revival of tragedy in Italy. As a scholar, Maffei shines most in the Istoria Diplomatica (1727), Verona Illustrata (1732), and Osservazioni Letterarie (1732-40). His Opere were published in 21 vols. at Venice (1790).

Mafia, a secret society in Sicily. Its members are bound to avenge and protect one another if punished for brigandage_or crime by the authorities. The government, though putting down its more violent manifestations, has failed to crush the secret organization of the society, which still keeps Sicily in a state of unrest and insecurity. With the large immigration of Italians to America it has been claimed that there have been manifestations of the activities of this organization in the U. S. This seems to have been proved in the case of a conspiracy of Italians in New Orleans in 1890 to murder the chief of police of that city, which led to an outbreak of mob violence that disturbed international relations. See Cutrera's La Mafia (1903).

Maffitt, JOHN NEWLAND (1819-86), American naval officer, born at sea. He entered the U. S. navy as midshipman in February, 1832, become a lieutenant in 1848, and was placed upon the reserve list in Sept., 1855. He resigned in 1861, and offered his services to the Confederate government. In 1862 he took a cargo of cotton abroad and assumed command of the Oreto, which had been constructed at Liverpool for the Confederacy. In spite of the opposition of Charles Francis Adams, the U. S. minister to England, the ship was taken to Green Cay, Fla., where she was equipped and renamed the Florida. The entire crew, including the captain, contracted yellow fever, and in order to refit the ship, by skilful handling, ran the blockade into Mobile, Sept. 4, 1862, and escaped Jan. 15, 1863. The Florida, together with several of the prizes which were fitted out as tenders, captured more than fifty prizes within a few

Magazines

months. While laid up for repairs in the harbor of Brest, France, Captain Maffitt, who had never recovered his health, was relieved at his own request.

Magadha, ancient kingdom of India, corresponding to the modern Behar and Oudh. Its capital, Pataliputra, was on the Ganges, possibly where Patna now is. Öne of its kings, Bimbisara, was the friend of Buddha in his early days.

Magadoxo. See MOGDISHU. Magaldan, pucb., Pangasinan prov., Luzon, Philippines, on s. shore of Gulf of Lingayen, 13 m. N.E. of Lingayen. It is an important road centre. Pop. (1903) 15,841.

Magalhaes, FERNAO DE. See MAGELLAN.

Magallanes, territory, Chile, lying s. of lat. 47° S. Area, 75,292 sq. m. Much of it is mountainous and forest-clad. The chief settlement is Punta Arenas, on the Strait of Magellan. Wool is the only export.

Magazines. The modern magazine may be said to have had its beginning in 1731 when Cave, a London bookseller, brought out the Gentleman's Magazine. There had been, and were afterwards, first in England and then on the Continent and in America, a great many periodicals of the type of the Tatler and the Spectator. These, however, were not magazines, because they consisted usually of a single essay each, while a magazine, as the name shows, was a gathering up of matters of interest into a collection. The Gentleman's Magazine was followed by the Scols (afterwards the Edinburgh) Magazine, but the great importance of this kind of periodical came much later. Meanwhile there appeared another form of periodical; the Monthly Review came out in 1749 and the Critical Review in 1756. They had for their object to publish a current view and criticism of literature, while the magazine presented all sorts of matters of general interest. These periodicals continued to hold a representative position till 1802, when the appearance of the Edinburgh Review put the whole matter on a higher foundation. The Edinburgh was soon followed by the Quarterly (1809), and their success probably had something to do with the foundation of Blackwood's Magazine, which gave to the magazine the distinctively literary character that the Edinburgh had given the review. It became at once one of the important influences of the day, and was followed by Fraser's (1830). By this time the magazine and the review had begun to approach each other, for the reviews often published articles that were book

