1849. height equal to that of the top of the hill, instead of that moderate exertion which is necessary to overcome the friction of the axis of the wagon, and the slight iue(|ii:ililics of a level road. Hence the absurdity of constructing roads m hilly couiiirijs, to puss directly over the tops of hills, instead of winding, by small circuits, along their base. A body descending freely on an inclined plane, moves with a velocity as much less than that with which it falls freely, as the height of the plane is less than the length. If the elevation were one sixteenth of the length, the body would roll down one foot in the first second, and four in two. It is on this principle that the equality in the vibrations of a pendulum maybe explained. A long vibration takes no more time than a short one, because the body begins to full, in this case, down a steep plane, and acquires great velocity. In a short vibration, the beginning of its path is a very gradual descent. A short pendulum vibrates more rapidly than a long one, because it has a shorter distance to move in a path of the same steepness. A body moving down an inclined plane, moves four times as far in two seconds as in one. A pendulum, to vibrate once in two seconds, must be, therefore, four times as long as one which beats seconds. The most remarkable application of the inclined plane is in the construction of the marine rail-way, on which, by the power of a few horses, a ship of GOO tons is drawn, with all its cargo, out of the water, high enough to allow workmen to pass uuder its keel. The Screw.—Imagine an inclined plane to pass round an immense building, like the tower of Babel, affording means of ascending to the top, and you have the first idea of the screw. It is an inclined plane, wrapped spirally round a solid cylinder. The advantage gained by it depends on the slowness of the ascent, that is, on the number of turns or threads, as they are called, in a given distance. It is always used in combination with a lever. It is a machine of great power, commonly employed to produce compression or to raise heavy weights. Hunters screw is n compound of two screws, with threads of different degrees of fineness, one moving within the other, the end advancing, at each revolution, through a distance equal to the difference of the threads. The Wedge is a double inclined plane, used commonly to cleave wood or stone, and sometimes to elevate a large mass, as part of a building, or ship. The effect of a wedge depends, apparently, upon friction, elasticity, and the slowness with which motion is communicated to a mass of matter. When a wedge is driven in, the particles immediately in contact with it are, for a moment, displaced, the friction against it prevents it from receding, and when the displaced particles endeavor to resume their relative position, the rift is lengthened. To the wedge may be referred various cutting tools, such as axes, knives, swords, chisels; and nails and spikes to be driven into wood, as well as pins, needles, awls, &c. The saw and the fde and rasp are modifications still more remote. The colter of a plough, the blade of a spade, and other instruments to penetrate the earth, are in the shape of a wedge. The Mope is considered, in theory, as destitute ot weight, and perfectly smooth and flexible. In this case, as in that of the other mechanical powers, the allowances to be made in practice for weight, rigidity, friction, &C., are ascertained by experiment, and combined with the results of theory. If a rope be stretched horizontally between two fixed points, by equal weights attached to the ends, any very small weight applied to the rope between these points will bend the rope, and thus raise the weights. If we suppose the rope to have been perfectly horizontal, the weight applied acts upon those at the ends with a mechanical advantage which may be considered infinite, as it acts at right angles to the directions of the opposite actions of those weights. This is a necessary consequence of the principles of the resolution of forces. The action of one or two forces can have no effect in counteracting a third, unless they act in such a direction that their action can be resolved into two, one of which is opposite to the direction of the third foroe. While the rope is horizontal, the two weights counterbalance each other, but produce no further effect, until the rope is bent into an angle. A bending of the rope must, therefore, take place, in consequence of the action of any force, however small. By bending the rope, it must raise the weights, and support them at a point above their former position, thus producing an equilibrium with them, however great they may be. This arrangement is one form of what is called the funicular machine. A necessary consequence of the principle on which it depends is, that when a rope or chain, of any material whatever, is stretched horizontally, its weight