interrogates Nature, is no longer listened tains an account of their verification by M. to with incredulity, nor pointed at with Pouillet, a French philosopher, some of scorn. If, indeed, any complaint can be whose remarks we shall have occasion to made against the present tendency of pub-quote. To the third work, that of Reichlic opinion in this matter, it is that the cur-enbach, we purpose to refer, both because rent has set in an entirely opposite direc-it bears somewhat upon our present subtion, it is that the reaction from the ject, and for the reason that it has attracted indifference and obstinacy of past ages but little attention in this country. carries us to the other extreme, and leads to the formation of great anticipations from trifling, insignificant, and insufficient data. But, comparatively speaking, this is of little importance-it is an error on the right side; Time, the great leveller, will soon separate the grain from the husk; discoveries of real importance will remain as permanent additions to our knowledge, while ill-founded anticipations and theories will inevitably be buried in oblivion, or only be remembered as examples of human fallibility, "to point a moral, or adorn a

tale."

In the present article, then, it is our intention to give such a sketch of the leading features of the discoveries recorded in the volumes before us, as we trust will be intelligible; for which purpose, however, as well as that the reader may the more correctly judge of their novelty and importance, it will be necessary briefly to sketch the history of this branch of science.

to a later date. True, it is generally asserted that the Chinese were acquainted with, and took advantage of, this directive power from a very early period. In a work entitled, 'General History of China,' by P. Duhalde, the following passage occurs. Speaking of some ambassadors, the author says :—

The attractive power exerted by the loadstone over iron, appears to have been known in times of very remote antiquity. It is mentioned by Homer, Pythagoras, Aristotle, Euripides, and Pliny. The latMagnetism has, equally with other de- ter author, indeed, seems further to have partments of physical science, been distin- been acquainted with the property of inguished for this rapid onward progress. duction, or the power possessed by the Scarcely a quarter of a century back, all loadstone of communicating its virtue to magnetic instruments, with the exception iron placed in its immediate vicinity; for of the mariner's compass, were but philo- he mentions the fact that an iron ring, supsophic toys. Since that period, however, ported by a loadstone, will in its turn susthe correlation of the two forces, magnet- tain the weight of another. But although it ism and electricity, has not only been thus appears clear that these two phenomeclearly proved, but has likewise been taken na were known, yet its directive power or advantage of in the construction of an in-polarity, that is to say, its property of strument, certainly one of the wonders of pointing north and south, seems to belong the age, by which time and space are almost annihilated-we allude to the electric telegraph; and, more recently still, the persevering researches of our illustrious countryman, Dr. Faraday, have led to the discovery of the intimate connexion existing between this force and another of the imponderables-light; and shown to us, moreover, the real nature of the action exercised by magnetism over all matter,-a "After they had their audience of leave in problem whose solution has been in vain order to return to their own country, Tcheonattempted at different periods by the most side pointed to the north, and the opposite side Kong gave them an instrument, which on one distinguished philosophers. The new fields to the south, to direct them better on their way of science thus opened to us, promise an home than they had been directed in coming ample harvest of discoveries-discoveries to China. The instrument was called Tchithe more likely to follow, from the eager- Nan, which is the same as the Chinese now ness with which the necessarily brief an- give to the sea-compass; and this has given nouncements in some of our public jour-occasion to think that Tcheon-Kong was the nals have been every where received, and the remarkable celerity with which the experiments have been tested and verified in all parts of the Continent. The experiments and deductions of Dr. Faraday are detailed in the volume first in the list which heads this article; the second con

the 22d cycle, more than 1040 years before inventor of the compass. This happened in the Christian era."

