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+*** START OF THE PROJECT GUTENBERG EBOOK 1225 ***
+
+FARADAY AS A DISCOVERER
+
+by John Tyndall
+
+
+
+
+Contents.
+
+  Preface.
+
+  Chapter 1.
+   Parentage: introduction to the royal institution:
+   earliest experiments: first royal society paper: marriage.
+
+  Chapter 2.
+   Early researches: magnetic rotations: liquefaction of gases:
+   heavy glass: Charles Anderson: contributions to physics.
+
+  Chapter 3.
+   Discovery of Magneto-electricity: Explanation of Argo's magnetism
+   of rotation: Terrestrial magneto-electric induction:
+   The extra current.
+
+  Chapter 4.
+   Points of Character.
+
+  Chapter 5.
+   Identity of electricities; first researches on electro-chemistry.
+
+  Chapter 6.
+   Laws of electro-chemical decomposition.
+
+  Chapter 7.
+   Origin of power in the voltaic pile.
+
+  Chapter 8.
+   Researches on frictional electricity: induction: conduction:
+   specific inductive capacity: theory of contiguous particles.
+
+  Chapter 9.
+   Rest needed--visit to Switzerland.
+
+  Chapter 10.
+   Magnetization of light.
+
+  Chapter 11.
+   Discovery of diamagnetism--researches on magne-crystallic action.
+
+  Chapter 12.
+   Magnetism of flame and gases--atmospheric magnetism.
+
+  Chapter 13.
+   Speculations: nature of matter: lines of force.
+
+  Chapter 14.
+   Unity and convertibility of natural forces: theory of the
+   electric current.
+
+  Chapter 15.
+   Summary.
+
+  Chapter 16.
+   Illustrations of Character.
+
+
+
+
+Preface to the fifth edition.
+
+Daily and weekly, from all parts of the world, I receive publications
+bearing upon the practical applications of electricity. This great
+movement, the ultimate outcome of which is not to be foreseen, had its
+origin in the discoveries made by Michael Faraday, sixty-two years ago.
+From these discoveries have sprung applications of the telephone order,
+together with various forms of the electric telegraph. From them have
+sprung the extraordinary advances made in electrical illumination.
+Faraday could have had but an imperfect notion of the expansions of
+which his discoveries were capable. Still he had a vivid and strong
+imagination, and I do not doubt that he saw possibilities which did not
+disclose themselves to the general scientific mind. He knew that his
+discoveries had their practical side, but he steadfastly resisted
+the seductions of this side, applying himself to the development of
+principles; being well aware that the practical question would receive
+due development hereafter.
+
+During my sojourn in Switzerland this year, I read through the proofs of
+this new edition, and by my reading was confirmed in the conviction that
+the book ought not to be suffered to go out of print. The memoir was
+written under great pressure, but I am not ashamed of it as it stands.
+Glimpses of Faraday's character and gleams of his discoveries are there
+to be found which will be of interest to humanity to the end of time.
+
+John Tyndall. Hind Head, December, 1893.
+
+
+
+[Note.--It was, I believe, my husband's intention to substitute
+this Preface, written a few days before his death, for all former
+Prefaces. As, however, he had not the opportunity of revising the old
+prefatory pages himself, they have been allowed to remain just as they
+stood in the last edition.
+
+Louisa C. Tyndall.]
+
+
+
+
+Preface to the fourth edition.
+
+When consulted a short time ago as to the republication of 'Faraday as a
+Discoverer,' it seemed to me that the labours, and points of character,
+of so great a worker and so good a man should not be allowed to vanish
+from the public eye. I therefore willingly fell in with the proposal of
+my Publishers to issue a new edition of the little book.
+
+Royal Institution, February, 1884.
+
+
+
+
+Preface to the second edition.
+
+The experimental researches of Faraday are so voluminous, their
+descriptions are so detailed, and their wealth of illustration is so
+great, as to render it a heavy labour to master them. The multiplication
+of proofs, necessary and interesting when the new truths had to be
+established, are however less needful now when these truths have become
+household words in science. I have therefore tried in the following
+pages to compress the body, without injury to the spirit, of these
+imperishable investigations, and to present them in a form which should
+be convenient and useful to the student of the present day.
+
+While I write, the volumes of the Life of Faraday by Dr. Bence Jones
+have reached my hands. To them the reader must refer for an account of
+Faraday's private relations. A hasty glance at the work shows me that
+the reverent devotion of the biographer has turned to admirable account
+the materials at his command.
+
+The work of Dr. Bence Jones enables me to correct a statement regarding
+Wollaston's and Faraday's respective relations to the discovery of
+Magnetic Rotation. Wollaston's idea was to make the wire carrying a
+current rotate round its own axis: an idea afterwards realised by the
+celebrated Ampere. Faraday's discovery was to make the wire carrying the
+current revolve round the pole of a magnet and the reverse.
+
+John Tyndall. Royal Institution: December, 1869.
+
+
+
+
+FARADAY AS A DISCOVERER.
+
+
+
+
+Chapter 1.
+
+     Parentage: introduction to the royal institution: earliest
+     experiments: first royal society paper: marriage.
+
+It has been thought desirable to give you and the world some image
+of MICHAEL FARADAY, as a scientific investigator and discoverer. The
+attempt to respond to this desire has been to me a labour of difficulty,
+if also a labour of love. For however well acquainted I may be with the
+researches and discoveries of that great master--however numerous the
+illustrations which occur to me of the loftiness of Faraday's character
+and the beauty of his life--still to grasp him and his researches as a
+whole; to seize upon the ideas which guided him, and connected them; to
+gain entrance into that strong and active brain, and read from it the
+riddle of the world--this is a work not easy of performance, and all but
+impossible amid the distraction of duties of another kind. That I should
+at one period or another speak to you regarding Faraday and his work is
+natural, if not inevitable; but I did not expect to be called upon to
+speak so soon. Still the bare suggestion that this is the fit and proper
+time for speech sent me immediately to my task: from it I have returned
+with such results as I could gather, and also with the wish that those
+results were more worthy than they are of the greatness of my theme.
+
+It is not my intention to lay before you a life of Faraday in the
+ordinary acceptation of the term. The duty I have to perform is to give
+you some notion of what he has done in the world; dwelling incidentally
+on the spirit in which his work was executed, and introducing such
+personal traits as may be necessary to the completion of your picture of
+the philosopher, though by no means adequate to give you a complete idea
+of the man.
+
+The newspapers have already informed you that Michael Faraday was born
+at Newington Butts, on September 22, 1791, and that he died at Hampton
+Court, on August 25, 1867. Believing, as I do, in the general truth
+of the doctrine of hereditary transmission--sharing the opinion of Mr.
+Carlyle, that 'a really able man never proceeded from entirely stupid
+parents'--I once used the privilege of my intimacy with Mr. Faraday
+to ask him whether his parents showed any signs of unusual ability. He
+could remember none. His father, I believe, was a great sufferer during
+the latter years of his life, and this might have masked whatever
+intellectual power he possessed. When thirteen years old, that is to
+say in 1804, Faraday was apprenticed to a bookseller and bookbinder in
+Blandford Street, Manchester Square: here he spent eight years of his
+life, after which he worked as a journeyman elsewhere.
+
+You have also heard the account of Faraday's first contact with the
+Royal Institution; that he was introduced by one of the members to Sir
+Humphry Davy's last lectures, that he took notes of those lectures;
+wrote them fairly out, and sent them to Davy, entreating him at the
+same time to enable him to quit trade, which he detested, and to pursue
+science, which he loved. Davy was helpful to the young man, and this
+should never be forgotten: he at once wrote to Faraday, and afterwards,
+when an opportunity occurred, made him his assistant.[1] Mr. Gassiot has
+lately favoured me with the following reminiscence of this time:--
+
+'Clapham Common, Surrey,
+
+'November 28, 1867.
+
+'My Dear Tyndall,--Sir H. Davy was accustomed to call on the late Mr.
+Pepys, in the Poultry, on his way to the London Institution, of which
+Pepys was one of the original managers; the latter told me that on one
+occasion Sir H. Davy, showing him a letter, said: "Pepys, what am I
+to do, here is a letter from a young man named Faraday; he has been
+attending my lectures, and wants me to give him employment at the Royal
+Institution--what can I do?" "Do?" replied Pepys, "put him to wash
+bottles; if he is good for anything he will do it directly, if he
+refuses he is good for nothing." "No, no," replied Davy; "we must try
+him with something better than that." The result was, that Davy engaged
+him to assist in the Laboratory at weekly wages.
+
+'Davy held the joint office of Professor of Chemistry and Director of
+the Laboratory; he ultimately gave up the former to the late Professor
+Brande, but he insisted that Faraday should be appointed Director of
+the Laboratory, and, as Faraday told me, this enabled him on subsequent
+occasions to hold a definite position in the Institution, in which he
+was always supported by Davy. I believe he held that office to the last.
+
+'Believe me, my dear Tyndall, yours truly,
+
+'J. P. Gassiot.
+
+
+
+'Dr. Tyndall.'
+
+From a letter written by Faraday himself soon after his appointment as
+Davy's assistant, I extract the following account of his introduction to
+the Royal Institution:--
+
+'London, Sept. 13, 1813.
+
+'As for myself, I am absent (from home) nearly day and night, except
+occasional calls, and it is likely shall shortly be absent entirely,
+but this (having nothing more to say, and at the request of my mother) I
+will explain to you. I was formerly a bookseller and binder, but am now
+turned philosopher,[2] which happened thus:--Whilst an apprentice, I,
+for amusement, learnt a little chemistry and other parts of philosophy,
+and felt an eager desire to proceed in that way further. After being
+a journeyman for six months, under a disagreeable master, I gave up
+my business, and through the interest of a Sir H. Davy, filled the
+situation of chemical assistant to the Royal Institution of Great
+Britain, in which office I now remain; and where I am constantly
+employed in observing the works of nature, and tracing the manner in
+which she directs the order and arrangement of the world. I have lately
+had proposals made to me by Sir Humphry Davy to accompany him in his
+travels through Europe and Asia, as philosophical assistant. If I go at
+all I expect it will be in October next--about the end; and my absence
+from home will perhaps be as long as three years. But as yet all is
+uncertain.'
+
+This account is supplemented by the following letter, written by Faraday
+to his friend De la Rive,[3] on the occasion of the death of Mrs.
+Marcet. The letter is dated September 2, 1858:--
+
+'My Dear Friend,--Your subject interested me deeply every way; for Mrs.
+Marcet was a good friend to me, as she must have been to many of the
+human race. I entered the shop of a bookseller and bookbinder at the age
+of thirteen, in the year 1804, remained there eight years, and during
+the chief part of my time bound books. Now it was in those books, in the
+hours after work, that I found the beginning of my philosophy.
+
+There were two that especially helped me, the "Encyclopaedia
+Britannica," from which I gained my first notions of electricity, and
+Mrs. Marcet's "Conversation on Chemistry," which gave me my foundation
+in that science.
+
+'Do not suppose that I was a very deep thinker, or was marked as a
+precocious person. I was a very lively imaginative person, and could
+believe in the "Arabian Nights" as easily as in the "Encyclopaedia."
+But facts were important to me, and saved me. I could trust a fact, and
+always cross-examined an assertion. So when I questioned Mrs. Marcet's
+book by such little experiments as I could find means to perform, and
+found it true to the facts as I could understand them, I felt that I
+had got hold of an anchor in chemical knowledge, and clung fast to
+it. Thence my deep veneration for Mrs. Marcet--first as one who had
+conferred great personal good and pleasure on me; and then as one able
+to convey the truth and principle of those boundless fields of knowledge
+which concern natural things to the young, untaught, and inquiring mind.
+
+'You may imagine my delight when I came to know Mrs. Marcet personally;
+how often I cast my thoughts backward, delighting to connect the
+past and the present; how often, when sending a paper to her as a
+thank-offering, I thought of my first instructress, and such like
+thoughts will remain with me.
+
+'I have some such thoughts even as regards your own father; who was,
+I may say, the first who personally at Geneva, and afterwards by
+correspondence, encouraged, and by that sustained me.'
+
+Twelve or thirteen years ago Mr. Faraday and myself quitted the
+Institution one evening together, to pay a visit to our friend Grove in
+Baker Street. He took my arm at the door, and, pressing it to his
+side in his warm genial way, said, 'Come, Tyndall, I will now show you
+something that will interest you.' We walked northwards, passed the
+house of Mr. Babbage, which drew forth a reference to the famous evening
+parties once assembled there. We reached Blandford Street, and after a
+little looking about he paused before a stationer's shop, and then went
+in. On entering the shop, his usual animation seemed doubled; he looked
+rapidly at everything it contained. To the left on entering was a door,
+through which he looked down into a little room, with a window in front
+facing Blandford Street. Drawing me towards him, he said eagerly, 'Look
+there, Tyndall, that was my working-place. I bound books in that
+little nook.' A respectable-looking woman stood behind the counter: his
+conversation with me was too low to be heard by her, and he now turned
+to the counter to buy some cards as an excuse for our being there. He
+asked the woman her name--her predecessor's name--his predecessor's
+name. 'That won't do,' he said, with good-humoured impatience; 'who was
+his predecessor?' 'Mr. Riebau,' she replied, and immediately added,
+as if suddenly recollecting herself, 'He, sir, was the master of Sir
+Charles Faraday.' 'Nonsense!' he responded, 'there is no such person.'
+Great was her delight when I told her the name of her visitor; but
+she assured me that as soon as she saw him running about the shop, she
+felt-though she did not know why--that it must be 'Sir Charles Faraday.'
+
+Faraday did, as you know, accompany Davy to Rome: he was re-engaged
+by the managers of the Royal Institution on May 15, 1815. Here he made
+rapid progress in chemistry, and after a time was entrusted with easy
+analyses by Davy. In those days the Royal Institution published 'The
+Quarterly Journal of Science,' the precursor of our own 'Proceedings.'
+Faraday's first contribution to science appeared in that journal in
+1816. It was an analysis of some caustic lime from Tuscany, which had
+been sent to Davy by the Duchess of Montrose. Between this period and
+1818 various notes and short papers were published by Faraday. In 1818
+he experimented upon 'Sounding Flames.' Professor Auguste De la Rive
+had investigated those sounding flames, and had applied to them an
+explanation which completely accounted for a class of sounds discovered
+by himself, but did not account for those known to his predecessors. By
+a few simple and conclusive experiments, Faraday proved the explanation
+insufficient. It is an epoch in the life of a young man when he finds
+himself correcting a person of eminence, and in Faraday's case, where
+its effect was to develop a modest self-trust, such an event could not
+fail to act profitably.
+
+From time to time between 1818 and 1820 Faraday published scientific
+notes and notices of minor weight. At this time he was acquiring, not
+producing; working hard for his master and storing and strengthening
+his own mind. He assisted Mr. Brande in his lectures, and so quietly,
+skilfully, and modestly was his work done, that Mr. Brande's vocation at
+the time was pronounced 'lecturing on velvet.' In 1820 Faraday published
+a chemical paper 'on two new compounds of chlorine and carbon, and on
+a new compound of iodine, carbon, and hydrogen.' This paper was read
+before the Royal Society on December 21, 1820, and it was the first of
+his that was honoured with a place in the 'Philosophical Transactions.'
+
+On June 12, 1821, he married, and obtained leave to bring his young wife
+into his rooms at the Royal Institution. There for forty-six years
+they lived together, occupying the suite of apartments which had been
+previously in the successive occupancy of Young, Davy, and Brande. At
+the time of her marriage Mrs. Faraday was twenty-one years of age, he
+being nearly thirty. Regarding this marriage I will at present limit
+myself to quoting an entry written in Faraday's own hand in his book of
+diplomas, which caught my eye while in his company some years ago. It
+ran thus:--
+
+'25th January, 1847. 'Amongst these records and events, I here insert
+the date of one which, as a source of honour and happiness, far exceeds
+all the rest. We were married on June 12, 1821.
+
+'M. Faraday.'
+
+Then follows the copy of the minutes, dated May 21, 1821, which gave him
+additional rooms, and thus enabled him to bring his wife to the Royal
+Institution. A feature of Faraday's character which I have often noticed
+makes itself apparent in this entry. In his relations to his wife he
+added chivalry to affection.
+
+
+Footnotes to Chapter 1
+
+     [1] Here is Davy's recommendation of Faraday, presented to
+     the managers of the Royal Institution, at a meeting on the
+     18th of March, 1813, Charles Hatchett, Esq., in the chair:--
+
+     '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.  As far as Sir H. Davy has been able to
+     observe or ascertain, he appears well fitted for the
+     situation.  His habits seem good; his disposition active and
+     cheerful, and his manner intelligent.  He is willing to
+     engage himself on the same terms as 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.'
+
+     [2] Faraday loved this word and employed it to the last; he
+     had an intense dislike to the modern term physicist.
+
+     [3] To whom I am indebted for a copy of the original letter.
+
+
+
+
+Chapter 2.
+
+     Early researches: magnetic rotations: liquefaction of gases:
+     heavy glass: Charles Anderson: contributions to physics.
+
+Oersted, in 1820, discovered the action of a voltaic current on a
+magnetic needle; and immediately afterwards the splendid intellect of
+Ampere succeeded in showing that every magnetic phenomenon then known
+might be reduced to the mutual action of electric currents. The subject
+occupied all men's thoughts: and in this country Dr. Wollaston sought
+to convert the deflection of the needle by the current into a permanent
+rotation of the needle round the current. He also hoped to produce the
+reciprocal effect of causing a current to rotate round a magnet. In
+the early part of 1821, Wollaston attempted to realise this idea in
+the presence of Sir Humphry Davy in the laboratory of the Royal
+Institution.[1] This was well calculated to attract Faraday's attention
+to the subject. He read much about it; and in the months of July,
+August, and September he wrote a 'history of the progress of
+electro-magnetism,' which he published in Thomson's 'Annals of
+Philosophy.' Soon afterwards he took up the subject of 'Magnetic
+Rotations,' and on the morning of Christmas-day, 1821, he called his
+wife to witness, for the first time, the revolution of a magnetic needle
+round an electric current. Incidental to the 'historic sketch,' he
+repeated almost all the experiments there referred to; and these, added
+to his own subsequent work, made him practical master of all that was
+then known regarding the voltaic current. In 1821, he also touched
+upon a subject which subsequently received his closer attention--the
+vaporization of mercury at common temperatures; and immediately
+afterwards conducted, in company with Mr. Stodart, experiments on the
+alloys of steel. He was accustomed in after years to present to his
+friends razors formed from one of the alloys then discovered.
+
+During Faraday's hours of liberty from other duties, he took up subjects
+of inquiry for himself; and in the spring of 1823, thus self-prompted,
+he began the examination of a substance which had long been regarded as
+the chemical element chlorine, in a solid form, but which Sir Humphry
+Davy, in 1810, had proved to be a hydrate of chlorine, that is, a
+compound of chlorine and water. Faraday first analysed this hydrate, and
+wrote out an account of its composition. This account was looked over
+by Davy, who suggested the heating of the hydrate under pressure in a
+sealed glass tube. This was done. The hydrate fused at a blood-heat, the
+tube became filled with a yellow atmosphere, and was afterwards found
+to contain two liquid substances. Dr. Paris happened to enter the
+laboratory while Faraday was at work. Seeing the oily liquid in his
+tube, he rallied the young chemist for his carelessness in employing
+soiled vessels. On filing off the end of the tube, its contents exploded
+and the oily matter vanished. Early next morning, Dr. Paris received the
+following note:--
+
+'Dear Sir,--The oil you noticed yesterday turns out to be liquid
+chlorine.
+
+'Yours faithfully,
+
+'M. Faraday.'[2]
+
+The gas had been liquefied by its own pressure. Faraday then tried
+compression with a syringe, and succeeded thus in liquefying the gas.
+
+To the published account of this experiment Davy added the following
+note:--'In desiring Mr. Faraday to expose the hydrate of chlorine in
+a closed glass tube, it occurred to me that one of three things would
+happen: that decomposition of water would occur;... or that the chlorine
+would separate in a fluid state.' Davy, moreover, immediately applied
+the method of self-compressing atmosphere to the liquefaction of
+muriatic gas. Faraday continued the experiments, and succeeded in
+reducing a number of gases till then deemed permanent to the liquid
+condition. In 1844 he returned to the subject, and considerably expanded
+its limits. These important investigations established the fact
+that gases are but the vapours of liquids possessing a very low
+boiling-point, and gave a sure basis to our views of molecular
+aggregation. The account of the first investigation was read before the
+Royal Society on April 10, 1823, and was published, in Faraday's name,
+in the 'Philosophical Transactions.' The second memoir was sent to
+the Royal Society on December 19, 1844. I may add that while he was
+conducting his first experiments on the liquefaction of gases, thirteen
+pieces of glass were on one occasion driven by an explosion into
+Faraday's eye.
+
+Some small notices and papers, including the observation that glass
+readily changes colour in sunlight, follow here. In 1825 and 1826
+Faraday published papers in the 'Philosophical Transactions' on 'new
+compounds of carbon and hydrogen,' and on 'sulphonaphthalic acid.' In
+the former of these papers he announced the discovery of Benzol, which,
+in the hands of modern chemists, has become the foundation of our
+splendid aniline dyes. But he swerved incessantly from chemistry into
+physics; and in 1826 we find him engaged in investigating the limits
+of vaporization, and showing, by exceedingly strong and apparently
+conclusive arguments, that even in the case of mercury such a limit
+exists; much more he conceived it to be certain that our atmosphere does
+not contain the vapour of the fixed constituents of the earth's crust.
+This question, I may say, is likely to remain an open one. Dr. Rankine,
+for example, has lately drawn attention to the odour of certain metals;
+whence comes this odour, if it be not from the vapour of the metal?
+
+In 1825 Faraday became a member of a committee, to which Sir John
+Herschel and Mr. Dollond also belonged, appointed by the Royal Society
+to examine, and if possible improve, the manufacture of glass for
+optical purposes. Their experiments continued till 1829, when the
+account of them constituted the subject of a 'Bakerian Lecture.' This
+lectureship, founded in 1774 by Henry Baker, Esq., of the Strand,
+London, provides that every year a lecture shall be given before the
+Royal Society, the sum of four pounds being paid to the lecturer. The
+Bakerian Lecture, however, has long since passed from the region of
+pay to that of honour, papers of mark only being chosen for it by
+the council of the Society. Faraday's first Bakerian Lecture, 'On the
+Manufacture of Glass for Optical Purposes,' was delivered at the
+close of 1829. It is a most elaborate and conscientious description of
+processes, precautions, and results: the details were so exact and
+so minute, and the paper consequently so long, that three successive
+sittings of the Royal Society were taken up by the delivery of the
+lecture.[3] This glass did not turn out to be of important practical
+use, but it happened afterwards to be the foundation of two of Faraday's
+greatest discoveries.[4]
+
+The experiments here referred to were commenced at the Falcon Glass
+Works, on the premises of Messrs. Green and Pellatt, but Faraday could
+not conveniently attend to them there. In 1827, therefore, a furnace was
+erected in the yard of the Royal Institution; and it was at this time,
+and with a view of assisting him at the furnace, that Faraday engaged
+Sergeant Anderson, of the Royal Artillery, the respectable, truthful,
+and altogether trustworthy man whose appearance here is so fresh in our
+memories. Anderson continued to be the reverential helper of Faraday and
+the faithful servant of this Institution for nearly forty years.[5]
+
+In 1831 Faraday published a paper, 'On a peculiar class of Optical
+Deceptions,' to which I believe the beautiful optical toy called the
+Chromatrope owes its origin. In the same year he published a paper on
+Vibrating Surfaces, in which he solved an acoustical problem which,
+though of extreme simplicity when solved, appears to have baffled many
+eminent men. The problem was to account for the fact that light bodies,
+such as the seed of lycopodium, collected at the vibrating parts of
+sounding plates, while sand ran to the nodal lines. Faraday showed that
+the light bodies were entangled in the little whirlwinds formed in the
+air over the places of vibration, and through which the heavier sand
+was readily projected. Faraday's resources as an experimentalist were so
+wonderful, and his delight in experiment was so great, that he sometimes
+almost ran into excess in this direction. I have heard him say that this
+paper on vibrating surfaces was too heavily laden with experiments.
+
+
+Footnotes to Chapter 2
+
+     [1] The reader's attention is directed to the concluding
+     paragraph of the 'Preface to the Second Edition written in
+     December, 1869. Also to the Life of Faraday by Dr. Bence
+     Jones, vol. i. p. 338 et seq.
