HISTORY OF DISCOVERY RELATIVE TO MAGNETISM.

COMPILED FOR THE INSTITUTION PRINCIPALLY FROM THE "AUS DER NATUR."

THERE are two great forces of nature everywhere present and at every moment exerting their influence, namely, gravitation and magnetism. They are similar in many particulars, all pervading and perhaps equally powerful. The magnetic phenomena of the earth, however, do not manifest themselves as freely to the senses as those of gravitation, and the naturalist is obliged to employ refined, and, in some cases, complicated apparatus to study the laws of its operation. In this article we purpose to present to our readers a sketch of the earlier discoveries relative to magnetism, and in doing so we shall also briefly explain the general principles of the science.

There is found in different parts of the earth a mineral of a dark color, principally composed of iron and oxygen, which has long been an object of interest to the ignorant as well as the learned, principally on account of the attraction which it exhibits for iron, and the wonderful property which it imparts to steel needles of pointing toward the poles of the earth. Its composition may be expressed chemically by the formula Fe 0 + Fe2O3, being a compound of the first and second oxide of iron. It is called loadstone, and occurs most generally in primary mountains of gneiss; chlorite slate, in primitive limestone, and sometimes in considerable masses in serpentine, and in trap. It is found in great quantity and purity at Rosslay, in Sweden, in Corsica, on the island of Elba, in Norway, Siberia, Saxony, Bohemia, and in the Hartz mountains. A hill in Swedish Lapland, and Mount Pumachanche, in Chili, are said to consist almost entirely of magnetic ore. Extensive beds of magnetic iron ore are found in various places in the United States, and in some of these occur masses of the mineral possessing polarity; such as those at Marshall's island, Maine, at Magnet's Cove, Arkansas, at Goshen, Chester county, Pennsylvania, and Franklin, New Jersey.

It has been asserted that this mineral is not magnetic in its natural condition in the mine, but that the pieces only exhibit this property after having been exposed to the light; but this statement has not been verified, and is apparently at variance with well-established facts.

The specimens of this mineral are usually so hard that they produce fire when struck with steel, and it is this circumstance which renders them so difficult to be worked into proper form for exhibiting in the best manner the magnetic property.

The name magnet, by which the mineral is known to us, is said to be derived from Magnesia, a city in Asia Minor, where it was first found. The Roman poet Lucretius bears testimony to this in a passage of his celebrated poem on the nature of things, in which he states that the Greeks called this stone magnet because it was found in the country of the Magnesians.

This statement is much more probable than the account given by Pliny, who derives the name of magnet from Magnes, a herdsman, who, in guarding his flock on Mount Ida, found himself suddenly held fast to a magnetic rock by the iron nails in his shoes and the iron point of his staff. But whatever may be the origin of the names by which the magnet has been designated in different languages, it is a remarkable fact that they show distinctly the idea that pre

vailed in every part of the world respecting the phenomenon of its attraction. of iron. In those cases where the roots of the languages have no analogy whatever, the ideas expressed by the terms are often identical. In some, indeed, the attraction itself is alone expressed; but in the majority of cases the motive of attraction is embodied with it-a supposed affection for the iron-a love for it is expressed. It is the same in the European and Asiatic languages; and as the magnet is found in all, or nearly all, the countries of the Old World, we can only suppose that it arose in most cases in every language independently of any other. Nor is this peculiarity wholly confined to the names amongst nations of the most poetic temperament, since even the Chinese have the same idea in their Thsu-chy (the common name) or lovestone. What may appear most surprising is, that the name of the magnet seldom occurs in the older poetry of any country; but probably this arose from the unpoetic subject, namely, that of iron, with which it was coupled. In the poetry of later times, however, allusion to the magnet often occurs, and in several beautiful passages of our own it would be easy to point it out, both in expressing love and constancy-the former by its attractive, and the latter by its direct power. No phrase, indeed, is more familiar than to call the object of affection "the magnet." From all the records which refer to the subject, we must conclude that the ancients had at an carly period a knowledge of some of the more obvious phenomena of magnetism, and that they possessed magnets of considerable lifting power. They appear also to have been acquainted with the means of increasing the attractive power of the loadstone by the application to its poles of what is called an armature, that is, by applying pieces of soft iron to the parts of the stone which exhibited the greatest attraction, and which, as we shall hereafter see, are called its poles. Thus, Claudenus, in his work entitled Magnes, states that the wonderful stone gains power by contact with iron, and loses it again by the separation of this metal.