In further support of this assertion, Dr. Gilbert affirms that Paulus Venetus brought the compass to Italy from China, in the year 1260. But, unfortunately for this assertion,

·

it is clear from many authors that the com- hazarded by different authors, but it was pass was in use in Europe in the twelfth not until the year 1759 that a rational hycentury. Cardinal James de Vitri, who pothesis was devised by Epinus, which emflourished about the year 1200, mentions braced and explained almost all the phenomthe magnetic needle in his History of ena observed by previous authors. He conJerusalem,' and he adds, that it was of in-ceived that in all magnetic bodies there exdispensable utility to those who travelled isted a power which may be called the magby sea. In an old French poem, entitled 'La Bible Guiot,' still extant in the Royal Library at Paris, allusion is evidently made to the magnetic needle. Its author was Guiot de Provence, who lived at the latter part of the twelfth century. The passage is so remarkable, that we are tempted to subjoin a translation :

netic fluid, whose particles repel each other with a force inversely as the squares of the distance; that the particles of this fluid attract the particles of iron, and are attracted by them in return with a similar force; that the particles of iron repel each other according to the same law; that the magnetic fluid moves through pores of iron and soft steel with very little obstruction; but its motion is more and more obstructed as the steel increases in hardness or temper, and it moves with the greatest difficulty in hard-tempered steel or the ores of iron. In this state did the science of magnet

"This (the pole) star does not move, and they (the mariners) have an art which cannot fail by virtue of the magnet-an ugly, brownish stone, to which iron adheres of its own accord. They look to the right point, and when they have touched a needle, and fixed it on a bit of straw ism remain for another half century. No lengthwise, exactly in the middle, the straw keeping it up, the point turns straight and unerringly towards the star. When the night is so dark and gloomy that you can neither see star nor moon, they bring a light to the needle: may they not then assure themselves of the situation of the star by the direction of the point? Thus, the mariner is enabled to keep the proper course. It is an art which cannot deceive."

We think there can be no question, from the whole of this singular passage, that the compass is clearly referred to.

That ferruginous substances always possess a greater or less degree of magnetism, has long been known. One Julius Cæsar, a surgeon of Rimini, first observed the conversion of iron into a magnet. In 1590, he noticed this effect on a bar of iron, which had supported a piece of brickwork on the top of a tower of the church of St. Augustin. The very same fact was observed about 1630 by Gassendi, on the cross of the church of St. John, at Aix, which had fallen down in consequence of having been struck by lightning. He found the foot of it wasted with rust, and possessing all the properties of a loadstone. During the succeeding century, the attention of those philosophers who devoted themselves to the study of the phenomena of magnetism was exclusively confined to the directive power of the needle, its variation, the variation of the variation, and the dip. Various speculations respecting the cause of the phenomena of magnetism were

new facts were added until the year 1800,
when the celebrated electrician Coulomb
directed his powerful mind to the subject.
Provided with the delicate instrument, the
torsion balance, he determined the correct
law of magnetic attraction and repulsion;
he showed that the magnetism in the mid-
dle of a bar was imperceptible, and that it
increased according to a regular law, and
with extreme rapidity towards each of the
poles. He established the important fact,
that the magnetic power resides on the sur-
face of iron bodies and is entirely inde-
pendent of their ma
mass. He also directed
his attention to the effect of temperature
on magnets; he found that the magnetism
of a bar magnetized to saturation diminish-
ed greatly by raising its temperature from
12 to 680 degs. Reaumur, and that when a
magnetic bar was tempered at 780, 860,
and 950 degs. Reaumur, the development
of its magnetism was gradually increased,
being more than double at 900 degs. of what
it was at 780 degs. Up to the period of these
researches of Coulomb, iron, steel, nickel,
and cobalt were regarded as the only mag-
netic bodies; but in the year 1802 he an-
nounced to the Institute of France, that all
bodies whatever are subject to the magnetic
influence, even to such a degree as to be
capable of accurate measurement. Since
this announcement of Coulomb, the belief
that magnetism affected all matter in the
same manner as iron, although in a less de-
gree,-a belief, as we shall subsequently
find,utterly erroneous,-has almost univer-
sally prevailed among philosophers.