+
+     [2] Paris: Life of Davy, p. 391.
+
+     [3] Viz., November 19, December 3 and 10.
+
+     [4] I make the following extract from a letter from Sir John
+     Herschel, written to me from Collingwood, on the 3rd of
+     November, 1867:--'I will take this opportunity to mention
+     that I believe myself to have originated the suggestion of
+     the employment of borate of lead for optical purposes.  It
+     was somewhere in the year 1822, as well as I can recollect,
+     that I mentioned it to Sir James (then Mr.) South; and, in
+     consequence, the trial was made in his laboratory in
+     Blackman Street, by precipitating and working a large
+     quantity of borate of lead, and fusing it under a muffle in
+     a porcelain evaporating dish.  A very limpid (though
+     slightly yellow) glass resulted, the refractive index 1.866!
+     (which you will find set down in my table of refractive
+     indices in my article "Light," Encyclopaedia Metropolitana).
+     It was, however, too soft for optical use as an object-
+     glass.  This Faraday overcame, at least to a considerable
+     degree, by the introduction of silica.'
+
+     [5] Regarding Anderson, Faraday writes thus in 1845:--'I
+     cannot resist the occasion that is thus offered to me of
+     mentioning the name of Mr. Anderson, who came to me as an
+     assistant in the glass experiments, and has remained ever
+     since in the laboratory of the Royal Institution.  He
+     assisted me in all the researches into which I have entered
+     since that time; and to his care, steadiness, exactitude,
+     and faithfulness in the performance of all that has been
+     committed to his charge, I am much indebted.--M. F.' (Exp.
+     Researches, vol. iii. p. 3, footnote.)
+
+
+
+
+Chapter 3.
+
+     Discovery of Magneto-electricity: Explanation of Argo's
+     magnetism of rotation: Terrestrial magneto-electric
+     induction: The extra current.
+
+The work thus referred to, though sufficient of itself to secure no
+mean scientific reputation, forms but the vestibule of Faraday's
+achievements. He had been engaged within these walls for eighteen years.
+During part of the time he had drunk in knowledge from Davy, and during
+the remainder he continually exercised his capacity for independent
+inquiry. In 1831 we have him at the climax of his intellectual strength,
+forty years of age, stored with knowledge and full of original power.
+Through reading, lecturing, and experimenting, he had become thoroughly
+familiar with electrical science: he saw where light was needed and
+expansion possible. The phenomena of ordinary electric induction
+belonged, as it were, to the alphabet of his knowledge: he knew that
+under ordinary circumstances the presence of an electrified body was
+sufficient to excite, by induction, an unelectrified body. He knew that
+the wire which carried an electric current was an electrified body, and
+still that all attempts had failed to make it excite in other wires a
+state similar to its own.
+
+What was the reason of this failure? Faraday never could work from the
+experiments of others, however clearly described. He knew well that
+from every experiment issues a kind of radiation, luminous in different
+degrees to different minds, and he hardly trusted himself to reason upon
+an experiment that he had not seen. In the autumn of 1831 he began to
+repeat the experiments with electric currents, which, up to that time,
+had produced no positive result. And here, for the sake of younger
+inquirers, if not for the sake of us all, it is worth while to dwell for
+a moment on a power which Faraday possessed in an extraordinary degree.
+He united vast strength with perfect flexibility. His momentum was that
+of a river, which combines weight and directness with the ability to
+yield to the flexures of its bed. The intentness of his vision in any
+direction did not apparently diminish his power of perception in other
+directions; and when he attacked a subject, expecting results he had the
+faculty of keeping his mind alert, so that results different from those
+which he expected should not escape him through preoccupation.
+
+He began his experiments 'on the induction of electric currents' by
+composing a helix of two insulated wires which were wound side by side
+round the same wooden cylinder. One of these wires he connected with
+a voltaic battery of ten cells, and the other with a sensitive
+galvanometer. When connection with the battery was made, and while the
+current flowed, no effect whatever was observed at the galvanometer. But
+he never accepted an experimental result, until he had applied to it the
+utmost power at his command. He raised his battery from 10 cells to 120
+cells, but without avail. The current flowed calmly through the battery
+wire without producing, during its flow, any sensible result upon the
+galvanometer.
+
+'During its flow,' and this was the time when an effect was
+expected--but here Faraday's power of lateral vision, separating, as it
+were, from the line of expectation, came into play--he noticed that a
+feeble movement of the needle always occurred at the moment when he made
+contact with the battery; that the needle would afterwards return to
+its former position and remain quietly there unaffected by the flowing
+current. At the moment, however, when the circuit was interrupted the
+needle again moved, and in a direction opposed to that observed on the
+completion of the circuit.
+
+This result, and others of a similar kind, led him to the conclusion
+'that the battery current through the one wire did in reality induce a
+similar current through the other; but that it continued for an instant
+only, and partook more of the nature of the electric wave from a common
+Leyden jar than of the current from a voltaic battery.' The momentary
+currents thus generated were called induced currents, while the current
+which generated them was called the inducing current. It was immediately
+proved that the current generated at making the circuit was always
+opposed in direction to its generator, while that developed on the
+rupture of the circuit coincided in direction with the inducing current.
+It appeared as if the current on its first rush through the primary wire
+sought a purchase in the secondary one, and, by a kind of kick, impelled
+backward through the latter an electric wave, which subsided as soon as
+the primary current was fully established.
+
+Faraday, for a time, believed that the secondary wire, though quiescent
+when the primary current had been once established, was not in its
+natural condition, its return to that condition being declared by the
+current observed at breaking the circuit. He called this hypothetical
+state of the wire the electro-tonic state: he afterwards abandoned
+this hypothesis, but seemed to return to it in later life. The term
+electro-tonic is also preserved by Professor Du Bois Reymond to express
+a certain electric condition of the nerves, and Professor Clerk Maxwell
+has ably defined and illustrated the hypothesis in the Tenth Volume of
+the 'Transactions of the Cambridge Philosophical Society.'
+
+The mere approach of a wire forming a closed curve to a second wire
+through which a voltaic current flowed was then shown by Faraday to be
+sufficient to arouse in the neutral wire an induced current, opposed
+in direction to the inducing current; the withdrawal of the wire also
+generated a current having the same direction as the inducing current;
+those currents existed only during the time of approach or withdrawal,
+and when neither the primary nor the secondary wire was in motion,
+no matter how close their proximity might be, no induced current was
+generated.
+
+Faraday has been called a purely inductive philosopher. A great deal of
+nonsense is, I fear, uttered in this land of England about induction and
+deduction. Some profess to befriend the one, some the other, while
+the real vocation of an investigator, like Faraday, consists in the
+incessant marriage of both. He was at this time full of the theory of
+Ampere, and it cannot be doubted that numbers of his experiments were
+executed merely to test his deductions from that theory. Starting from
+the discovery of Oersted, the illustrious French philosopher had shown
+that all the phenomena of magnetism then known might be reduced to the
+mutual attractions and repulsions of electric currents. Magnetism had
+been produced from electricity, and Faraday, who all his life long
+entertained a strong belief in such reciprocal actions, now attempted to
+effect the evolution of electricity from magnetism. Round a welded iron
+ring he placed two distinct coils of covered wire, causing the coils to
+occupy opposite halves of the ring. Connecting the ends of one of
+the coils with a galvanometer, he found that the moment the ring
+was magnetised, by sending a current through the other coil, the
+galvanometer needle whirled round four or five times in succession. The
+action, as before, was that of a pulse, which vanished immediately.
+On interrupting the circuit, a whirl of the needle in the opposite
+direction occurred. It was only during the time of magnetization or
+demagnetization that these effects were produced. The induced currents
+declared a change of condition only, and they vanished the moment the
+act of magnetization or demagnetization was complete.
+
+The effects obtained with the welded ring were also obtained with
+straight bars of iron. Whether the bars were magnetised by the electric
+current, or were excited by the contact of permanent steel magnets,
+induced currents were always generated during the rise, and during the
+subsidence of the magnetism. The use of iron was then abandoned, and the
+same effects were obtained by merely thrusting a permanent steel magnet
+into a coil of wire. A rush of electricity through the coil accompanied
+the insertion of the magnet; an equal rush in the opposite direction
+accompanied its withdrawal. The precision with which Faraday describes
+these results, and the completeness with which he defines the boundaries
+of his facts, are wonderful. The magnet, for example, must not be passed
+quite through the coil, but only half through; for if passed wholly
+through, the needle is stopped as by a blow, and then he shows how this
+blow results from a reversal of the electric wave in the helix. He next
+operated with the powerful permanent magnet of the Royal Society, and
+obtained with it, in an exalted degree, all the foregoing phenomena.
+
+And now he turned the light of these discoveries upon the darkest
+physical phenomenon of that day. Arago had discovered, in 1824, that
+a disk of non-magnetic metal had the power of bringing a vibrating
+magnetic needle suspended over it rapidly to rest; and that on causing
+the disk to rotate the magnetic needle rotated along with it. When both
+were quiescent, there was not the slightest measurable attraction or
+repulsion exerted between the needle and the disk; still when in motion
+the disk was competent to drag after it, not only a light needle, but
+a heavy magnet. The question had been probed and investigated with
+admirable skill both by Arago and Ampere, and Poisson had published a
+theoretic memoir on the subject; but no cause could be assigned for so
+extraordinary an action. It had also been examined in this country by
+two celebrated men, Mr. Babbage and Sir John Herschel; but it still
+remained a mystery. Faraday always recommended the suspension of
+judgment in cases of doubt. 'I have always admired,' he says, 'the
+prudence and philosophical reserve shown by M. Arago in resisting the
+temptation to give a theory of the effect he had discovered, so long
+as he could not devise one which was perfect in its application, and in
+refusing to assent to the imperfect theories of others.' Now, however,
+the time for theory had come. Faraday saw mentally the rotating disk,
+under the operation of the magnet, flooded with his induced currents,
+and from the known laws of interaction between currents and magnets he
+hoped to deduce the motion observed by Arago. That hope he realised,
+showing by actual experiment that when his disk rotated currents
+passed through it, their position and direction being such as must, in
+accordance with the established laws of electro-magnetic action, produce
+the observed rotation.
+
+Introducing the edge of his disk between the poles of the large
+horseshoe magnet of the Royal Society, and connecting the axis and the
+edge of the disk, each by a wire with a galvanometer, he obtained, when
+the disk was turned round, a constant flow of electricity. The direction
+of the current was determined by the direction of the motion, the
+current being reversed when the rotation was reversed. He now states the
+law which rules the production of currents in both disks and wires, and
+in so doing uses, for the first time, a phrase which has since become
+famous. When iron filings are scattered over a magnet, the particles
+of iron arrange themselves in certain determinate lines called magnetic
+curves. In 1831, Faraday for the first time called these curves 'lines
+of magnetic force'; and he showed that to produce induced currents
+neither approach to nor withdrawal from a magnetic source, or centre, or
+pole, was essential, but that it was only necessary to cut appropriately
+the lines of magnetic force. Faraday's first paper on Magneto-electric
+Induction, which I have here endeavoured to condense, was read before
+the Royal Society on the 24th of November, 1831.
+
+On January 12, 1832, he communicated to the Royal Society a second
+paper on Terrestrial Magneto-electric Induction, which was chosen as
+the Bakerian Lecture for the year. He placed a bar of iron in a coil of
+wire, and lifting the bar into the direction of the dipping needle, he
+excited by this action a current in the coil. On reversing the bar,
+a current in the opposite direction rushed through the wire. The same
+effect was produced when, on holding the helix in the line of dip, a bar
+of iron was thrust into it. Here, however, the earth acted on the coil
+through the intermediation of the bar of iron. He abandoned the bar and
+simply set a copper plate spinning in a horizontal plane; he knew that
+the earth's lines of magnetic force then crossed the plate at an angle
+of about 70degrees. When the plate spun round, the lines of force were
+intersected and induced currents generated, which produced their proper
+effect when carried from the plate to the galvanometer. 'When the plate
+was in the magnetic meridian, or in any other plane coinciding with
+the magnetic dip, then its rotation produced no effect upon the
+galvanometer.'
+
+At the suggestion of a mind fruitful in suggestions of a profound and
+philosophic character--I mean that of Sir John Herschel--Mr. Barlow, of
+Woolwich, had experimented with a rotating iron shell. Mr. Christie had
+also performed an elaborate series of experiments on a rotating iron
+disk. Both of them had found that when in rotation the body exercised
+a peculiar action upon the magnetic needle, deflecting it in a manner
+which was not observed during quiescence; but neither of them was aware
+at the time of the agent which produced this extraordinary deflection.
+They ascribed it to some change in the magnetism of the iron shell and
+disk.
+
+But Faraday at once saw that his induced currents must come into play
+here, and he immediately obtained them from an iron disk. With a hollow
+brass ball, moreover, he produced the effects obtained by Mr. Barlow.
+Iron was in no way necessary: the only condition of success was that
+the rotating body should be of a character to admit of the formation of
+currents in its substance: it must, in other words, be a conductor of
+electricity. The higher the conducting power the more copious were the
+currents. He now passes from his little brass globe to the globe of the
+earth. He plays like a magician with the earth's magnetism. He sees the
+invisible lines along which its magnetic action is exerted, and sweeping
+his wand across these lines evokes this new power. Placing a simple loop
+of wire round a magnetic needle he bends its upper portion to the west:
+the north pole of the needle immediately swerves to the east: he bends
+his loop to the east, and the north pole moves to the west. Suspending a
+common bar magnet in a vertical position, he causes it to spin round its
+own axis. Its pole being connected with one end of a galvanometer
+wire, and its equator with the other end, electricity rushes round the
+galvanometer from the rotating magnet. He remarks upon the 'singular
+independence' of the magnetism and the body of the magnet which carries
+it. The steel behaves as if it were isolated from its own magnetism.
+
+And then his thoughts suddenly widen, and he asks himself whether the
+rotating earth does not generate induced currents as it turns round its
+axis from west to east. In his experiment with the twirling magnet the
+galvanometer wire remained at rest; one portion of the circuit was in
+motion relatively to another portion. But in the case of the twirling
+planet the galvanometer wire would necessarily be carried along with the
+earth; there would be no relative motion. What must be the consequence?
+Take the case of a telegraph wire with its two terminal plates dipped
+into the earth, and suppose the wire to lie in the magnetic meridian.
+The ground underneath the wire is influenced like the wire itself by the
+earth's rotation; if a current from south to north be generated in the
+wire, a similar current from south to north would be generated in the
+earth under the wire; these currents would run against the same terminal
+plate, and thus neutralise each other.
+
+This inference appears inevitable, but his profound vision perceived
+its possible invalidity. He saw that it was at least possible that the
+difference of conducting power between the earth and the wire might
+give one an advantage over the other, and that thus a residual or
+differential current might be obtained. He combined wires of different
+materials, and caused them to act in opposition to each other, but
+found the combination ineffectual. The more copious flow in the better
+conductor was exactly counterbalanced by the resistance of the worse.
+Still, though experiment was thus emphatic, he would clear his mind of
+all discomfort by operating on the earth itself. He went to the round
+lake near Kensington Palace, and stretched 480 feet of copper wire,
+north and south, over the lake, causing plates soldered to the wire
+at its ends to dip into the water. The copper wire was severed at the
+middle, and the severed ends connected with a galvanometer. No effect
+whatever was observed. But though quiescent water gave no effect, moving
+water might. He therefore worked at London Bridge for three days during
+the ebb and flow of the tide, but without any satisfactory result. Still
+he urges, 'Theoretically it seems a necessary consequence, that where
+water is flowing there electric currents should be formed. If a line
+be imagined passing from Dover to Calais through the sea, and returning
+through the land, beneath the water, to Dover, it traces out a circuit
+of conducting matter one part of which, when the water moves up or down
+the channel, is cutting the magnetic curves of the earth, whilst the
+other is relatively at rest.... There is every reason to believe that
+currents do run in the general direction of the circuit described,
+either one way or the other, according as the passage of the waters is
+up or down the channel.' This was written before the submarine cable was
+thought of, and he once informed me that actual observation upon
+that cable had been found to be in accordance with his theoretic
+deduction.[1]
+
+Three years subsequent to the publication of these researches--that is
+to say, on January 29, 1835--Faraday read before the Royal Society
+a paper 'On the influence by induction of an electric current upon
+itself.' A shock and spark of a peculiar character had been observed
+by a young man named William Jenkin, who must have been a youth of some
+scientific promise, but who, as Faraday once informed me, was dissuaded
+by his own father from having anything to do with science. The
+investigation of the fact noticed by Mr. Jenkin led Faraday to the
+discovery of the extra current, or the current induced in the primary
+wire itself at the moments of making and breaking contact, the phenomena
+of which he described and illustrated in the beautiful and exhaustive
+paper referred to.
+
+Seven-and-thirty years have passed since the discovery of
+magneto-electricity; but, if we except the extra current, until quite
+recently nothing of moment was added to the subject. Faraday entertained
+the opinion that the discoverer of a great law or principle had a right
+to the 'spoils'--this was his term--arising from its illustration; and
+guided by the principle he had discovered, his wonderful mind, aided by
+his wonderful ten fingers, overran in a single autumn this vast domain,
+and hardly left behind him the shred of a fact to be gathered by his
+successors.
+
+And here the question may arise in some minds, What is the use of
+it all? The answer is, that if man's intellectual nature thirsts for
+knowledge, then knowledge is useful because it satisfies this thirst. If
+you demand practical ends, you must, I think, expand your definition of
+the term practical, and make it include all that elevates and enlightens
+the intellect, as well as all that ministers to the bodily health and
+comfort of men. Still, if needed, an answer of another kind might be
+given to the question 'What is its use?' As far as electricity has been
+applied for medical purposes, it has been almost exclusively Faraday's
+electricity. You have noticed those lines of wire which cross the
+streets of London. It is Faraday's currents that speed from place to
+place through these wires. Approaching the point of Dungeness, the
+mariner sees an unusually brilliant light, and from the noble phares
+of La Heve the same light flashes across the sea. These are Faraday's
+sparks exalted by suitable machinery to sunlike splendour. At the
+present moment the Board of Trade and the Brethren of the Trinity House,
+as well as the Commissioners of Northern Lights, are contemplating the
+introduction of the Magneto-electric Light at numerous points upon our
+coasts; and future generations will be able to refer to those guiding
+stars in answer to the question. What has been the practical use of the
+labours of Faraday? But I would again emphatically say, that his work
+needs no such justification, and that if he had allowed his vision to
+be disturbed by considerations regarding the practical use of his
+discoveries, those discoveries would never have been made by him. 'I
+have rather,' he writes in 1831, 'been desirous of discovering new
+facts and new relations dependent on magneto-electric induction, than
+of exalting the force of those already obtained; being assured that the
+latter would find their full development hereafter.'
+
+In 1817, when lecturing before a private society in London on the
+element chlorine, Faraday thus expressed himself with reference to this
+question of utility. 'Before leaving this subject, I will point out the
+history of this substance, as an answer to those who are in the habit of
+saying to every new fact. "What is its use?" Dr. Franklin says to such,
+"What is the use of an infant?" The answer of the experimentalist is,
+"Endeavour to make it useful." When Scheele discovered this substance,
+it appeared to have no use; it was in its infancy and useless state, but
+having grown up to maturity, witness its powers, and see what endeavours
+to make it useful have done.'
+
+
+Footnote to Chapter 3
+
+     [1] I am indebted to a friend for the following exquisite
+     morsel:--'A short time after the publication of Faraday's
+     first researches in magneto-electricity, he attended the
+     meeting of the British Association at Oxford, in 1832.  On
+     this occasion he was requested by some of the authorities to
+     repeat the celebrated experiment of eliciting a spark from a
+     magnet, employing for this purpose the large magnet in the
+     Ashmolean Museum.  To this he consented, and a large party
+     assembled to witness the experiments, which, I need not say,
+     were perfectly successful.  Whilst he was repeating them a
+     dignitary of the University entered the room, and addressing
+     himself to Professor Daniell, who was standing near Faraday,
+     inquired what was going on.  The Professor explained to him
+     as popularly as possible this striking result of Faraday's
+     great discovery. The Dean listened with attention and looked
+     earnestly at the brilliant spark, but a moment after he
+     assumed a serious countenance and shook his head; "I am
+     sorry for it," said he, as he walked away; in the middle of
+     the room he stopped for a moment and repeated, "I am sorry
+     for it:" then walking towards the door, when the handle was
+     in his hand he turned round and said, "Indeed I am sorry for
+     it; it is putting new arms into the hands of the
+     incendiary."  This occurred a short time after the papers
+     had been filled with the doings of the hayrick burners.  An
+     erroneous statement of what fell from the Dean's mouth was
+     printed at the time in one of the Oxford papers. He is there
+     wrongly stated to have said, "It is putting new arms into
+     the hands of the infidel."'
+
+
+
+
+Chapter 4.
+
+     Points of Character.
+
+A point highly illustrative of the character of Faraday now comes into
+view. He gave an account of his discovery of Magneto-electricity in a
+letter to his friend M. Hachette, of Paris, who communicated the letter
+to the Academy of Sciences. The letter was translated and published; and
+immediately afterwards two distinguished Italian philosophers took up
+the subject, made numerous experiments, and published their results
+before the complete memoirs of Faraday had met the public eye. This
+evidently irritated him. He reprinted the paper of the learned Italians
+in the 'Philosophical Magazine,' accompanied by sharp critical notes
+from himself. He also wrote a letter dated Dec. 1, 1832, to Gay Lussac,
+who was then one of the editors of the 'Annales de Chimie,' in which
+he analysed the results of the Italian philosophers, pointing out their
+errors, and defending himself from what he regarded as imputations on
+his character. The style of this letter is unexceptionable, for Faraday
+could not write otherwise than as a gentleman; but the letter shows that
+had he willed it he could have hit hard. We have heard much of Faraday's
+gentleness and sweetness and tenderness. It is all true, but it is very
+incomplete. You cannot resolve a powerful nature into these elements,
+and Faraday's character would have been less admirable than it was had
+it not embraced forces and tendencies to which the silky adjectives
+'gentle' and 'tender' would by no means apply. Underneath his sweetness
+and gentleness was the heat of a volcano. He was a man of excitable and
+fiery nature; but through high self-discipline he had converted the fire
+into a central glow and motive power of life, instead of permitting it
+to waste itself in useless passion. 'He that is slow to anger,' saith
+the sage, 'is greater than the mighty, and he that ruleth his own spirit
+than he that taketh a city.' Faraday was not slow to anger, but he
+completely ruled his own spirit, and thus, though he took no cities, he
+captivated all hearts.
+
+As already intimated, Faraday had contributed many of his minor
+papers--including his first analysis of caustic lime--to the 'Quarterly
+Journal of Science.' In 1832, he collected those papers and others
+together in a small octavo volume, labelled them, and prefaced them
+thus:--
+
+'PAPERS, NOTES, NOTICES, &c., &c.,published in octavo, up to 1832. M.
+Faraday.'
+
+'Papers of mine, published in octavo, in the "Quarterly Journal of
+Science," and elsewhere, since the time that Sir H. Davy encouraged me
+to write the analysis of caustic lime.
+
+'Some, I think (at this date), are good; others moderate; and some bad.
+But I have put all into the volume, because of the utility they have
+been of to me--and none more than the bad--in pointing out to me in
+future, or rather, after times, the faults it became me to watch and to
+avoid.
+
+'As I never looked over one of my papers a year after it was written
+without believing both in philosophy and manner it could have been much
+better done, I still hope the collection may be of great use to me.
+
+'M. Faraday.
+
+'Aug. 18, 1832.'
+
+'None more than the bad!' This is a bit of Faraday's innermost nature;
+and as I read these words I am almost constrained to retract what I have
+said regarding the fire and excitability of his character. But is he not
+all the more admirable, through his ability to tone down and subdue that
+fire and that excitability, so as to render himself able to write thus
+as a little child? I once took the liberty of censuring the conclusion
+of a letter of his to the Dean of St. Paul's. He subscribed himself
+'humbly yours,' and I objected to the adverb. 'Well, but, Tyndall,' he
+said, 'I am humble; and still it would be a great mistake to think that
+I am not also proud.' This duality ran through his character. A democrat
+in his defiance of all authority which unfairly limited his freedom of
+thought, and still ready to stoop in reverence to all that was really
+worthy of reverence, in the customs of the world or the characters of
+men.
