Part 23

The furnace which he employs for drying his moulds is about fourteen feet long, twelve feet high, and twelve feet broad. When it is raised to its highest temperature, with the doors closed, the thermometer stands at 350°, and the iron floor is red-hot. The workmen often enter it at a temperature of 340°, walking over the iron floor with wooden clogs, which are of course charred on the surface. On one occasion, Mr. Chantrey, accompanied by five or six of his friends, entered the furnace; and after remaining two minutes they brought out a thermometer which stood at 320°. Some of the party experienced sharp pains in the tips of their ears and in the septum of the nose, while others felt a pain in their eyes.--_Natural Magic_, 1833.

In some cases the clothing worn by the experimenters conducts away the heat. Thus, in 1828, a Spaniard entered a heated oven, at the New Tivoli, near Paris; he sang a song while a fowl was roasted by his side, he then ate the fowl and drank a bottle of wine, and on coming out his pulse beat 176°, and the thermometer was at 110° Reaumur. He then stretched himself upon a plank in the oven surrounded by lighted candles, when the mouth of the oven was closed; he remained there five minutes, and on being taken out, all the candles were extinguished and melted, and the Spaniard’s pulse beat 200°. Now much of the surprise ceases when it is added that he wore wide woollen pantaloons, a loose mantle of wool, and a great quilted cap; the several materials of this clothing being bad conductors of heat.

In 1829 M. Chabert, the “Fire-King,” exhibited similar feats at the Argyll Rooms in Regent Street. He first swallowed forty grains of phosphorus, then two spoonfuls of oil at 330°, and next held his head over the fumes of sulphuric acid. He had previously provided himself with an antidote for the poison of the phosphorus. Dressed in a loose woollen coat, he then entered a heated oven, and in five minutes cooked two steaks; he then came out of the oven, when the thermometer stood at 380°. Upon another occasion, at White Conduit House, some of his feats were detected.

The scientific secret is as follows: Muscular tissue is an extremely bad conductor; and to this in a great measure the constancy of the temperature of the human body in various zones is to be attributed. To this fact also Sir Charles Blagden and Chantrey owed their safety in exposing their bodies to a high temperature; from the almost impervious character of the tissues of the body, the irritation produced was confined to the surface.

Magnetism and Electricity.

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.

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.”[45] 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.

MINUTE MEASUREMENT OF TIME.

By observing the magnet in the highly-convenient and delicate manner introduced by Gauss and Weber, which consists in attaching a mirror to the magnet and determining the constant factor necessary to convert the differences of oscillation into differences of time, Professor Helmholtz has been able, with comparatively simple apparatus, to make accurate determinations up to the 1/10000th part of a second.

POWER OF A MAGNET.

The Power of a Magnet is estimated by the weight its poles are able to carry. Each pole singly is able to support a smaller weight than when they both act together by means of a keeper, for which reason horse-shoe magnets are superior to bar magnets of similar dimensions and character. It has further been ascertained that small magnets have a much greater relative force than large ones.

When magnetism is excited in a piece of steel in the ordinary mode, by friction with a magnet, it would seem that its inductive power is able to overcome the coercive power of the steel only to a certain depth below the surface; hence we see why small pieces of steel, especially if not very hard, are able to carry greater relative weights than large magnets. Sir Isaac Newton wore in a ring a magnet weighing only 3 grains, which would lift 760 grains, _i. e._ 250 times its own weight.

Bar-magnets are seldom found capable of carrying more than their own weight; but horse-shoe magnets of similar steel will bear considerably more. Small ones of from half an ounce to 1 ounce in weight will carry from 30 to 40 times their own weight; while such as weigh from 1 to 2 lbs. will rarely carry more than from 10 to 15 times their weight. The writer found a 1 lb. horse-shoe magnet that he impregnated by means of the feeder able to bear 26½ times its own weight; and Fischer, having adopted the like mode of magnetising the steel, which he also carefully heated, has made magnets of from 1 to 3 lbs. weight that would carry 30 times, and others of from 4 to 6 lbs. weight that would carry 20 times, their own weight.--_Professor Peschel._

HOW ARTIFICIAL MAGNETS ARE MADE.

In 1750, Mr. Canton, F.R.S., “one of the most successful experimenters in the golden age of electricity,”[46] communicated to the Royal Society his “Method of making Artificial Magnets without the use of natural ones.” This he effected by using a poker and tongs to communicate magnetism to steel bars. He derived his first hint from observing them one evening, as he was sitting by the fire, to be nearly in the same direction with the earth as the dipping needle. He thence concluded that they must, from their position and the frequent blows they receive, have acquired some magnetic virtue, which on trial he found to be the case; and therefore he employed them to impregnate his bars, instead of having recourse to the natural loadstone. Upon the reading of the above paper, Canton exhibited to the Royal Society his experiments, for which the Copley Medal was awarded to him in 1751.

Canton had, as early as 1747, turned his attention, with complete success, to the production of powerful artificial magnets, principally in consequence of the expense of procuring those made by Dr. Gowan Knight, who kept his process secret. Canton for several years abstained from communicating his method even to his most intimate friends, lest it might be injurious to Dr. Knight, who procured considerable pecuniary advantages by touching needles for the mariner’s compass.

At length Dr. Knight’s method of making artificial magnets was communicated to the world by Mr. Wilson, in a paper published in the 69th volume of the _Philosophical Transactions_. He provided himself with a large quantity of clean iron-filings, which he put into a capacious tub about half full of clear water; he then agitated the tub to and fro for several hours, until the filings were reduced by attrition to an almost impalpable powder. This powder was then dried, and formed into paste by admixture with linseed-oil. The paste was then moulded into convenient shapes, which were exposed to a moderate heat until they had attained a sufficient degree of hardness.