The same author describes a performance in a temple in which a statue of Venus, cut from a magnet, lifted an iron statue of Mars into the air. Lucian, in his work on the Syrian goddess, mentions a similar performance, in which a statue of Apollo was lifted before his eyes by the priests without being touched, and remained suspended in the air. Pliny also relates that Dinocrates, an architect of Ptolemy Philadelphus, commenced to build a temple at Alexandria, in honor of Arsinoe, sister of the King, of which the vault was to be built of magnets, so that an iron statue of the former might be suspended in the air. This temple, however, was not finished because both Ptolemy and his architect died before it could be completed.

According to Cedrenus and Augustine, a similar performance was actually exhibited in a temple of antiquity. The former asserts that the statue of an ancient god was held suspended by magnetic power in the serapium at Alexandria, and the latter, without mentioning any particular temple, states that the suspension was such as to cause the people to believe that the statue was soaring in the air. Matheolus, a commentator of Galenus, relates a similar story of the coffin of Mahomet, which is said to soar in the air in a sanctuary built of magnetic stones.

These statements, though probably founded on a limited knowledge of magnetic phenomena, are now known to be fabulous, since, after a full investigation of the subject, we are certain that it is impossible to suspend in mid air, without contact, a piece of iron by means of magnetism. The magnetic power diminishes very rapidly with the distance from the poles, and, in order that the iron should be suspended, it must be placed at the exact point in space at which the attraction of the magnet upwards would be equal to the force of gravity downwards; but if it could be placed in this position, it would not retain it for a moment, since the slightest jar or the least breath of air would disturb the equilibrium, and the iron would immediately fall to the floor, or spring up into

contact with the poles of the magnet. Some plausibility was, however, given to these stories, because magnets have been obtained which could sustain a heavy weight of iron when the latter was in contact with the poles of the latter. Thus, Wolf mentions examples of natural magnets which could support, by means of an armature, from sixteen to forty times, and even three hundred and twenty times their own weight. Dufay had in his possession a magnet of nine pounds in weight, which could hold seventy-six pounds. As a general rule, smaller magnets can support comparatively more than larger ones. Such, for example, as weigh from twenty to thirty grains will sometimes support fifty times their weight, whilst magnets weighing two pounds scarcely ever sustain ten times their own weight. According to Dr. Martin, Sir Isaac Newton had a magnet which was set in a finger-ring, and which, though only of three grains in weight, could hold seven hundred and forty-six grains. In the philosophical cabinet of the university at Dorpat there is a magnet weighing forty pounds, including the armature and a copper case, which is able to sustain eighty-seven pounds. A still larger one is found in Tyler's museum, which weighs three hundred and seven pounds, the armature inclusive, and holds more than two hundred and thirty pounds. Not less considerable was the magnet which John I, King of Portugal, received as a present from the Emperor of China, which weighed a little over thirty-eight pounds, and was able to support two hundred and two pounds.

