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Magnetism

n. Something acting upon a magnet.

The two definitions immediately foregoing are condensed from the works of one thousand eminent scientists, who have illuminated the subject with a great white light, to the inexpressible advancement of human knowledge.

The Aurora Borealis

Halley, upon his return from his voyage to verify his theory of the variation of the compass, in 1700, hazarded the conjecture that the Aurora Borealis is a magnetic phenomenon. And Faraday's brilliant discovery of the evolution of light by magnetism has raised Halley's hypothesis, enounced in 1714, to the rank of an experimental certainty.

Rotation-Magnetism

The unexpected discovery of Rotation-Magnetism by Arago, in 1825, has shown practically that every kind of matter is susceptible of magnetism; and the recent investigations of Faraday on diamagnetic substances have, under special conditions of meridian or equatorial direction, and of solid, fluid, or gaseous inactive conditions of the bodies, confirmed this important result.

The Sun and Terrestrial Magnetism

The important influence exerted by the Sun's body, as a mass, upon Terrestrial Magnetism, is confirmed by Sabine in the ingenious observation, that the period at which the intensity of the magnetic force is greatest, and the direction of the needle most near to the vertical line, falls in both hemispheres between the months of October and February; that is to say, precisely at the time when the earth is nearest to the sun, and moves in its orbit with the greatest velocity.

The Onion and Magnetism

A popular notion has long been current, more especially on the shores of the Mediterranean, that if a magnetic rod be rubbed with an onion, or brought in contact with the emanations of the plant, the directive force will be diminished, while a compass thus treated will mislead the steersman. It is difficult to conceive what could have given rise to so singular a popular error.[1]—Humboldt's Cosmos, vol. v.


[1] This is mentioned in Procli Diadochi Paraphrasis Ptolem., 1635. (Delambre, Hist. de l'Astronomie ancienne .)

Colour of A Body and Its Magnetic Properties

Solar rays bleach dead vegetable matter with rapidity, while in living parts of plants their action is frequently to strengthen the colour. Their power is perhaps best seen on the sides of peaches, apples, &c., which, exposed to a midsummer's sun, become highly coloured. In the open winter of 1850, Mr. Adie, of Liverpool, found in a wallflower plant proof of a like effect: in the dark months there was a slow succession of one or two flowers, of uniform pale yellow hue; in March streaks of a darker colour appeared on the flowers, and continued to slowly increase till in April they were variegated brown and yellow, of rich strong colours. On the supposition that these changes are referable to magnetic properties, may hereafter be explained Mrs. Somerville's experiments on steel needles exposed to the sun's rays under envelopes of silk of various colours; the magnetisation of steel needles has failed in the coloured rays of the spectrum, but Mr. Adie considers that under dyed silk the effect will hinge on the chemical change wrought in the silk and its dye by the solar rays.

The Chinese and the Magnetic Needle

More than a thousand years before our era, a people living in the extremest eastern portions of Asia had magnetic carriages, on which the movable arm of the figure of a man continually pointed to the south, as a guide by which to find the way across the boundless grass-plains of Tartary; nay, even in the third century of our era, therefore at least 700 years before the use of the mariner's compass in European seas, Chinese vessels navigated the Indian Ocean under the direction of Magnetic Needles pointing to the south.

Now the Western nations, the Greeks and the Romans, knew that magnetism could be communicated to iron, and that that metal  would retain it for a length of time. The great discovery of the terrestrial directive force depended, therefore, alone on this—that no one in the West had happened to observe an elongated fragment of magnetic iron-stone, or a magnetic iron rod, floating by the aid of a piece of wood in water, or suspended in the air by a thread, in such a position as to admit of free motion.—Humboldt's Cosmos, vol. i.

Kircher's “Magnetism.”

More than two centuries since, Athanasius Kircher published his strange book on Magnetism, in which he anticipated the supposed virtue of magnetic traction in the curative art, and advocated the magnetism of the sun and moon, of the divining-rod, and showed his firm belief in animal magnetism. “In speaking of the vegetable world,” says Mr. Hunt, “and the remarkable processes by which the leaf, the flower, and the fruit are produced, this sage brings forward the fact of the diamagnetic (repelled by the magnet) character of the plant which was in 1852 rediscovered; and he refers the motions of the sunflower, the closing of the convolvulus, and the directions of the spiral formed by the twining plants, to this particular influence.”[1] Nor were Kircher's anticipations random guesses, but the result of deductions from experiment and observation; and the universality of magnetism is now almost recognised by philosophers.