After allowing them to remain for some time in this state, Dr. Knight gave them their magnetic virtue in any direction he pleased, by placing them between the extreme ends of his large magazine of artificial magnets for a second or more, as he saw occasion. By this method the virtue they acquired was such, that when any one of these pieces was held between two of his best ten-guinea bars, with its poles purposely inverted, it immediately of itself turned about to recover its natural direction, which the force of those very powerful bars was not sufficient to counteract.

Dr. Knight’s powerful battery of magnets above mentioned is in the possession of the Royal Society, having been presented by Dr. John Fothergill in 1776.

POWER OF THE SUN’S RAYS IN INCREASING THE STRENGTH OF MAGNETS.

Professor Barlocci found that an armed natural loadstone, which would carry 1½ Roman pounds, had its power nearly _doubled_ by twenty-four hours’ exposure to the strong light of the sun. M. Zantedeschi found that an artificial horse-shoe loadstone, which carried 13½ oz., carried 3½ more by three days’ exposure, and at last arrived to 31 oz. by continuing it in the sun’s light. He found that while the strength increased in oxidated magnets, it diminished in those which were not oxidated, the diminution becoming insensible when the loadstone was highly polished. He now concentrated the solar rays upon the loadstone by means of a lens; and he found that, both in oxidated and polished magnets, they _acquire_ strength when their _north_ pole is exposed to the sun’s rays, and _lose_ strength when the _south_ pole is exposed.--_Sir David Brewster._

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 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.[47]--_Humboldt’s Cosmos_, vol. v.

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,[48] 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.”

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.

EFFECT OF LIGHT ON THE MAGNET.

In 1854, Sir John Ross stated to the British Association, in proof of the effect of every description of light on the magnet, that during his last voyage in the _Felix_, when frozen in about one hundred miles north of the magnetic pole, he concentrated the rays of the full moon on the magnetic needle, when he found it was five degrees attracted by it.

MAGNETO-ELECTRICITY.

In 1820, the Copley Medal was adjudicated to M. Oersted of Copenhagen, “when,” says Dr. Whewell, “the philosopher announced that the conducting-wire of a voltaic circuit acts upon a magnetic needle; and thus recalled into activity that endeavour to connect magnetism with electricity which, though apparently on many accounts so hopeful, had hitherto been attended with no success. Oersted found that the needle has a tendency to place itself at _right angles_ to the wire; a kind of action altogether different from any which had been suspected.”

ELECTRO-MAGNETS OF THE HORSE-SHOE FORM

were discovered by Sturgeon in 1825. Of two Magnets made by a process devised by M. Elias, and manufactured by M. Logemeur at Haerlem, one, a single horse-shoe magnet weighing about 1 lb., lifts 28½ lbs.; the other, a triple horse-shoe magnet of about 10 lbs. weight, is capable of lifting about 150 lbs. Similar magnets are made by the same person capable of supporting 5 cwt. In the process of making them, a helix of copper and a galvanic battery are used. The smaller magnet has twice the power expressed by Haecker’s formula for the best artificial steel magnet.

Subsequently Henry and Ten Eyk, in America, constructed some electro-magnets on a large scale. One horse-shoe magnet made by them, weighing 60 lbs., would support more than 2000 lbs.

In September 1858, there were constructed for the Atlantic-telegraph cable at Valentia two permanent magnets, from which the electric induction is obtained: each is composed of 30 horse-shoe magnets, 2½ feet long and from 4 to 5 inches broad; the induction coils attached to these each contain six miles of wire, and a shock from them, if passed through the human body, would be sufficient to destroy life.

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.

INFLUENCE OF PENDULUMS ON EACH OTHER.

About a century since it became known, that when two clocks are in action upon the same shelf, they will disturb each other: that the pendulum of the one will stop that of the other; and that the pendulum that was stopped will after a while resume its vibrations, and in its turn stop that of the other clock. When two clocks are placed near one another in cases very slightly fixed, or when they stand on the boards of a floor, they will affect a little each other’s pendulum. Mr. Ellicote observed that two clocks resting against the same rail, which agreed to a second for several days, varied one minute thirty-six seconds in twenty-four hours when separated. The slower, having a longer pendulum, set the other in motion in 16-1/3 minutes, and stopped itself in 36-2/3 minutes.

WEIGHT OF THE EARTH ASCERTAINED BY THE PENDULUM.

By a series of comparisons with Pendulums placed at the surface and the interior of the Earth, the Astronomer-Royal has ascertained the variation of gravity in descending to the bottom of a deep mine, as the Harton coal-pit, near South Shields. By calculations from these experiments, he has found the mean density of the earth to be 6·566, the specific gravity of water being represented by unity. In other words, it has been ascertained by these experiments that if the earth’s mass possessed every where its average density, it would weigh, bulk for bulk, 6·566 times as much as water. It is curious to note the different values of the earth’s mean density which have been obtained by different methods. The Schehallien experiment indicated a mean density equal to about 4½; the Cavendish apparatus, repeated by Baily and Reich, about 5½; and Professor Airy’s pendulum experiment furnishes a value amounting to about 6½.

The immediate result of the computations of the Astronomer-Royal is: supposing a clock adjusted to go true time at the top of the mine, it would gain 2¼ seconds per day at the bottom. Or it may be stated thus: that gravity is greater at the bottom of a mine than at the top by 1/19190th part.--_Letter to James Mather, Esq., South Shields._ See also _Professor Airy’s Lecture_, 1854.

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,[49] 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.