+
+And here, as well as elsewhere, may be introduced a letter which bears
+upon this question of self-control, written long years subsequent to the
+period at which we have now arrived. I had been at Glasgow in 1855, at
+a meeting of the British Association. On a certain day, I communicated a
+paper to the physical section, which was followed by a brisk discussion.
+Men of great distinction took part in it, the late Dr. Whewell among the
+number, and it waxed warm on both sides. I was by no means content
+with this discussion; and least of all, with my own part in it. This
+discontent affected me for some days, during which I wrote to
+Faraday, giving him no details, but expressing, in a general way, my
+dissatisfaction. I give the following extract from his reply:--
+
+'Sydenham, Oct. 6, 1855.
+
+'My Dear Tyndall,--These great meetings, of which I think very well
+altogether, advance science chiefly by bringing scientific men together
+and making them to know and be friends with each other; and I am sorry
+when that is not the effect in every part of their course. I know
+nothing except from what you tell me, for I have not yet looked at the
+reports of the proceedings; but let me, as an old man, who ought by this
+time to have profited by experience, say that when I was younger I found
+I often misinterpreted the intentions of people, and found they did not
+mean what at the time I supposed they meant; and, further, that as a
+general rule, it was better to be a little dull of apprehension where
+phrases seemed to imply pique, and quick in perception when, on the
+contrary, they seemed to imply kindly feeling. The real truth never
+fails ultimately to appear; and opposing parties, if wrong, are sooner
+convinced when replied to forbearingly, than when overwhelmed. All
+I mean to say is, that it is better to be blind to the results of
+partisanship, and quick to see good will. One has more happiness in
+oneself in endeavouring to follow the things that make for peace. You
+can hardly imagine how often I have been heated in private when opposed,
+as I have thought, unjustly and superciliously, and yet I have striven,
+and succeeded, I hope, in keeping down replies of the like kind. And I
+know I have never lost by it. I would not say all this to you did I not
+esteem you as a true philosopher and friend.[1]
+
+'Yours, very truly,
+
+'M. Faraday.'
+
+
+Footnote to Chapter 4
+
+     [1] Faraday would have been rejoiced to learn that, during
+     its last meeting at Dundee, the British Association
+     illustrated in a striking manner the function which he here
+     describes as its principal one. In my own case, a brotherly
+     welcome was everywhere manifested. In fact, the differences
+     of really honourable and sane men are never beyond healing.
+
+
+
+
+Chapter 5.
+
+     Identity of electricities; first researches on
+     electro-chemistry.
+
+I have already once used the word 'discomfort' in reference to the
+occasional state of Faraday's mind when experimenting. It was to him a
+discomfort to reason upon data which admitted of doubt. He hated what he
+called 'doubtful knowledge,' and ever tended either to transfer it
+into the region of undoubtful knowledge, or of certain and definite
+ignorance. Pretence of all kinds, whether in life or in philosophy, was
+hateful to him. He wished to know the reality of our nescience as well
+as of our science. 'Be one thing or the other,' he seemed to say to
+an unproved hypothesis; 'come out as a solid truth, or disappear as a
+convicted lie.' After making the great discovery which I have attempted
+to describe, a doubt seemed to beset him as regards the identity of
+electricities. 'Is it right,' he seemed to ask, 'to call this agency
+which I have discovered electricity at all? Are there perfectly
+conclusive grounds for believing that the electricity of the
+machine, the pile, the gymnotus and torpedo, magneto-electricity and
+thermo-electricity, are merely different manifestations of one and the
+same agent?' To answer this question to his own satisfaction he formally
+reviewed the knowledge of that day. He added to it new experiments
+of his own, and finally decided in favour of the 'Identity of
+Electricities.' His paper upon this subject was read before the Royal
+Society on January 10 and 17, 1833.
+
+After he had proved to his own satisfaction the identity of
+electricities, he tried to compare them quantitatively together. The
+terms quantity and intensity, which Faraday constantly used, need a word
+of explanation here. He might charge a single Leyden jar by twenty turns
+of his machine, or he might charge a battery of ten jars by the same
+number of turns. The quantity in both cases would be sensibly the same,
+but the intensity of the single jar would be the greatest, for here the
+electricity would be less diffused. Faraday first satisfied himself that
+the needle of his galvanometer was caused to swing through the same arc
+by the same quantity of machine electricity, whether it was condensed
+in a small battery or diffused over a large one. Thus the electricity
+developed by thirty turns of his machine produced, under very variable
+conditions of battery surface, the same deflection. Hence he inferred
+the possibility of comparing, as regards quantity, electricities which
+differ greatly from each other in intensity. His object now is to
+compare frictional with voltaic electricity. Moistening bibulous paper
+with the iodide of potassium--a favourite test of his--and subjecting
+it to the action of machine electricity, he decomposed the iodide, and
+formed a brown spot where the iodine was liberated. Then he immersed
+two wires, one of zinc, the other of platinum, each 1/13th of an inch
+in diameter, to a depth of 5/8ths of an inch in acidulated water during
+eight beats of his watch, or 3/20ths of a second; and found that the
+needle of his galvanometer swung through the same arc, and coloured
+his moistened paper to the same extent, as thirty turns of his large
+electrical machine. Twenty-eight turns of the machine produced an effect
+distinctly less than that produced by his two wires. Now, the quantity
+of water decomposed by the wires in this experiment totally eluded
+observation; it was immeasurably small; and still that amount of
+decomposition involved the development of a quantity of electric force
+which, if applied in a proper form, would kill a rat, and no man would
+like to bear it.
+
+In his subsequent researches 'On the absolute Quantity of Electricity
+associated with the Particles or Atoms of matter,' he endeavours to give
+an idea of the amount of electrical force involved in the decomposition
+of a single grain of water. He is almost afraid to mention it, for he
+estimates it at 800,000 discharges of his large Leyden battery. This, if
+concentrated in a single discharge, would be equal to a very great flash
+of lightning; while the chemical action of a single grain of water
+on four grains of zinc would yield electricity equal in quantity to a
+powerful thunderstorm. Thus his mind rises from the minute to the
+vast, expanding involuntarily from the smallest laboratory fact till it
+embraces the largest and grandest natural phenomena.[1]
+
+In reality, however, he is at this time only clearing his way, and
+he continues laboriously to clear it for some time afterwards. He is
+digging the shaft, guided by that instinct towards the mineral lode
+which was to him a rod of divination. 'Er riecht die Wahrheit,' said the
+lamented Kohlrausch, an eminent German, once in my hearing:--'He smells
+the truth.' His eyes are now steadily fixed on this wonderful voltaic
+current, and he must learn more of its mode of transmission.
+
+On May 23, 1833, he read a paper before the Royal Society 'On a new
+Law of Electric Conduction.' He found that, though the current passed
+through water, it did not pass through ice:--why not, since they are
+one and the same substance? Some years subsequently he answered this
+question by saying that the liquid condition enables the molecule
+of water to turn round so as to place itself in the proper line of
+polarization, while the rigidity of the solid condition prevents this
+arrangement. This polar arrangement must precede decomposition, and
+decomposition is an accompaniment of conduction. He then passed on to
+other substances; to oxides and chlorides, and iodides, and salts, and
+sulphurets, and found them all insulators when solid, and conductors
+when fused. In all cases, moreover, except one--and this exception he
+thought might be apparent only--he found the passage of the current
+across the fused compound to be accompanied by its decomposition. Is
+then the act of decomposition essential to the act of conduction in
+these bodies? Even recently this question was warmly contested. Faraday
+was very cautious latterly in expressing himself upon this subject;
+but as a matter of fact he held that an infinitesimal quantity of
+electricity might pass through a compound liquid without producing its
+decomposition. De la Rive, who has been a great worker on the chemical
+phenomena of the pile, is very emphatic on the other side. Experiment,
+according to him and others, establishes in the most conclusive manner
+that no trace of electricity can pass through a liquid compound without
+producing its equivalent decomposition.[2]
+
+Faraday has now got fairly entangled amid the chemical phenomena of the
+pile, and here his previous training under Davy must have been of the
+most important service to him. Why, he asks, should decomposition thus
+take place?--what force is it that wrenches the locked constituents
+of these compounds asunder? On the 20th of June, 1833, he read a paper
+before the Royal Society 'On Electro-chemical Decomposition,' in which
+he seeks to answer these questions. The notion had been entertained
+that the poles, as they are called, of the decomposing cell, or in other
+words the surfaces by which the current enters and quits the liquid,
+exercised electric attractions upon the constituents of the liquid and
+tore them asunder. Faraday combats this notion with extreme vigour.
+Litmus reveals, as you know, the action of an acid by turning red,
+turmeric reveals the action of an alkali by turning brown. Sulphate of
+soda, you know, is a salt compounded of the alkali soda and sulphuric
+acid. The voltaic current passing through a solution of this salt
+so decomposes it, that sulphuric acid appears at one pole of the
+decomposing cell and alkali at the other. Faraday steeped a piece of
+litmus paper and a piece of turmeric paper in a solution of sulphate of
+soda: placing each of them upon a separate plate of glass, he connected
+them together by means of a string moistened with the same solution.
+He then attached one of them to the positive conductor of an electric
+machine, and the other to the gas-pipes of this building. These he
+called his 'discharging train.' On turning the machine the electricity
+passed from paper to paper through the string, which might be varied in
+length from a few inches to seventy feet without changing the result.
+The first paper was reddened, declaring the presence of sulphuric acid;
+the second was browned, declaring the presence of the alkali soda. The
+dissolved salt, therefore, arranged in this fashion, was decomposed by
+the machine, exactly as it would have been by the voltaic current.
+When instead of using the positive conductor he used the negative,
+the positions of the acid and alkali were reversed. Thus he satisfied
+himself that chemical decomposition by the machine is obedient to the
+laws which rule decomposition by the pile.
+
+And now he gradually abolishes those so-called poles, to the attraction
+of which electric decomposition had been ascribed. He connected a piece
+of turmeric paper moistened with the sulphate of soda with the positive
+conductor of his machine; then he placed a metallic point in connection
+with his discharging train opposite the moist paper, so that the
+electricity should discharge through the air towards the point. The
+turning of the machine caused the corners of the piece of turmeric paper
+opposite to the point to turn brown, thus declaring the presence of
+alkali. He changed the turmeric for litmus paper, and placed it, not
+in connection with his conductor, but with his discharging train, a
+metallic point connected with the conductor being fixed at a couple of
+inches from the paper; on turning the machine, acid was liberated at
+the edges and corners of the litmus. He then placed a series of pointed
+pieces of paper, each separate piece being composed of two halves,
+one of litmus and the other of turmeric paper, and all moistened with
+sulphate of soda, in the line of the current from the machine. The
+pieces of paper were separated from each other by spaces of air. The
+machine was turned; and it was always found that at the point where the
+electricity entered the paper, litmus was reddened, and at the point
+where it quitted the paper, turmeric was browned. 'Here,' he urges,
+'the poles are entirely abandoned, but we have still electrochemical
+decomposition.' It is evident to him that instead of being attracted by
+the poles, the bodies separated are ejected by the current. The effects
+thus obtained with poles of air he also succeeded in obtaining with
+poles of water. The advance in Faraday's own ideas made at this time is
+indicated by the word 'ejected.' He afterwards reiterates this view:
+the evolved substances are expelled from the decomposing body, and 'not
+drawn out by an attraction.
+
+Having abolished this idea of polar attraction, he proceeds to enunciate
+and develop a theory of his own. He refers to Davy's celebrated Bakerian
+Lecture, given in 1806, which he says 'is almost entirely occupied in
+the consideration of electrochemical decompositions.' The facts recorded
+in that lecture Faraday regards as of the utmost value. But 'the mode
+of action by which the effects take place is stated very generally;
+so generally, indeed, that probably a dozen precise schemes of
+electrochemical action might be drawn up, differing essentially from
+each other, yet all agreeing with the statement there given.'
+
+It appears to me that these words might with justice be applied to
+Faraday's own researches at this time. They furnish us with results of
+permanent value; but little help can be found in the theory advanced
+to account for them. It would, perhaps, be more correct to say that
+the theory itself is hardly presentable in any tangible form to the
+intellect. Faraday looks, and rightly looks, into the heart of the
+decomposing body itself; he sees, and rightly sees, active within it
+the forces which produce the decomposition, and he rejects, and rightly
+rejects, the notion of external attraction; but beyond the hypothesis of
+decompositions and recompositions, enunciated and developed by Grothuss
+and Davy, he does not, I think, help us to any definite conception as
+to how the force reaches the decomposing mass and acts within it. Nor,
+indeed, can this be done, until we know the true physical process which
+underlies what we call an electric current.
+
+Faraday conceives of that current as 'an axis of power having contrary
+forces exactly equal in amount in opposite directions'; but this
+definition, though much quoted and circulated, teaches us nothing
+regarding the current. An 'axis' here can only mean a direction; and
+what we want to be able to conceive of is, not the axis along which the
+power acts, but the nature and mode of action of the power itself. He
+objects to the vagueness of De la Rive; but the fact is, that both
+he and De la Rive labour under the same difficulty. Neither wishes
+to commit himself to the notion of a current compounded of two
+electricities flowing in two opposite directions: but the time had
+not come, nor is it yet come, for the displacement of this provisional
+fiction by the true mechanical conception. Still, however indistinct the
+theoretic notions of Faraday at this time may be, the facts which are
+rising before him and around him are leading him gradually, but surely,
+to results of incalculable importance in relation to the philosophy of
+the voltaic pile.
+
+He had always some great object of research in view, but in the pursuit
+of it he frequently alighted on facts of collateral interest, to examine
+which he sometimes turned aside from his direct course. Thus we find the
+series of his researches on electrochemical decomposition interrupted
+by an inquiry into 'the power of metals and other solids, to induce the
+combination of gaseous bodies.' This inquiry, which was received by the
+Royal Society on Nov. 30, 1833, though not so important as those
+which precede and follow it, illustrates throughout his strength as an
+experimenter. The power of spongy platinum to cause the combination of
+oxygen and hydrogen had been discovered by Dobereiner in 1823, and had
+been applied by him in the construction of his well-known philosophic
+lamp. It was shown subsequently by Dulong and Thenard that even a
+platinum wire, when perfectly cleansed, may be raised to incandescence
+by its action on a jet of cold hydrogen.
+
+In his experiments on the decomposition of water, Faraday found that
+the positive platinum plate of the decomposing cell possessed in
+an extraordinary degree the power of causing oxygen and hydrogen to
+combine. He traced the cause of this to the perfect cleanness of
+the positive plate. Against it was liberated oxygen, which, with the
+powerful affinity of the 'nascent state,' swept away all impurity from
+the surface against which it was liberated. The bubbles of gas liberated
+on one of the platinum plates or wires of a decomposing cell are always
+much smaller, and they rise in much more rapid succession than those
+from the other. Knowing that oxygen is sixteen times heavier than
+hydrogen, I have more than once concluded, and, I fear, led others
+into the error of concluding, that the smaller and more quickly rising
+bubbles must belong to the lighter gas. The thing appeared so obvious
+that I did not give myself the trouble of looking at the battery, which
+would at once have told me the nature of the gas. But Faraday would
+never have been satisfied with a deduction if he could have reduced it
+to a fact. And he has taught me that the fact here is the direct reverse
+of what I supposed it to be. The small bubbles are oxygen, and their
+smallness is due to the perfect cleanness of the surface on which they
+are liberated. The hydrogen adhering to the other electrode swells
+into large bubbles, which rise in much slower succession; but when the
+current is reversed, the hydrogen is liberated upon the cleansed wire,
+and then its bubbles also become small.
+
+Footnotes to Chapter 5
+
+     [1] Buff finds the quantity of electricity associated with
+     one milligramme of hydrogen in water to be equal to 45,480
+     charges of a Leyden jar, with a height of 480 millimetres,
+     and a diameter of 160 millimetres.  Weber and Kohlrausch
+     have calculated that, if the quantity of electricity
+     associated with one milligramme of hydrogen in water were
+     diffused over a cloud at a height of 1000 metres above the
+     earth, it would exert upon an equal quantity of the opposite
+     electricity at the earth's surface an attractive force of
+     2,268,000 kilogrammes.  (Electrolytische Maasbestimmungen,
+     1856, p. 262.)
+
+     [2] Faraday, sa Vie et ses Travaux, p. 20.
+
+
+
+
+Chapter 6.
+
+     Laws of electro-chemical decomposition.
+
+In our conceptions and reasonings regarding the forces of nature,
+we perpetually make use of symbols which, when they possess a high
+representative value, we dignify with the name of theories. Thus,
+prompted by certain analogies, we ascribe electrical phenomena to the
+action of a peculiar fluid, sometimes flowing, sometimes at rest. Such
+conceptions have their advantages and their disadvantages; they afford
+peaceful lodging to the intellect for a time, but they also circumscribe
+it, and by-and-by, when the mind has grown too large for its lodging, it
+often finds difficulty in breaking down the walls of what has become its
+prison instead of its home.[1]
+
+No man ever felt this tyranny of symbols more deeply than Faraday, and
+no man was ever more assiduous than he to liberate himself from them,
+and the terms which suggested them. Calling Dr. Whewell to his aid
+in 1833, he endeavoured to displace by others all terms tainted by
+a foregone conclusion. His paper on Electro-chemical Decomposition,
+received by the Royal Society on January 9, 1834, opens with the
+proposal of a new terminology. He would avoid the word 'current' if he
+could.[2] He does abandon the word 'poles' as applied to the ends of
+a decomposing cell, because it suggests the idea of attraction,
+substituting for it the perfectly natural term Electrodes. He applied
+the term Electrolyte to every substance which can be decomposed by the
+current, and the act of decomposition he called Electrolysis. All these
+terms have become current in science. He called the positive electrode
+the Anode, and the negative one the Cathode, but these terms, though
+frequently used, have not enjoyed the same currency as the others. The
+terms Anion and Cation, which he applied to the constituents of the
+decomposed electrolyte, and the term Ion, which included both anions and
+cations, are still less frequently employed.
+
+Faraday now passes from terminology to research; he sees the necessity
+of quantitative determinations, and seeks to supply himself with a
+measure of voltaic electricity. This he finds in the quantity of water
+decomposed by the current. He tests this measure in all possible ways,
+to assure himself that no error can arise from its employment. He
+places in the course of one and the same current a series of cells with
+electrodes of different sizes, some of them plates of platinum, others
+merely platinum wires, and collects the gas liberated on each distinct
+pair of electrodes. He finds the quantity of gas to be the same for all.
+Thus he concludes that when the same quantity of electricity is caused
+to pass through a series of cells containing acidulated water, the
+electro-chemical action is independent of the size of the electrodes.[3]
+He next proves that variations in intensity do not interfere with this
+equality of action. Whether his battery is charged with strong acid
+or with weak; whether it consists of five pairs or of fifty pairs; in
+short, whatever be its source, when the same current is sent through his
+series of cells the same amount of decomposition takes place in all. He
+next assures himself that the strength or weakness of his dilute acid
+does not interfere with this law. Sending the same current through
+a series of cells containing mixtures of sulphuric acid and water of
+different strengths, he finds, however the proportion of acid to water
+might vary, the same amount of gas to be collected in all the cells.
+A crowd of facts of this character forced upon Faraday's mind the
+conclusion that the amount of electro-chemical decomposition depends,
+not upon the size of the electrodes, not upon the intensity of the
+current, not upon the strength of the solution, but solely upon the
+quantity of electricity which passes through the cell. The quantity
+of electricity he concludes is proportional to the amount of chemical
+action. On this law Faraday based the construction of his celebrated
+Voltameter, or Measure of Voltaic electricity.
+
+But before he can apply this measure he must clear his ground of
+numerous possible sources of error. The decomposition of his acidulated
+water is certainly a direct result of the current; but as the varied and
+important researches of MM. Becquerel, De la Rive, and others had shown,
+there are also secondary actions which may materially interfere with and
+complicate the pure action of the current. These actions may occur in
+two ways: either the liberated ion may seize upon the electrode against
+which it is set free, forming a chemical compound with that electrode;
+or it may seize upon the substance of the electrolyte itself, and thus
+introduce into the circuit chemical actions over and above those due to
+the current. Faraday subjected these secondary actions to an exhaustive
+examination. Instructed by his experiments, and rendered competent by
+them to distinguish between primary and secondary results, he proceeds
+to establish the doctrine of 'Definite Electro-chemical Decomposition.'
+
+Into the same circuit he introduced his voltameter, which consisted of
+a graduated tube filled with acidulated water and provided with platinum
+plates for the decomposition of the water, and also a cell containing
+chloride of tin. Experiments already referred to had taught him that
+this substance, though an insulator when solid, is a conductor when
+fused, the passage of the current being always accompanied by the
+decomposition of the chloride. He wished to ascertain what relation this
+decomposition bore to that of the water in his voltameter.
+
+Completing his circuit, he permitted the current to continue until 'a
+reasonable quantity of gas' was collected in the voltameter. The circuit
+was then broken, and the quantity of tin liberated compared with the
+quantity of gas. The weight of the former was 3.2 grains, that of the
+latter 0.49742 of a grain. Oxygen, as you know, unites with hydrogen in
+the proportion of 8 to 1, to form water. Calling the equivalent, or as
+it is sometimes called, the atomic weight of hydrogen 1, that of oxygen
+is 8; that of water is consequently 8 + 1 or 9. Now if the quantity of
+water decomposed in Faraday's experiment be represented by the number 9,
+or in other words by the equivalent of water, then the quantity of tin
+liberated from the fused chloride is found by an easy calculation to be
+57.9, which is almost exactly the chemical equivalent of tin. Thus both
+the water and the chloride were broken up in proportions expressed
+by their respective equivalents. The amount of electric force which
+wrenched asunder the constituents of the molecule of water was
+competent, and neither more nor less than competent, to wrench asunder
+the constituents of the molecules of the chloride of tin. The fact
+is typical. With the indications of his voltameter he compared the
+decompositions of other substances, both singly and in series. He
+submitted his conclusions to numberless tests. He purposely introduced
+secondary actions. He endeavoured to hamper the fulfilment of those laws
+which it was the intense desire of his mind to see established. But
+from all these difficulties emerged the golden truth, that under every
+variety of circumstances the decompositions of the voltaic current are
+as definite in their character as those chemical combinations which gave
+birth to the atomic theory. This law of Electro-chemical Decomposition
+ranks, in point of importance, with that of Definite Combining
+Proportions in chemistry.
+
+
+Footnotes to Chapter 6
+
+     [1] I copy these words from the printed abstract of a Friday
+     evening lecture, given by myself, because they remind me of
+     Faraday's voice, responding to the utterance by an emphatic
+     'hear! hear!'--Proceedings of the Royal Institution, vol.
+     ii. p. 132.
+
+     [2] In 1838 he expresses himself thus:--'The word current is
+     so expressive in common language that when applied in the
+     consideration of electrical phenomena, we can hardly divest
+     it sufficiently of its meaning, or prevent our minds from
+     being prejudiced by it.'--Exp. Resear., vol. i. p. 515. ($
+     1617.)
+
+     [3] This conclusion needs qualification.  Faraday overlooked
+     the part played by ozone.
+
+
+
+
+Chapter 7.
+
+     Origin of power in the voltaic pile.
+
+In one of the public areas of the town of Como stands a statue with no
+inscription on its pedestal, save that of a single name, 'Volta.' The
+bearer of that name occupies a place for ever memorable in the history
+of science. To him we owe the discovery of the voltaic pile, to which
+for a brief interval we must now turn our attention.
+
+The objects of scientific thought being the passionless laws and
+phenomena of external nature, one might suppose that their investigation
+and discussion would be completely withdrawn from the region of the
+feelings, and pursued by the cold dry light of the intellect alone.
+This, however, is not always the case. Man carries his heart with him
+into all his works. You cannot separate the moral and emotional from the
+intellectual; and thus it is that the discussion of a point of science
+may rise to the heat of a battle-field. The fight between the rival
+optical theories of Emission and Undulation was of this fierce
+character; and scarcely less fierce for many years was the contest as
+to the origin and maintenance of the power of the voltaic pile. Volta
+himself supposed it to reside in the Contact of different metals.
+Here was exerted his 'Electro-motive force,' which tore the combined
+electricities asunder and drove them as currents in opposite directions.
+To render the circulation of the current possible, it was necessary to
+connect the metals by a moist conductor; for when any two metals were
+connected by a third, their relation to each other was such that a
+complete neutralisation of the electric motion was the result. Volta's
+theory of metallic contact was so clear, so beautiful, and apparently
+so complete, that the best intellects of Europe accepted it as the
+expression of natural law.
