MICHAEL FARADAY.

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The work of Michael Faraday introduced a new era in the history of physical science. Unencumbered by pre-existing theories, and untrammelled by the methods of the mathematician, he set forth on a line of his own, and, while engaged in the highest branches of experimental research, he sought to explain his results by reference to the most elementary mechanical principles only. Hence it was that those conclusions which had been obtained by mathematicians only by the help of advanced analytical methods, and which were expressed by them only in the language of the integral calculus, Faraday achieved without any such artificial aids to thought, and expressed in simple language, having reference to the mechanism which he conceived to be the means by which such results were brought about. For a long time Faraday's methods were regarded by mathematicians with something more than suspicion, and, while they could not but admire his experimental skill and were compelled to admit the accuracy of his conclusions, his mode of thought differed too widely from that to which they were accustomed to command their assent. In Sir William Thomson, and in Clerk Maxwell, Faraday at length found interpreters between him and the mathematical world, and to the mathematician perhaps the greatest monument of the genius of Faraday is the "Electricity and Magnetism" of Clerk Maxwell.

Michael Faraday was born at Newington, Surrey, on September 22, 1791, and was the third of four children. His father, James Faraday, was the son of Robert and Elizabeth Faraday, of Clapham Wood Hall, in the north-west of Yorkshire, and was brought up as a blacksmith. He was the third of ten children, and, in 1786, married Margaret Hastwell, a farmer's daughter. Soon after his marriage he came to London, where Michael was born. In 1796 James Faraday, with his family, moved from Newington, and took rooms over a coach-house in Jacob's Well Mews, Charles Street, Manchester Square. In looking at this humble abode one can scarcely help thinking that the Yorkshire blacksmith and his little family would have been far happier in a country "smiddy" near his native moors than in a crowded London court; but, had he remained there, it is difficult to see how the genius of young Michael could have met with the requisites for its development.

James Faraday was far from enjoying good health, and his illness often necessitated his absence from work, and, as a consequence, his family were frequently in very straitened circumstances. The early education of Michael was, therefore, not of a very high order, and consisted "of little more than the rudiments of reading, writing, and arithmetic." Like most boys in a similar position in London, he found his amusement for the most part in the streets, but, except that in his games at marbles we may assume that he played with other boys, we have no evidence whether his time was spent mostly by himself, or whether he was one of a "set" of street companions.

In 1804, when thirteen years of age, Michael Faraday went as errand-boy to Mr. Geo. Riebau, a bookseller in Blandford Street. Part of his duty in this capacity was to carry round papers lent on hire by his master, and in his "Life of Faraday," Dr. Bence Jones tells how anxious the young errand-boy was to collect his papers on Sunday morning in time to attend the Sandemanian service with the other members of his family.

Faraday was apprenticed to Mr. Riebau on October 7, 1805, and learned the business of a bookbinder. He occasionally occupied his spare time in reading the scientific books he had to bind, and was particularly interested in Mrs. Marcet's "Conversations in Chemistry," and in the article on "Electricity" in the "EncyclopÆdia Britannica." These were days before the existence of the London Society for the Extension of University Teaching, and, though Professor Anderson in Glasgow had shown how the advantages of a university might be extended to those whose fortunes prevented them from becoming regular university students, Professor Stuart had not yet taught the English universities that they had responsibilities outside their own borders, and that the national universities of the future must be the teachers of all classes of the community. But private enterprise supplied in a measure the neglect of public bodies. Mr. Tatum, of 43, Dorset Street, Fleet Street, advertised a course of lectures on natural philosophy, to be delivered at his residence at eight o'clock in the evenings. The price of admission was high, being a shilling for each lecture, but Michael's brother Robert frequently supplied him with the money, and in attending these lectures Faraday made many friendships which were valuable to him afterwards.

Faraday appears to have been aware of the value of skill in drawing—a point to which much attention has recently been called by those interested in technical education—and he spent some portion of his time in studying perspective, so as to be better able to illustrate his notes of Mr. Tatum's lectures, as well as of some of Sir Humphry Davy's, which he was enabled to hear at the Royal Institution through the kindness of a customer at Mr. Riebau's shop.

In 1812, before the end of his apprenticeship, Faraday was engaged in experiments with voltaic batteries of his own construction. Having cut out seven discs of zinc the size of halfpence, and covered them with seven halfpence, he formed a pile by inserting pieces of paper soaked in common salt between each pair, and found that the pile so constructed was capable of decomposing Epsom salts. With a somewhat larger pile he decomposed copper sulphate and lead acetate, and made some experiments on the decomposition of water. On July 21, 1812, in writing to his friend Abbott, he mentions the movements of camphor when floating on water, and adds, "Science may be illustrated by those minute actions and effects, almost as much as by more evident and obvious phenomena.... My knife is so bad that I cannot mend my pen with it; it is now covered with copper, having been employed to precipitate that metal from the muriatic acid."

Something of Faraday's disposition, as well as of the results of his self-education, may be gathered from the following quotations from letters to Abbott, written at this time:—

I have again gone over your letter, but am so blinded that I cannot see any subject except chlorine to write on; but before entering on what I intend shall fill up the letter, I will ask your pardon for having maintained an opinion against one who was so ready to give his own up. I suspect from that circumstance I am wrong.... In the present case I conceive that experiments may be divided into three classes: first, those which are for the old theory of oxymuriatic acid, and consequently oppose the new one; second, those which are for the new one, and oppose the old theory; and third, those which can be explained by both theories—apparently so only, for in reality a false theory can never explain a fact."