But to return to the direct continuation of our history, we should state that a tradition of a very ancient date still exists in China respecting a mountain of magnetic ore rising in the midst of the sea, the intensity of attraction of which is so great as to draw the nails and iron bolts with which the planks of a ship are fastened together from their places with such force as to cause the vessel to fall to pieces. This tradition is not confined to China, but is very general throughout all Asia; and the Chinese historians assign to the mountain a specific place which they call Tchang-haï, the southern sea, between Tonquin and Cochin-China. Ptolemy, also, in a remarkable passage in his geography, places this mountain in the Chinese seas. In a work attributed to St. Ambrose there is an account of one of the islands of the Persian Gulf, called Mammoles, in which the magnet is found, and the precautions necessary to be taken in building ships without iron to navigate in that vicinity is distinctly specified. In two passages of the work of the Arabian geographer, Cherif-Edrïsï, and in a remarkable one in the apocryphal Arabian translation of the "Treatise on Stones," attributed to Aristotle, the existence of this mountain is again specifically stated. A reference to it also occurs in Vincent de Beauvais, a French writer, who had been in the holy wars; and, after his time, in the works of a great number of European writers.

A circumstance remarkable enough is, that the Chinese writers place this magnetic mountain in precisely the same geographical region in which it is stated to exist by the author of the voyages of Sinbad the Sailor. This has been justly looked upon as a confirmation of an opinion as to the oriental origin of a great number of the tales, half fiction, half fact, which are so universally diffused among the legendary literature of every country as to appear indigenous in each of them. We would not, however, go to the extent of saying that all our nursery fictions are derived from the east, though it cannot be denied that a great number of them are of oriental origin.

It is not surprising that the magnet which exhibited such extraordinary physical effects should have attributed to it wonderful moral and medicinal powers. Accordingly we find the belief entertained that it could enable its possessor to gain the confidence of princes, the affection of women, and to secure conjugal love, as well as cure the gout, the headache, and the heartache. In a little book of secrets, extracted from Albertus Magnus and others, was one to ascertain whether your sweetheart did really love you, and another to dis

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whether your bride had married you from motives of affection or otherwise. Both were to be effected by the mystical use of the magnet.

It has already been mentioned that on the surface of a magnet there are two points at which the attractive power manifests itself with the greatest intensity, and that these points are called poles. If a piece of soft iron is presented to one of these poles, the iron itself will become a magnet of inferior power, will exhibit two poles, and attract a second piece of iron; this second piece of iron will in turn become a magnet, and attract a third, and so on. The power may thus be developed in a series of iron bars placed end to end, provided the original magnet has considerable power. If, instead of bars of iron, small particles, such as filings of iron, be placed under the influence of the magnet, they will adhere together in masses, and form a kind of beard around the poles, or, if they are sprinkled on a sheet of paper placed over the magnet, they will be attracted to the poles and to each other, forming curves of great regularity and beauty.* These experiments were known to the ancients, and Lucretius must have seen them performed by the priests, since he describes them minutely in his poem to which we have previously alluded. In this he states that iron filings contained in a brass basin appeared to boil when a magnet was moved under them; that a row of iron rings would hang one below the other on a magnet, and that these experiments were performed by the priests in connexion with the Samothracean mysteries. A similar experiment was exhibited at a festival held every ninth year in honor of Apollo at Thebes, in Boetia, which consisted in hanging one iron ball on another. These experiments were undoubtedly made by means of a strong magnet inducing its power in pieces of soft iron, the latter exhibiting the attraction as long as they were in metallic contact with the former, but immediately losing the power when the contact was severed.

It is only when the iron has been rendered hard by hammering or twisting that it is able to retain a small amount of magnetism. But if, instead of soft iron, bars of tempered steel are placed in contact with the pole of a magnet, they will at first not be attracted as powerfully as those of iron; but if they are allowed to remain in contact for some time, or if rubbed with the magnet, they will fully acquire the magnetic property, and retain it after they have been separated from the inducing magnet.

If a bar of steel, which has thus been rendered permanently magnetic, and of which its poles are at its ends, be placed on a piece of cork, and allowed to float horizontally on water, or if it be supported on a firm point at its centre of gravity, or, still more simply, by a fine thread, so as to have free motion in every direction horizontally, it will not remain at rest indifferently in any direction, but will turn itself so as to point with its poles to a definite region of the earth, the one to the north, and the other to the south. If two such movable magnetic bars are brought near each other, the poles of both which point to the north, and also those which point to the south, will repel each other, whilst the pole which points to the north in the one will attract the pole which points to the south in the other, and vice versa.