Magazines

reviews only by a literary fiction (e.g.) Macaulay's essay on Macchiavelli), and the magazines often dealt with current literature. In the U. S. the Analectic Magazine (1813) was chiefly made up of material from European sources, but the North American Review (1815) was an original and valuable production. In Bentley's Miscellany (1837)afterwards incorporated with Temple Bar (1860)-is to be found the first example of a magazine devoted purely to light literature; and it was followed by a great development of cheap weeklies and miscellanies, of which the most famous are Chambers's Journal, Household Words (edited by Dickens), All the Year Round, and Once a Week, of which only the first named survives. In 1860 the Cornhill Magazine was produced under Thackeray's editorship, and for many years occupied a unique place in periodical literature-a place that was only challenged on the appearance of the illustrated magazines in the early eighties. In this direction the Americans had taken the lead, Harper's, Scribner's, St. Nicholas, McClure's, Munsey, and the Century carrying the art of illustration first by wood engraving and then by process work to a point unattempted in Britain, except in such special publications as the Art Journal (1849) and the Magazine of Art (1878). Meanwhile the reviews had somewhat changed their character. There were several important quarterlies besides those named, especially the Westminster (1824); but with the appearance of the Fortnightly Review (1865) and the Contemporary (1866), followed by the Nineteenth Century (1877), the review lost

one

characteristic which had held it apart from the magazine and became a monthly periodical. The articles in these latter reviews, following a common custom of the older quarterlies, were no longer reviews of books only, but often considerations of subjects of interest in any direction. In fact the word 'review' ceased to mean the review of books, but meant rather a review of current interests in the cultivated world. The chief difference to-day between a review and a magazine is that the review generally has more serious articles on subjects of literary, political, or scientific interest; in the magazines, on the other hand, fiction, poetry, and essays of a lighter character make up the chief content. In America the Atlantic Monthly (1858) is an excellent example of a literary magazine of the older type. At present the number of magazines is very great, owing in some degree to the great mechanical

519

development in printing and_in processes of illustration. Be

sides this, industrial possibilities and commercial necessities and scientific interests have caused a great number of professional, trade, and technical periodicals. The number of magazines published in America cannot be exactly stated, but is probably not far short of 1,500, of which most are devoted to some especial profession, trade, or interest. Of what are commonly thought of literary there magazines, are in America about 100, of which the majority have no title to continued consideration. The last edition of Poole's Index to Periodicals (in the English language) included references 427 magazines, of which 175 are still published. This would give a good idea of the number of magazines of importance.

as

to

Magazines, FIELD, small chambers in field-works for the safe storage of powder and ammunition. usually They are placed either in the interior of thick parapets or of traverses, or else built up against their inner (revetted) slopes. All magazines should be carefully drained.

Magdala, tn. and hill fort near the centre of Abyssinia, s. of Lake Dembea, 150 m. s.E. of Gondar, on a huge, steep isolated mass of basalt 3,300 ft. above the Beshilo. It was stormed (April 13, 1868) by the British under Sir Robert Napier.

Magdalena. (1.) Department, Colombia. A branch of the E. Cordillera runs along the E._side separating the basin of Lake Maracaibo from that of the Magdalena R. It is a promising agricultural country, and contains coal Santa fields near the Atlantic. Marta is the capital. Area, 24,440 sq. m. Pop. 100,000. (2.) River, Colombia, traversing the republic almost from its s. boundary to the Caribbean Sea. It has a length of 1,060 m., and drains a basin of 95,880 sq. m. At Neiva, 750 m. from its mouth, it becomes navigable by steamers. But at Honda navigation is interrupted by the great rapid, El Salto; consequently a railway, 21 m. long, has been constructed to connect the upper and lower Magdalena. Of the tributaries the most important are the Saldana, Sagamoso, Lebrija and Cauca.'

Magdalene, MARY. See MARY MAGDALENE.

Magdeburg, tn., Prussian prov. of Saxony, 88 m. by rail w.s.w. of Berlin. It is intersected by the Elbe, is strongly fortified, and is a commercial centre. Its industries comprise shipbuilding and the construction of engines, machinery, armor-plate, and ordnance. The principal articles of commerce are sugar, chicory, and

Magee, WILLIAM CONNOR (1821-91), archbishop of York, was born at Cork in Ireland. his day, as an orator, debater, and conversationalist, he had few equals. He was successively dean of Cork (1864), bishop of Peterborough (1868), archbishop of York (1891). He was respected

as

a clearheaded exponent of masculine Christianity and a defender of the privileges of the Irish Church, but held heterodox views on the condemnatory clauses of the Athanasian creed. Many of his sermons have been published in the U. S.