It is not for me to affirm that I am right and you wrong; speaking impartially, I can as well say that I am wrong and you right, or that we both are wrong and a third right. I am not so self-opinionated as to suppose that my judgment and perception in this or other matters is better or clearer than that of other persons; nor do I mean to affirm that this is the true theory in reality, but only that my judgment conceives it to be so. Judgments sometimes oppose each other, as in this case; and as there cannot be two opposing facts in nature, so there cannot be two opposing truths in the intellectual world. Consequently, when judgments oppose, one must be wrong—one must be false; and mine may be so for aught I can tell. I am not of a superior nature to estimate exactly the strength and correctness of my own and other men's understanding, and will assure you, dear A——, that I am far from being convinced that my own is always right. I have given you the theory—not as the true one, but as the one which appeared true to me—and when I perceive errors in it, I will immediately renounce it, in part or wholly, as my judgment may direct. From this, dear friend, you will see that I am very open to conviction; and from the manner in which I shall answer your letter, you will also perceive that I must be convinced before I renounce.

On October 7, 1812, Faraday's apprenticeship terminated, and immediately afterwards he started life as a journeyman bookbinder. He now found that he had less time at his disposal for scientific work than he had enjoyed when an apprentice, and his desire to give up his trade and enter fully upon scientific pursuits became stronger than ever. During his apprenticeship he had written to Sir Joseph Banks, then President of the Royal Society, in the hope of obtaining some scientific employment; he now applied to Sir Humphry Davy. In a letter written to Dr. Paris, in 1829, Faraday gave an account of this application.

"My desire to escape from trade, which I thought vicious and selfish, and to enter into the service of science, which I imagined made its pursuers amiable and liberal, induced me at last to take the bold and simple step of writing to Sir H. Davy, expressing my wishes, and a hope that, if an opportunity came in his way, he would favour my views; at the same time, I sent the notes I had taken of his lectures.

"The answer, which makes all the point of my communication, I send you in the original, requesting you to take great care of it, and to let me have it back, for you may imagine how much I value it.

"You will observe that this took place at the end of the year 1812; and early in 1813 he requested to see me, and told me of the situation of assistant in the laboratory of the Royal Institution, then just vacant.

"At the same time that he thus gratified my desires as to scientific employment, he still advised me not to give up the prospects I had before me, telling me that Science was a harsh mistress, and, in a pecuniary point of view, but poorly rewarding those who devoted themselves to her service. He smiled at my notion of the superior moral feelings of philosophic men, and said he would leave me to the experience of a few years to set me right on that matter.

"Finally, through his good efforts, I went to the Royal Institution, early in March of 1813, as assistant in the laboratory; and in October of the same year went with him abroad, as his assistant in experiments and in writing. I returned with him in April, 1815, resumed my station in the Royal Institution, and have, as you know, ever since remained there."

Sir H. Davy's letter was as follows:—

"Sir,

"I am far from displeased with the proof you have given me of your confidence, and which displays great zeal, power of memory, and attention. I am obliged to go out of town, and shall not be settled in town till the end of January; I will then see you at any time you wish. It would gratify me to be of any service to you; I wish it may be in my power.

"I am, sir,

Your obedient humble servant,

H. Davy.

The minutes of the meeting of managers of the Royal Institution, on March 1, 1813, contain the following entry:—"Sir Humphry Davy has the honour to inform the managers that he has found a person who is desirous to occupy the situation in the institution lately filled by William Payne. His name is Michael Faraday. He is a youth of twenty-two years of age. His habits seem good, his disposition active and cheerful, and his manner intelligent. He is willing to engage himself on the same terms as those given to Mr. Payne at the time of quitting the institution.

"Resolved, that Michael Faraday be engaged to fill the situation lately occupied by Mr. Payne, on the same terms."

About this time Faraday joined the City Philosophical Society, which had been started at Mr. Tatum's house in 1808. The members met every Wednesday evening, either for a lecture or discussion; and perhaps the society did not widely differ from some of the "students' associations" which have more recently been started in connection with other educational enterprises. Magrath was secretary of this society, and from it there sprang a smaller band of students, who, meeting once a week, either at Magrath's warehouse in Wood Street, or at Faraday's private rooms in the attics of the Royal Institution, for mutual improvement, read together, and freely criticized each other's pronunciation and composition. In a letter to Abbott six weeks after commencing work at the Royal Institution, Faraday says:—

A stranger would certainly think you and I were a couple of very simple beings, since we find it necessary to write to each other, though we so often personally meet; but the stranger would, in so judging, only fall into that error which envelops all those who decide from the outward appearances of things.... When writing to you I seek that opportunity of striving to describe a circumstance or an experiment clearly; so that you will see I am urged on by selfish motives partly to our mutual correspondence, but, though selfish, yet not censurable.

During the summer of 1813 Faraday, in his letters to Abbott, gave his friend the benefit of his experience "on the subject of lectures and lecturers in general," in a manner that speaks very highly of his power of observation of men as well as things. He was of opinion that a lecture should not last more than an hour, and that the subject should "fit the audience."

"A lecturer may consider his audience as being polite or vulgar (terms I wish you to understand according to Shuffleton's new dictionary), learned or unlearned (with respect to the subject), listeners or gazers. Polite company expect to be entertained, not only by the subject of the lecture, but by the manner of the lecturer; they look for respect, for language consonant to their dignity, and ideas on a level with their own. The vulgar—that is to say, in general, those who will take the trouble of thinking, and the bees of business—wish for something that they can comprehend. This may be deep and elaborate for the learned, but for those who are as yet tyros and unacquainted with the subject, must be simple and plain. Lastly, listeners expect reason and sense, whilst gazers only require a succession of words."