Such, then, was the state of magnetic | which we shall immediately have to descience up to the year 1820. The analo- scribe.

gies between the phenomena of magnetism This discovery of Ersted, where elecand those of electricity, in their general tricity was made to evolve magnetism, incharacter, in the laws which govern them, duced philosophers to attempt to produce a and in the various combinations they pre- converse effect; that is, to educe electricity sent, are so extensive and so remarkable, from a permanent magnet. During the ten as naturally to lead to the belief that the years succeeding the publication of Œrforces themselves must be closely allied sted's researches, unnumbered experiments to each other. This connexion between were made to produce this effect; but all magnetism and electricity was a favorite these experiments failed, for the reason that subject of speculation and inquiry among all their devisers were led away with the philosophers during the last, and the com- expectation of making a stationary magnet mencement of the present century. Many a source of electricity; in which, had they attempts were made to solve this seductive succeeded, they would have realized a reproblem, which continued, however, to baf-sult now deemed so absurd and hopeless, fle the labors of each succeeding experi- perpetual motion. The error of such mentalist, who multiplied his efforts and anticipations was seen by Faraday; and in varied his processes without approaching the year 1831 he proved that to render any nearer to the point he aimed at; and magnetism a source of electricity it was also to elude the reasonings of those who necessary to superadd to the former, motheorized upon every new fact until they tion that when a piece of metal is passed bewildered both themselves and their read-before a single pole, or between the opposite ers in the mazes of visionary and con- poles of a magnet, electrical currents, transflicting hypotheses. To Ersted was re- verse to the direction of motion, are proserved the honor of discovering the link duced across it; and that magnets, while which binds these two sciences. In the in motion, induce electricity in contiguous year 1820, Ersted proved that the two conductors, the direction of the electric forces, electricity and magnetism, act upon currents being tangential to the polar direceach other, not in straight lines, but at tion of the magnet. From these fundamenright angles to each other; that is to say, tal laws originates the science of magnetothat bodies which conduct a current of electricity, the true converse of electroelectricity tend to place magnets at right magnetism. By this science are we placed angles to them, and inversely, magnets have in possession of one of the most beautiful a tendency to place such conducting bod- and instructive instruments of modern sciies at right angles to them; and this ten-ence, the magneto-electric machine, by the dency is, of course, in proportion to the which we see exemplified the close connexpower of the electric current. An electric ion between, if not the identity of, the eleccurrent, therefore, appears to have a mag-tric and magnetic forces; the same heating, netic action, in a direction cutting its own magnetizing, and decomposing power, the at right angles; or, supposing its section to same velocity of motion, the same physiobe a circle, tangential to it; if, then, we logical and chemical effects, are thus shown reverse the position, and make the electric to be common to both :current form a series of tangents to an imaginary cylinder, this cylinder should be a "In the discoveries of Ersted and Faraday," magnet. This is effected in practice by observes an eloquent author of the present day, coiling a wire as a helix or spiral; and this, we having a striking example of the superiwhen electrified, is, to all intents and pur- and didactic theories; in each case a connexority of intuitive perception over formal rules poses, a magnet. A soft iron core placed ion was generally suspected and strongly bewithin such a helix has the property of lieved; theories without number were proconcentrating its power; and then, by con- pounded, and fallacies authoritatively enforced; nexion or disconnexion with a voltaic bat- failure succeeded failure, until the eagle-flight tery, we can at pleasure make or unmake of genius swooped upon the citadel, which a powerful magnet. The magnets former- theory had vainly attempted to scale."

66

former-theory

ly in use are utterly insignificant when Such then, in brief, is the history of the compared with these electro-magnets; and science of magnetism; and we now turn it is only by the vastly increased power so to the consideration of the researches of obtained that Professor Faraday has been Faraday. The first paper in the 'Philoenabled to make the important discoveries | sophical Transactions' before us is, "On

the magnetization of Light, and the illumination of magnetic lines of Force;" and to this we shall necessarily first direct attention.