Magellan, FERDINAND-in Portuguese FERNÃO DE MAGALHAES

P1470-1521), Portuguese naviborn gator and explorer, was probably at Villa de Sabrosa in Traz-os-Montes. He distinguished himself in the Indies and Malacca, as also in Africa (1510-12); but losing the king's favor on his return, he offered his services to Charles v. (1517). Aided by him, Magellan (1519) crossed the Atlantic to Brazil (Rio), quelled a dangerous mutiny at San Julian, and discovered the strait called by his name. then traversed and named the Pacific, and reaching the Philippines, fell in fight with the natives of Matan. See First Voyage round the World by Magellan (Hakluyt Society, 1874); Guillemard's Magellan and the Pacific (1891), and E. E. Hale's Magellan's Discovery (in Narrative and Critical History of America, vol. ii. 1886).

He

Magellan, STRAIT OF, between Tierra del Fuego and the mainland of Chile. Its length is 360 m., while its breadth varies from 2 m.to 17 m. It was discovered in 1520 by Magellan, and explored by the Beagle in 1826-36. The only important harbor is Punta Arenas.

Magellanic Clouds, two round

Magendie

patches of milky light near the s. pole of the heavens, described in 1516 by Andrea Corsali, the navigator, and named after Magellan. The Greater Cloud is situated in the constellation Dorado. The Lesser Cloud lies in a blank space between Hydrus and Toucan. See Knowledge, xiv. 51, and Harvard Circulars, Nos. 82, 96.

Magendie, FRANÇOIS (17831855), French physiologist, born at Bordeaux; was professor of anatomy at the Collège de France (1830), and member of the Academy of Sciences (1819). He studied the action of various new drugs on animals and the human body, and particularly advanced our knowledge of nerve function. Author of Formulaire pour l'Emploi et la Préparation de plusieurs Nouveaux Médicaments (1821), and Leçons sur les Fonctions et les Maladies du Système Nerveux (1839); edited (1821-31) Journal de la Physiologie Expérimentale.

Magenta. See FUCHSIN.

Magenta, tn., prov. Milan, Lombardy, Italy, 15 m. w. of Milan; has manufactures of silk and matches. It was the scene of the victory of the French and Sardinians over the Austrians, June 4, 1859. Pop. (1901) 8,012.

Maggiore, or LOCARNO, LAGO, lake, lies mainly in North Italy, and is nearly 40 m. in length, with an average breadth of from 1 m. to 3 m. It is very irregular in shape, and has an area of 82 sq.m.; its greatest depth is 1,221 ft., and its altitude is 636 ft. The upper part, for 9 m., is called the Lake of Locarno, and belongs to the Swiss canton of Ticino. Opposite Pallanza are the Borromean Is. This is the warmest spot on the lake, and a famous winter resort.

Maggot, a name applied to certain degraded forms of insect larvæ, but often used without any great precision. A typical maggot is a larva in which legs are absent, and the head is not distinctly defined from the body. Such an animal hatches from an egg deposited by the parent in the midst of an abundant food-supply. A good example is the maggot of the common blue-bottle fly. As such maggots live concealed, and are typically colorless, the term is often applied by analogy to all insect larvæ of similar habit whatever their structure-for example, the 'maggots' of plums are the caterpillars of such a moth as Graptolitha.

Magi, the priestly caste among the ancient Medians, and later also among the Persians. Ma

gism is a worship of the elements, particularly of fire; and the Magi pretended to possess supernatural powers, whence our word magic. On the accession

of the Persian Darius to the throne in 521 B.C., many of the

520

Magi were massacred. Their headquarters were at Pasargadæ. It is suggested that the Magi were of Scythian origin, and became incorporated with the Medes.

Magic is the supposed supernatural art, or art of controlling the actions of spiritual or superhuman beings. It is divided into