alone will prevent itl Being perfectly straight, and no force is sufficient to straighten a rope unless it hangs perpendicularly. Advantage is often taken of this power by seamen in tightening ropes, which have previously heeu drawn as closely as possible by the direct action of their strength. The Pulley is a small wheel, moving on an axis or pin, which is fixed in a frame called a block. The circumference of the wheel has a groove for a rope to move in. The pulley is said to be fxtd or movable, according as its block admits of motion or noL A fixed pulley gives no mechanical advantage, but it enables us to apply force more conveniently, by changing its direction. A man standing on the deck of a ship is able, by means of one fixed at the lop of die mast, to raise a weight to that point by drawing downwards. In the same manner, ore is raised from mines, and water from deep wells. The wheel, in the grooved circumference of wl/ich the rope passes, gives facility to its motion by preventing the necessity of its bending suddenly round a sharp edge, and diminishes the friction by transferring it from the rope to the axis of the wheel. One or more grooved wheels, called sheaves, set in a block, and moving freely round an iron axis, constitute a pulley, and the combination of pulley and ropes, a tackle. If the rope, instead of being attached to the weight, passes through a movable pulley attached to the weight, and terminates in a hook or ring in the upper block, the tackle becomes an engine by which another advantage is gained. As, in this cose, the weight is supported by two parts of a rope, each part sustaining one halfj the power necessary to support one of these parts, is equal to only one half the weight supported, and, by drawing upon one end of the rope, with a power a little greater than one half of the weight, the whole weight will be raised. It is on this principle that advantage is gained by the pulley. If the weight were supported by the four ports of a rope, which passed through two fixed and two movable pulleys, each part sustaining one fourth of the weight, a power equal to one fourth part of the weight, attached to the free end of the rope, would balance the whole weight, and something more than one fourth would raise it. This advantage is purchased by the spac« through which the power must move, and the time occupied by the motion. To raise a weight 50 feet, by the combination last mentioned, the power must move over a space of 200 feet. The pulley is employed to elevate large weights to the tops of buildings, or to upper lulls in store-houses. Its numerous varieties are chiefly used on board ships. A great many experiments made by Rondelet, have shown that, for most purposes, the best proportions for the wheel of a pulley are, 1. that its diameter should be five times its thickness; 2. that the diameter of the pin should be one twelfth of that of the wheel; 3. that the wheel should have about one twelfth of its thickness on each side for its play in the block. Additions might be made to the list of mechanical powers, with as much propriety as some of those enumerated are retained. The engine of oblique action, called usually the toggle joint, might be called a mechanical power. It is, however, more properly, a combination of levers, acting on the principle of the funicular machine. ^For the hydraulic press, see Hydraulics.) Several popular treatises on mechanics have appeared within a few years. The last, and one of the best, is the volume on mechanics iu Lardners Encyclopaedia, republished in Boston by the Society for the Diffusion of useful Knowledge. Arnotts Physics contains a valuable treatise, suited to the general reader. The treatise on mechanics, in the Library of Useful Knowledge, is short and clear. The Cambridge Mechanics is a very full view of the subject, compiled from the best continental authors. The Principia of Newton, the Micanique Jlnalytiqw of Lagrange, and the Mecanique Celeste of Laplace, occupy the highest place among works of abstract science. The translation of the latter by Bowditcb, has brought the work within the reach of many to whom the original was inaccessible. Mecheln, or Meckemen, Israel Of; two artists, father and son, the former of whom appears to have been a pointer, the latter a goldsmith, and one of the earliest and most distinguished engravers. They lived between 1450 and 1503. The son was born at Mecheln, near Bocholt. From his drawing, we may conjecture that he was a scholar of Van Eyk. Of the circumstances of his life, little else is known than that he lived, during his latter years, at Bocholt, and died there in 1503. His engravings are rare, and much sought after; yet they bear the marks of a rude taste and imperfect drawing, incorrect perspective, nnd othrr traits which characterize the pel iod. They are chiefly valuable for the minute accuracy of their execution, and as ni.