In favour of experimental illustration he says:—

"I need not point out ... the difference in the perceptive powers of the eye and the ear, and the facility and clearness with which the first of these organs conveys ideas to the mind—ideas which, being thus gained, are held far more retentively and firmly in the memory than when introduced by the ear.... Apparatus, therefore, is an essential part of every lecture in which it can be introduced.... When ... apparatus is to be exhibited, some kind of order should be observed in the arrangement of them on the lecture-table. Every particular part illustrative of the lecture should be in view, no one thing should hide another from the audience, nor should anything stand in the way of or obstruct the lecturer. They should be so placed, too, as to produce a kind of uniformity in appearance. No one part should appear naked and another crowded, unless some particular reason exists and makes it necessary to be so."

On October 13, 1813, Faraday left the Royal Institution, in order to accompany Sir Humphry Davy in a tour on the Continent. His journal gives some interesting details, showing the inconveniences of foreign travel at that time. Sir Humphry Davy took his carriage with him in pieces, and these had to be put together after escaping the dangers of the French custom-house on the quay at Morlaix, two years before the battle of Waterloo.

One apparently trivial incident somewhat marred Faraday's pleasure throughout this journey. It was originally intended that the party should comprise Sir Humphry and Lady Davy, Faraday, and Sir Humphry's valet, but at the last moment that most important functionary declined to leave his native shores. Davy then requested Faraday to undertake such of the duties of valet as were essential to the well-being of the party, promising to secure the services of a suitable person in Paris. But no eligible candidate appeared for the appointment, and thus Faraday had throughout to take charge of domestic affairs as well as to assist in experiments. Had there been only Sir Humphry and himself, this would have been no hardship. Sir Humphry had been accustomed to humble life in his early days; but the case was different with his lady, and, apparently, Faraday was more than once on the point of leaving his patron and returning home alone. A circumstance which occurred at Geneva illustrates the position of affairs. Professor E. de la Rive invited Sir Humphry and Lady Davy and Faraday to dinner. Sir Humphry could not go into society with one who, in some respects, acted as his valet. When this point was represented to the professor, he replied that he was sorry, as it would necessitate his giving another dinner-party. Faraday subsequently kept up a correspondence with De la Rive, and continued it with his son. In writing to the latter he says, in speaking of Professor E. de la Rive, that he was "the first who personally at Geneva, and afterwards by correspondence, encouraged and by that sustained me."

At Paris Faraday met many of the most distinguished men of science of the time. One morning AmpÈre, ClÉment, and Desormes called on Davy, to show him some iodine, a substance which had been discovered only about two years before, and Davy, while in Paris, and afterwards at Montpellier, executed a series of experiments upon it. After three months' stay, the party left Paris for Italy, vi Montpellier, Aix, and Nice, whence they crossed the Col de Tende to Turin. The transfer of the carriage and baggage across the Alps was effected by a party of sixty-five men, with sledges and a number of mules. The description of the journey, as recorded in Faraday's diary, makes us respect the courage of an Englishman who, in the early part of this century, would attempt the conveyance of a carriage across the Alps in the winter.

"From Turin we proceeded to Genoa, which place we left afterwards in an open boat, and proceeded by sea towards Lerici. This place we reached after a very disagreeable passage, and not without apprehensions of being overset by the way. As there was nothing there very enticing, we continued our route to Florence; and, after a stay of three weeks or a month, left that fine city, and in four days arrived here at Rome." The foregoing is from Faraday's letter to his mother. At Florence a good deal of time was spent in the Academia del Cimento. Here Faraday saw the telescope with which Galileo discovered Jupiter's satellites, with its tube of wood and paper about three feet and a half long, and simple object-glass and eye-glass. A red velvet electric machine with a rubber of gold paper, Leyden jars pierced by the discharge between their armatures, the first lens constructed by Galileo, and a number of other objects, were full of interest to the recently enfranchised bookbinder's apprentice; but it was the great burning-glass of the grand-duke which was the most serviceable of all the treasures of the museum. With this glass—which consisted of two convex lenses about three feet six inches apart, the first lens having a diameter of about fourteen or fifteen inches, and the second a diameter of three inches—Davy succeeded in burning several diamonds in oxygen gas, and in proving that the diamond consists of little else than carbon. In 1818 Faraday published a paper on this subject in the Quarterly Journal of Science. At Genoa some experiments were made with the torpedo, but the specimens caught were very small and weak, and their shocks so feeble that no definite results were obtained. At Rome Davy attempted to repeat an experiment of Signor Morrichini, whereby a steel needle was magnetized by causing the concentrated violet and blue rays from the sun to traverse the needle from the middle to the north end several times. The experiment did not succeed in the hands of Davy and Faraday, and it was left to the latter to discover a relation between magnetism and light. From Rome they visited Naples and ascended Vesuvius, and shortly afterwards left Italy for Geneva. In the autumn of 1814 they returned from Switzerland through Germany, visiting Berne, Zurich, the Tyrol, Padua, Venice, and Bologne, to Florence, where Davy again carried out some chemical investigations in the laboratory of the academy. Thence they returned to Rome, and in the spring went on to Naples, and again visited Vesuvius, returning to England in April, vi Rome, the Tyrol, Stuttgart, Brussels, and Ostend.

A fortnight after his return from the Continent Faraday was again assistant at the Royal Institution, but with a salary of thirty shillings a week. His character will be sufficiently evident from the quotations which have been given from his diary and letters. Henceforth we must be mainly occupied with the consideration of his scientific work.