[1] See Mr. Hunt's popular work, The Poetry of Science; or, Studies of Physical Phenomena of Nature . Third edition, revised and enlarged. Bohn, 1854.

Declination of the Needle—the Earth A Magnet

The Inclination or Dip of the Needle was first recorded by Robert Norman, in a scarce book published in 1576 entitled The New Attractive; containing a short Discourse of the Magnet or Loadstone, &c.

Columbus has not only the merit of being the first to discover a line without magnetic variation, but also of having first excited a taste for the study of terrestrial magnetism in Europe, by means of his observations on the progressive increase of western declination in receding from that line.

The first chart showing the variation of the compass,[1] or the declination of the needle, based on the idea of employing curves drawn through points of equal declination, is due to Halley, who is justly entitled the father and founder of terrestrial magnetism. And it is curious to find that in No. 195 of the Philosophical Transactions, in 1683, Halley had previously expressed his belief that he has put it past doubt that the globe of the earth is one great magnet, having four magnetical poles or points of attraction, near each pole of the equator two; and that in those parts of the world which lie near adjacent to any one of those magnetical poles, the needle is chiefly governed thereby, the nearest pole being always predominant over the more remote.

“To Halley” (says Sir John Herschel) “we owe the first appreciation of the real complexity of the subject of magnetism. It is wonderful indeed, and a striking proof of the penetration and sagacity of this extraordinary man, that with his means of information he should have been able to draw such conclusions, and to take so large and comprehensive a view of the subject as he appears to have done.”

And, in our time, “the earth is a great magnet,” says Faraday: “its power, according to Gauss, being equal to that which would be conferred if every cubic yard of it contained six one-pound magnets; the sum of the force is therefore equal to 8,464,000,000,000,000,000,000 such magnets.”


[1] The first Variation-Compass was constructed, before 1525, by an ingenious apothecary of Seville, Felisse Guillen. So earnest were the endeavours to learn more exactly the direction of the curves of magnetic declination, that in 1585 Juan Jayme sailed with Francisco Gali from Manilla to Acapulco, for the sole purpose of trying in the Pacific a declination instrument which he had invented.—Humboldt.

Magnetic Hypotheses

As an instance of the obstacles which erroneous hypotheses throw in the way of scientific discovery, Professor Faraday adduces the unsuccessful attempts that had been made in England to educe Magnetism from Electricity until Oersted showed the simple way. Faraday relates, that when he came to the Royal Institution as an assistant in the laboratory, he saw Davy, Wollaston, and Young trying, by every way that suggested itself to them, to produce magnetic effects from an electric current; but having their minds diverted from the true course by their existing hypotheses, it did not occur to them to try the effect of holding a wire through which an electric current was passing over a suspended magnetic needle. Had they done so, as Oersted afterwards did, the immediate deflection of the needle would have proved the magnetic property of an electric current. Faraday has shown that the magnetism of a steel bar is caused by the accumulated action of all the particles of which it is composed: this he proves by first magnetising a small steel bar, and then breaking it successively into smaller and smaller pieces, each one of which possesses a separate pole; and the same operation may be continued until the particles become so small as not to be distinguishable without a microscope.

We quote the above from a late Number of the Philosophical Magazine, wherein also we find the following noble tribute to the genius and public and private worth of Faraday:

The public never can know and appreciate the national value of such a man as Faraday. He does not work to please the public, nor to win its guineas; and the said public, if asked its opinion as to the practical value of his researches, can see no possible practical issue there. The public does not know that we need prophets more than mechanics in science,—inspired men, who, by patient self-denial and the exercise of the high intellectual gifts of the Creator, bring us intelligence of His doings in Nature. To them their pursuits are good in themselves. Their chief reward is the delight of being admitted into communion with Nature, the pleasure of tracing out and proclaiming her laws, wholly forgetful whether those laws will ever augment our banker's account or improve our knowledge of cookery. Such men, though not honoured by the title of “practical,” are they which make practical men possible. They bring us the tamed forces of Nature, and leave it to others to contrive the machinery to which they may be yoked. If we are rightly informed, it was Faradaic electricity which shot the glad tidings of the fall of Sebastopol from Balaklava to Varna. Had this man converted his talent to commercial purposes, as so many do, we should not like to set a limit to his professional income. The quality of his services cannot be expressed by pounds; but that brave body, which for forty years has been the instrument of that great soul, is a fit object for a nation's care, as the achievements of the man are, or will one day be, the object of a nation's pride and gratitude.