>numens of the lun tory of the art. Mechlin, or Mecheljt (in French, Malines); a city lately belonging to the kingdom of the Netherlands, in the Belgic province of Antwerp, five leagues south of the city of Antwerp, and four and a half north-east of Brussels, on the Dyle and the Louvain canal; archiepiscojial see; population, 18,000. The streets are broad and well paved, and the buildings in>hi-.ii11-: the cathedral, with a tower 348 feet high; the Beguine house, which serves as an asylum for 800 widows or aged women; the arsenal, with a cannon foundery; the archbishops palace, &.C., are the principal. The lace, woollen, calico and hat manufactures are extensive, and the tanneries and breweries are considerable. Its commerce by the Dyle, which is navigable for large ships, is important in grain, oil, flax and hops. The lime of its foundation is not known: it is an old city, and was surrounded by ramparts in the tenth century. It has been repeatedly inundated by the Dyle, and captured by the S[>onisli, Dutch, English and French. The latter destroyed its fortifications in 1804. (See Netherlands.) Mecuoacax, or Valladolid; one of the slates of the Mexican republic, formed, in 1824, of the former province or intcudancy of Mechoacan or Valladolid, bounded by the states of Guanaxuato and Mexico, and the Pacific ocean; kit. 18° to 20° 3(X N.; Ion. 104° 207 to 108° 50* W. Its productions are cotton, com, sugar-cane, indigo, gold, silver, copper, lead, &c. Meclioacan was an Indian kingdom at the time of the arrival of the Spaniards in Mexico, and was conquered by one of the generals of Cortez, in 1524. There are, at present, three tribes of Indians, forming the greatest part of its population, within its limits—the Tarascos, the Otomites and Chichimeks. The population was estimated by Humboldt, hi 1803, at 376,400. (See Mexico.) Capital, Valladolid. (q. v.J Meckel, John Frederic, doctor and professor at Halle, the third of this name of a family which has rendered much service to anatomy and medicine, was bom at Halle, in 1781. His grandfather, John Frederic, who died in 1774, acquired the reputation of one of the first anatomists, by several treatises in the Transactions of the Academy of Berlin, especially by his dissertation De Quinlo Pare J\~ervorumCerebri (Gottingen, 1748). His father, Philip Frederic, who died in 1803, was professor of surgery and midwifery at Halle, and united the reputation of a scientific teacher with that of a popular and successful practitioner. The son, after mak ing himself known as a scion worthy of his family, by his inaugural dissertation De Coiuiltionibus Cordis almormibus, undertook a course of scientific travels through Germany, Italy and France. He prosecuted chiefly the study of comparative anatomy, for which be has unquestionably done more than any of his countrymen. In his translation of Cuviers Comparative Anatomy (Leipsic, 1809—10, 4 vols.), he embodied, in notes and observations, a mass of most valuable information. His Contributions to Comparative Anatomy (Lcipsic, 1809—13, 2 vols.) soon followed, rich in original and sagacious views; after which he began to compose a System of Comparative Anatomy, the first part of which (Halle, 1821) has excited great expectations of the rest. His Manual of Pathological Anatomy (Lcipsic, 1812—18, 3 vols.), his Manual of Human Anatomy (Halle, 1815—20,4 vols.), the Tabula; Jlnatomico-paihologica (Leipsic, 1817—26, 4 vols., fol.), the Degr.riptio Monstrorum (Leipsic, 1826, with plates, 4to.), all bear witness of the most labori ous investigation, of rare sagacity, and of a deep insight into the laws of life, which he developes in a masterly manner. An idea, principally formed and practically illustrated by him, with success, is, that the human organization is developed, in its formation, by degrees, and these gradations correspond to the permanent forms of the different kinds of animals; and in monstrous births, he sees merely formations whose developement has ceased prematurely. As professor of anatomy and physiology at Halle, Meckcl is one of the first ornaments of this university. His anatomical museum is unique among private collections of its kind in Germany. It was founded by his grandfather, and enlarged by his father, and he is himself continually enriching it with invaluable additions, especially for comparative anatomy. He has travelled, for scientific purposes, extensively, through Germany, Holland, France and England. He also made, in 1824, a tour through Naples and Sicily; all which have yielded many rich accessions to his science and his collections. Mecklenbcro-schwerin; n grandduchy in the north of Germany, lying between the Baltic, the kingdom of Hancver and the Prussian territories; a member of the Germanic confederation. The population is 430,927, principally Lutherans (3058 Jews); the superficial extent of the grand-duchy, 4833 square miles; revenue of the state, 2,200,000 guilders; debt, between