In January, 1816, he gave his first lecture to the City Philosophical Society. In a lecture delivered shortly afterwards before the same society, the following passage, which gives an idea of one of the current beliefs of the time, occurs:—

"The conclusion that is now generally received appears to be that light consists of minute atoms of matter of an octahedral form, possessing polarity, and varying in size or in velocity....

"If now we conceive a change as far beyond vaporization as that is above fluidity, and then take into account also the proportional increased extent of alteration as the changes rise, we shall, perhaps, if we can form any conception at all, not fall far short of radiant matter;[6] and as in the last conversion many qualities were lost, so here also many more would disappear.

[6] Not Crookes's.

"It was the opinion of Newton, and of many other distinguished philosophers, that this conversion was possible, and continually going on in the processes of nature, and they found that the idea would bear without injury the application of mathematical reasoning—as regards heat, for instance. If assumed, we must also assume the simplicity of matter; for it would follow that all the variety of substances with which we are acquainted could be converted into one of three kinds of radiant matter, which again may differ from one another only in the size of their particles or their form. The properties of known bodies would then be supposed to arise from the varied arrangements of their ultimate atoms, and belong to substances only as long as their compound nature existed; and thus variety of matter and variety of properties would be found co-essential. The simplicity of such a system is singularly beautiful, the idea grand and worthy of Newton's approbation. It was what the ancients believed, and it may be what a future race will realize."

In the closing words of his fifth lecture to the City Philosophical Society, Faraday said:—

"The philosopher should be a man willing to listen to every suggestion, but determined to judge for himself. He should not be biassed by any appearances; have no favourite hypothesis; be of no school; and in doctrine have no master. He should not be a respecter of persons, but of things. Truth should be his primary object. If to these qualities be added industry, he may indeed hope to walk within the veil of the temple of nature."

Many years afterwards he stated that, of all the suggestions to which he had patiently listened after his lectures at the Royal Institution, only one proved on investigation to be of any value, and that led to the discovery of the "extra current" and the whole subject of self-induction.

Faraday always kept a note-book, in which he jotted down any thoughts which occurred to him in reference to his work, as well as extracts from books or other publications which attracted his attention. He called it his "commonplace-book." Many of the queries which he here took note of he subsequently answered by experiment. For example:—

"Query: the nature of sounds produced by flame in tubes."

"Convert magnetism into electricity."

"General effects of compression, either in condensing gases or producing solutions, or even giving combinations at low temperature."

"Do the pith-balls diverge by the disturbance of electricity through mutual induction or not?"

Speaking of this book, he says, "I already owe much to these notes, and think such a collection worth the making by every scientific man. I am sure none would think the trouble lost after a year's experience."

In a letter dated May 3, 1818, he writes:—

I have this evening been busy with an atmospherical electrical apparatus. It was a very temporary thing, but answered the purpose completely. A wire, with some small brush-wire rolled round the top of it, was elevated into the atmosphere by a thin wood rod having a glass tube at the end, and tied to a chimney-pot on the housetop; and this wire was continued down (taking care that it touched nothing in its way) into the lecture-room; and we succeeded, at intervals, in getting sparks from it nearly a quarter of an inch in length, and in charging a Leyden jar, so as to give a strong shock. The electricity was positive. Now, I think you could easily make an apparatus of this kind, and it would be a constant source of interesting matter; only take care you do not kill yourself or knock down the house.

On June 12, 1820, he married Miss Sarah Barnard, third daughter of Mr. Barnard, of Paternoster Row—"an event which," to use his own words, "more than any other contributed to his earthly happiness and healthful state of mind." It was his wish that the day should be "just like any other day"—that there should be "no bustle, no noise, no hurry occasioned even in one day's proceeding," though in carrying out this plan he offended some of his relations by not inviting them to his wedding.

Up to this time Faraday's experimental researches had been for the most part in the domain of chemistry, and for two years a great part of his energy had been expended in investigating, in company with Mr. Stodart, a surgical instrument-maker, the properties of certain alloys of steel, with a view to improve its manufacture for special purposes. It was in 1821 that he commenced his great discoveries in electricity. In the autumn of that year he wrote an historical sketch of electro-magnetism for the "Annals of Philosophy," and he repeated for himself most of the experiments which he described. In the course of these experiments, in September, 1821, he discovered the rotation of a wire conveying an electric current around the pole of a magnet. Œrsted had discovered, in 1820, the tendency of a magnetic needle to set itself at right angles to a wire conveying a current. This action is due to a tendency on the part of the north pole to revolve in a right-handed direction around the current, while the south pole tends to revolve in the opposite direction. The principle that action and reaction are equal and opposite indicates that, if a magnetic pole tend to rotate around a conductor conveying a current, there must be an equal tendency for the conductor to rotate around the pole. It was this rotation that constituted Faraday's first great discovery in electro-dynamics. On December 21, in the same year, Faraday showed that the earth's magnetism was capable of exerting a directive action on a wire conveying a current. Writing to De la Rive on the subject, he says:—

I find all the usual attractions and repulsions of the magnetic needle by the conjunctive wire are deceptions, the motions being, not attractions or repulsions, nor the result of any attractive or repulsive forces, but the result of a force in the wire, which, instead of bringing the pole of the needle nearer to or further from the wire, endeavours to make it move round it in a never-ending circle and motion whilst the battery remains in action. I have succeeded, not only in showing the existence of this motion theoretically, but experimentally, and have been able to make the wire revolve round a magnetic pole, or a magnetic pole round the wire, at pleasure. The law of revolution, and to which all the other motions of the needle are reducible, is simple and beautiful.