Origin of Terrestrial Magnetism

The earliest view of Terrestrial Magnetism supposed the existence of a magnet at the earth's centre. As this does not accord with the observations on declination, inclination, and intensity, Tobias Meyer gave this fictitious magnet an eccentric position, placing it one-seventh part of the earth's radius from the centre. Hansteen imagined that there were two such magnets, different in position and intensity. Ampère set aside these unsatisfactory hypotheses by the view, derived from his discovery, that the earth itself is an electro-magnet, magnetised by an electric current circulating about it from east to west perpendicularly to the plane of the magnetic meridian, to which the same currents give direction as well as magnetise the ores of iron: the currents being thermo-electric currents, excited by the action of the sun's heat successively on the different parts of the earth's surface as it revolves towards the east.

William Gilbert,[1] who wrote an able work on magnetic and electric forces in the year 1600, regarded terrestrial magnetism and electricity as two emanations of a single fundamental source pervading all matter, and he therefore treated of both at once. According to Gilbert's idea, the earth itself is a magnet; whilst he considered that the inflections of the lines of equal declination and inclination depend upon the distribution of mass, the configuration of continents, or the form and extent of the deep intervening oceanic basins.

Till within the last eighty years, it appears to have been the received opinion that the intensity of terrestrial magnetism was the same at all parts of the earth's surface. In the instructions drawn up by the French Academy for the expedition under La Pérouse, the first intimation is given of a contrary opinion. It is recommended that the time of vibration of a dipping-needle should be observed at stations widely remote, as a test of the equality or difference of the magnetic intensity; suggesting also that such observations should particularly be made at those parts of the earth where the dip was greatest and where it was least. The experiments, whatever their results may have been, which, in compliance with this recommendation, were made in the expedition of La Pérouse, perished in its general catastrophe; but the instructions survived.

In 1811, Hansteen took up the subject, and in 1819 published his celebrated work, clearly demonstrating the fluctuations which this element has undergone during the last two centuries; confirming in great detail the position of Halley, that “the whole magnetic system is in motion, that the moving force is very great as extending its effects from pole to pole, and that its motion is not per saltum, but a gradual and regular motion.”


[1] Gilbert was surgeon to Queen Elizabeth and James I., and died in 1603. Whewell justly assigns him an important place among the “practical reformers of the physical sciences.” He adopted the Copernican doctrine, which Lord Bacon's inferior aptitude for physical research led him to reject.

Magnetism

Is there any connection between magnetism and electricity?

There is every reason to believe that magnetism and electricity are but modifications of one force.

What is a loadstone or a natural magnet?

It is an ore of iron, known as the “protoxide of iron,” or “magnetic oxide of iron,” which is capable of attracting other pieces of iron to itself; and if suspended freely by a thread, and left to take its own position, it will arrange itself so that its extremities will point towards the north and south poles of the earth.

Are natural magnets rare?

They are not ; they are found in many places in the United States. In Arkansas, especially, an ore of iron possessing remarkably strong attractive powers is very abundant.

The magnetic ore is usually of a dark gray hue, and possesses but little metallic luster. If a piece of this ore be dipped in iron filings, or a number of small needles, they will generally be found collected and clinging together in great quantities at two opposite extremities, whilst the middle portion is nearly destitute. The magnetic property, whatever it may be, seems therefore to be collected and act with the greatest energy at two opposite extremes; these have been termed poles.

What is the origin of the terms “magnet” and “magnetism”?

The loadstone or natural magnet was first found at Magnesia, in Lydia, Asia, whence were derived the names.

Can a natural magnet communicate its attractive properties to other bodies by contact?