+
+Volta himself knew nothing of the chemical phenomena of the pile; but
+as soon as these became known, suggestions and intimations appeared that
+chemical action, and not metallic contact, might be the real source of
+voltaic electricity. This idea was expressed by Fabroni in Italy, and
+by Wollaston in England. It was developed and maintained by those
+'admirable electricians,' Becquerel, of Paris, and De la Rive, of
+Geneva. The Contact Theory, on the other hand, received its chief
+development and illustration in Germany. It was long the scientific
+creed of the great chemists and natural philosophers of that country,
+and to the present hour there may be some of them unable to liberate
+themselves from the fascination of their first-love.
+
+After the researches which I have endeavoured to place before you, it
+was impossible for Faraday to avoid taking a side in this controversy.
+He did so in a paper 'On the Electricity of the Voltaic Pile,' received
+by the Royal Society on the 7th of April, 1834. His position in the
+controversy might have been predicted. He saw chemical effects going
+hand in hand with electrical effects, the one being proportional to the
+other; and, in the paper now before us, he proved that when the former
+was excluded, the latter were sought for in vain. He produced a current
+without metallic contact; he discovered liquids which, though competent
+to transmit the feeblest currents--competent therefore to allow the
+electricity of contact to flow through them if it were able to form a
+current--were absolutely powerless when chemically inactive.
+
+One of the very few experimental mistakes of Faraday occurred in
+this investigation. He thought that with a single voltaic cell he
+had obtained the spark before the metals touched, but he subsequently
+discovered his error. To enable the voltaic spark to pass through air
+before the terminals of the battery were united, it was necessary
+to exalt the electro-motive force of the battery by multiplying its
+elements; but all the elements Faraday possessed were unequal to the
+task of urging the spark across the shortest measurable space of air.
+Nor, indeed, could the action of the battery, the different metals of
+which were in contact with each other, decide the point in question.
+Still, as regards the identity of electricities from various sources,
+it was at that day of great importance to determine whether or not
+the voltaic current could jump, as a spark, across an interval before
+contact. Faraday's friend, Mr. Gassiot, solved this problem. He erected
+a battery of 4000 cells, and with it urged a stream of sparks from
+terminal to terminal, when separated from each other by a measurable
+space of air.
+
+The memoir on the 'Electricity of the Voltaic Pile,' published in 1834,
+appears to have produced but little impression upon the supporters of
+the contact theory. These indeed were men of too great intellectual
+weight and insight lightly to take up, or lightly to abandon a theory.
+Faraday therefore resumed the attack in a paper, communicated to the
+Royal Society on the 6th of February, 1840. In this paper he hampered
+his antagonists by a crowd of adverse experiments. He hung difficulty
+after difficulty about the neck of the contact theory, until in its
+efforts to escape from his assaults it so changed its character as to
+become a thing totally different from the theory proposed by Volta. The
+more persistently it was defended, however, the more clearly did it
+show itself to be a congeries of devices, bearing the stamp of dialectic
+skill rather than of natural truth.
+
+In conclusion, Faraday brought to bear upon it an argument which, had
+its full weight and purport been understood at the time, would have
+instantly decided the controversy. 'The contact theory,' he urged,
+'assumed that a force which is able to overcome powerful resistance,
+as for instance that of the conductors, good or bad, through which the
+current passes, and that again of the electrolytic action where bodies
+are decomposed by it, can arise out of nothing; that, without any change
+in the acting matter, or the consumption of any generating force, a
+current shall be produced which shall go on for ever against a constant
+resistance, or only be stopped, as in the voltaic trough, by the ruins
+which its exertion has heaped up in its own course. This would indeed be
+a creation of power, and is like no other force in nature. We have many
+processes by which the form of the power may be so changed, that an
+apparent conversion of one into the other takes place. So we can change
+chemical force into the electric current, or the current into chemical
+force. The beautiful experiments of Seebeck and Peltier show the
+convertibility of heat and electricity; and others by Oersted and myself
+show the convertibility of electricity and magnetism. But in no case,
+not even in those of the Gymnotus and Torpedo, is there a pure creation
+or a production of power without a corresponding exhaustion of something
+to supply it.'
+
+These words were published more than two years before either Mayer
+printed his brief but celebrated essay on the Forces of Inorganic
+Nature, or Mr. Joule published his first famous experiments on the
+Mechanical Value of Heat. They illustrate the fact that before any great
+scientific principle receives distinct enunciation by individuals,
+it dwells more or less clearly in the general scientific mind. The
+intellectual plateau is already high, and our discoverers are those who,
+like peaks above the plateau, rise a little above the general level of
+thought at the time.
+
+But many years prior even to the foregoing utterance of Faraday, a
+similar argument had been employed. I quote here with equal pleasure
+and admiration the following passage written by Dr. Roget so far back as
+1829. Speaking of the contact theory, he says:--'If there could exist a
+power having the property ascribed to it by the hypothesis, namely,
+that of giving continual impulse to a fluid in one constant direction,
+without being exhausted by its own action, it would differ essentially
+from all the known powers in nature. All the powers and sources of
+motion with the operation of which we are acquainted, when producing
+these peculiar effects, are expended in the same proportion as those
+effects are produced; and hence arises the impossibility of obtaining by
+their agency a perpetual effect; or in other words a perpetual motion.
+But the electro-motive force, ascribed by Volta to the metals, when in
+contact, is a force which, as long as a free course is allowed to the
+electricity it sets in motion, is never expended, and continues to be
+excited with undiminished power in the production of a never-ceasing
+effect. Against the truth of such a supposition the probabilities are
+all but infinite.' When this argument, which he employed independently,
+had clearly fixed itself in his mind, Faraday never cared to experiment
+further on the source of electricity in the voltaic pile. The argument
+appeared to him 'to remove the foundation itself of the contact theory,'
+and he afterwards let it crumble down in peace.[1]
+
+
+Footnote to Chapter 7
+
+     [1] To account for the electric current, which was really
+     the core of the whole discussion, Faraday demonstrated the
+     impotence of the Contact Theory as then enunciated and
+     defended.  Still, it is certain that two different metals,
+     when brought into contact, charge themselves, the one with
+     positive and the other with negative electricity.  I had the
+     pleasure of going over this ground with Kohlrausch in 1849,
+     and his experiments left no doubt upon my mind that the
+     contact electricity of Volta was a reality, though it could
+     produce no current.  With one of the beautiful instruments
+     devised by himself, Sir William Thomson has rendered this
+     point capable of sure and easy demonstration; and he and
+     others now hold what may be called a contact theory, which,
+     while it takes into account the action of the metals, also
+     embraces the chemical phenomena of the circuit.  Helmholtz,
+     I believe, was the first to give the contact theory this new
+     form, in his celebrated essay, Ueber die Erhaltung der
+     Kraft, p. 45.
+
+
+
+
+Chapter 8.
+
+     Researches on frictional electricity: induction: conduction:
+     specific inductive capacity: theory of contiguous particles.
+
+The burst of power which had filled the four preceding years with an
+amount of experimental work unparalleled in the history of science
+partially subsided in 1835, and the only scientific paper contributed
+by Faraday in that year was a comparatively unimportant one, 'On an
+improved Form of the Voltaic Battery.' He brooded for a time: his
+experiments on electrolysis had long filled his mind; he looked, as
+already stated, into the very heart of the electrolyte, endeavouring to
+render the play of its atoms visible to his mental eye. He had no doubt
+that in this case what is called 'the electric current' was propagated
+from particle to particle of the electrolyte; he accepted the doctrine
+of decomposition and recomposition which, according to Grothuss and
+Davy, ran from electrode to electrode. And the thought impressed him
+more and more that ordinary electric induction was also transmitted and
+sustained by the action of 'contiguous particles.'
+
+His first great paper on frictional electricity was sent to the Royal
+Society on November 30, 1837. We here find him face to face with an idea
+which beset his mind throughout his whole subsequent life,--the idea of
+action at a distance. It perplexed and bewildered him. In his attempts
+to get rid of this perplexity, he was often unconsciously rebelling
+against the limitations of the intellect itself. He loved to quote
+Newton upon this point; over and over again he introduces his memorable
+words, 'That gravity should be innate, inherent, and essential to
+matter, so that one body may act upon another at a distance through a
+vacuum and without the mediation of anything else, by and through which
+this action and force may be conveyed from one to another, is to me
+so great an absurdity, that I believe no man who has in philosophical
+matters a competent faculty of thinking, can ever fall into it. Gravity
+must be caused by an agent acting constantly according to certain laws;
+but whether this agent be material or immaterial, I have left to the
+consideration of my readers.'[1]
+
+Faraday does not see the same difficulty in his contiguous particles.
+And yet, by transferring the conception from masses to particles, we
+simply lessen size and distance, but we do not alter the quality of the
+conception. Whatever difficulty the mind experiences in conceiving
+of action at sensible distances, besets it also when it attempts to
+conceive of action at insensible distances. Still the investigation of
+the point whether electric and magnetic effects were wrought out through
+the intervention of contiguous particles or not, had a physical interest
+altogether apart from the metaphysical difficulty. Faraday grapples with
+the subject experimentally. By simple intuition he sees that action at a
+distance must be exerted in straight lines. Gravity, he knows, will not
+turn a corner, but exerts its pull along a right line; hence his aim and
+effort to ascertain whether electric action ever takes place in curved
+lines. This once proved, it would follow that the action is carried on
+by means of a medium surrounding the electrified bodies. His experiments
+in 1837 reduced, in his opinion, this point of demonstration. He then
+found that he could electrify, by induction, an insulated sphere placed
+completely in the shadow of a body which screened it from direct action.
+He pictured the lines of electric force bending round the edges of the
+screen, and reuniting on the other side of it; and he proved that in
+many cases the augmentation of the distance between his insulated sphere
+and the inducing body, instead of lessening, increased the charge of
+the sphere. This he ascribed to the coalescence of the lines of electric
+force at some distance behind the screen.
+
+Faraday's theoretic views on this subject have not received general
+acceptance, but they drove him to experiment, and experiment with him
+was always prolific of results. By suitable arrangements he placed a
+metallic sphere in the middle of a large hollow sphere, leaving a space
+of something more than half an inch between them. The interior
+sphere was insulated, the external one uninsulated. To the former he
+communicated a definite charge of electricity. It acted by induction
+upon the concave surface of the latter, and he examined how this act of
+induction was effected by placing insulators of various kinds between
+the two spheres. He tried gases, liquids, and solids, but the solids
+alone gave him positive results. He constructed two instruments of the
+foregoing description, equal in size and similar in form. The interior
+sphere of each communicated with the external air by a brass stem ending
+in a knob. The apparatus was virtually a Leyden jar, the two coatings of
+which were the two spheres, with a thick and variable insulator between
+them. The amount of charge in each jar was determined by bringing
+a proof-plane into contact with its knob and measuring by a torsion
+balance the charge taken away. He first charged one of his instruments,
+and then dividing the charge with the other, found that when air
+intervened in both cases the charge was equally divided. But when
+shellac, sulphur, or spermaceti was interposed between the two spheres
+of one jar, while air occupied this interval in the other, then he found
+that the instrument occupied by the 'solid dielectric' takes more than
+half the original charge. A portion of the charge was absorbed by
+the dielectric itself. The electricity took time to penetrate the
+dielectric. Immediately after the discharge of the apparatus, no trace
+of electricity was found upon its knob. But after a time electricity was
+found there, the charge having gradually returned from the dielectric
+in which it had been lodged. Different insulators possess this power
+of permitting the charge to enter them in different degrees. Faraday
+figured their particles as polarized, and he concluded that the force of
+induction is propagated from particle to particle of the dielectric from
+the inner sphere to the outer one. This power of propagation possessed
+by insulators he called their 'Specific Inductive Capacity.'
+
+Faraday visualizes with the utmost clearness the state of his contiguous
+particles; one after another they become charged, each succeeding
+particle depending for its charge upon its predecessor. And now he seeks
+to break down the wall of partition between conductors and insulators.
+'Can we not,' he says, 'by a gradual chain of association carry up
+discharge from its occurrence in air through spermaceti and water, to
+solutions, and then on to chlorides, oxides, and metals, without any
+essential change in its character?' Even copper, he urges, offers
+a resistance to the transmission of electricity. The action of its
+particles differs from those of an insulator only in degree. They are
+charged like the particles of the insulator, but they discharge with
+greater ease and rapidity; and this rapidity of molecular discharge is
+what we call conduction. Conduction then is always preceded by atomic
+induction; and when, through some quality of the body which Faraday
+does not define, the atomic discharge is rendered slow and difficult,
+conduction passes into insulation.
+
+Though they are often obscure, a fine vein of philosophic thought runs
+through those investigations. The mind of the philosopher dwells amid
+those agencies which underlie the visible phenomena of Induction and
+Conduction; and he tries by the strong light of his imagination to see
+the very molecules of his dielectrics. It would, however, be easy to
+criticise these researches, easy to show the looseness, and sometimes
+the inaccuracy, of the phraseology employed; but this critical spirit
+will get little good out of Faraday. Rather let those who ponder his
+works seek to realise the object he set before him, not permitting
+his occasional vagueness to interfere with their appreciation of his
+speculations. We may see the ripples, and eddies, and vortices of a
+flowing stream, without being able to resolve all these motions into
+their constituent elements; and so it sometimes strikes me that Faraday
+clearly saw the play of fluids and ethers and atoms, though his
+previous training did not enable him to resolve what he saw into its
+constituents, or describe it in a manner satisfactory to a mind versed
+in mechanics. And then again occur, I confess, dark sayings, difficult
+to be understood, which disturb my confidence in this conclusion. It
+must, however, always be remembered that he works at the very boundaries
+of our knowledge, and that his mind habitually dwells in the 'boundless
+contiguity of shade' by which that knowledge is surrounded.
+
+In the researches now under review the ratio of speculation and
+reasoning to experiment is far higher than in any of Faraday's previous
+works. Amid much that is entangled and dark we have flashes of wondrous
+insight and utterances which seem less the product of reasoning than of
+revelation. I will confine myself here to one example of this divining
+power. By his most ingenious device of a rapidly rotating mirror,
+Wheatstone had proved that electricity required time to pass through
+a wire, the current reaching the middle of the wire later than its
+two ends. 'If,' says Faraday, 'the two ends of the wire in Professor
+Wheatstone's experiments were immediately connected with two large
+insulated metallic surfaces exposed to the air, so that the primary act
+of induction, after making the contact for discharge, might be in part
+removed from the internal portion of the wire at the first instance,
+and disposed for the moment on its surface jointly with the air and
+surrounding conductors, then I venture to anticipate that the middle
+spark would be more retarded than before. And if those two plates were
+the inner and outer coatings of a large jar or Leyden battery, then
+the retardation of the spark would be much greater.' This was only
+a prediction, for the experiment was not made.[2] Sixteen years
+subsequently, however, the proper conditions came into play, and Faraday
+was able to show that the observations of Werner Siemens, and Latimer
+Clark, on subterraneous and submarine wires were illustrations, on a
+grand scale, of the principle which he had enunciated in 1838. The wires
+and the surrounding water act as a Leyden jar, and the retardation of
+the current predicted by Faraday manifests itself in every message sent
+by such cables.
+
+The meaning of Faraday in these memoirs on Induction and Conduction is,
+as I have said, by no means always clear; and the difficulty will
+be most felt by those who are best trained in ordinary theoretic
+conceptions. He does not know the reader's needs, and he therefore
+does not meet them. For instance he speaks over and over again of
+the impossibility of charging a body with one electricity, though the
+impossibility is by no means evident. The key to the difficulty is this.
+He looks upon every insulated conductor as the inner coating of a Leyden
+jar. An insulated sphere in the middle of a room is to his mind such a
+coating; the walls are the outer coating, while the air between both is
+the insulator, across which the charge acts by induction. Without this
+reaction of the walls upon the sphere you could no more, according to
+Faraday, charge it with electricity than you could charge a Leyden jar,
+if its outer coating were removed. Distance with him is immaterial. His
+strength as a generalizer enables him to dissolve the idea of magnitude;
+and if you abolish the walls of the room--even the earth itself--he
+would make the sun and planets the outer coating of his jar. I dare not
+contend that Faraday in these memoirs made all his theoretic positions
+good. But a pure vein of philosophy runs through these writings; while
+his experiments and reasonings on the forms and phenomena of electrical
+discharge are of imperishable importance.
+
+
+Footnotes to Chapter 8
+
+     [1] Newton's third letter to Bentley.
+
+     [2] Had Sir Charles Wheatstone been induced to resume his
+     measurements, varying the substances through which, and the
+     conditions under which, the current is propagated, he might
+     have rendered great service to science, both theoretic and
+     experimental.
+
+
+
+
+Chapter 9.
+
+     Rest needed--visit to Switzerland.
+
+The last of these memoirs was dated from the Royal Institution in June,
+1838. It concludes the first volume of his 'Experimental Researches on
+Electricity.' In 1840, as already stated, he made his final assault on
+the Contact Theory, from which it never recovered.[1] He was now feeling
+the effects of the mental strain to which he had been subjected for so
+many years. During these years he repeatedly broke down. His wife alone
+witnessed the extent of his prostration, and to her loving care we, and
+the world, are indebted for the enjoyment of his presence here so long.
+He found occasional relief in a theatre. He frequently quitted London
+and went to Brighton and elsewhere, always choosing a situation which
+commanded a view of the sea, or of some other pleasant horizon, where he
+could sit and gaze and feel the gradual revival of the faith that
+
+          'Nature never did betray
+           The heart that loved her.'
+
+But very often for some days after his removal to the country, he would
+be unable to do more than sit at a window and look out upon the sea and
+sky.
+
+In 1841, his state became more serious than it had ever been before. A
+published letter to Mr. Richard Taylor, dated March 11, 1843, contains
+an allusion to his previous condition. 'You are aware,' he says, 'that
+considerations regarding health have prevented me from working or
+reading on science for the last two years.' This, at one period
+or another of their lives, seems to be the fate of most great
+investigators. They do not know the limits of their constitutional
+strength until they have transgressed them. It is, perhaps, right that
+they should transgress them, in order to ascertain where they lie.
+Faraday, however, though he went far towards it, did not push his
+transgression beyond his power of restitution. In 1841 Mrs. Faraday and
+he went to Switzerland, under the affectionate charge of her brother,
+Mr. George Barnard, the artist. This time of suffering throws fresh
+light upon his character. I have said that sweetness and gentleness were
+not its only constituents; that he was also fiery and strong. At the
+time now referred to, his fire was low and his strength distilled away;
+but the residue of his life was neither irritability nor discontent. He
+was unfit to mingle in society, for conversation was a pain to him; but
+let us observe the great Man-child when alone. He is at the village of
+Interlaken, enjoying Jungfrau sunsets, and at times watching the Swiss
+nailers making their nails. He keeps a little journal, in which he
+describes the process of nailmaking, and incidentally throws a luminous
+beam upon himself.
+
+'August 2, 1841.--Clout nailmaking goes on here rather considerably, and
+is a very neat and pretty operation to observe. I love a smith's shop
+and anything relating to smithery. My father was a smith.'
+
+From Interlaken he went to the Falls of the Giessbach, on the pleasant
+lake of Brientz. And here we have him watching the shoot of the cataract
+down its series of precipices. It is shattered into foam at the base of
+each, and tossed by its own recoil as water-dust through the air. The
+sun is at his back, shining on the drifting spray, and he thus describes
+and muses on what he sees:--
+
+'August 12, 1841.--To-day every fall was foaming from the abundance of
+water, and the current of wind brought down by it was in some places too
+strong to stand against. The sun shone brightly, and the rainbows seen
+from various points were very beautiful. One at the bottom of a fine but
+furious fall was very pleasant,--there it remained motionless, whilst
+the gusts and clouds of spray swept furiously across its place and were
+dashed against the rock. It looked like a spirit strong in faith and
+steadfast in the midst of the storm of passions sweeping across it, and
+though it might fade and revive, still it held on to the rock as in hope
+and giving hope. And the very drops, which in the whirlwind of their
+fury seemed as if they would carry all away, were made to revive it and
+give it greater beauty.'
+
+
+Footnote to Chapter 9
+
+     [1] See note, p. 77.
+
+
+
+
+Chapter 10.
+
+     Magnetization of light.
+
+But we must quit the man and go on to the discoverer: we shall return
+for a brief space to his company by-and-by. Carry your thoughts back to
+his last experiments, and see him endeavouring to prove that induction
+is due to the action of contiguous particles. He knew that polarized
+light was a most subtle and delicate investigator of molecular
+condition. He used it in 1834 in exploring his electrolytes, and he
+tried it in 1838 upon his dielectrics. At that time he coated two
+opposite faces of a glass cube with tinfoil, connected one coating with
+his powerful electric machine and the other with the earth, and examined
+by polarized light the condition of the glass when thus subjected to
+strong electric influence. He failed to obtain any effect; still he was
+persuaded an action existed, and required only suitable means to call it
+forth.
+
+After his return from Switzerland he was beset by these thoughts; they
+were more inspired than logical: but he resorted to magnets and proved
+his inspiration true. His dislike of 'doubtful knowledge' and his
+efforts to liberate his mind from the thraldom of hypotheses have been
+already referred to. Still this rebel against theory was incessantly
+theorising himself. His principal researches are all connected by an
+undercurrent of speculation. Theoretic ideas were the very sap of his
+intellect--the source from which all his strength as an experimenter was
+derived. While once sauntering with him through the Crystal Palace, at
+Sydenham, I asked him what directed his attention to the magnetization
+of light. It was his theoretic notions. He had certain views regarding
+the unity and convertibility of natural forces; certain ideas regarding
+the vibrations of light and their relations to the lines of magnetic
+force; these views and ideas drove him to investigation. And so it must
+always be: the great experimentalist must ever be the habitual theorist,
+whether or not he gives to his theories formal enunciation.
+
+Faraday, you have been informed, endeavoured to improve the manufacture
+of glass for optical purposes. But though he produced a heavy glass of
+great refractive power, its value to optics did not repay him for
+the pains and labour bestowed on it. Now, however, we reach a result
+established by means of this same heavy glass, which made ample amends
+for all.
+
+In November, 1845, he announced his discovery of the 'Magnetization of
+Light and the Illumination of the Lines of Magnetic Force.' This title
+provoked comment at the time, and caused misapprehension. He therefore
+added an explanatory note; but the note left his meaning as entangled as
+before. In fact Faraday had notions regarding the magnetization of light
+which were peculiar to himself, and untranslatable into the scientific
+language of the time. Probably no other philosopher of his day would
+have employed the phrases just quoted as appropriate to the discovery
+announced in 1845. But Faraday was more than a philosopher; he was
+a prophet, and often wrought by an inspiration to be understood by
+sympathy alone. The prophetic element in his character occasionally
+coloured, and even injured, the utterance of the man of science;
+but subtracting that element, though you might have conferred on him
+intellectual symmetry, you would have destroyed his motive force.
+
+But let us pass from the label of this casket to the jewel it
+contains. 'I have long,' he says, 'held an opinion, almost amounting
+to conviction, in common, I believe, with many other lovers of natural
+knowledge, that the various forms under which the forces of matter are
+made manifest have one common origin; in other words, are so directly
+related and mutually dependent, that they are convertible, as it were,
+into one another, and possess equivalents of power in their action....
+This strong persuasion,' he adds, 'extended to the powers of light.'
+And then he examines the action of magnets upon light. From conversation
+with him and Anderson, I should infer that the labour preceding this
+discovery was very great. The world knows little of the toil of the
+discoverer. It sees the climber jubilant on the mountain top, but
+does not know the labour expended in reaching it. Probably hundreds of
+experiments had been made on transparent crystals before he thought of
+testing his heavy glass. Here is his own clear and simple description
+of the result of his first experiment with this substance:--'A piece of
+this glass, about two inches square, and 0.5 of an inch thick, having
+flat and polished edges, was placed as a diamagnetic[1] between the
+poles (not as yet magnetized by the electric current), so that the
+polarized ray should pass through its length; the glass acted as air,
+water, or any other transparent substance would do; and if the eye-piece
+were previously turned into such a position that the polarized ray was
+extinguished, or rather the image produced by it rendered invisible,
+then the introduction of the glass made no alteration in this respect.
+In this state of circumstances, the force of the electro-magnet
+was developed by sending an electric current through its coils, and
+immediately the image of the lamp-flame became visible and continued so
+as long as the arrangement continued magnetic. On stopping the electric
+current, and so causing the magnetic force to cease, the light instantly
+disappeared. These phenomena could be renewed at pleasure, at any
+instant of time, and upon any occasion, showing a perfect dependence of
+cause and effect.'