Conceive a portion of connecting wire north and south, the north end being attached to the positive pole of a battery, the south to the negative. A north magnetic pole would then pass round it continually in the apparent direction of the sun, from east to west above, and from west to east below. Reverse the connections with the battery, and the motion of the pole is reversed; or, if the south pole be made to revolve, the motions will be in the opposite direction, as with the north pole.

If the wire be made to revolve round the pole, the motions are according to those mentioned.... Now, I have been able, experimentally, to trace this motion into its various forms, as exhibited by AmpÈre's helices, etc., and in all cases to show that the attractions and repulsions are only appearances due to this circulation of the pole; to show that dissimilar poles repel as well as attract, and that similar poles attract as well as repel; and to make, I think, the analogy between the helix and common bar magnet far stronger than before. But yet I am by no means decided that there are currents of electricity in the common magnet. I have no doubt that electricity puts the circles of the helix into the same state as those circles are in that may be conceived in the bar magnet; but I am not certain that this state is directly dependent on the electricity, or that it cannot be produced by other agencies; and therefore, until the presence of electric currents be proved in the magnet by other than magnetical effects, I shall remain in doubt about AmpÈre's theory.

The most convenient rule by which to remember the direction of these electro-magnetic rotations is probably that given by Clerk Maxwell, which will be stated in its place.[7] If a circular plate of copper and another of zinc be connected by a piece (or better, by three pieces) of insulated wire, so that the zinc is about an inch above the copper, and the combined plates be suspended by a silk fibre in a small beaker of dilute sulphuric acid, which is placed on the pole of a large magnet, the liquid will be seen to rotate about a vertical axis in one direction, and the two plates with their connecting wires in the opposite direction. On reversing the polarity of the magnet, both rotations will be reversed. This is a very simple mode of exhibiting Faraday's discovery. A little powdered resin renders the motion of the liquid readily visible.

[7] See p. 302.

In 1823 Faraday published his work on the liquefaction of gases, from which he concluded that there was no difference in kind between gases and vapours. In the course of this work he met with more than one serious explosion. On January 8, 1824, he was elected a Fellow of the Royal Society, and in 1825, on the recommendation of Sir Humphry Davy, he was appointed Director of the Laboratory of the Royal Institution, and in this capacity he instituted the laboratory conferences, which developed into the Friday evening lectures. For five years after this, the greater part of Faraday's spare time was occupied in some investigations in connection with optical glass, made at the request of the Royal Society, and at the expense of the Government. Mr. Dollond and Sir John Herschel were associated with him on this committee, but the results obtained were not of much value to opticians. The silico-borate of lead which Faraday prepared in the course of these experiments was, however, the substance with which he first demonstrated the effect of a magnetic field on the plane of polarization of light, and with which he discovered diamagnetic action.

Faraday's experimental researches were generally guided by theoretical considerations. Frequently these theories were based on very slender premises, and sometimes were little else than flights of a scientific imagination, but they served to guide him into fruitful fields of discovery, and he seldom placed much confidence in his conclusions till he had succeeded in verifying them experimentally. For many years he had held the opinion that electric currents should exhibit phenomena analogous to those of electro-static induction. Again and again he returned to the investigation, and attempted to obtain an induced current in one wire through the passage of a powerful current through a neighbouring conductor; but he looked for a permanent induced current to be maintained during the whole time that the primary current was flowing. At length, employing two wires wound together as a helix on a wooden rod, the first capable of transmitting a powerful current from a battery, while the second was connected with a galvanometer, he observed that, when the current started in the primary, there was a movement of the galvanometer, and when it ceased there was a movement in the opposite direction, though the galvanometer remained at zero while the current continued steady. Hence it was apparent that it is by changes in the primary current that induced currents may be generated, and not by their steady continuance; and it was demonstrated that, when a current is started in a conductor, a temporary current is induced in a neighbouring conductor in the opposite direction, while a current is induced in the same direction as the primary when the latter ceases to flow. Before obtaining this result with the wires on a wooden bobbin, he had experimented with a wrought-iron ring about six inches in diameter, and made of 7/8-inch round iron. He wound two sets of coils round it, one occupying nearly half the ring, and the other filling most of the other half. One of these he connected with a galvanometer, the other could be connected at will with a battery. On sending the battery current through the latter coil, the galvanometer needle swung completely round four or five times, and a similar action took place, but in the opposite direction, on stopping the current. Here it was clearly the magnetism induced in the iron ring which produced so powerful a current in the galvanometer circuit. Next he wound a quantity of covered copper wire on a small iron bar, and connecting the ends to a galvanometer, he placed the little bobbin between the opposite poles of a pair of bar magnets, whose other ends were in contact. As soon as the iron core touched the magnets, a current appeared in the galvanometer. On breaking contact, the current was in the opposite direction. Then came the experiment above mentioned, in which no iron was employed. After this, one end of a cylindrical bar magnet was introduced into a helix of copper wire, and then suddenly thrust completely in. The galvanometer connected with the coil showed a transient current. On withdrawing the magnet, the current appeared in the opposite direction; so that currents were induced merely by the relative motion of a magnet and a conductor.