(1.) Black magic, which is evil magic, or magic used with evil purpose-for example, to harm others or bring evil upon them. The evil eye and the use of evil spells come under this heading. (2.) Natural magic, which is the making use of superior knowledge of the powers of nature to work wonders-for example, the knowledge of chemistry and magnetism possessed by magicians in the middle ages enabled them to work natural magic. (3.) White magic, or the magic used for good purposes-as, for instance, for healing the sick or curing diseases by means of spells. White magic did not deal with witchcraft, sorcery, evil spirits, or enchantment. (4.) Celestial magic, or the supposed supernatural power that gave spirits influence over the planets, and the planets influence over human destiny. Astrology comes under this heading. (5.) Superstitious or goetic magic, or the invocation of devils and a supposed agreement between them and man, whereby they consented to serve him in his ends in return for some service by him. Magic is a very old science. In ancient Babylonia and Egypt it flourished side by side with religion. In classical times magic became known as sorcery, and the. magician was believed to hold communication with the unseen world. When Christianity spread, the gods of the heathen world were declared to be demons, with whom no converse should be held by good Christians. Amongst native races magic has always had influence, as among the Australian natives, who attribute to magic the various conditions of their health. If a man dies, it is by the magic of some enemy, and rarely from natural causes. In South America the native smokes narcotics, and generally brings himself into a state of spiritual intoxication, when he will prophesy good or evil, work spells, and exorcise spirits. In Africa there is the medicine-man and rain-maker, who has power over life and death, and can influence the elements at will. India swarms with soothsayers, astrologers, and magicians; but these are different from the sorcerers, who live on their dupes. Amongst Mohammedans the belief in magic is rife, but it extends only to a belief in the efficacy of amulets, charms, exorcisms, and spells. Egypt and Chaldæa were

Magic Squares

the original homes of magic, and it is from the magic practised in those countries that all later practices have sprung; Amongst the Egyptians good magic that is, magic for curative purposes was much used; but black magic was considered a crime. Magicians were believed to have power over all nature animate and inanimate, and to have power to reinfuse life into the dead. To the magician the future was as well known as the past, and the thoughts of all were an open book. In Chaldæa, Assyria, and Babylon magic was chiefly astrological; the magicians studied the stars and gave horoscopes on the birth of all children. Greek magic consisted in the consultation of oracles and in the working of charms and spells. Roman magic consisted in divination and the drawing of signs from portents. Philosophic and theurgic magic was much used by the Jews, and Hebrew words came to be used when spells were worked. The pentagram became a sign of the brotherhood of magicians from this variety of the art. all magic the influences of hostile action on the part of those who were implacable could only be terminated by the use of an amulet secret name, magical formula or figure. In Egyptian magic each member of the body was placed under the protection of some amulet. Amulets were in numerous cases inscribed with magic formulæ. See Horst's Zauberbibliothek (6 vols., 1820 - 6); Tylor's Primitive Culture (ed. 1903); Lenormant's Magic among the Chaldeans (Eng. trans. 1877); Conway's Demonology and Devil Lore (1878); V. Rydberg's Magic of the Middle Ages (Eng. trans. 1879); Fabart's Histoire... .de P'Occulte, Magie, etc. (1885); and Adam's Witch, Warlock, and Magician (1889). See also CONJURING, DIVINATION, WITCH

CRAFT.

In

Magic Lantern. See OPTICAL PROJECTION.

Magic Squares consist of numbers set in a square in such a manner that the sums of the numbers in a row, column, and diagonal, are the same. In Fig. 1 five numbers are thus arranged. It will be noticed that each number occupies cells connected by the knights' move in chess, and when the square is crossed the next cell may be taken in a contiguous square, and then the number may be moved to the corresponding cell in the original square; but other paths may be taken. Squares with different numbers in each cell may be formed by making another square with four numbers, and adding the numbers in corresponding cells. This is De la Hire's method.

521

Maginn, WILLIAM (1793-1842), Irish journalist and critic, was born at Cork. Established in London in 1823, he carried on editorial and journalistic work, producing at the same time The City of the Demons (1828), a story which was one of his best achievements. In conjunction with Hugh Fraser, he founded Fraser's Magazine in 1830, Maginn's own Homeric Ballads and Gallery of Literary Characters, illustrated by Maclise, appearing in it. Owing to intemperance and a lack of conscientiousness, except in scholarship, Maginn died in great poverty. See Memoir in Dublin University Magazine (Jan., 1844), and R. S. Mackenzie, Miscel lanies (1855-57).

Magister equitum, the master of the horse,' an official in the Roman state, who, in the time of the kings, commanded the cavalry; under the republic he only existed when a dictator was appointed.

Magliabechi, ANTONIO (16331714), Italian bibliomaniac and librarian, famous for his extraordinary memory, learning, and eccentric habits, was a native of Florence. He became (1673) librarian to the Grand Duke Cosimo III. and his successors. At his death he bequeathed his library to the city of Florence.