+
+In a beam of ordinary light the particles of the luminiferous ether
+vibrate in all directions perpendicular to the line of progression; by
+the act of polarization, performed here by Faraday, all oscillations
+but those parallel to a certain plane are eliminated. When the plane
+of vibration of the polarizer coincides with that of the analyzer, a
+portion of the beam passes through both; but when these two planes
+are at right angles to each other, the beam is extinguished. If by any
+means, while the polarizer and analyzer remain thus crossed, the plane
+of vibration of the polarized beam between them could be changed,
+then the light would be, in part at least, transmitted. In Faraday's
+experiment this was accomplished. His magnet turned the plane of
+polarization of the beam through a certain angle, and thus enabled it
+to get through the analyzer; so that 'the magnetization of light and the
+illumination of the magnetic lines of force' becomes, when expressed
+in the language of modern theory, the rotation of the plane of
+polarization.
+
+To him, as to all true philosophers, the main value of a fact was its
+position and suggestiveness in the general sequence of scientific truth.
+Hence, having established the existence of a phenomenon, his habit
+was to look at it from all possible points of view, and to develop its
+relationship to other phenomena. He proved that the direction of the
+rotation depends upon the polarity of his magnet; being reversed when
+the magnetic poles are reversed. He showed that when a polarized ray
+passed through his heavy glass in a direction parallel to the magnetic
+lines of force, the rotation is a maximum, and that when the direction
+of the ray is at right angles to the lines of force, there is no
+rotation at all. He also proved that the amount of the rotation is
+proportional to the length of the diamagnetic through which the ray
+passes. He operated with liquids and solutions. Of aqueous solutions he
+tried 150 and more, and found the power in all of them. He then examined
+gases; but here all his efforts to produce any sensible action upon
+the polarized beam were ineffectual. He then passed from magnets to
+currents, enclosing bars of heavy glass, and tubes containing liquids
+and aqueous solutions within an electro-magnetic helix. A current sent
+through the helix caused the plane of polarization to rotate, and always
+in the direction of the current. The rotation was reversed when the
+current was reversed. In the case of magnets, he observed a gradual,
+though quick, ascent of the transmitted beam from a state of darkness
+to its maximum brilliancy, when the magnet was excited. In the case of
+currents, the beam attained at once its maximum. This he showed to be
+due to the time required by the iron of the electro-magnet to assume its
+full magnetic power, which time vanishes when a current, without iron,
+is employed. 'In this experiment,' he says, 'we may, I think, justly
+say that a ray of light is electrified, and the electric forces
+illuminated.' In the helix, as with the magnets, he submitted air to
+magnetic influence 'carefully and anxiously,' but could not discover any
+trace of action on the polarized ray.
+
+Many substances possess the power of turning the plane of polarization
+without the intervention of magnetism. Oil of turpentine and quartz
+are examples; but Faraday showed that, while in one direction, that is,
+across the lines of magnetic force, his rotation is zero, augmenting
+gradually from this until it attains its maximum, when the direction of
+the ray is parallel to the lines of force; in the oil of turpentine the
+rotation is independent of the direction of the ray. But he showed that
+a still more profound distinction exists between the magnetic rotation
+and the natural one. I will try to explain how. Suppose a tube with
+glass ends containing oil of turpentine to be placed north and south.
+Fixing the eye at the south end of the tube, let a polarized beam be
+sent through it from the north. To the observer in this position
+the rotation of the plane of polarization, by the turpentine, is
+right-handed. Let the eye be placed at the north end of the tube, and
+a beam be sent through it from the south; the rotation is still
+right-handed. Not so, however, when a bar of heavy glass is subjected
+to the action of an electric current. In this case if, in the first
+position of the eye, the rotation be right-handed, in the second
+position it is left-handed. These considerations make it manifest that
+if a polarized beam, after having passed through the oil of turpentine
+in its natural state, could by any means be reflected back through the
+liquid, the rotation impressed upon the direct beam would be exactly
+neutralized by that impressed upon the reflected one. Not so with the
+induced magnetic effect. Here it is manifest that the rotation would
+be doubled by the act of reflection. Hence Faraday concludes that the
+particles of the oil of turpentine which rotate by virtue of their
+natural force, and those which rotate in virtue of the induced force,
+cannot be in the same condition. The same remark applies to all bodies
+which possess a natural power of rotating the plane of polarization.
+
+And then he proceeded with exquisite skill and insight to take advantage
+of this conclusion. He silvered the ends of his piece of heavy glass,
+leaving, however, a narrow portion parallel to two edges diagonally
+opposed to each other unsilvered. He then sent his beam through this
+uncovered portion, and by suitably inclining his glass caused the beam
+within it to reach his eye first direct, and then after two, four, and
+six reflections. These corresponded to the passage of the ray once,
+three times, five times, and seven times through the glass. He thus
+established with numerical accuracy the exact proportionality of the
+rotation to the distance traversed by the polarized beam. Thus in one
+series of experiments where the rotation required by the direct beam
+was 12degrees, that acquired by three passages through the glass was
+36degrees, while that acquired by five passages was 60degrees. But even
+when this method of magnifying was applied, he failed with various
+solid substances to obtain any effect; and in the case of air, though he
+employed to the utmost the power which these repeated reflections placed
+in his hands, he failed to produce the slightest sensible rotation.
+
+These failures of Faraday to obtain the effect with gases seem to
+indicate the true seat of the phenomenon. The luminiferous ether
+surrounds and is influenced by the ultimate particles of matter. The
+symmetry of the one involves that of the other. Thus, if the molecules
+of a crystal be perfectly symmetrical round any line through the
+crystal, we may safely conclude that a ray will pass along this line
+as through ordinary glass. It will not be doubly refracted. From the
+symmetry of the liquid figures, known to be produced in the planes of
+freezing, when radiant heat is sent through ice, we may safely infer
+symmetry of aggregation, and hence conclude that the line perpendicular
+to the planes of freezing is a line of no double refraction; that it is,
+in fact, the optic axis of the crystal. The same remark applies to the
+line joining the opposite blunt angles of a crystal of Iceland spar.
+The arrangement of the molecules round this line being symmetrical,
+the condition of the ether depending upon these molecules shares their
+symmetry; and there is, therefore, no reason why the wavelength should
+alter with the alteration of the azimuth round this line. Annealed glass
+has its molecules symmetrically arranged round every line that can
+be drawn through it; hence it is not doubly refractive. But let the
+substance be either squeezed or strained in one direction, the molecular
+symmetry, and with it the symmetry of the ether, is immediately
+destroyed and the glass becomes doubly refractive. Unequal heating
+produces the same effect. Thus mechanical strains reveal themselves by
+optical effects; and there is little doubt that in Faraday's experiment
+it is the magnetic strain that produces the rotation of the plane of
+polarization.[2]
+
+
+Footnotes to Chapter 10
+
+     [1] 'By a diamagnetic,' says Faraday, 'I mean a body through
+     which lines of magnetic force are passing,  and which does
+     not by their action assume the usual magnetic state of iron
+     or loadstone.' Faraday subsequently used this term in a
+     different sense from that here given, as will immediately
+     appear.
+
+     [2] The power of double refraction conferred on the centre
+     of a glass rod, when it is caused to sound the fundamental
+     note due to its longitudinal vibration, and the absence of
+     the same power in the case of vibrating air (enclosed in a
+     glass organ-pipe), seems to be analogous to the presence and
+     absence of Faraday's effect in the same two substances.
+     Faraday never, to my knowledge, attempted to give, even in
+     conversation, a picture of the molecular condition of his
+     heavy glass when subjected to magnetic influence.  In a
+     mathematical investigation of the subject, published in the
+     Proceedings of the Royal Society for 1856, Sir William
+     Thomson arrives at the conclusion that the 'diamagnetic' is
+     in a state of molecular rotation.
+
+
+
+
+Chapter 11.
+
+     Discovery of diamagnetism--researches on magne-crystallic
+     action.
+
+Faraday's next great step in discovery was announced in a memoir on the
+'Magnetic Condition of all matter,' communicated to the Royal Society on
+December 18, 1845. One great source of his success was the employment
+of extraordinary power. As already stated, he never accepted a negative
+answer to an experiment until he had brought to bear upon it all the
+force at his command. He had over and over again tried steel magnets and
+ordinary electro-magnets on various substances, but without detecting
+anything different from the ordinary attraction exhibited by a few of
+them. Stronger coercion, however, developed a new action. Before the
+pole of an electro-magnet, he suspended a fragment of his famous heavy
+glass; and observed that when the magnet was powerfully excited the
+glass fairly retreated from the pole. It was a clear case of magnetic
+repulsion. He then suspended a bar of the glass between two poles;
+the bar retreated when the poles were excited, and set its length
+equatorially or at right angles to the line joining them. When an
+ordinary magnetic body was similarly suspended, it always set axially,
+that is, from pole to pole.
+
+Faraday called those bodies which were repelled by the poles of a
+magnet, diamagnetic bodies; using this term in a sense different from
+that in which he employed it in his memoir on the magnetization of
+light. The term magnetic he reserved for bodies which exhibited the
+ordinary attraction. He afterwards employed the term magnetic to cover
+the whole phenomena of attraction and repulsion, and used the word
+paramagnetic to designate such magnetic action as is exhibited by iron.
+
+Isolated observations by Brugmanns, Becquerel, Le Baillif, Saigy, and
+Seebeck had indicated the existence of a repulsive force exercised by
+the magnet on two or three substances; but these observations, which
+were unknown to Faraday, had been permitted to remain without extension
+or examination. Having laid hold of the fact of repulsion, Faraday
+immediately expanded and multiplied it. He subjected bodies of the most
+varied qualities to the action of his magnet:--mineral salts, acids,
+alkalis, ethers, alcohols, aqueous solutions, glass, phosphorus,
+resins, oils, essences, vegetable and animal tissues, and found them
+all amenable to magnetic influence. No known solid or liquid proved
+insensible to the magnetic power when developed in sufficient strength.
+All the tissues of the human body, the blood--though it contains
+iron--included, were proved to be diamagnetic. So that if you could
+suspend a man between the poles of a magnet, his extremities would
+retreat from the poles until his length became equatorial.
+
+Soon after he had commenced his researches on diamagnetism, Faraday
+noticed a remarkable phenomenon which first crossed my own path in the
+following way: In the year 1849, while working in the cabinet of my
+friend, Professor Knoblauch, of Marburg, I suspended a small copper coin
+between the poles of an electro-magnet. On exciting the magnet, the coin
+moved towards the poles and then suddenly stopped, as if it had struck
+against a cushion. On breaking the circuit, the coin was repelled, the
+revulsion being so violent as to cause it to spin several times round
+its axis of suspension. A Silber-groschen similarly suspended exhibited
+the same deportment. For a moment I thought this a new discovery; but on
+looking over the literature of the subject, it appeared that Faraday
+had observed, multiplied, and explained the same effect during his
+researches on diamagnetism. His explanation was based upon his own great
+discovery of magneto-electric currents. The effect is a most singular
+one. A weight of several pounds of copper may be set spinning between
+the electro-magnetic poles; the excitement of the magnet instantly stops
+the rotation. Though nothing is apparent to the eye, the copper, if
+moved in the excited magnetic field, appears to move through a viscous
+fluid; while, when a flat piece of the metal is caused to pass to and
+fro like a saw between the poles, the sawing of the magnetic field
+resembles the cutting through of cheese or butter.[1] This virtual
+friction of the magnetic field is so strong, that copper, by its rapid
+rotation between the poles, might probably be fused. We may easily
+dismiss this experiment by saying that the heat is due to the electric
+currents excited in the copper. But so long as we are unable to reply
+to the question, 'What is an electric current?' the explanation is only
+provisional. For my own part, I look with profound interest and hope on
+the strange action here referred to.
+
+Faraday's thoughts ran intuitively into experimental combinations,
+so that subjects whose capacity for experimental treatment would, to
+ordinary minds, seem to be exhausted in a moment, were shown by him to
+be all but inexhaustible. He has now an object in view, the first step
+towards which is the proof that the principle of Archimedes is true of
+magnetism. He forms magnetic solutions of various degrees of strength,
+places them between the poles of his magnet, and suspends in the
+solutions various magnetic bodies. He proves that when the solution
+is stronger than the body plunged in it, the body, though magnetic,
+is repelled; and when an elongated piece of it is surrounded by the
+solution, it sets, like a diamagnetic body, equatorially between the
+excited poles. The same body when suspended in a solution of weaker
+magnetic power than itself, is attracted as a whole, while an elongated
+portion of it sets axially.
+
+And now theoretic questions rush in upon him. Is this new force a true
+repulsion, or is it merely a differential attraction? Might not the
+apparent repulsion of diamagnetic bodies be really due to the greater
+attraction of the medium by which they are surrounded? He tries the
+rarefaction of air, but finds the effect insensible. He is averse to
+ascribing a capacity of attraction to space, or to any hypothetical
+medium supposed to fill space. He therefore inclines, but still with
+caution, to the opinion that the action of a magnet upon bismuth is a
+true and absolute repulsion, and not merely the result of differential
+attraction. And then he clearly states a theoretic view sufficient to
+account for the phenomena. 'Theoretically,' he says, 'an explanation of
+the movements of the diamagnetic bodies, and all the dynamic phenomena
+consequent upon the action of magnets upon them, might be offered in the
+supposition that magnetic induction caused in them a contrary state to
+that which it produced in ordinary matter.' That is to say, while in
+ordinary magnetic influence the exciting pole excites adjacent to itself
+the contrary magnetism, in diamagnetic bodies the adjacent magnetism is
+the same as that of the exciting pole. This theory of reversed polarity,
+however, does not appear to have ever laid deep hold of Faraday's mind;
+and his own experiments failed to give any evidence of its truth. He
+therefore subsequently abandoned it, and maintained the non-polarity of
+the diamagnetic force.
+
+He then entered a new, though related field of inquiry. Having dealt
+with the metals and their compounds, and having classified all of
+them that came within the range of his observation under the two heads
+magnetic and diamagnetic, he began the investigation of the phenomena
+presented by crystals when subjected to magnetic power. This action of
+crystals had been in part theoretically predicted by Poisson,[2] and
+actually discovered by Plucker, whose beautiful results, at the period
+which we have now reached, profoundly interested all scientific men.
+Faraday had been frequently puzzled by the deportment of bismuth, a
+highly crystalline metal. Sometimes elongated masses of the substance
+refused to set equatorially, sometimes they set persistently oblique,
+and sometimes even, like a magnetic body, from pole to pole.
+
+'The effect,' he says, 'occurs at a single pole; and it is then striking
+to observe a long piece of a substance so diamagnetic as bismuth
+repelled, and yet at the same moment set round with force, axially, or
+end on, as a piece of magnetic substance would do.' The effect perplexed
+him; and in his efforts to release himself from this perplexity, no
+feature of this new manifestation of force escaped his attention. His
+experiments are described in a memoir communicated to the Royal Society
+on December 7, 1848.
+
+I have worked long myself at magne-crystallic action, amid all the light
+of Faraday's and Plucker's researches. The papers now before me were
+objects of daily and nightly study with me eighteen or nineteen years
+ago; but even now, though their perusal is but the last of a series of
+repetitions, they astonish me. Every circumstance connected with the
+subject; every shade of deportment; every variation in the energy of
+the action; almost every application which could possibly be made of
+magnetism to bring out in detail the character of this new force,
+is minutely described. The field is swept clean, and hardly anything
+experimental is left for the gleaner. The phenomena, he concludes, are
+altogether different from those of magnetism or diamagnetism: they would
+appear, in fact, to present to us 'a new force, or a new form of force,
+in the molecules of matter,' which, for convenience sake, he designates
+by a new word, as 'the magne-crystallic force.'
+
+He looks at the crystal acted upon by the magnet. From its mass he
+passes, in idea, to its atoms, and he asks himself whether the power
+which can thus seize upon the crystalline molecules, after they have
+been fixed in their proper positions by crystallizing force, may
+not, when they are free, be able to determine their arrangement? He,
+therefore, liberates the atoms by fusing the bismuth. He places the
+fused substance between the poles of an electro-magnet, powerfully
+excited; but he fails to detect any action. I think it cannot be doubted
+that an action is exerted here, that a true cause comes into play; but
+its magnitude is not such as sensibly to interfere with the force of
+crystallization, which, in comparison with the diamagnetic force, is
+enormous. 'Perhaps,' adds Faraday, 'if a longer time were allowed, and
+a permanent magnet used, a better result might be obtained. I had built
+many hopes upon the process.' This expression, and his writings
+abound in such, illustrates what has been already said regarding his
+experiments being suggested and guided by his theoretic conceptions. His
+mind was full of hopes and hypotheses, but he always brought them to an
+experimental test. The record of his planned and executed experiments
+would, I doubt not, show a high ratio of hopes disappointed to hopes
+fulfilled; but every case of fulfilment abolished all memory of defeat;
+disappointment was swallowed up in victory.
+
+After the description of the general character of this new force,
+Faraday states with the emphasis here reproduced its mode of
+action: 'The law of action appears to be that the line or axis of
+MAGNE-CRYSTALLIC force (being the resultant of the action of all the
+molecules) tends to place itself parallel, or as a tangent, to the
+magnetic curve, or line of magnetic force, passing through the place
+where the crystal is situated.' The magne-crystallic force, moreover,
+appears to him 'to be clearly distinguished from the magnetic or
+diamagnetic forces, in that it causes neither approach nor recession,
+consisting not in attraction or repulsion, but in giving a certain
+determinate position to the mass under its influence.' And then he goes
+on 'very carefully to examine and prove the conclusion that there was no
+connection of the force with attractive or repulsive influences.' With
+the most refined ingenuity he shows that, under certain circumstances,
+the magne-crystallic force can cause the centre of gravity of a highly
+magnetic body to retreat from the poles, and the centre of gravity of a
+highly diamagnetic body to approach them. His experiments root his mind
+more and more firmly in the conclusion that 'neither attraction nor
+repulsion causes the set, or governs the final position' of the crystal
+in the magnetic field. That the force which does so is therefore
+'distinct in its character and effects from the magnetic and diamagnetic
+forms of force. On the other hand,' he continues, 'it has a most
+manifest relation to the crystalline structure of bismuth and other
+bodies, and therefore to the power by which their molecules are able to
+build up the crystalline masses.'
+
+And here follows one of those expressions which characterize the
+conceptions of Faraday in regard to force generally:--'It appears to me
+impossible to conceive of the results in any other way than by a mutual
+reaction of the magnetic force, and the force of the particles of the
+crystals upon each other.' He proves that the action of the force,
+though thus molecular, is an action at a distance; he shows that a
+bismuth crystal can cause a freely suspended magnetic needle to set
+parallel to its magne-crystallic axis. Few living men are aware of the
+difficulty of obtaining results like this, or of the delicacy necessary
+to their attainment. 'But though it thus takes up the character of
+a force acting at a distance, still it is due to that power of the
+particles which makes them cohere in regular order and gives the mass
+its crystalline aggregation, which we call at other times the
+attraction of aggregation, and so often speak of as acting at insensible
+distances.' Thus he broods over this new force, and looks at it from all
+possible points of inspection. Experiment follows experiment, as thought
+follows thought. He will not relinquish the subject as long as a hope
+exists of throwing more light upon it. He knows full well the anomalous
+nature of the conclusion to which his experiments lead him. But
+experiment to him is final, and he will not shrink from the conclusion.
+'This force,' he says, 'appears to me to be very strange and striking
+in its character. It is not polar, for there is no attraction
+or repulsion.' And then, as if startled by his own utterance, he
+asks--'What is the nature of the mechanical force which turns the
+crystal round, and makes it affect a magnet?'... 'I do not remember,' he
+continues 'heretofore such a case of force as the present one, where a
+body is brought into position only, without attraction or repulsion.'
+
+Plucker, the celebrated geometer already mentioned, who pursued
+experimental physics for many years of his life with singular devotion
+and success, visited Faraday in those days, and repeated before him
+his beautiful experiments on magneto-optic action. Faraday repeated and
+verified Plucker's observations, and concluded, what he at first seemed
+to doubt, that Plucker's results and magne-crystallic action had the
+same origin.
+
+At the end of his papers, when he takes a last look along the line of
+research, and then turns his eyes to the future, utterances quite as
+much emotional as scientific escape from Faraday. 'I cannot,' he says,
+at the end of his first paper on magne-crystallic action, 'conclude
+this series of researches without remarking how rapidly the knowledge of
+molecular forces grows upon us, and how strikingly every investigation
+tends to develop more and more their importance, and their extreme
+attraction as an object of study. A few years ago magnetism was to us an
+occult power, affecting only a few bodies, now it is found to influence
+all bodies, and to possess the most intimate relations with electricity,
+heat, chemical action, light, crystallization, and through it, with
+the forces concerned in cohesion; and we may, in the present state of
+things, well feel urged to continue in our labours, encouraged by the
+hope of bringing it into a bond of union with gravity itself.'
+
+
+Supplementary remarks
+
+A brief space will, perhaps, be granted me here to state the further
+progress of an investigation which interested Faraday so much. Drawn by
+the fame of Bunsen as a teacher, in the year 1848 I became a student in
+the University of Marburg, in Hesse Cassel. Bunsen's behaviour to me
+was that of a brother as well as that of a teacher, and it was also my
+happiness to make the acquaintance and gain the friendship of Professor
+Knoblauch, so highly distinguished by his researches on Radiant Heat.
+Plucker's and Faraday's investigations filled all minds at the time,
+and towards the end of 1849, Professor Knoblauch and myself commenced
+a joint investigation of the entire question. Long discipline was
+necessary to give us due mastery over it. Employing a method proposed by
+Dove, we examined the optical properties of our crystals ourselves;
+and these optical observations went hand in hand with our magnetic
+experiments. The number of these experiments was very great, but for
+a considerable time no fact of importance was added to those already
+published. At length, however, it was our fortune to meet with various
+crystals whose deportment could not be brought under the laws of
+magne-crystallic action enunciated by Plucker. We also discovered
+instances which led us to suppose that the magne-crystallic force was
+by no means independent, as alleged, of the magnetism or diamagnetism of
+the mass of the crystal. Indeed, the more we worked at the subject, the
+more clearly did it appear to us that the deportment of crystals in the
+magnetic field was due, not to a force previously unknown, but to
+the modification of the known forces of magnetism and diamagnetism by
+crystalline aggregation.
+
+An eminent example of magne-crystallic action adduced by Plucker, and
+experimented on by Faraday, was Iceland spar. It is what in optics is
+called a negative crystal, and according to the law of Plucker, the axis
+of such a crystal was always repelled by a magnet. But we showed that it
+was only necessary to substitute, in whole or in part, carbonate of iron
+for carbonate of lime, thus changing the magnetic but not the optical
+character of the crystal, to cause the axis to be attracted. That the
+deportment of magnetic crystals is exactly antithetical to that of
+diamagnetic crystals isomorphous with the magnetic ones, was proved
+to be a general law of action. In all cases, the line which in
+a diamagnetic crystal set equatorially, always set itself in an
+isomorphous magnetic crystal axially. By mechanical compression other
+bodies were also made to imitate the Iceland spar.
+
+These and numerous other results bearing upon the question were
+published at the time in the 'Philosophical Magazine' and in
+'Poggendorff's Annalen'; and the investigation of diamagnetism and
+magne-crystallic action was subsequently continued by me in the
+laboratory of Professor Magnus of Berlin. In December, 1851, after I had
+quitted Germany, Dr. Bence Jones went to the Prussian capital to see
+the celebrated experiments of Du Bois Reymond. Influenced, I suppose, by
+what he there heard, he afterwards invited me to give a Friday evening
+discourse at the Royal Institution. I consented, not without fear and
+trembling. For the Royal Institution was to me a kind of dragon's den,
+where tact and strength would be necessary to save me from destruction.
+On February 11, 1853, the discourse was given, and it ended happily.
+I allude to these things, that I may mention that, though my aim and
+object in that lecture was to subvert the notions both of Faraday and
+Plucker, and to establish in opposition to their views what I regarded
+as the truth, it was very far from producing in Faraday either enmity or
+anger. At the conclusion of the lecture, he quitted his accustomed seat,
+crossed the theatre to the corner into which I had shrunk, shook me by
+the hand, and brought me back to the table. Once more, subsequently,
+and in connection with a related question, I ventured to differ from him
+still more emphatically. It was done out of trust in the greatness of
+his character; nor was the trust misplaced. He felt my public dissent
+from him; and it pained me afterwards to the quick to think that I had
+given him even momentary annoyance. It was, however, only momentary. His
+soul was above all littleness and proof to all egotism. He was the same
+to me afterwards that he had been before; the very chance expression
+which led me to conclude that he felt my dissent being one of kindness
+and affection.