A copper disc was mounted so that it could be made to rotate rapidly. A wire was placed in connection with the centre of the disc, and the circuit completed by a rubbing contact on the circumference. A galvanometer was inserted in the circuit, and the large horseshoe magnet of the Royal Institution so placed that the portion of the disc between the centre and the rubbing contact passed between the poles of the magnet. A current flowed through the galvanometer as long as the disc was kept spinning. Then he found that the mere passage of a copper wire between the poles of the magnet was sufficient to induce a current in it, and concluded that the production of the current was connected with the cutting of the "magnetic curves," or "lines of magnetic force" which would be depicted by iron filings. Thus in the course of ten days' experimental work, in the autumn of 1831, Faraday so completely investigated the phenomena of electro-magnetic induction as to leave little, except practical applications, to his successors. A few weeks later he obtained induction currents by means of the earth's magnetism only, first with a coil of wire wound upon an iron bar in which a strong current was produced when it was being quickly placed in the direction of the magnetic dip or being removed from that position, and afterwards with a coil of wire without an iron core. On February 8, 1832, he succeeded in obtaining a spark from the induced current. Unless the electro-motive force is very great, it is not possible to obtain a spark between two metallic surfaces which are separated by a sensible thickness of air. If, however, the circuit of a wire is broken while the current is passing, a little bridge of metallic vapour is formed, across which for an instant the spark leaps. The induced current being of such short duration, the difficulty was to break the circuit while it was flowing. Faraday wound a considerable length of fine wire around a short bar of iron; the ends of the wire were crossed so as just to be in contact with one another, but free to separate if exposed to a slight shock. The ends of the iron bar projected beyond the coil, and were held just over the poles of the magnet. On releasing the bar it fell so as to strike the magnetic poles and close the circuit of the magnet. An induced current was generated in the wire, but, while this was passing, the shock caused by the bar striking the magnet separated the ends of the wire, thus breaking the circuit of the conductor, and a spark appeared at the gap. In this little spark was the germ of the electric light of to-day. Subsequently Faraday improved the apparatus, by attaching a little disc of amalgamated copper to one end of the wire, and bending over the other end so as just to press lightly against the surface of the disc. With this apparatus he showed the "magnetic spark" at the meeting of the British Association at Oxford.

Faraday supposed that when a coil of wire was in the neighbourhood of a magnet, or near to a conductor conveying a current, the coil was thrown into a peculiar condition, which he called the electro-tonic state, and that the induced currents appeared whenever this state was assumed or lost by the coil. He frequently reverted to his conception of the electro-tonic state, though he saw clearly that, when the currents were induced by the relative motion of a wire and a magnet, the current induced depended on the rate at which the lines of magnetic force had been cut by the wire. Of his conception of lines of force filling the whole of space, we shall have more to say presently. It is sufficient to remark here that, in the electro-tonic state of Faraday, Clerk Maxwell recognized the number of lines of magnetic force enclosed by the circuit, and showed that the electro-motive force induced is proportional to the rate of change of the number of lines of force thus enclosed.

It is seldom that a great discovery is made which has not been gradually led up to by several observed phenomena which awaited that discovery for their explanation. In the case of electro-magnetic induction, however, there appears to have been but one experiment which had baffled philosophers, and the key to which was found in Faraday's discovery, while the complete explanation was given by Faraday himself. Arago had found that, if a copper plate were made rapidly to rotate beneath a freely suspended magnetic needle, the needle followed (slowly) the plate in its revolution, though a sheet of glass were inserted between the two to prevent any air-currents acting on the magnet. The experiment had been repeated by Sir John Herschel and Mr. Babbage, but no explanation was forthcoming. Faraday saw that the revolution of the disc beneath the poles of the magnet must generate induced currents in the disc, as the different portions of the metal would be constantly cutting the lines of force of the magnet. These currents would react upon the magnet, causing a mechanical stress to act between the two, which, as stated by Lenz, would be in the direction tending to oppose the relative motion, and therefore to drag the magnet after the disc in its revolution. In the above figure the unfledged arrows show the general distribution of the currents in the disc, while the winged arrows indicate the direction of the disc's rotation. The currents in the semicircle A will repel the north pole and attract the south pole. Those in the semicircle B will produce the opposite effect, and hence there will be a tendency for the magnet to revolve in the direction of the disc, while the motion of the disc will be resisted. This resistance to the motion of a conductor in a magnetic field was noticed by Faraday, and, independently, by Tyndall, and it is sufficiently obvious in the power absorbed by dynamos when they are generating large currents.

Faraday's next series of researches was devoted to the experimental proof of the identity of frictional and voltaic electricity. He showed that a magnet could be deflected and iodide of potassium decomposed by the current from his electrical machine, and came to the conclusion that the amount of electricity required to decompose a grain of water was equal to 800,000 charges of his large Leyden battery. The current from the frictional machine also served to deflect the needle of his galvanometer. These investigations led on to a complete series of researches on the laws of electrolysis, wherein Faraday demonstrated the principle that, however the strength of the current may be varied, the amount of any compound decomposed is proportional to the whole quantity of electricity which has passed through the electrolyte. When the same current is sent through different compounds, there is a constant relation between the amounts of the several compounds decomposed. In modern language, Faraday's laws may be thus expressed:—

If the same current be made to pass through several different electrolytes, the quantity of each ion produced will be proportional to its combining weight divided by its valency, and if the current vary, the quantity of each ion liberated per second will be proportional to the current.

This is the great law of electro-chemical equivalents. The amount of hydrogen liberated per second by a current of one ampÈre is about ·00001038 gramme, or nearly one six-thousandth of a grain. This is the electro-chemical equivalent of hydrogen. That of any other substance may be found by Faraday's law.