It can, and that too without any apparent loss  of attractive strength.

What bodies are capable of being magnetized by contact with natural magnets?

Iron  and steel  are the substances most susceptible of this influence, but brass, nickel, and cobalt can also become magnets.

Does the magnetism imparted to a piece of soft iron, or steel, by contact with a natural magnet, remain permanent in their substances?

In the steel  it does, but the soft iron loses its power  as soon as it is removed from the magnet.

Is it necessary that absolute contact should take place between a magnet and a piece of soft iron to render the latter a magnet?

No, every piece of soft iron brought near  a magnet becomes by induction itself a magnet.

What do you mean by induction?

It is the production of like effects  in contiguous bodies. In electricity or magnetism, it is the influence exerted by an electrified or magnetized body through a non-conducting medium without any apparent communication of a current.

What is meant by the directive power of the magnet?

It is that power which will cause a magnet, when suspended freely, to constantly turn the same part  towards the north pole and the opposite part towards the south pole of the earth.

What are the poles of a magnet?

They are the ends  of the magnet, and are denominated north and south, according as they point to the north or south poles of the earth.

What are the poles of the earth?

The extremities of the earth's axis, or the points on the surface of the globe through which the axis passes.

What is a magnetic needle?

Simply a bar of steel  which is a magnet, suspended in such a way that it can freely turn  to the north or south.

DIAGRAM SHOWING THE VARIATION OF THE MAGNETIC AND GEOGRAPHICAL POLES

What is a mariner's compass?

It is a delicate steel bar or needle  balanced upon a pivot placed beneath its center of gravity in such a way that it can turn horizontally without obstruction. This needle is usually inclosed in a box, upon the bottom of which is a card, with the various points—north, south, east, west, etc., etc., marked upon it.

Such a needle, if the box containing it be placed on a level surface, will generally be observed to vibrate more or less, till it settles in such a direction that one of its extremities or poles will point towards the north, and the other consequently towards the south. If the position of the box be altered or reversed, the needle will always turn and vibrate again, till its poles have attained the same direction as before.

Does the compass needle always point exactly north and south?

It does not ; its natural direction is towards the north and south poles, but it seldom points due north or south.

Who first discovered the fact that a magnet would invariably point to the north and the south, and made use of this knowledge in constructing a compass?

It is claimed to have been discovered by the Chinese : it was known in Europe, and used in the Mediterranean, in the thirteenth century.

How were the compasses of that time constructed?

They were merely pieces of loadstone  fixed to a cork, which floated on the surface of water.

Is the earth itself supposed to be a magnet?

It is undoubtedly a great  magnet.

Is iron under certain circumstances rendered magnetic by the inductive action of the earth's magnetism?

Most iron bars  and rails, as the vertical bars of windows, that have stood for a considerable time in a perpendicular position, will be found to be magnetic.

If we suspend a bar of soft iron sufficiently long in the air, will it assume magnetic properties?

It will  gradually become magnetic; and although when it is first suspended it points indifferently in any direction, it will at last point north and south.

How may a bar of iron, such as a kitchen poker, be made immediately magnetic, without resorting to the use of other magnets?

If the bar devoid of magnetism is placed with one end on the ground, slightly inclined towards the north, and then struck one smart blow  with a hammer  upon the upper end, it will immediately acquire polarity, and exhibit the attractive and repellant properties of a magnet.

What is a horseshoe magnet?

It is a magnetic bar  bent into the form of a horseshoe.

When a piece of iron not magnetic is brought in contact with a common magnet, it will be attracted by either pole; but the most powerful attraction takes place when both poles can be applied to the surface of the piece of iron at once. The magnetic bars are for this purpose bent into the shape of the letter U, and are termed horseshoe magnets. Several of these are frequently joined together with their similar poles in contact; they then constitute a magnetic battery, and are very powerful, either for lifting weights, or charging other magnets.

If we break a magnet across the middle, what happens?

Each fragment becomes converted into a perfect magnet ; the part which originally had a north pole acquires a south pole at the fractured end, and the part which originally had a south pole, gets a north pole.

If we divide a magnet to the extreme degree of mechanical fineness possible, will the pieces possess magnetic powers?

Each fragment, however small, will be a perfect magnet.