+
+It required long subsequent effort to subdue the complications of
+magne-crystallic action, and to bring under the dominion of elementary
+principles the vast mass of facts which the experiments of Faraday and
+Plucker had brought to light. It was proved by Reich, Edmond Becquerel,
+and myself, that the condition of diamagnetic bodies, in virtue of which
+they were repelled by the poles of a magnet, was excited in them by
+those poles; that the strength of this condition rose and fell with, and
+was proportional to, the strength of the acting magnet. It was not then
+any property possessed permanently by the bismuth, and which merely
+required the development of magnetism to act upon it, that caused the
+repulsion; for then the repulsion would have been simply proportional to
+the strength of the influencing magnet, whereas experiment proved it to
+augment as the square of the strength. The capacity to be repelled was
+therefore not inherent in the bismuth, but induced. So far an identity
+of action was established between magnetic and diamagnetic bodies.
+After this the deportment of magnetic bodies, 'normal' and 'abnormal';
+crystalline, amorphous, and compressed, was compared with that of
+crystalline, amorphous, and compressed diamagnetic bodies; and by a
+series of experiments, executed in the laboratory of this Institution,
+the most complete antithesis was established between magnetism and
+diamagnetism. This antithesis embraced the quality of polarity,--the
+theory of reversed polarity, first propounded by Faraday, being proved
+to be true. The discussion of the question was very brisk. On the
+Continent Professor Wilhelm Weber was the ablest and most successful
+supporter of the doctrine of diamagnetic polarity; and it was with an
+apparatus, devised by him and constructed under his own superintendence,
+by Leyser of Leipzig, that the last demands of the opponents of
+diamagnetic polarity were satisfied. The establishment of this point was
+absolutely necessary to the explanation of magne-crystallic action.
+
+With that admirable instinct which always guided him, Faraday had seen
+that it was possible, if not probable, that the diamagnetic force acts
+with different degrees of intensity in different directions, through
+the mass of a crystal. In his studies on electricity, he had sought an
+experimental reply to the question whether crystalline bodies had not
+different specific inductive capacities in different directions, but
+he failed to establish any difference of the kind. His first attempt
+to establish differences of diamagnetic action in different directions
+through bismuth, was also a failure; but he must have felt this to be
+a point of cardinal importance, for he returned to the subject in 1850,
+and proved that bismuth was repelled with different degrees of force in
+different directions. It seemed as if the crystal were compounded of
+two diamagnetic bodies of different strengths, the substance being more
+strongly repelled across the magne-crystallic axis than along it. The
+same result was obtained independently, and extended to various
+other bodies, magnetic as well as diamagnetic, and also to compressed
+substances, a little subsequently by myself.
+
+The law of action in relation to this point is, that in diamagnetic
+crystals, the line along which the repulsion is a maximum, sets
+equatorially in the magnetic field; while in magnetic crystals the line
+along which the attraction is a maximum sets from pole to pole. Faraday
+had said that the magne-crystallic force was neither attraction nor
+repulsion. Thus far he was right. It was neither taken singly, but it
+was both. By the combination of the doctrine of diamagnetic polarity
+with these differential attractions and repulsions, and by paying due
+regard to the character of the magnetic field, every fact brought
+to light in the domain of magne-crystallic action received complete
+explanation. The most perplexing of those facts were shown to result
+from the action of mechanical couples, which the proved polarity both
+of magnetism and diamagnetism brought into play. Indeed the thoroughness
+with which the experiments of Faraday were thus explained, is the most
+striking possible demonstration of the marvellous precision with which
+they were executed.
+
+
+Footnotes to Chapter 11
+
+     [1] See Heat as a Mode of Motion, ninth edition, p. 75.
+
+     [2] See Sir Wm. Thomson on Magne-crystallic Action. Phil.
+     Mag., 1851.
+
+
+
+
+Chapter 12.
+
+     Magnetism of flame and gases--atmospheric magnetism
+
+When an experimental result was obtained by Faraday it was instantly
+enlarged by his imagination. I am acquainted with no mind whose power
+and suddenness of expansion at the touch of new physical truth could be
+ranked with his. Sometimes I have compared the action of his experiments
+on his mind to that of highly combustible matter thrown into a furnace;
+every fresh entry of fact was accompanied by the immediate development
+of light and heat. The light, which was intellectual, enabled him to see
+far beyond the boundaries of the fact itself, and the heat, which was
+emotional, urged him to the conquest of this newly-revealed domain. But
+though the force of his imagination was enormous, he bridled it like a
+mighty rider, and never permitted his intellect to be overthrown.
+
+In virtue of the expansive power which his vivid imagination conferred
+upon him, he rose from the smallest beginnings to the grandest ends.
+Having heard from Zantedeschi that Bancalari had established the
+magnetism of flame, he repeated the experiments and augmented the
+results. He passed from flames to gases, examining and revealing their
+magnetic and diamagnetic powers; and then he suddenly rose from his
+bubbles of oxygen and nitrogen to the atmospheric envelope of the
+earth itself, and its relations to the great question of terrestrial
+magnetism. The rapidity with which these ever-augmenting thoughts
+assumed the form of experiments is unparalleled. His power in this
+respect is often best illustrated by his minor investigations, and,
+perhaps, by none more strikingly than by his paper 'On the Diamagnetic
+Condition of Flame and Gases,' published as a letter to Mr. Richard
+Taylor, in the 'Philosophical Magazine' for December, 1847. After
+verifying, varying, and expanding the results of Bancalari, he submitted
+to examination heated air-currents, produced by platinum spirals placed
+in the magnetic field, and raised to incandescence by electricity. He
+then examined the magnetic deportment of gases generally. Almost all
+of these gases are invisible; but he must, nevertheless, track them in
+their unseen courses. He could not effect this by mingling smoke with
+his gases, for the action of his magnet upon the smoke would have
+troubled his conclusions. He, therefore, 'caught' his gases in tubes,
+carried them out of the magnetic field, and made them reveal themselves
+at a distance from the magnet.
+
+Immersing one gas in another, he determined their differential action;
+results of the utmost beauty being thus arrived at. Perhaps the
+most important are those obtained with atmospheric air and its two
+constituents. Oxygen, in various media, was strongly attracted by the
+magnet; in coal-gas, for example, it was powerfully magnetic, whereas
+nitrogen was diamagnetic. Some of the effects obtained with oxygen
+in coal-gas were strikingly beautiful. When the fumes of chloride of
+ammonium (a diamagnetic substance) were mingled with the oxygen, the
+cloud of chloride behaved in a most singular manner,--'The attraction
+of iron filings,' says Faraday, 'to a magnetic pole is not more striking
+than the appearance presented by the oxygen under these circumstances.'
+
+On observing this deportment the question immediately occurs to
+him,--Can we not separate the oxygen of the atmosphere from its nitrogen
+by magnetic analysis? It is the perpetual occurrence of such questions
+that marks the great experimenter. The attempt to analyze atmospheric
+air by magnetic force proved a failure, like the previous attempt to
+influence crystallization by the magnet. The enormous comparative power
+of the force of crystallization I have already assigned as a reason for
+the incompetence of the magnet to determine molecular arrangement; in
+the present instance the magnetic analysis is opposed by the force of
+diffusion, which is also very strong comparatively. The same remark
+applies to, and is illustrated by, another experiment subsequently
+executed by Faraday. Water is diamagnetic, sulphate of iron is strongly
+magnetic. He enclosed 'a dilute solution of sulphate of iron in a tube,
+and placed the lower end of the tube between the poles of a powerful
+horseshoe magnet for days together,' but he could produce 'no
+concentration of the solution in the part near the magnet.' Here also
+the diffusibility of the salt was too powerful for the force brought
+against it.
+
+The experiment last referred to is recorded in a paper presented to
+the Royal Society on the 2nd August, 1850, in which he pursues the
+investigation of the magnetism of gases. Newton's observations on
+soap-bubbles were often referred to by Faraday. His delight in a
+soap-bubble was like that of a boy, and he often introduced them into
+his lectures, causing them, when filled with air, to float on invisible
+seas of carbonic acid, and otherwise employing them as a means of
+illustration. He now finds them exceedingly useful in his experiments
+on the magnetic condition of gases. A bubble of air in a magnetic field
+occupied by air was unaffected, save through the feeble repulsion of its
+envelope. A bubble of nitrogen, on the contrary, was repelled from the
+magnetic axis with a force far surpassing that of a bubble of air.
+The deportment of oxygen in air 'was very impressive, the bubble being
+pulled inward or towards the axial line, sharply and suddenly, as if the
+oxygen were highly magnetic.'
+
+He next labours to establish the true magnetic zero, a problem not so
+easy as might at first sight be imagined. For the action of the magnet
+upon any gas, while surrounded by air or any other gas, can only be
+differential; and if the experiment were made in vacuo, the action of
+the envelope, in this case necessarily of a certain thickness, would
+trouble the result. While dealing with this subject, Faraday makes
+some noteworthy observations regarding space. In reference to the
+Torricellian vacuum, he says, 'Perhaps it is hardly necessary for me to
+state that I find both iron and bismuth in such vacua perfectly obedient
+to the magnet. From such experiments, and also from general observations
+and knowledge, it seems manifest that the lines of magnetic force can
+traverse pure space, just as gravitating force does, and as statical
+electrical forces do, and therefore space has a magnetic relation of its
+own, and one that we shall probably find hereafter to be of the utmost
+importance in natural phenomena. But this character of space is not
+of the same kind as that which, in relation to matter, we endeavour to
+express by the terms magnetic and diamagnetic. To confuse these
+together would be to confound space with matter, and to trouble all
+the conceptions by which we endeavour to understand and work out a
+progressively clearer view of the mode of action, and the laws of
+natural forces. It would be as if in gravitation or electric forces,
+one were to confound the particles acting on each other with the space
+across which they are acting, and would, I think, shut the door to
+advancement. Mere space cannot act as matter acts, even though the
+utmost latitude be allowed to the hypothesis of an ether; and admitting
+that hypothesis, it would be a large additional assumption to suppose
+that the lines of magnetic force are vibrations carried on by it, whilst
+as yet we have no proof that time is required for their propagation, or
+in what respect they may, in general character, assimilate to or differ
+from their respective lines of gravitating, luminiferous, or electric
+forces.'
+
+Pure space he assumes to be the true magnetic zero, but he pushes his
+inquiries to ascertain whether among material substances there may not
+be some which resemble space. If you follow his experiments, you will
+soon emerge into the light of his results. A torsion-beam was
+suspended by a skein of cocoon silk; at one end of the beam was fixed
+a cross-piece 1 1/2 inch long. Tubes of exceedingly thin glass, filled
+with various gases, and hermetically sealed, were suspended in pairs
+from the two ends of the cross-piece. The position of the rotating
+torsion-head was such that the two tubes were at opposite sides of,
+and equidistant from, the magnetic axis, that is to say from the line
+joining the two closely approximated polar points of an electro-magnet.
+His object was to compare the magnetic action of the gases in the
+two tubes. When one tube was filled with oxygen, and the other with
+nitrogen, on the supervention of the magnetic force, the oxygen was
+pulled towards the axis, the nitrogen being pushed out. By turning
+the torsion-head they could be restored to their primitive position of
+equidistance, where it is evident the action of the glass envelopes was
+annulled. The amount of torsion necessary to re-establish equidistance
+expressed the magnetic difference of the substances compared.
+
+And then he compared oxygen with oxygen at different pressures. One of
+his tubes contained the gas at the pressure of 30 inches of mercury,
+another at a pressure of 15 inches of mercury, a third at a pressure
+of 10 inches, while a fourth was exhausted as far as a good air-pump
+renders exhaustion possible. 'When the first of these was compared with
+the other three, the effect was most striking.' It was drawn towards
+the axis when the magnet was excited, the tube containing the rarer gas
+being apparently driven away, and the greater the difference between the
+densities of the two gases, the greater was the energy of this action.
+
+And now observe his mode of reaching a material magnetic zero. When
+a bubble of nitrogen was exposed in air in the magnetic field, on the
+supervention of the power, the bubble retreated from the magnet. A less
+acute observer would have set nitrogen down as diamagnetic; but Faraday
+knew that retreat, in a medium composed in part of oxygen, might be due
+to the attraction of the latter gas, instead of to the repulsion of the
+gas immersed in it. But if nitrogen be really diamagnetic, then a bubble
+or bulb filled with the dense gas will overcome one filled with the
+rarer gas. From the cross-piece of his torsion-balance he suspended his
+bulbs of nitrogen, at equal distances from the magnetic axis, and found
+that the rarefaction, or the condensation of the gas in either of the
+bulbs had not the slightest influence. When the magnetic force was
+developed, the bulbs remained in their first position, even when one
+was filled with nitrogen, and the other as far as possible exhausted.
+Nitrogen, in fact, acted 'like space itself'; it was neither magnetic
+nor diamagnetic.
+
+He cannot conveniently compare the paramagnetic force of oxygen with
+iron, in consequence of the exceeding magnetic intensity of the latter
+substance; but he does compare it with the sulphate of iron, and finds
+that, bulk for bulk, oxygen is equally magnetic with a solution of this
+substance in water 'containing seventeen times the weight of the oxygen
+in crystallized proto-sulphate of iron, or 3.4 times its weight of
+metallic iron in that state of combination.' By its capability to
+deflect a fine glass fibre, he finds that the attraction of this bulb
+of oxygen, containing only 0.117 of a grain of the gas, at an average
+distance of more than an inch from the magnetic axis, is about equal to
+the gravitating force of the same amount of oxygen as expressed by its
+weight.
+
+These facts could not rest for an instant in the mind of Faraday without
+receiving that expansion to which I have already referred. 'It is hardly
+necessary,' he writes, 'for me to say here that this oxygen cannot exist
+in the atmosphere exerting such a remarkable and high amount of magnetic
+force, without having a most important influence on the disposition of
+the magnetism of the earth, as a planet; especially if it be remembered
+that its magnetic condition is greatly altered by variations of its
+density and by variations of its temperature. I think I see here the
+real cause of many of the variations of that force, which have been, and
+are now so carefully watched on different parts of the surface of the
+globe. The daily variation, and the annual variation, both seem likely
+to come under it; also very many of the irregular continual variations,
+which the photographic process of record renders so beautifully
+manifest. If such expectations be confirmed, and the influence of the
+atmosphere be found able to produce results like these, then we shall
+probably find a new relation between the aurora borealis and the
+magnetism of the earth, namely, a relation established, more or less,
+through the air itself in connection with the space above it; and even
+magnetic relations and variations, which are not as yet suspected,
+may be suggested and rendered manifest and measurable, in the further
+development of what I will venture to call Atmospheric Magnetism. I may
+be over-sanguine in these expectations, but as yet I am sustained in
+them by the apparent reality, simplicity, and sufficiency of the
+cause assumed, as it at present appears to my mind. As soon as I
+have submitted these views to a close consideration, and the test of
+accordance with observation, and, where applicable, with experiments
+also, I will do myself the honour to bring them before the Royal
+Society.'
+
+Two elaborate memoirs are then devoted to the subject of Atmospheric
+Magnetism; the first sent to the Royal Society on the 9th of October,
+and the second on the 19th of November, 1850. In these memoirs he
+discusses the effects of heat and cold upon the magnetism of the air,
+and the action on the magnetic needle, which must result from thermal
+changes. By the convergence and divergence of the lines of terrestrial
+magnetic force, he shows how the distribution of magnetism, in
+the earth's atmosphere, is effected. He applies his results to the
+explanation of the Annual and of the Diurnal Variation: he also
+considers irregular variations, including the action of magnetic storms.
+He discusses, at length, the observations at St. Petersburg, Greenwich,
+Hobarton, St. Helena, Toronto, and the Cape of Good Hope; believing
+that the facts, revealed by his experiments, furnish the key to the
+variations observed at all these places.
+
+In the year 1851, I had the honour of an interview with Humboldt, in
+Berlin, and his parting words to me then were, 'Tell Faraday that I
+entirely agree with him, and that he has, in my opinion, completely
+explained the variation of the declination.' Eminent men have since
+informed me that Humboldt was hasty in expressing this opinion. In
+fact, Faraday's memoirs on atmospheric magnetism lost much of their
+force--perhaps too much--through the important discovery of the relation
+of the variation of the declination to the number of the solar spots.
+But I agree with him and M. Edmond Becquerel, who worked independently
+at this subject, in thinking, that a body so magnetic as oxygen,
+swathing the earth, and subject to variations of temperature, diurnal
+and annual, must affect the manifestations of terrestrial magnetism.[1]
+The air that stands upon a single square foot of the earth's surface
+is, according to Faraday, equivalent in magnetic force to 8160 lbs.
+of crystallized protosulphate of iron. Such a substance cannot be
+absolutely neutral as regards the deportment of the magnetic needle. But
+Faraday's writings on this subject are so voluminous, and the theoretic
+points are so novel and intricate, that I shall postpone the complete
+analysis of these researches to a time when I can lay hold of them more
+completely than my other duties allow me to do now.
+
+
+Footnote to Chapter 12
+
+     [1] This persuasion has been greatly strengthened by the
+     recent perusal of a paper by Mr. Baxendell.
+
+
+
+
+Chapter 13.
+
+     Speculations: nature of matter: lines of force
+
+The scientific picture of Faraday would not be complete without a
+reference to his speculative writings. On Friday, January 19, 1844,
+he opened the weekly evening-meetings of the Royal Institution by a
+discourse entitled 'A speculation touching Electric Conduction and the
+nature of Matter.' In this discourse he not only attempts the overthrow
+of Dalton's Theory of Atoms, but also the subversion of all ordinary
+scientific ideas regarding the nature and relations of Matter and Force.
+He objected to the use of the term atom:--'I have not yet found a
+mind,' he says, 'that did habitually separate it from its accompanying
+temptations; and there can be no doubt that the words definite
+proportions, equivalent, primes, &c., which did and do fully express all
+the facts of what is usually called the atomic theory in chemistry, were
+dismissed because they were not expressive enough, and did not say all
+that was in the mind of him who used the word atom in their stead.'
+
+A moment will be granted me to indicate my own view of Faraday's
+position here. The word 'atom' was not used in the stead of definite
+proportions, equivalents, or primes. These terms represented facts that
+followed from, but were not equivalent to, the atomic theory. Facts
+cannot satisfy the mind: and the law of definite combining proportions
+being once established, the question 'why should combination take place
+according to that law?' is inevitable. Dalton answered this question by
+the enunciation of the Atomic Theory, the fundamental idea of which
+is, in my opinion, perfectly secure. The objection of Faraday to Dalton
+might be urged with the same substantial force against Newton: it might
+be stated with regard to the planetary motions that the laws of
+Kepler revealed the facts; that the introduction of the principle of
+gravitation was an addition to the facts. But this is the essence of
+all theory. The theory is the backward guess from fact to principle;
+the conjecture, or divination regarding something, which lies behind
+the facts, and from which they flow in necessary sequence. If Dalton's
+theory, then, account for the definite proportions observed in the
+combinations of chemistry, its justification rests upon the same basis
+as that of the principle of gravitation. All that can in strictness be
+said in either case is that the facts occur as if the principle existed.
+
+The manner in which Faraday himself habitually deals with his hypotheses
+is revealed in this lecture. He incessantly employed them to gain
+experimental ends, but he incessantly took them down, as an architect
+removes the scaffolding when the edifice is complete. 'I cannot but
+doubt,' he says, 'that he who as a mere philosopher has most power of
+penetrating the secrets of nature, and guessing by hypothesis at her
+mode of working, will also be most careful for his own safe progress
+and that of others, to distinguish the knowledge which consists of
+assumption, by which I mean theory and hypothesis, from that which is
+the knowledge of facts and laws.' Faraday himself, in fact, was
+always 'guessing by hypothesis,' and making theoretic divination the
+stepping-stone to his experimental results.
+
+I have already more than once dwelt on the vividness with which he
+realised molecular conditions; we have a fine example of this strength
+and brightness of imagination in the present 'speculation.' He grapples
+with the notion that matter is made up of particles, not in absolute
+contact, but surrounded by interatomic space. 'Space,' he observes,
+'must be taken as the only continuous part of a body so constituted.
+Space will permeate all masses of matter in every direction like a net,
+except that in place of meshes it will form cells, isolating each atom
+from its neighbours, itself only being continuous.'
+
+Let us follow out this notion; consider, he argues, the case of a
+non-conductor of electricity, such for example as shell-lac, with its
+molecules, and intermolecular spaces running through the mass. In its
+case space must be an insulator; for if it were a conductor it would
+resemble 'a fine metallic web,' penetrating the lac in every direction.
+But the fact is that it resembles the wax of black sealing-wax, which
+surrounds and insulates the particles of conducting carbon, interspersed
+throughout its mass. In the case of shell-lac, therefore, space is an
+insulator.
+
+But now, take the case of a conducting metal. Here we have, as before,
+the swathing of space round every atom. If space be an insulator there
+can be no transmission of electricity from atom to atom. But there is
+transmission; hence space is a conductor. Thus he endeavours to hamper
+the atomic theory. 'The reasoning,' he says, 'ends in a subversion of
+that theory altogether; for if space be an insulator it cannot exist
+in conducting bodies, and if it be a conductor it cannot exist in
+insulating bodies. Any ground of reasoning,' he adds, as if carried away
+by the ardour of argument, 'which tends to such conclusions as these
+must in itself be false.'
+
+He then tosses the atomic theory from horn to horn of his dilemmas. What
+do we know, he asks, of the atom apart from its force? You imagine a
+nucleus which may be called a, and surround it by forces which may
+be called m; 'to my mind the a or nucleus vanishes, and the substance
+consists in the powers of m. And indeed what notion can we form of the
+nucleus independent of its powers? What thought remains on which to hang
+the imagination of an a independent of the acknowledged forces?' Like
+Boscovich, he abolishes the atom, and puts a 'centre of force' in its
+place.
+
+With his usual courage and sincerity he pushes his view to its utmost
+consequences. 'This view of the constitution of matter,' he continues,
+'would seem to involve necessarily the conclusion that matter fills
+all space, or at least all space to which gravitation extends; for
+gravitation is a property of matter dependent on a certain force, and it
+is this force which constitutes the matter. In that view matter is
+not merely mutually penetrable;[1] but each atom extends, so to say,
+throughout the whole of the solar system, yet always retaining its own
+centre of force.'
+
+It is the operation of a mind filled with thoughts of this profound,
+strange, and subtle character that we have to take into account in
+dealing with Faraday's later researches. A similar cast of thought
+pervades a letter addressed by Faraday to Mr. Richard Phillips, and
+published in the 'Philosophical Magazine' for May, 1846. It is entitled
+'Thoughts on Ray-vibrations,' and it contains one of the most singular
+speculations that ever emanated from a scientific mind. It must be
+remembered here, that though Faraday lived amid such speculations he did
+not rate them highly, and that he was prepared at any moment to change
+them or let them go. They spurred him on, but they did not hamper him.
+His theoretic notions were fluent; and when minds less plastic than his
+own attempted to render those fluxional images rigid, he rebelled. He
+warns Phillips moreover, that from first to last, 'he merely threw out
+as matter for speculation the vague impressions of his mind; for he gave
+nothing as the result of sufficient consideration, or as the settled
+conviction, or even probable conclusion at which he had arrived.'
+
+The gist of this communication is that gravitating force acts in lines
+across space, and that the vibrations of light and radiant heat consist
+in the tremors of these lines of force. 'This notion,' he says, 'as far
+as it is admitted, will dispense with the ether, which, in another view
+is supposed to be the medium in which these vibrations take place.' And
+he adds further on, that his view 'endeavours to dismiss the ether but
+not the vibrations.' The idea here set forth is the natural supplement
+of his previous notion, that it is gravitating force which constitutes
+matter, each atom extending, so to say, throughout the whole of the
+solar system.
+
+The letter to Mr. Phillips winds up with this beautiful conclusion:--
+
+'I think it likely that I have made many mistakes in the preceding
+pages, for even to myself my ideas on this point appear only as the
+shadow of a speculation, or as one of those impressions upon the mind
+which are allowable for a time as guides to thought and research. He who
+labours in experimental inquiries, knows how numerous these are, and how
+often their apparent fitness and beauty vanish before the progress and
+development of real natural truth.'