Magna Charta. The Great Charter, called by Hallam the 'keystone of English liberty,' was granted by King John at Runnymede in the year 1215. In addition to the preamble, the Charter contains sixty-three clauses, and is partly remedial and partly, as Coke says, 'declaratory of the principal grounds of the fundamental laws of England.' Its principal provisions are:- (1.) A declaration that the Church of England is free. (2.) Feudal obligations are defined and limited. (3.) Law courts are to be held at fixed places, assize courts are established, and earls and barons are to be tried by their peers. (4.) No extraordinary taxation without consent. (5.) No banishment or imprisonment save by judgment of peers and the law of the land. (6.) No denial, sale, or delay of justice. (7.) One standard of weights and measures. The Magna Charta was confirmed many times by different kings, and the form which appears in the Revised Statutes is the confirmation by Edward I. in 1297. See M'Kechnie's Magna Charta (1905).

Magnesia. See MAGNESIUM. Magnesia. (1.) M. AD SIPYLUM, city, at the foot of Mt. Sipylus, N. W. Lydia; near it Scipio Asiaticus defeated Antiochus

the Great of Syria in 190 B.C. (2.) M. AD MEANDRUM, city, near the

Magnesium

Mæander, S. W. Lydia; was destroyed by the Cimmerians about 700 B.C., and restored by Milesian colonists.

Magnesian Limestone contains a variable percentage of magnesium carbonate. The term is also used as synonymous with dolomite especially for those carrying more than 20 per cent. of magnesium carbonate. As to origin the magnesium is supposed to have in part replaced the calcium of ordinary limestones. It is usually a pale yellow rock, containing few fossils, and yielding beds which are admirably adapted for building purposes. Magnesian limestones are abundant in America. Most of the older limestones of the Mississippi valley are magnesian, and the Knox dolomite of the southeastern states is the most extensive formation of the region.

Magnesite, a mineral consisting of magnesium carbonate. It bears a close resemblance to calcite, except that it is less easily soluble in acids and shows far less variety of crystalline forms. It occurs mostly as a secondary product associated with serpentine, is soft (h. = 3.5 4.5; sp. gr. 3.- 3.2), effervesces with dilute acids, and is used as a source of magnesium compounds and for the preparation of the magnesia bricks, obtained by calcination, and employed for furnaces where a basic lining is required.

Magnesium (Mg 24.36), a metallic element occurring, very widely distributed, in nature

in combination, as magnesite (MgCO3, dolomite (MgCa)CO3, Epsom salts (MgSO,7H2O), carnallite (KCIMgCl2OH2O), kieserite (MgSO4H2O), and kanite (KCIMgSO43H2O). Magnesium was formerly obtained by the action of sodium on dried carnallite, but is now prepared by The carnallite electrolysis. fused by external heating in a cylindrical steel vessel, which is made the cathode of the dynamo, the anode being a carbon rod in a perforated porcelain cylinder that is immersed in the melted electrolyte. The magnesium separates at the cathode and rises to the surface, while the chlorine is set free at the anode, and is collected in the porcelain cylinder and led off. Magnesium is a light (sp. gr. 1.7), white, hard, and fairly tough metal, that melts at 750° c. and boils at about 1,000°. It tarnishes but slightly when exposed to the air, but if heated catches fire and burns with a dazzling white light, forming the oxide. It is thus used for pyrotechnic purposes; and as the light contains a good proportion of rays of higher refrangibility, magnesium ribbon, and particularly powder (flash-light'), is

