Heroes of Science: Physicists Part 12

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 Inst.i.tution, 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 inst.i.tution 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 inst.i.tution.

"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'

a.s.sociations" 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 Inst.i.tution, for mutual improvement, read together, and freely criticized each other's p.r.o.nunciation and composition. In a letter to Abbott six weeks after commencing work at the Royal Inst.i.tution, 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 circ.u.mstance 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 ill.u.s.tration 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 ill.u.s.trative 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 Inst.i.tution, 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 sh.o.r.es. 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 a.s.sist in experiments. Had there been only Sir Humphry and himself, this would have been no hards.h.i.+p. 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 circ.u.mstance which occurred at Geneva ill.u.s.trates 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 Ampere, Clement, 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, _via_ 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 pa.s.sage, 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-gla.s.s and eye-gla.s.s. 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-gla.s.s of the grand-duke which was the most serviceable of all the treasures of the museum. With this gla.s.s--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, _via_ Rome, the Tyrol, Stuttgart, Brussels, and Ostend.

A fortnight after his return from the Continent Faraday was again a.s.sistant at the Royal Inst.i.tution, but with a salary of thirty s.h.i.+llings 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 pa.s.sage, 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.

[Footnote 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 a.s.sumed, we must also a.s.sume 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 bia.s.sed 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 Inst.i.tution, 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-b.a.l.l.s 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 gla.s.s 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.

[OE]rsted 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 const.i.tuted 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 pa.s.s 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 Ampere'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 a.n.a.logy 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 Ampere'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.

[Footnote 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 Inst.i.tution, and in this capacity he inst.i.tuted 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 gla.s.s, made at the request of the Royal Society, and at the expense of the Government. Mr.

Dollond and Sir John Herschel were a.s.sociated 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 a.n.a.logous 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 pa.s.sage 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 quant.i.ty 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 circ.u.mference. A galvanometer was inserted in the circuit, and the large horseshoe magnet of the Royal Inst.i.tution so placed that the portion of the disc between the centre and the rubbing contact pa.s.sed 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 pa.s.sage 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.