+
+Let it then be remembered that Faraday entertained notions regarding
+matter and force altogether distinct from the views generally held by
+scientific men. Force seemed to him an entity dwelling along the line in
+which it is exerted. The lines along which gravity acts between the sun
+and earth seem figured in his mind as so many elastic strings; indeed
+he accepts the assumed instantaneity of gravity as the expression of the
+enormous elasticity of the 'lines of weight.' Such views, fruitful in
+the case of magnetism, barren, as yet, in the case of gravity, explain
+his efforts to transform this latter force. When he goes into the open
+air and permits his helices to fall, to his mind's eye they are
+tearing through the lines of gravitating power, and hence his hope and
+conviction that an effect would and ought to be produced. It must
+ever be borne in mind that Faraday's difficulty in dealing with these
+conceptions was at bottom the same as that of Newton; that he is in
+fact trying to overleap this difficulty, and with it probably the limits
+prescribed to the intellect itself.
+
+The idea of lines of magnetic force was suggested to Faraday by the
+linear arrangement of iron filings when scattered over a magnet. He
+speaks of and illustrates by sketches, the deflection, both convergent
+and divergent, of the lines of force, when they pass respectively
+through magnetic and diamagnetic bodies. These notions of concentration
+and divergence are also based on the direct observation of his filings.
+So long did he brood upon these lines; so habitually did he associate
+them with his experiments on induced currents, that the association
+became 'indissoluble,' and he could not think without them. 'I have been
+so accustomed,' he writes, 'to employ them, and especially in my last
+researches, that I may have unwittingly become prejudiced in their
+favour, and ceased to be a clear-sighted judge. Still, I have always
+endeavoured to make experiment the test and controller of theory
+and opinion; but neither by that nor by close cross-examination in
+principle, have I been made aware of any error involved in their use.'
+
+In his later researches on magne-crystallic action, the idea of lines of
+force is extensively employed; it indeed led him to an experiment which
+lies at the root of the whole question. In his subsequent researches on
+Atmospheric Magnetism the idea receives still wider application, showing
+itself to be wonderfully flexible and convenient. Indeed without this
+conception the attempt to seize upon the magnetic actions, possible or
+actual, of the atmosphere would be difficult in the extreme; but the
+notion of lines of force, and of their divergence and convergence,
+guides Faraday without perplexity through all the intricacies of the
+question. After the completion of those researches, and in a paper
+forwarded to the Royal Society on October 22, 1851, he devotes himself
+to the formal development and illustration of his favourite idea. The
+paper bears the title, 'On lines of magnetic force, their definite
+character, and their distribution within a magnet and through space.'
+A deep reflectiveness is the characteristic of this memoir. In his
+experiments, which are perfectly beautiful and profoundly suggestive, he
+takes but a secondary delight. His object is to illustrate the utility
+of his conception of lines of force. 'The study of these lines,' he
+says, 'has at different times been greatly influential in leading me to
+various results which I think prove their utility as well as fertility.'
+
+Faraday for a long period used the lines of force merely as 'a
+representative idea.' He seemed for a time averse to going further in
+expression than the lines themselves, however much further he may
+have gone in idea. That he believed them to exist at all times round a
+magnet, and irrespective of the existence of magnetic matter, such as
+iron filings, external to the magnet, is certain. No doubt the space
+round every magnet presented itself to his imagination as traversed by
+loops of magnetic power; but he was chary in speaking of the physical
+substratum of those loops. Indeed it may be doubted whether the physical
+theory of lines of force presented itself with any distinctness to his
+own mind. The possible complicity of the luminiferous ether in magnetic
+phenomena was certainly in his thoughts. 'How the magnetic force,' he
+writes, 'is transferred through bodies or through space we know not;
+whether the result is merely action at a distance, as in the case of
+gravity; or by some intermediate agency, as in the case of light, heat,
+the electric current, and (as I believe) static electric action. The
+idea of magnetic fluids, as applied by some, or of Magnetic centres of
+action, does not include that of the latter kind of transmission, but
+the idea of lines of force does.' And he continues thus:--'I am more
+inclined to the notion that in the transmission of the [magnetic] force
+there is such an action [an intermediate agency] external to the magnet,
+than that the effects are merely attraction and repulsion at a distance.
+Such an affection may be a function of the ether; for it is not at all
+unlikely that, if there be an ether, it should have other uses than
+simply the conveyance of radiations.' When he speaks of the magnet in
+certain cases, 'revolving amongst its own forces,' he appears to have
+some conception of this kind in view.
+
+A great part of the investigation completed in October, 1851, was
+taken up with the motions of wires round the poles of a magnet and the
+converse. He carried an insulated wire along the axis of a bar magnet
+from its pole to its equator, where it issued from the magnet, and was
+bent up so as to connect its two ends. A complete circuit, no part of
+which was in contact with the magnet, was thus obtained. He found that
+when the magnet and the external wire were rotated together no current
+was produced; whereas, when either of them was rotated and the other
+left at rest currents were evolved. He then abandoned the axial wire,
+and allowed the magnet itself to take its place; the result was the
+same.[2] It was the relative motion of the magnet and the loop that was
+effectual in producing a current.
+
+The lines of force have their roots in the magnet, and though they may
+expand into infinite space, they eventually return to the magnet. Now
+these lines may be intersected close to the magnet or at a distance from
+it. Faraday finds distance to be perfectly immaterial so long as the
+number of lines intersected is the same. For example, when the loop
+connecting the equator and the pole of his barmagnet performs one
+complete revolution round the magnet, it is manifest that all the lines
+of force issuing from the magnet are once intersected. Now it matters
+not whether the loop be ten feet or ten inches in length, it matters
+not how it may be twisted and contorted, it matters not how near to the
+magnet or how distant from it the loop may be, one revolution always
+produces the same amount of current electricity, because in all
+these cases all the lines of force issuing from the magnet are once
+intersected and no more.
+
+From the external portion of the circuit he passes in idea to the
+internal, and follows the lines of force into the body of the magnet
+itself. His conclusion is that there exist lines of force within the
+magnet of the same nature as those without. What is more, they are
+exactly equal in amount to those without. They have a relation in
+direction to those without; and in fact are continuations of them....
+'Every line of force, therefore, at whatever distance it may be taken
+from the magnet, must be considered as a closed circuit, passing in some
+part of its course through the magnet, and having an equal amount of
+force in every part of its course.'
+
+All the results here described were obtained with moving metals. 'But,'
+he continues with profound sagacity, 'mere motion would not generate a
+relation, which had not a foundation in the existence of some previous
+state; and therefore the quiescent metals must be in some relation to
+the active centre of force,' that is to the magnet. He here touches the
+core of the whole question, and when we can state the condition into
+which the conducting wire is thrown before it is moved, we shall then
+be in a position to understand the physical constitution of the electric
+current generated by its motion.
+
+In this inquiry Faraday worked with steel magnets, the force of which
+varies with the distance from the magnet. He then sought a uniform field
+of magnetic force, and found it in space as affected by the magnetism
+of the earth. His next memoir, sent to the Royal Society, December 31,
+1851, is 'on the employment of the Induced Magnetoelectro Current as a
+test and measure of magnetic forces.' He forms rectangles and rings, and
+by ingenious and simple devices collects the opposed currents which are
+developed in them by rotation across the terrestrial lines of magnetic
+force. He varies the shapes of his rectangles while preserving their
+areas constant, and finds that the constant area produces always the
+same amount of current per revolution. The current depends solely on
+the number of lines of force intersected, and when this number is kept
+constant the current remains constant too. Thus the lines of magnetic
+force are continually before his eyes, by their aid he colligates his
+facts, and through the inspirations derived from them he vastly expands
+the boundaries of our experimental knowledge. The beauty and exactitude
+of the results of this investigation are extraordinary. I cannot
+help thinking while I dwell upon them, that this discovery of
+magneto-electricity is the greatest experimental result ever obtained by
+an investigator. It is the Mont Blanc of Faraday's own achievements.
+He always worked at great elevations, but a higher than this he never
+subsequently attained.
+
+
+Footnotes to Chapter 13
+
+     [1] He compares the interpenetration of two atoms to the
+     coalescence of two distinct waves, which though for a moment
+     blended to a single mass, preserve their individuality, and
+     afterwards separate.
+
+     [2] In this form the experiment is identical with one made
+     twenty years earlier.  See page 34.
+
+
+
+
+Chapter 14.
+
+     Unity and convertibility of natural forces: theory of the
+     electric current.
+
+The terms unity and convertibility, as applied to natural forces, are
+often employed in these investigations, many profound and beautiful
+thoughts respecting these subjects being expressed in Faraday's memoirs.
+Modern inquiry has, however, much augmented our knowledge of the
+relationship of natural forces, and it seems worth while to say a few
+words here, tending to clear up certain misconceptions which appear to
+exist among philosophic writers regarding this relationship.
+
+The whole stock of energy or working-power in the world consists of
+attractions, repulsions, and motions. If the attractions and repulsions
+are so circumstanced as to be able to produce motion, they are sources
+of working-power, but not otherwise. Let us for the sake of simplicity
+confine our attention to the case of attraction. The attraction exerted
+between the earth and a body at a distance from the earth's surface is
+a source of working-power; because the body can be moved by the
+attraction, and in falling to the earth can perform work. When it rests
+upon the earth's surface it is not a source of power or energy, because
+it can fall no further. But though it has ceased to be a source of
+energy, the attraction of gravity still acts as a force, which holds the
+earth and weight together.
+
+The same remarks apply to attracting atoms and molecules. As long as
+distance separates them, they can move across it in obedience to the
+attraction, and the motion thus produced may, by proper appliances,
+be caused to perform mechanical work. When, for example, two atoms of
+hydrogen unite with one of oxygen, to form water the atoms are first
+drawn towards each other--they move, they clash, and then by virtue of
+their resiliency, they recoil and quiver. To this quivering motion
+we give the name of heat. Now this quivering motion is merely the
+redistribution of the motion produced by the chemical affinity; and this
+is the only sense in which chemical affinity can be said to be converted
+into heat. We must not imagine the chemical attraction destroyed, or
+converted into anything else. For the atoms, when mutually clasped to
+form a molecule of water, are held together by the very attraction which
+first drew them towards each other. That which has really been expended
+is the pull exerted through the space by which the distance between the
+atoms has been diminished.
+
+If this be understood, it will be at once seen that gravity may in this
+sense be said to be convertible into heat; that it is in reality no more
+an outstanding and inconvertible agent, as it is sometimes stated to
+be, than chemical affinity. By the exertion of a certain pull, through
+a certain space, a body is caused to clash with a certain definite
+velocity against the earth. Heat is thereby developed, and this is the
+only sense in which gravity can be said to be converted into heat. In no
+case is the force which produces the motion annihilated or changed into
+anything else. The mutual attraction of the earth and weight exists when
+they are in contact as when they were separate; but the ability of that
+attraction to employ itself in the production of motion does not exist.
+
+The transformation, in this case, is easily followed by the mind's
+eye. First, the weight as a whole is set in motion by the attraction
+of gravity. This motion of the mass is arrested by collision with the
+earth; being broken up into molecular tremors, to which we give the name
+of heat.
+
+And when we reverse the process, and employ those tremors of heat to
+raise a weight, as is done through the intermediation of an elastic
+fluid in the steam-engine, a certain definite portion of the molecular
+motion is destroyed in raising the weight. In this sense, and this
+sense only, can the heat be said to be converted into gravity, or
+more correctly, into potential energy of gravity. It is not that the
+destruction of the heat has created any new attraction, but simply that
+the old attraction has now a power conferred upon it, of exerting a
+certain definite pull in the interval between the starting-point of the
+falling weight and its collision with the earth.
+
+So also as regards magnetic attraction: when a sphere of iron placed
+at some distance from a magnet rushes towards the magnet, and has its
+motion stopped by collision, an effect mechanically the same as that
+produced by the attraction of gravity occurs. The magnetic attraction
+generates the motion of the mass, and the stoppage of that motion
+produces heat. In this sense, and in this sense only, is there a
+transformation of magnetic work into heat. And if by the mechanical
+action of heat, brought to bear by means of a suitable machine, the
+sphere be torn from the magnet and again placed at a distance, a power
+of exerting a pull through that distance, and producing a new motion of
+the sphere, is thereby conferred upon the magnet; in this sense, and in
+this sense only, is the heat converted into magnetic potential energy.
+
+When, therefore, writers on the conservation of energy speak of tensions
+being 'consumed' and 'generated,' they do not mean thereby that old
+attractions have been annihilated and new ones brought into existence,
+but that, in the one case, the power of the attraction to produce
+motion has been diminished by the shortening of the distance between
+the attracting bodies, and that in the other case the power of producing
+motion has been augmented by the increase of the distance. These remarks
+apply to all bodies, whether they be sensible masses or molecules.
+
+Of the inner quality that enables matter to attract matter we know
+nothing; and the law of conservation makes no statement regarding that
+quality. It takes the facts of attraction as they stand, and affirms
+only the constancy of working-power. That power may exist in the form
+of MOTION; or it may exist in the form of FORCE, with distance to act
+through. The former is dynamic energy, the latter is potential
+energy, the constancy of the sum of both being affirmed by the law of
+conservation. The convertibility of natural forces consists solely
+in transformations of dynamic into potential, and of potential into
+dynamic, energy, which are incessantly going on. In no other sense has
+the convertibility of force, at present, any scientific meaning.
+
+By the contraction of a muscle a man lifts a weight from the earth. But
+the muscle can contract only through the oxidation of its own tissue or
+of the blood passing through it. Molecular motion is thus converted into
+mechanical motion. Supposing the muscle to contract without raising the
+weight, oxidation would also occur, but the whole of the heat produced
+by this oxidation would be liberated in the muscle itself. Not so when
+it performs external work; to do that work a certain definite portion of
+the heat of oxidation must be expended. It is so expended in pulling the
+weight away from the earth. If the weight be permitted to fall, the heat
+generated by its collision with the earth would exactly make up for that
+lacking in the muscle during the lifting of the weight. In the case
+here supposed, we have a conversion of molecular muscular action into
+potential energy of gravity; and a conversion of that potential energy
+into heat; the heat, however, appearing at a distance from its real
+origin in the muscle. The whole process consists of a transference of
+molecular motion from the muscle to the weight, and gravitating force is
+the mere go-between, by means of which the transference is effected.
+
+These considerations will help to clear our way to the conception of
+the transformations which occur when a wire is moved across the lines
+of force in a magnetic field. In this case it is commonly said we have
+a conversion of magnetism into electricity. But let us endeavour to
+understand what really occurs. For the sake of simplicity, and with a
+view to its translation into a different one subsequently, let us adopt
+for a moment the provisional conception of a mixed fluid in the wire,
+composed of positive and negative electricities in equal quantities, and
+therefore perfectly neutralizing each other when the wire is still. By
+the motion of the wire, say with the hand, towards the magnet, what the
+Germans call a Scheidungs-Kraft--a separating force--is brought into
+play. This force tears the mixed fluids asunder, and drives them in
+two currents, the one positive and the other negative, in two opposite
+directions through the wire. The presence of these currents evokes a
+force of repulsion between the magnet and the wire; and to cause the one
+to approach the other, this repulsion must be overcome. The overcoming
+of this repulsion is, in fact, the work done in separating and impelling
+the two electricities. When the wire is moved away from the magnet, a
+Scheidungs-Kraft, or separating force, also comes into play; but now it
+is an attraction that has to be surmounted. In surmounting it, currents
+are developed in directions opposed to the former; positive takes the
+place of negative, and negative the place of positive; the overcoming of
+the attraction being the work done in separating and impelling the two
+electricities.
+
+The mechanical action occurring here is different from that occurring
+where a sphere of soft iron is withdrawn from a magnet, and again
+attracted. In this case muscular force is expended during the act of
+separation; but the attraction of the magnet effects the reunion. In the
+case of the moving wire also we overcome a resistance in separating it
+from the magnet, and thus far the action is mechanically the same as the
+separation of the sphere of iron. But after the wire has ceased moving,
+the attraction ceases; and so far from any action occurring similar to
+that which draws the iron sphere back to the magnet, we have to overcome
+a repulsion to bring them together.
+
+There is no potential energy conferred either by the removal or by
+the approach of the wire, and the only power really transformed or
+converted, in the experiment, is muscular power. Nothing that could in
+strictness be called a conversion of magnetism into electricity occurs.
+The muscular oxidation that moves the wire fails to produce within the
+muscle its due amount of heat, a portion of that heat, equivalent to the
+resistance overcome, appearing in the moving wire instead.
+
+Is this effect an attraction and a repulsion at a distance? If so, why
+should both cease when the wire ceases to move? In fact, the deportment
+of the wire resembles far more that of a body moving in a resisting
+medium than anything else; the resistance ceasing when the motion is
+suspended. Let us imagine the case of a liquid so mobile that the hand
+may be passed through it to and fro, without encountering any sensible
+resistance. It resembles the motion of a conductor in the unexcited
+field of an electro-magnet. Now, let us suppose a body placed in
+the liquid, or acting on it, which confers upon it the property of
+viscosity; the hand would no longer move freely. During its motion, but
+then only, resistance would be encountered and overcome. Here we have
+rudely represented the case of the excited magnetic field, and the
+result in both cases would be substantially the same. In both cases heat
+would, in the end, be generated outside of the muscle, its amount being
+exactly equivalent to the resistance overcome.
+
+Let us push the analogy a little further; suppose in the case of the
+fluid rendered viscous, as assumed a moment ago, the viscosity not to be
+so great as to prevent the formation of ripples when the hand is passed
+through the liquid. Then the motion of the hand, before its final
+conversion into heat, would exist for a time as wave-motion, which, on
+subsiding, would generate its due equivalent of heat. This intermediate
+stage, in the case of our moving wire, is represented by the period
+during which the electric current is flowing through it; but that
+current, like the ripples of our liquid, soon subsides, being, like
+them, converted into heat.
+
+Do these words shadow forth anything like the reality? Such speculations
+cannot be injurious if they are enunciated without dogmatism. I do
+confess that ideas such as these here indicated exercise a strong
+fascination on my mind. Is then the magnetic field really viscous,
+and if so, what substance exists in it and the wire to produce the
+viscosity? Let us first look at the proved effects, and afterwards turn
+our thoughts back upon their cause. When the wire approaches the magnet,
+an action is evoked within it, which travels through it with a velocity
+comparable to that of light. One substance only in the universe has
+been hitherto proved competent to transmit power at this velocity;
+the luminiferous ether. Not only its rapidity of progression, but its
+ability to produce the motion of light and heat, indicates that the
+electric current is also motion.[1] Further, there is a striking
+resemblance between the action of good and bad conductors as regards
+electricity, and the action of diathermanous and adiathermanous bodies
+as regards radiant heat. The good conductor is diathermanous to the
+electric current; it allows free transmission without the development of
+heat. The bad conductor is adiathermanous to the electric current, and
+hence the passage of the latter is accompanied by the development of
+heat. I am strongly inclined to hold the electric current, pure and
+simple, to be a motion of the ether alone; good conductors being so
+constituted that the motion may be propagated through their ether
+without sensible transfer to their atoms, while in the case of bad
+conductors this transfer is effected, the transferred motion appearing
+as heat.[2]
+
+I do not know whether Faraday would have subscribed to what is here
+written; probably his habitual caution would have prevented him from
+committing himself to anything so definite. But some such idea filled
+his mind and coloured his language through all the later years of his
+life. I dare not say that he has been always successful in the treatment
+of these theoretic notions. In his speculations he mixes together light
+and darkness in varying proportions, and carries us along with him
+through strong alternations of both. It is impossible to say how a
+certain amount of mathematical training would have affected his work.
+We cannot say what its influence would have been upon that force of
+inspiration that urged him on; whether it would have daunted him, and
+prevented him from driving his adits into places where no theory pointed
+to a lode. If so, then we may rejoice that this strong delver at the
+mine of natural knowledge was left free to wield his mattock in his own
+way. It must be admitted, that Faraday's purely speculative writings
+often lack that precision which the mathematical habit of thought
+confers. Still across them flash frequent gleams of prescient wisdom
+which will excite admiration throughout all time; while the facts,
+relations, principles, and laws which his experiments have established
+are sure to form the body of grand theories yet to come.
+
+
+Footnotes to Chapter 14
+
+     [1] Mr. Clerk Maxwell has recently published an exceedingly
+     important investigation connected with this question.  Even
+     in the non-mathematical portions of the memoirs of Mr.
+     Maxwell, the admirable spirit of his philosophy is
+     sufficiently revealed. As regards the employment of
+     scientific imagery, I hardly know his equal in power of
+     conception and clearness of definition.
+
+     [2] One important difference, of course, exists between the
+     effect of motion in the magnetic field, and motion in a
+     resisting medium. In the former case the heat is generated
+     in the moving conductor, in the latter it is in part
+     generated in the medium.
+
+
+
+
+Chapter 15.
+
+     Summary.
+
+When from an Alpine height the eye of the climber ranges over the
+mountains, he finds that for the most part they resolve themselves into
+distinct groups, each consisting of a dominant mass surrounded by peaks
+of lesser elevation. The power which lifted the mightier eminences, in
+nearly all cases lifted others to an almost equal height. And so it is
+with the discoveries of Faraday. As a general rule, the dominant result
+does not stand alone, but forms the culminating point of a vast and
+varied mass of inquiry. In this way, round about his great discovery of
+Magneto-electric Induction, other weighty labours group themselves. His
+investigations on the Extra Current; on the Polar and other Condition of
+Diamagnetic Bodies; on Lines of Magnetic Force, their definite character
+and distribution; on the employment of the Induced Magneto-electric
+Current as a measure and test of Magnetic Action; on the Revulsive
+Phenomena of the magnetic field, are all, notwithstanding the diversity
+of title, researches in the domain of Magneto-electric Induction.
+
+Faraday's second group of researches and discoveries embrace the
+chemical phenomena of the current. The dominant result here is the great
+law of definite Electro-chemical Decomposition, around which are massed
+various researches on Electro-chemical Conduction and on Electrolysis
+both with the Machine and with the Pile. To this group also belongs
+his analysis of the Contact Theory, his inquiries as to the Source of
+Voltaic Electricity, and his final development of the Chemical Theory of
+the pile.
+
+His third great discovery is the Magnetization of Light, which I should
+liken to the Weisshorn among mountains--high, beautiful, and alone.
+
+The dominant result of his fourth group of researches is the discovery
+of Diamagnetism, announced in his memoir as the Magnetic Condition of
+all Matter, round which are grouped his inquiries on the Magnetism
+of Flame and Gases; on Magne-crystallic action, and on Atmospheric
+Magnetism, in its relations to the annual and diurnal variation of the
+needle, the full significance of which is still to be shown.
+
+These are Faraday's most massive discoveries, and upon them his fame
+must mainly rest. But even without them, sufficient would remain to
+secure for him a high and lasting scientific reputation. We should
+still have his researches on the Liquefaction of Gases; on Frictional
+Electricity; on the Electricity of the Gymnotus; on the source of
+Power in the Hydro-electric machine, the last two investigations being
+untouched in the foregoing memoir; on Electro-magnetic Rotations; on
+Regelation; all his more purely Chemical Researches, including his
+discovery of Benzol. Besides these he published a multitude of minor
+papers, most of which, in some way or other, illustrate his genius. I
+have made no allusion to his power and sweetness as a lecturer. Taking
+him for all in all, I think it will be conceded that Michael Faraday
+was the greatest experimental philosopher the world has ever seen; and
+I will add the opinion, that the progress of future research will tend,
+not to dim or to diminish, but to enhance and glorify the labours of
+this mighty investigator.
+
+
+
+
+Chapter 16.
+
+    Illustrations of Character.
+
+Thus far I have confined myself to topics mainly interesting to the man
+of science, endeavouring, however, to treat them in a manner unrepellent
+to the general reader who might wish to obtain a notion of Faraday as
+a worker. On others will fall the duty of presenting to the world
+a picture of the man. But I know you will permit me to add to the
+foregoing analysis a few personal reminiscences and remarks, tending to
+connect Faraday with a wider world than that of science--namely, with
+the general human heart.
+
+One word in reference to his married life, in addition to what has been
+already said, may find a place here. As in the former case, Faraday
+shall be his own spokesman. The following paragraph, though written in
+the third person, is from his hand:--'On June 12, 1821, he married, an
+event which more than any other contributed to his earthly happiness and
+healthful state of mind. The union has continued for twenty-eight years
+and has in no wise changed, except in the depth and strength of its
+character.'