Magnetic Pole

much used for photography by artificial light. Magnesíum also used as a reducing agent, to render nickel castings sound, and along with aluminium to form a valuable alloy, magnalium. Of the compounds of magnesium, that termed magnesia is properly the oxide, MgO; but the name is also applied to the basic carbonates. These compounds differ somewhat according to the methods of preparation. The following are the principal commercial varieties: Light magnesium carbonate or magnesia alba levis, prepared by mixing cold dilute solutions of sodium carbonate and magnesium sulphate; and heavy magnesium carbonate, obtained when the solutions are concentrated and evaporated to dryness. Both are basic carbonates, approximating to the formula 3MgCO3, Mg(OH)2, 4H2O. Both are white powders, soluble in acids with effervescence, and mainly differing in their density. On calcination they yield the oxide, a white powder that does not effervesce with acids, and differs in density according to the carbonate it is prepared from, the two forms being magnesia usta levis and ponderosa. Sulphate of magnesium or Epsom salts is a white crystalline solid that is soluble in water and present in many mineral springs. Magnesium chloride is a deliquescent and very soluble salt that gives off hydrochloric acid when evaporated; a reaction is employed to prepare the latter substance. Magnesium chloride is also utilized to 'weight' cotton goods. Both the carbonates, the oxide, the sulphate, and their preparations, such as 'fluid magnesia,' which is a solution of the bicarbonate in water containing carbon dioxide under pressure, and 'citrate' of magnesia, act as saline purgatives; the oxides and carbonate are also mildly alkaline. Of the rest of the magnesium compounds the natural silicates, such as asbestos, soapstone (French chalk') and meerschaum are the most useful. Magnetic Pole. See MAGNETISM, TERRESTRIAL.

Magnetic Units. See UNITS. Magnetism. The natural magnet, lodestone or loadstone, called by mineralogists magnetite or siderite, the black or magnetic oxide of iron, was known to the ancients, and certain of its properties ascertained. Lumps of it tend to set themselves with a certain line in them approximately north and south; if dipped into filings of iron, these collect in a cluster round two places which are the ends of the above-mentioned line, and these two patches exert attraction or repulsion on similar patches on other lode

522

stones. The patches are called the 'poles' of the magnet, and the line is the magnetic axis. If a strip of hard steel is rubbed from the centre to one end with one pole, and from the centre to the other end with the other pole of the lodestone, it is found to take on all the properties of the lodestone, and the end rubbed with the north-seeking pole turns to the south, and vice versa. The north-seeking poles are found to repel each other, and south-seeking poles repel each other, while north poles attract south poles. Such a strip of steel, if mounted on a pivot, forms a magnetic needle or mariner's compass. Such a bar magnet, if dipped into iron filings, will attract a bunch, thick at the ends, and thinning rapidly towards the middle. The strength of the pole is measured by the mechanical force it exerts on a similar pole, the unit pole being taken to be one that will exert a force of one dyne on a pole of the same strength placed at one centimetre distance. It was shown by Coulomb that the force is inversely proportional to the square of the distance from the pole.

The Magnetic Field.-The influence of a magnet extends out in all directions, and its sphere of influence is called its magnetic field. Its form was investigated by Faraday by the sprinkling of iron filings over a sheet of card or glass laid over a magnet. When the sheet is tapped, the filings arrange themselves in strings, which radiate out approximately from each end of the magnet, bending round, some in small, others in large curves, to join those from the other end. These lines are called 'lines of force,' as they indicate the direction of the combined magnetic forces from the two poles, and in general they take the form shown in Fig. 1, where the dotted lines

FIG. 1.

indicate the direction of the force in the air, and the full lines inside the bar represent their assumed direction in the magnet. In a real magnet it will be seen that the magnetism is not confined to the ends, but spreads over a considerable length. But for purposes of calculation it is convenient to consider the magnetism as concentrated at a point, and accordingly, a point is selected near to each end, which will give

Magnetism

the same magnetic effect on distant objects as the actual magnetism would do. These are called the 'virtual poles,' and the distance between the two points is called 'the virtual length' of the magnet. The virtual length is from three-quarters to five-sixths of the real length, according to the shape of the bar. The lines of force of a virtual magnet are supposed to radiate out from the points (Fig. 2), and hence do not exactly corre

FIG. 2.

spond to those of a real magnet, but at a distance they are identical with those of Fig. 1. These lines of force may be drawn to represent not only the direction of the magnetic force, but also its intensity. Thus at points close to the poles the field is very intense, but the strength rapidly diminishes with distance from the magnet, and on account of the partial neutralizing effects of the two poles on each other the strength of field due to a magnet is inversely proportional to the cube of the distance along a straight line drawn through the centre of the magnet. To give a numerical value to the lines of force, the unit strength of magnetic field is taken as that produced at one centimetre distance from the unit pole, and is represented by one line of force through each square centimetre. Hence there will be 4 lines of force issuing from unit pole, since the area of a sphere of unit radius is 4.

Magnetic Moment.-It can be shown that the influence of a magnet is proportional to the strength of the poles and to the virtual length. This product is