Sand 10 millions; capital, Scliwerin, with ]J,230 inhabitants. The grand-duke has two votes in the plenum, and, with the grand-duke of MecklenburgStrelitz, the 14th vote in the diet. The two duchies have also a common supreme court of appeal at Parehim. The population of Mecklenburg-Schwcrin is principally agricultural : the manufactures are inconsiderable; the foreign commerce is carried on chiefly from the ports of Rostock and Wismar; com and cattle are the principal articles. Mf.cklf.nburo-sthelitz; a grandduchy in the north of Germany, divided into two parts by the grand-duchy of Mecklenburg-Schwcrin. (q. v.) It Im3 75,500 inhabitants on a superficial area of 1590 square miles. It has one vote in the German plenum. The capital is Neustrelitz, with 5400 inhabitants. The productions, and the condition and employment of the inhabitants, arc the same as iu Mecklenburg-Sell werin. MKn.u.Lio^s. The term medallion is applied to those productions of the mint which, if gold, exceed the. aureus in size; if silver, the denarius; and if copper, the first, or large brass. Antiquaries have long differed as to the purposes for which they were designed; they are generally, however, supposed to have been struck, like the medals of our time, toconiincinorate some remarkable event. Yet circumstances are not wanting to render it probable that they were intended for circulation ns money. Perhaps both objects were united, nt least in many instances, a large number of pieces, of a definite value, being coined in memory of a great event, ami thus adapted, at the same time, for current us-. Medallions are not numerous. The Greek, or those struck in the Greek provinces of the Roman empire, are more common than the Roman, but of inferior workmanship. A gold medallion exists of Augustus, and one of Domitian; but few, in any metal, arc found prior to the reigns of Adrian and Antonine; those in brass are the largest, many of them hcing several inches in diameter. (See jV«mifmatles.) Medals. (See Numismatics.) Medea ; daughter of Actes, king of Colchis. By some, her mother is said to be Jdyia, daughter of Oceanus; by others, Hecate. Mythology ascribes to her a profound knowledge of the secret virtues of vegetables, by means of which she practised witchcraft. She saved the lives of many foreigners by her prayers and the aid which she rendered them, but there by incurred the suspicions of her father, and was thrown by him into prison, from which she escaped to the temple of the sun. Her connexion with Jason (q.v.), the leader of the Argonauts, is celebrated. For ten years she lived with him in wedlock, after having supported him in every danger, till the charms of Glance, or Cretisa, the daughter of king Creon, kindled a new passion in him, and he discarded the unhappy Medea. According to some, Jason separated from her because of the reproaches heaped on him for having a foreign sorceress for wife. Under the semblance of patient resignation, she brooded on revenge. With this purpose, she sent the bride, as a wedding gift, a garment which, when she put it on, enveloped her in a consuming flame, so that she died a death of the utmost anguish. Another account is, that she sent her rival a poisoned crown of gold by her step-sons. She reduced Croons palace to ashes by a shower of fire, murdered her two children by Jason, and then mounted her dragonchariot, and escaped. Some say that she went to Hercules, others to Athens, to king jEgc-us, by whom she had Medos. From Athens, also, she was banished as a sorceress. She finally returned to her home, where she reinstated her father, who had been dethroned by his brother Perses, after which she died. Accordingto later accounts, she became reconciled with Jason, and was deified by the Colchians. Modes is said to have taken possession of the kingdom of his grandfather, and to have called it, from himself, Media. The story of Medea has often been a subject of poetry, especially of tragic poetry. The tragedies of this name, by ^Eschylus and Ovid, have perished, as well as the Colchides of Sophocles. TheMedeasof Euripides and Seneca are alone extant. The story has lately been made the subject of a tragedy by Grillparzer. Media ; the largest and most important province of the ancient Persian empire, bounded cast by Hyrcania and Parthia, south by Persis «nd Susiana, west by Assyria and Armenia, and north by the Caspian sea; so that it comprised the modem Iran, Aderbidshan, Ghilan, and the western half of Mazanderan. According tu Hammer, it belonged to Aria, or Ariana, of the Zend, the land of the Medes, in ita widest extent. This Aria is bounded by the ancient Bactria, the centre of the great national intercourse of Asia, of the religion of the Magi, and of the ancient Persian civilization. (See Zoroaster.) Media, on account of its mountains, was not easily accessible, was inhabited by warlike people, and, in part, well cultivated. Even