From Faraday's results it appears that the passage of the same amount of electricity is required in order to decompose one molecule of any compound of the same chemical type, but it does not follow that the same amount of energy is employed in the decomposition. For example, the combining weights of copper and zinc are nearly equal. Hence it will require the passage of about the same amount of electricity to liberate a pound of copper from, say, the copper sulphate as to liberate a pound of zinc from zinc sulphate; but the work to be done is much less in the case of the copper. This is made manifest in the following way:—A battery, which will just decompose the copper salt slowly, liberating copper, oxygen, and sulphuric acid, will not decompose the zinc salt at all so as to liberate metallic zinc, but immediately on sending the current through the electrolyte, polarization will set in, and the opposing electro-motive force thus introduced will become equal to that of the battery, and stop the current before metallic zinc makes its appearance. In the case of the copper, polarization also sets in, but never attains to equality with the electro-motive force of the primary battery. In fact, in all cases of electrolysis, polarization produces an opposing electro-motive force strictly proportional to the work done in the cell by the passage of each unit of electricity. If the strength of the battery be increased, so that it is able to decompose the zinc sulphate, and if this battery be applied to the copper sulphate solution, the latter will be rapidly decomposed, and the excess of energy developed by the battery will be converted into heat in the circuit.

One important point in connection with electrolysis which Faraday demonstrated is that the decomposition is the result of the passage of the current, and is not simply due to the attraction of the electrodes. Thus he showed that potassium iodide could be decomposed by a stream of electricity coming from a metallic point on the prime conductor of his electric machine, though the point did not touch the test-paper on which the iodide was placed.

It was in 1834 that Mr. Wm. Jenkin, after one of the Friday evening lectures at the Royal Institution, called the attention of Faraday to a shock which he had experienced in breaking the circuit of an electro-magnet, though the battery employed consisted of only one pair of plates. Faraday repeated the experiment, and found that, with a large magnet in circuit, a strong spark could thus be obtained. On November 14, 1834, he writes, "The phenomenon of increased spark is merely a case of the induction of electric currents. If a current be established in a wire, and another wire forming a complete circuit be placed parallel to it, at the moment the current in the first is stopped it induces a current in the same direction in the second, itself then showing but a feeble spark. But if the second be away, it induces a current in its own wire in the same direction, producing a strong spark. The strong spark in the current when alone is therefore the equivalent of the current it can produce in a neighbouring wire when in company." The strong spark does, in fact, represent the energy of the current due to the self-induction of its circuit, which energy would, in part at least, be expended in inducing a current in a neighbouring wire if such existed.

His time from 1835 till 1838 was largely taken up with his work on electro-static induction. Faraday could never be content with any explanation based on direct action at a distance; he always sought for the machinery through which the action was communicated. In this search the lines of magnetic force, which he had so often delineated in iron filings, came to his aid. Faraday made many pictures in iron filings of magnetic fields due to various combinations of magnets. He employed gummed paper, and when the filings were arranged on the hard gummed surface, he projected a feeble jet of steam on the paper, which melted the gum and fixed the filings. Several of his diagrams were exhibited at the Loan Collection at South Kensington. He conceived electrical action to be transmitted along such lines as these, and to him the whole electric field was filled with lines passing always from positive to negative electrification, and in some respects resembling elastic strings. The action at any place could then be expressed in terms of the lines of force that existed there, the electrifications by which these lines were produced being left out of consideration. The acting bodies were thus replaced by the field of force they produced. He showed that it was impossible to call into existence a charge of positive electricity without at the same time producing an equal negative charge. From every unit of positive electricity he conceived a line of force to start, and thus, with the origin of the line, there was created simultaneously a charge of negative electricity on which the line might terminate. By the famous ice-pail experiment he showed that, when a charged body is inserted in a closed or nearly closed hollow conductor, an equal amount of the same kind of electricity appeared on the outside of the hollow conductor, while an equal amount of the opposite kind appeared on the interior surface of the conductor. With the ice-pail and the butterfly-net he showed that there could be no free electricity on the interior of a conductor. Lines of force cannot pass through the material of a conductor without producing electric displacement. Every element of electricity must be joined to an equal amount of the opposite kind by a line of force. Such lines cannot pass through the conductor itself; hence the charge must be entirely on the outside of the conductor, so that every element of the charge may be associated with an equal amount of the opposite electricity upon the surfaces of surrounding objects. Thus to Faraday every electrical action was an exhibition of electric induction. All this work had been done before by Henry Cavendish, but neither Faraday nor any one else knew about it at the time. From the fact that there could be no electricity in the interior of a hollow conductor, Cavendish deduced, in the best way possible, the truth of the law of inverse squares as applied to electrical attraction and repulsion, and thus laid the foundation of the mathematical theory of electricity. To Cavendish every electrical action was a displacement of an incompressible fluid which filled the whole of space, producing no effect in conductors on account of the freedom of its motion, but producing strains in insulators by displacing the material of the body. Faraday, in his lines of force, saw, as it were, the lines along which the displacements of Cavendish's fluid took place.

Faraday thought that, if he could show that electric induction could take place along curved lines, it would prove that the action took place through a medium, and not directly at a distance. He succeeded in experimentally demonstrating the curvature of these lines; but his conclusions were not warranted, for if we conceive of two or more centres of force acting directly at a distance according to the law of inverse squares, the resultant lines of force will generally be curved. Of course, this does not prove the possibility of direct action at a distance, but only shows that the curvature of the lines is as much a consequence of the one hypothesis as of the other.