+
+Faraday's immediate forefathers lived in a little place called Clapham
+Wood Hall, in Yorkshire. Here dwelt Robert Faraday and Elizabeth his
+wife, who had ten children, one of them, James Faraday, born in 1761,
+being father to the philosopher. A family tradition exists that the
+Faradays came originally from Ireland. Faraday himself has more than
+once expressed to me his belief that his blood was in part Celtic, but
+how much of it was so, or when the infusion took place, he was unable to
+say. He could imitate the Irish brogue, and his wonderful vivacity may
+have been in part due to his extraction. But there were other qualities
+which we should hardly think of deriving from Ireland. The most
+prominent of these was his sense of order, which ran like a luminous
+beam through all the transactions of his life. The most entangled and
+complicated matters fell into harmony in his hands. His mode of
+keeping accounts excited the admiration of the managing board of this
+Institution. And his science was similarly ordered. In his Experimental
+Researches, he numbered every paragraph, and welded their various parts
+together by incessant reference. His private notes of the Experimental
+Researches, which are happily preserved, are similarly numbered: their
+last paragraph bears the figure 16,041. His working qualities, moreover,
+showed the tenacity of the Teuton. His nature was impulsive, but there
+was a force behind the impulse which did not permit it to retreat. If in
+his warm moments he formed a resolution, in his cool ones he made that
+resolution good. Thus his fire was that of a solid combustible, not that
+of a gas, which blazes suddenly, and dies as suddenly away.
+
+And here I must claim your tolerance for the limits by which I am
+confined. No materials for a life of Faraday are in my hands, and what
+I have now to say has arisen almost wholly out of our close personal
+relationship.
+
+Letters of his, covering a period of sixteen years, are before me,
+each one of which contains some characteristic utterance;--strong, yet
+delicate in counsel, joyful in encouragement, and warm in affection.
+References which would be pleasant to such of them as still live are
+made to Humboldt, Biot, Dumas, Chevreul, Magnus, and Arago. Accident
+brought these names prominently forward; but many others would be
+required to complete his list of continental friends. He prized the love
+and sympathy of men--prized it almost more than the renown which his
+science brought him. Nearly a dozen years ago it fell to my lot to
+write a review of his 'Experimental Researches' for the 'Philosophical
+Magazine.' After he had read it, he took me by the hand, and said,
+'Tyndall, the sweetest reward of my work is the sympathy and good will
+which it has caused to flow in upon me from all quarters of the world.'
+Among his letters I find little sparks of kindness, precious to no one
+but myself, but more precious to me than all. He would peep into the
+laboratory when he thought me weary, and take me upstairs with him to
+rest. And if I happened to be absent, he would leave a little note for
+me, couched in this or some other similar form:--'Dear Tyndall,--I was
+looking for you, because we were at tea--we have not yet done--will you
+come up?' I frequently shared his early dinner; almost always, in fact,
+while my lectures were going on. There was no trace of asceticism in his
+nature. He preferred the meat and wine of life to its locusts and wild
+honey. Never once during an intimacy of fifteen years did he mention
+religion to me, save when I drew him on to the subject. He then spoke
+to me without hesitation or reluctance; not with any apparent desire to
+'improve the occasion,' but to give me such information as I sought.
+He believed the human heart to be swayed by a power to which science
+or logic opened no approach, and, right or wrong, this faith, held in
+perfect tolerance of the faiths of others, strengthened and beautified
+his life.
+
+From the letters just referred to, I will select three for publication
+here. I choose the first, because it contains a passage revealing the
+feelings with which Faraday regarded his vocation, and also because it
+contains an allusion which will give pleasure to a friend.
+
+
+'Royal Institution. [ this is crossed out by Faraday ]
+
+'Ventnor, Isle of Wight, June 28, 1854.
+
+'My Dear Tyndall,--You see by the top of this letter how much habit
+prevails over me; I have just read yours from thence, and yet I think
+myself there. However, I have left its science in very good keeping, and
+I am glad to learn that you are at experiment once more. But how is the
+health? Not well, I fear. I wish you would get yourself strong first
+and work afterwards. As for the fruits, I am sure they will be good, for
+though I sometimes despond as regards myself, I do not as regards you.
+You are young, I am old.... But then our subjects are so glorious,
+that to work at them rejoices and encourages the feeblest; delights and
+enchants the strongest.
+
+'I have not yet seen anything from Magnus. Thoughts of him always
+delight me. We shall look at his black sulphur together. I heard from
+Schonbein the other day. He tells me that Liebig is full of ozone, i.e.,
+of allotropic oxygen.
+
+'Good-bye for the present.
+
+'Ever, my dear Tyndall,
+
+'Yours truly,
+
+'M. Faraday.'
+
+
+The contemplation of Nature, and his own relation to her, produced in
+Faraday a kind of spiritual exaltation which makes itself manifest here.
+His religious feeling and his philosophy could not be kept apart; there
+was an habitual overflow of the one into the other.
+
+Whether he or another was its exponent, he appeared to take equal
+delight in science. A good experiment would make him almost dance with
+delight. In November, 1850, he wrote to me thus:--'I hope some day to
+take up the point respecting the magnetism of associated particles.
+In the meantime I rejoice at every addition to the facts and reasoning
+connected with the subject. When science is a republic, then it gains:
+and though I am no republican in other matters, I am in that.' All his
+letters illustrate this catholicity of feeling. Ten years ago, when
+going down to Brighton, he carried with him a little paper I had just
+completed, and afterwards wrote to me. His letter is a mere sample of
+the sympathy which he always showed to me and my work.
+
+
+'Brighton, December 9, 1857.
+
+'My Dear Tyndall,--I cannot resist the pleasure of saying how very much
+I have enjoyed your paper. Every part has given me delight. It goes on
+from point to point beautifully. You will find many pencil marks, for I
+made them as I read. I let them stand, for though many of them receive
+their answer as the story proceeds, yet they show how the wording
+impresses a mind fresh to the subject, and perhaps here and there you
+may like to alter it slightly, if you wish the full idea, i.e., not an
+inaccurate one, to be suggested at first; and yet after all I believe
+it is not your exposition, but the natural jumping to a conclusion that
+affects or has affected my pencil.
+
+'We return on Friday, when I will return you the paper.
+
+'Ever truly yours,
+
+'M. Faraday.'
+
+
+The third letter will come in its proper place towards the end.
+
+While once conversing with Faraday on science, in its relations to
+commerce and litigation, he said to me, that at a certain period of his
+career, he was forced definitely to ask himself, and finally to decide
+whether he should make wealth or science the pursuit of his life. He
+could not serve both masters, and he was therefore compelled to choose
+between them. After the discovery of magneto-electricity his fame was
+so noised abroad, that the commercial world would hardly have considered
+any remuneration too high for the aid of abilities like his. Even before
+he became so famous, he had done a little 'professional business.' This
+was the phrase he applied to his purely commercial work. His friend,
+Richard Phillips, for example, had induced him to undertake a number of
+analyses, which produced, in the year 1830, an addition to his income
+of more than a thousand pounds; and in 1831 a still greater addition. He
+had only to will it to raise in 1832 his professional business income
+to 5000L. a year. Indeed double this sum would be a wholly insufficient
+estimate of what he might, with ease, have realised annually during the
+last thirty years of his life.
+
+While restudying the Experimental Researches with reference to the
+present memoir, the conversation with Faraday here alluded to came to
+my recollection, and I sought to ascertain the period when the question,
+'wealth or science,' had presented itself with such emphasis to his
+mind. I fixed upon the year 1831 or 1832, for it seemed beyond the range
+of human power to pursue science as he had done during the subsequent
+years, and to pursue commercial work at the same time. To test this
+conclusion I asked permission to see his accounts, and on my own
+responsibility, I will state the result. In 1832, his professional
+business income, instead of rising to 5000L., or more, fell from 1090L.
+4s. to 155L. 9s. From this it fell with slight oscillations to 92L. in
+1837, and to zero in 1838. Between 1839 and 1845, it never, except in
+one instance, exceeded 22L.; being for the most part much under this.
+The exceptional year referred to was that in which he and Sir Charles
+Lyell were engaged by Government to write a report on the Haswell
+Colliery explosion, and then his business income rose to 112L. From
+the end of 1845 to the day of his death, Faraday's annual professional
+business income was exactly zero. Taking the duration of his life into
+account, this son of a blacksmith, and apprentice to a bookbinder,
+had to decide between a fortune of 150,000L. on the one side, and his
+undowered science on the other. He chose the latter, and died a poor
+man. But his was the glory of holding aloft among the nations the
+scientific name of England for a period of forty years.
+
+The outward and visible signs of fame were also of less account to him
+than to most men. He had been loaded with scientific honours from all
+parts of the world. Without, I imagine, a dissentient voice, he was
+regarded as the prince of the physical investigators of the present age.
+The highest scientific position in this country he had, however, never
+filled. When the late excellent and lamented Lord Wrottesley resigned
+the presidency of the Royal Society, a deputation from the council,
+consisting of his Lordship, Mr. Grove, and Mr. Gassiot, waited upon
+Faraday, to urge him to accept the president's chair. All that argument
+or friendly persuasion could do was done to induce him to yield to the
+wishes of the council, which was also the unanimous wish of scientific
+men. A knowledge of the quickness of his own nature had induced in
+Faraday the habit of requiring an interval of reflection, before he
+decided upon any question of importance. In the present instance he
+followed his usual habit, and begged for a little time.
+
+On the following morning, I went up to his room and said on entering
+that I had come to him with some anxiety of mind. He demanded its cause,
+and I responded:--'Lest you should have decided against the wishes of
+the deputation that waited on you yesterday.' 'You would not urge me to
+undertake this responsibility,' he said. 'I not only urge you,' was my
+reply, 'but I consider it your bounden duty to accept it.' He spoke of
+the labour that it would involve; urged that it was not in his nature to
+take things easy; and that if he became president, he would surely have
+to stir many new questions, and agitate for some changes. I said that in
+such cases he would find himself supported by the youth and strength
+of the Royal Society. This, however, did not seem to satisfy him. Mrs.
+Faraday came into the room, and he appealed to her. Her decision was
+adverse, and I deprecated her decision. 'Tyndall,' he said at length, 'I
+must remain plain Michael Faraday to the last; and let me now tell you,
+that if I accepted the honour which the Royal Society desires to confer
+upon me, I would not answer for the integrity of my intellect for a
+single year.' I urged him no more, and Lord Wrottesley had a most worthy
+successor in Sir Benjamin Brodie.
+
+After the death of the Duke of Northumberland, our Board of Managers
+wished to see Mr. Faraday finish his career as President of the
+Institution, which he had entered on weekly wages more than half a
+century before. But he would have nothing to do with the presidency. He
+wished for rest, and the reverent affection of his friends was to him
+infinitely more precious than all the honours of official life.
+
+The first requisite of the intellectual life of Faraday was the
+independence of his mind; and though prompt to urge obedience where
+obedience was due, with every right assertion of manhood he intensely
+sympathized. Even rashness on the side of honour found from him ready
+forgiveness, if not open applause. The wisdom of years, tempered by a
+character of this kind, rendered his counsel peculiarly precious to
+men sensitive like himself. I often sought that counsel, and, with
+your permission, will illustrate its character by one or two typical
+instances.
+
+In 1855, I was appointed examiner under the Council for Military
+Education. At that time, as indeed now, I entertained strong convictions
+as to the enormous utility of physical science to officers of artillery
+and engineers, and whenever opportunity offered, I expressed this
+conviction without reserve. I did not think the recognition, though
+considerable, accorded to physical science in those examinations at
+all proportionate to its importance; and this probably rendered me more
+jealous than I otherwise should have been of its claims.
+
+In Trinity College, Dublin, a school had been organized with reference
+to the Woolwich examinations, and a large number of exceedingly
+well-instructed young gentlemen were sent over from Dublin, to compete
+for appointments in the artillery and the engineers. The result of
+one examination was particularly satisfactory to me; indeed the marks
+obtained appeared so eloquent that I forbore saying a word about them.
+My colleagues, however, followed the usual custom of sending in brief
+reports with their returns of marks. After the results were published,
+a leading article appeared in 'The Times,' in which the reports were
+largely quoted, praise being bestowed on all the candidates, except the
+excellent young fellows who had passed through my hands.
+
+A letter from Trinity College drew my attention to this article,
+bitterly complaining that whereas the marks proved them to be the best
+of all, the science candidates were wholly ignored. I tried to set
+matters right by publishing, on my own responsibility, a letter in
+'The Times.' The act, I knew, could not bear justification from the War
+Office point of view; and I expected and risked the displeasure of my
+superiors. The merited reprimand promptly came. 'Highly as the Secretary
+of State for War might value the expression of Professor Tyndall's
+opinion, he begged to say that an examiner, appointed by His Royal
+Highness the Commander-in-Chief, had no right to appear in the public
+papers as Professor Tyndall has done, without the sanction of the War
+Office.' Nothing could be more just than this reproof, but I did not
+like to rest under it. I wrote a reply, and previous to sending it took
+it up to Faraday. We sat together before his fire, and he looked very
+earnest as he rubbed his hands and pondered. The following conversation
+then passed between us:--
+
+F. You certainly have received a reprimand, Tyndall; but the matter is
+over, and if you wish to accept the reproof, you will hear no more about
+it.
+
+T. But I do not wish to accept it.
+
+F. Then you know what the consequence of sending that letter will be?
+
+T. I do.
+
+F. They will dismiss you.
+
+T. I know it.
+
+F. Then send the letter!
+
+The letter was firm, but respectful; it acknowledged the justice of the
+censure, but expressed neither repentance nor regret. Faraday, in
+his gracious way, slightly altered a sentence or two to make it more
+respectful still. It was duly sent, and on the following day I entered
+the Institution with the conviction that my dismissal was there before
+me. Weeks, however, passed. At length the well-known envelope appeared,
+and I broke the seal, not doubting the contents. They were very
+different from what I expected. 'The Secretary of State for War has
+received Professor Tyndall's letter, and deems the explanation therein
+given perfectly satisfactory.' I have often wished for an opportunity of
+publicly acknowledging this liberal treatment, proving, as it did, that
+Lord Panmure could discern and make allowance for a good intention,
+though it involved an offence against routine. For many years
+subsequently it was my privilege to act under that excellent body, the
+Council for Military Education.
+
+On another occasion of this kind, having encouraged me in a somewhat
+hardy resolution I had formed, Faraday backed his encouragement by an
+illustration drawn from his own life. The subject will interest you, and
+it is so sure to be talked about in the world, that no avoidable harm
+can rise from its introduction here.
+
+In the year 1835, Sir Robert Peel wished to offer Faraday a pension, but
+that great statesman quitted office before he was able to realise his
+wish. The Minister who founded these pensions intended them, I believe,
+to be marks of honour which even proud men might accept without
+compromise of independence. When, however, the intimation first
+reached Faraday in an unofficial way, he wrote a letter announcing his
+determination to decline the pension; and stating that he was quite
+competent to earn his livelihood himself. That letter still exists, but
+it was never sent, Faraday's repugnance having been overruled by
+his friends. When Lord Melbourne came into office, he desired to see
+Faraday; and probably in utter ignorance of the man--for unhappily for
+them and us, Ministers of State in England are only too often ignorant
+of great Englishmen--his Lordship said something that must have deeply
+displeased his visitor. All the circumstances were once communicated to
+me, but I have forgotten the details. The term 'humbug,' I think, was
+incautiously employed by his Lordship, and other expressions were used
+of a similar kind. Faraday quitted the Minister with his own resolves,
+and that evening he left his card and a short and decisive note at the
+residence of Lord Melbourne, stating that he had manifestly mistaken his
+Lordship's intention of honouring science in his person, and declining
+to have anything whatever to do with the proposed pension. The
+good-humoured nobleman at first considered the matter a capital joke;
+but he was afterwards led to look at it more seriously. An excellent
+lady, who was a friend both to Faraday and the Minister, tried to
+arrange matters between them; but she found Faraday very difficult to
+move from the position he had assumed. After many fruitless efforts, she
+at length begged of him to state what he would require of Lord Melbourne
+to induce him to change his mind. He replied, 'I should require from his
+Lordship what I have no right or reason to expect that he would grant--a
+written apology for the words he permitted himself to use to me.' The
+required apology came, frank and full, creditable, I thought, alike to
+the Prime Minister and the philosopher.
+
+Considering the enormous strain imposed on Faraday's intellect, the
+boy-like buoyancy even of his later years was astonishing. He was often
+prostrate, but he had immense resiliency, which he brought into action
+by getting away from London whenever his health failed. I have already
+indicated the thoughts which filled his mind during the evening of his
+life. He brooded on magnetic media and lines of force; and the great
+object of the last investigation he ever undertook was the decision of
+the question whether magnetic force requires time for its propagation.
+How he proposed to attack this subject we may never know. But he has
+left some beautiful apparatus behind; delicate wheels and pinions,
+and associated mirrors, which were to have been employed in the
+investigation. The mere conception of such an inquiry is an illustration
+of his strength and hopefulness, and it is impossible to say to what
+results it might have led him. But the work was too heavy for his tired
+brain. It was long before he could bring himself to relinquish it and
+during this struggle he often suffered from fatigue of mind. It was at
+this period, and before he resigned himself to the repose which marked
+the last two years of his life, that he wrote to me the following
+letter--one of many priceless letters now before me--which reveals, more
+than anything another pen could express, the state of his mind at the
+time. I was sometimes censured in his presence for my doings in the
+Alps, but his constant reply was, 'Let him alone, he knows how to take
+care of himself.' In this letter, anxiety on this score reveals itself
+for the first time.
+
+
+'Hampton Court, August 1, 1864.
+
+'My Dear Tyndall,--I do not know whether my letter will catch you, but I
+will risk it, though feeling very unfit to communicate with a man whose
+life is as vivid and active as yours; but the receipt of your kind
+letter makes me to know that, though I forget, I am not forgotten, and
+though I am not able to remember at the end of a line what was said at
+the beginning of it, the imperfect marks will convey to you some sense
+of what I long to say. We had heard of your illness through Miss Moore,
+and I was therefore very glad to learn that you are now quite well;
+do not run too many risks or make your happiness depend too much upon
+dangers, or the hunting of them. Sometimes the very thinking of you, and
+what you may be about, wearies me with fears, and then the cogitations
+pause and change, but without giving me rest. I know that much of this
+depends upon my own worn-out nature, and I do not know why I write
+it, save that when I write to you I cannot help thinking it, and the
+thoughts stand in the way of other matter.
+
+* * * * *
+
+'See what a strange desultory epistle I am writing to you, and yet I
+feel so weary that I long to leave my desk and go to the couch.
+
+'My dear wife and Jane desire their kindest remembrances: I hear them in
+the next room:... I forget--but not you, my dear Tyndall, for I am
+
+'Ever yours,
+
+'M. Faraday.'
+
+
+This weariness subsided when he relinquished his work, and I have a
+cheerful letter from him, written in the autumn of 1865. But towards
+the close of that year he had an attack of illness, from which he never
+completely rallied. He continued to attend the Friday Evening Meetings,
+but the advance of infirmity was apparent to us all. Complete rest
+became finally essential to him, and he ceased to appear among us. There
+was no pain in his decline to trouble the memory of those who loved him.
+Slowly and peacefully he sank towards his final rest, and when it came,
+his death was a falling asleep. In the fulness of his honours and of his
+age he quitted us; the good fight fought, the work of duty--shall I not
+say of glory?--done. The 'Jane' referred to in the foregoing letter is
+Faraday's niece, Miss Jane Barnard, who with an affection raised almost
+to religious devotion watched him and tended him to the end.
+
+I saw Mr. Faraday for the first time on my return from Marburg in 1850.
+I came to the Royal Institution, and sent up my card, with a copy of the
+paper which Knoblauch and myself had just completed. He came down and
+conversed with me for half an hour. I could not fail to remark the
+wonderful play of intellect and kindly feeling exhibited by his
+countenance. When he was in good health the question of his age would
+never occur to you. In the light and laughter of his eyes you never
+thought of his grey hairs. He was then on the point of publishing one
+of his papers on Magnecrystallic action, and he had time to refer in
+a flattering Note to the memoir I placed in his hands. I returned to
+Germany, worked there for nearly another year, and in June, 1851, came
+back finally from Berlin to England. Then, for the first time, and on my
+way to the meeting of the British Association, at Ipswich, I met a man
+who has since made his mark upon the intellect of his time; who has long
+been, and who by the strong law of natural affinity must continue to
+be, a brother to me. We were both without definite outlook at the time,
+needing proper work, and only anxious to have it to perform. The chairs
+of Natural History and of Physics being advertised as vacant in the
+University of Toronto, we applied for them, he for the one, I for the
+other; but, possibly guided by a prophetic instinct, the University
+authorities declined having anything to do with either of us. If I
+remember aright, we were equally unlucky elsewhere.
+
+One of Faraday's earliest letters to me had reference to this Toronto
+business, which he thought it unwise in me to neglect. But Toronto had
+its own notions, and in 1853, at the instance of Dr. Bence Jones, and on
+the recommendation of Faraday himself, a chair of Physics at the Royal
+Institution was offered to me. I was tempted at the same time to go
+elsewhere, but a strong attraction drew me to his side. Let me say
+that it was mainly his and other friendships, precious to me beyond all
+expression, that caused me to value my position here more highly than
+any other that could be offered to me in this land. Nor is it for its
+honour, though surely that is great, but for the strong personal ties
+that bind me to it, that I now chiefly prize this place. You might not
+credit me were I to tell you how lightly I value the honour of being
+Faraday's successor compared with the honour of having been Faraday's
+friend. His friendship was energy and inspiration; his 'mantle' is a
+burden almost too heavy to be borne.
+
+Sometimes during the last year of his life, by the permission or
+invitation of Mrs. Faraday, I went up to his rooms to see him. The deep
+radiance, which in his time of strength flashed with such extraordinary
+power from his countenance, had subsided to a calm and kindly light, by
+which my latest memory of him is warmed and illuminated. I knelt one day
+beside him on the carpet and placed my hand upon his knee; he stroked
+it affectionately, smiled, and murmured, in a low soft voice, the last
+words that I remember as having been spoken to me by Michael Faraday.
+
+It was my wish and aspiration to play the part of Schiller to this
+Goethe: and he was at times so strong and joyful--his body so active,
+and his intellect so clear--as to suggest to me the thought that
+he, like Goethe, would see the younger man laid low. Destiny ruled
+otherwise, and now he is but a memory to us all. Surely no memory could
+be more beautiful. He was equally rich in mind and heart. The
+fairest traits of a character sketched by Paul, found in him perfect
+illustration. For he was 'blameless, vigilant, sober, of good behaviour,
+apt to teach, not given to filthy lucre.' He had not a trace of worldly
+ambition; he declared his duty to his Sovereign by going to the levee
+once a year, but beyond this he never sought contact with the great.
+The life of his spirit and of his intellect was so full, that the things
+which men most strive after were absolutely indifferent to him. 'Give me
+health and a day,' says the brave Emerson, 'and I will make the pomp of
+emperors ridiculous.' In an eminent degree Faraday could say the same.
+What to him was the splendour of a palace compared with a thunderstorm
+upon Brighton Downs?--what among all the appliances of royalty to
+compare with the setting sun? I refer to a thunderstorm and a sunset,
+because these things excited a kind of ecstasy in his mind, and to
+a mind open to such ecstasy the pomps and pleasures of the world are
+usually of small account. Nature, not education, rendered Faraday strong
+and refined. A favourite experiment of his own was representative of
+himself. He loved to show that water in crystallizing excluded all
+foreign ingredients, however intimately they might be mixed with it. Out
+of acids, alkalis, or saline solutions, the crystal came sweet and pure.
+By some such natural process in the formation of this man, beauty and
+nobleness coalesced, to the exclusion of everything vulgar and low. He
+did not learn his gentleness in the world, for he withdrew himself from
+its culture; and still this land of England contained no truer gentleman
+than he. Not half his greatness was incorporate in his science, for
+science could not reveal the bravery and delicacy of his heart.
+
+But it is time that I should end these weak words, and lay my poor
+garland on the grave of this
+
+         Just and faithful knight of God.
+
+
+
+
+
+End of the Project Gutenberg EBook of Faraday As A Discoverer, by John Tyndall
+
+*** END OF THE PROJECT GUTENBERG EBOOK 1225 ***