In common with many philosophers, Dr. Faraday has long entertained an opinion, that the various physical forces have one common origin, or, in other words, are so directly related, and mutually dependent, that they are convertible, as it were, one into another, and possess equivalents of power in their action. We have said that this opinion was not confined to Dr. Faraday alone. In the season 1843-44, Mr. Grove, the Professor of Natural Philosophy in the London Institution, delivered in that institution a course of lectures on the "Correlation of Physical Forces." His object was to show that motion, chemical affinity, heat, light, electricity, and magnetism, are all convertible affections of matter-that either being taken as an initial mode of force is able to produce any of the others; thus moving bodies may be made, mediately, or immediately, to produce heat, light, electricity, chemical af finity, or magnetism. Matter affected by chemical affinity may be made to produce motion, heat, light, electricity, and magnetism, and so of the rest. In each lecture, one of the above forces was taken as the initial or starting point, and it was shown experimentally how the others were produced by it.

"The violet light was obtained in the usual manner by means of a common prism, and was collected into a focus by a lens of sufficient size. The needle was made of soft wire, and was found, upon trial, to possess neither polarity, nor any power of attracting iron filings. It was fixed horizontally in a support by means of wax, and in such a direction as to cut the magnetic meridian at right angles. The focus of violet rays carried slowly along the needle, proceeding from the centre, towards one of the extremities, care being taken never to go back in the same direction, and never to touch the other half of the needle. At the end of half an hour after the needle had been exposed to the action of the violet rays, it was carefully examined, and it had acquired neither polarity nor any force of attraction; but after continuing the operation twenty-five minutes longer, when it was taken off and placed on its pivot, it traversed with great alacrity, and settled in the direction of the magnetic meridian, with the end, over which the rays had passed, turned towards the north. It also attracted and suspended a fringe of iron filings. The extremity of a needle that was exposed to the action of the violet rays repelled the north pole of a compass needle. This effect was so distinctly marked, as to leave no doubt in the minds of any one present, that the needle had received its magnetism from the action of the violet rays."*

In the summer of 1825, Mrs. Somerville was induced, by the clearness of the weather, to make some experiments on the subject. A sewing-needle, an inch long, and devoid of magnetism, was half covered with Of all these physical forces, however, paper, while the other half was exposed to light had most completely resisted the ef- the violet rays of the spectrum, five feet disforts of philosophers to demonstrate, expe- tant from the prism. In two hours it acrimentally, its connexion with the other quired magnetism, the exposed end exhibitforms under which the forces of matter are ing north polarity. The indigo rays promade manifest. That a relation did exist duced an equal effect, and the blue and the between them was not doubted, and some green the same in a less degree. In no one experiments, first devised by Dr. Morichini, instance was magnetism produced by the an eminent physician at Rome, gave great- yellow, orange, or red rays; though, in er force to this opinion. He announced some instances, the same needles were exit as an experimental fact that an unmagnet-posed to their influence for three successive ized needle, exposed in a particular man- days; neither did the calorific rays of the ner to the concentrated violet rays of the spectrum produce any sensible effect. solar spectrum, became magnetic. These Pieces of clock and watch-spring were also experiments were successfully repeated by tried with similar success, and were found Dr. Carpi, at Rome, and the Marquis Ri- to be even more susceptible of this peculiar dolfi, at Florence; but the failure of the magnetic influence than needles. The vioexperiments, when tried by others, created let rays concentrated by a lens produced great doubt of the accuracy of the result magnetism in a shorter time than the prism as reported by Morichini. Sir Humphrey alone. But notwithstanding these simple Davy and Professor Playfair both witnessed and well-conducted experiments, which and paid diligent attention to the experiments of Morichini, the results of which were thus subsequently described by the latter philosopher :

*It is a fact, which may perhaps be unknown to some readers, that the violet rays are also the most effective in the decomposition of the vari ous compounds used as photographic agents.

A modification of this apparatus, excellently adapted for the exhibition of this experiment was a short time since exhibited at the London Institution. It consists simply of a glass tube, furnished at either extremity with a tourmaline, and placed within a core of soft iron which is wound round with covered copper wire. The ray of light is polarized by the first tourmaline-the second tourmaline, which answers to the Nicholls' eye-it to view.