It soon appeared to Faraday that the nature of the dielectric had very much to do with electric induction. The capacity of a condenser, for instance, depends on the nature of the dielectric as well as on the configuration of the conductors. To express this property, Faraday employed the term "specific inductive capacity." He compared the electric capacity of condensers, equal in all other respects, but one possessing air for its dielectric, and the other having other media, and thus roughly determined the specific inductive capacities of several insulators. These results turned out afterwards to be of great value in connection with the insulation of submarine cables. Even now the student of electricity is sometimes puzzled by the manner in which specific inductive capacity is introduced to his notice as modifying the capacity of condensers, after learning that the capacity of any system of conductors can be calculated from its geometrical configuration; but the fact is that the intensity of all electrical actions depends on the nature of the medium through which they take place, and it will require more electricity to exert upon an equal charge a unit force at unit distance when the intervening medium has a high than when it possesses a low specific inductive capacity.

In 1835 Faraday received a pension from the civil list; in 1836 he was appointed scientific adviser to the Elder Brethren of the Trinity House. In the same year he was made a member of the Senate of the University of London, and in that capacity he has exerted no small influence on the scientific education of the country, for he was one of those who drew up the schedules of the various examinations.

In his early years, Faraday thought that all kinds of matter might ultimately consist of three materials only, and that as gases and vapours appeared more nearly to resemble one another than the liquids or solids to which they corresponded, so each might be subject to a still higher change in the same direction, and the gas or vapour become radiant matter—either heat, light, or electricity. Later on, Faraday clearly recognized the dynamical nature of heat and light; but his work was always guided by his theoretical conceptions of the "correlation of the physical forces." For a long time he had tried to discover relations between electricity and light; at length, on September 13, 1845, after experimenting on a number of other substances, he placed a piece of silico-borate of lead, or heavy-glass, in the field of the magnet, and found that, when a beam of polarized light was transmitted through the glass in the direction of the lines of magnetic force, there was a rotation of the plane of polarization. Afterwards it appeared that all the transparent solids and liquids experimented on were capable of producing this rotation in a greater or less degree, and in the case of all non-magnetic substances the rotation was in the direction of the electric current, which, passing round the substance, would produce the magnetic field employed. Abandoning the magnet, and using only a coil of wire with the transparent substance within it, similar effects were obtained. Thus at length a relation was found between light and electricity.

On November 4, employing a piece of heavy-glass and a new horseshoe magnet, Faraday noticed that the magnet appeared to have a directive action upon the glass. Further examination showed that the glass was repelled by the magnetic poles. Three days afterwards he found that all sorts of substances, including most metals, were acted upon like the heavy-glass. Small portions of them were repelled, while elongated cylinders tended to set with their lengths perpendicular to the lines of magnetic force. Such actions could be imitated by suspending a feebly magnetic body in a medium more magnetic than itself. Faraday, therefore, sought for some medium which would be absolutely neutral to magnetic action. Filling a glass tube with compressed oxygen, and suspending it in an atmosphere of oxygen at ordinary pressure, the compressed gas behaved like iron or other magnetic substances. Faraday compared the intensity of its action with that of ferrous sulphate, and this led to an explanation of the diurnal variations of the compass-needle based on the sun's heat diminishing the magnetic permeability of the oxygen of the air. Repeating the experiment with nitrogen, he found that the compressed gas behaved in a perfectly neutral manner when surrounded by the gas at ordinary pressure. Hence he inferred that in nitrogen he had found the neutral medium required. Repeating his experiments in an atmosphere of nitrogen, it still appeared that most bodies were repelled by the magnetic poles, and set equatorially, or at right angles to the lines of force when elongated portions were tested. To this action Faraday gave the name of diamagnetism.

About a month after his marriage, Faraday joined the Sandemanian Church, to which his family had for several generations belonged, by confession of sin and profession of faith. Not unfrequently he used to speak at the meetings of his Church, but in 1840 he was elected an elder, and then he took his turn regularly in conducting the services. The notes of his addresses he generally made on small pieces of card. He had a curious habit of separating his religious belief from his scientific work, although the spirit of his religion perpetually pervaded his life. A lecture on mental education, given in 1854, at the Royal Institution, in the presence of the late Prince Consort, he commenced as follows:

"Before entering on this subject, I must make one distinction, which, however it may appear to others, is to me of the utmost importance. High as man is placed above the creatures around him, there is a higher and far more exalted position within his view; and the ways are infinite in which he occupies his thoughts about the fears, or hopes, or expectations of a future life. I believe that the truth of that future cannot be brought to his knowledge by any exertion of his mental powers, however exalted they may be; that it is made known to him by other teaching than his own, and is received through simple belief of the testimony given. Let no one suppose for a moment that the self-education I am about to commend, in respect of the things of this life, extends to any considerations of the hope set before us, as if man by reasoning could find out God. It would be improper here to enter upon this subject further than to claim an absolute distinction between religious and ordinary belief. I shall be reproached with the weakness of refusing to apply those mental operations which I think good in respect of high things to the very highest. I am content to bear the reproach. Yet even in earthly matters I believe that 'the invisible things of Him from the creation of the world are clearly seen, being understood by the things that are made, even His eternal power and Godhead;' and I have never seen anything incompatible between those things of man which can be known by the spirit of man which is within him, and those higher things concerning his future which he cannot know by that spirit."

On more than one occasion the late Prince Consort had discussed physical questions with Faraday, and in 1858 the Queen offered him a house on Hampton Court Green. This was his home until August 25, 1867. He saw not only the magnetic spark, which he had first produced, employed in the lighthouses at the South Foreland and Dungeness, but he saw also his views respecting lines of electric induction examined and confirmed by the investigations of Thomson and Clerk Maxwell.

Of the ninety-five distinctions conferred upon him, we need only mention that of Commandant of the Legion of Honour, which he received in January, 1856.


                                                                                                                                                                                                                                                                                                           

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