The directive property of a freely suspended magnetic bar towards certain points of the horizon, which is generally called the polarity of the needle, was not known to western nations as early as the attractive power of the magnet.

A very interesting experiment, which may be called the exhibition of magnetic spectres, consists in tracing on a polished plate of steel, such as the blade of a wide handsaw, an image in outline with a pencil, and afterwards passing slowly and with some pressure along the lines of this image one of the tapered poles of a straight magnet of considerable power If a sheet of white paper is afterwards pasted smoothly over this steel surface, and against this, while it is held vertically, fine iron filings are projected from a box with a perforated cover, the image will start into existence on the blank paper, as if by magic, in lines of bristling filings.

The image is interestingly shown by drawing a serpentine line on a long saw blade, to represent a snake; the configuration of the filings gives a peculiar effect to this exhibition.

for iron. It is true that King Solomon is said to have been acquainted with the use of the mariner's compass, and the Hebrew Parvaim, to which he sent his vessels for treasures, is said to have been no other country than Peru itself; but, since Solomon employed Phenician seamen, the compass would necessarily have been known to the Phenicians, and from these the Greeks and the Romans would most certainly have learnt its application.

The claims of the Chinese to the discovery of the directive power of the magnet, and its application to navigation, has long been affirmed and denied; but it has of late been defended by an author of much learning and ability, namely, Klaproth, in a letter to Humboldt. It is difficult to mention any useful contrivance which is not in some degree known to this singular people, or any period in history when they did not know it. The great obstacle which has stood in the way of admitting the claims of the Chinese to many of these inventions is the high antiquity to which their records profess to ascend, and their consequent incompatibility with our own received chronology; but whoever has looked with any degree of attention upon the fragments of their scientific history, and the incidental mention made of things which were familiar to the writers, but which did not form the principal object of the record, cannot fail to be struck with the apparent general consistency which runs through all their claims to high antiquity, and to be forced to the conclusion that there is still wanting a key to that consistency which is not furnished by the sweeping charge of the forgery of their annals.

It has been said that the fine arts of China appear more like being in a condition of gradual decay than in a state of freshness and energy, and that it may be possible that their arts, as well as those of Egypt, were transferred from some older people, who were in a condition of decline; but this is mere conjecture, unsupported by any evidence, either written or oral. In regard to the Chinese, it would appear, from the little progress they have made since they became known to history, and their want of knowledge and appreciation of the scien tific principles on which art is founded, that their condition is just such as would be produced in an ingenious people in a long time by the accidental discoveries of facts, and their empirical application to the wants and conveniences of life. After a certain time, such a people would make no further progress; the facts which could be gathered from casual observation would be exhausted, and the advance in civilization, as well as the increase in population, would become exceedingly tardy.

Duhalde, in his account of China, states that the inhabitants of that country were acquainted with the polarity of the needle in the earliest times; that hundreds of years before our era they used, in their land excursions, an instrument in which the movable arm of a human figure invariably pointed towards the south, as a means of assistance in finding their way through the grass-covered plains of Tartary. Even as early as the third century of our era, about seven hundred years before the introduction of the mariner's compass into the European seas, it is asserted that Chinese vessels sailed on the Indian ocean, directed by magnetic polarity pointing towards the south. Humboldt has shown that, according to the "Fún-Tsaou," (a work on medicine and natural history, written four hundred years before the time of Columbus,) the Chinese suspended the magnetic needle by a fibre of silk, and found that it did not point directly towards the south, but deviated somewhat towards the southeast.

The directing property of the magnetic needle, and its use in navigation, became known in Europe at a considerably later period. It is mentioned, for the first time, by Are Frode, an Icelandic historian, who was born in 1068, according to the testimony of Snorro Sturleson, and who must have written his History of the Discovery of Iceland towards the end of the eleventh century. In this work he states, in the most unequivocal manner, that, in his time, the directing property of the magnetic stone was known. He also states that in