before the Persian period, it was an independent kingdom. Its history begins with Dejoces, who, according to Herodotus, collected the people in villages and towns, and accustomed them to laws. He is said to have conquered Ecbalaua. Ninus, the founder of the Assyrian monarchy, conquered this country. After the downfall ot the Assyrian empire, a governor of the province of* Media succeeded in rendering it once more independent, and it soon became the most powerful of the states which had arisen from the ruins of the Assyrian monarchy. According to tradition, as given by Herodotus, another Dejoces begins a scries of Median kings at Ecbatana, which continues uninterrupted from 700 B. C. to 500 B. C. The last were Phraortes, Cyoxares and Astyages. Respecting the then existing •.ounexion of Media with Buctria and India, nothing certain is known. Cyrus . q. v.) subjected the Medes to the Persians. This latter people had, till then, been conaidered by the former as of little importance, on account of then* poverty. The conquered soon became the teachers of the conquerors, not only in the arts and manners of private life, but also in their public policy. After Cyrus, Media remained connected with the other parts of the Persian empire, excepting that the north-western parts, which, before the time of Cyrus, seem to have belonged to Assyria, were separated, for a time, from the Persian monarchy. When Alexander had conquered the Persian empire, he gave to Media a native governor, named Atropales, who maintained himself in the northern mountains, even after the death of Alexander, when Media had received a Macedonian governor. His posterity inherited his power, and, in spite of their dangerous neighbors, the Parthians, Armenians and Romans, maintained possession of it, partly by prudence, partly by arms. In the time of the first Roman emperors, Media was still independent; at a later period, it came under the yoke of the Parthians. Media consisted of Southern, or Proper Media, also called Great Media, whose capital was Ecbattuia; of toe country of Atropates, (Atropatene), and of the northern parts, along the shores of the Caspian sea, called ./VbrtA Media. Median Wall, in ancient geography, also called If all of Semiramis (not built, however, by Semiramis), is reported to have been 300 feet high, about 140 miles long, imd 20 feet thick, in Mesopotamia, ninning north-west from the Tigris, about 30 miles distant from the present Bagdad • erected against the invasions of the Medians. It was built of brick and asphaltum. Mediation, Mediator. In international politics, a power which endeavors to prevent, by peaceable interference, an approaching war, or close one which has broken out, is called a mediator. Mediation is essentially different from arbitration, which takes place if two powers submit points in dispute between them to the decision of a third power, which is to confine itself strictly to the points at issue, —a proviso which often affords a dissatisfied party a pretext for rejecting the decision.* Mediation generally takes place in consequence of a request. In 1818, Spain asked the mediation of the powers assembled at Aix-la-Chapelle in her quarrel with her American colonies, which, however, was refused, on the ground that the aid desired would amount to assistance in making a re-conquest. The Poles, in 1831, sought for the mediation of England between themselves and Russia. France has been, very often, the mediator between Russia and Turkey, or Austria and Turkey, from interested motives, to prevent Russia or Austria from becoming too powerful. Several powers may act jointly as mediators. Mediation, particularly of late, has often been performed by congresses, as, for instance, in the case of the treaty of London (July 6, 1827) for the pacification of Greece, or the pending mediation of the congress at London between Holland and Belgium. This kind of mediation, however, was introduced by a most arbitrary declaration at Aix-laChapelle, that the five great powers of Europe, Austria, France, Great Britain, Russia and Prussia, would be the mediators in all disputes between minor powers. Their ministers in Paris, Frankfort and Vienna were provided with the necessary authorities. This led to the adoption of the principle of armed intervention at I -aybach and Verona. (See Intervention.) Napoleon took the title of mediator ot Switzerland. (See Steiizerland.) By a law of the German empire, disputes between the ineml>ers were left to the decision of a third member—a proceeding culled Jlus/riigalinstanz. (See German Empire.) The same rule has been established in the Germanic confederacy. Mediator, in theology, is an appellation * A late decision of the king of Ibc Netherlands, umpire between the U. Slates and England, in the dispute respecting the boundary line between New Uninswick and Maine, has given rise to
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