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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 ***
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+  <head>
+    <title>
+      Faraday As a Discoverer, by John Tyndall
+    </title>
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+
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+  <body>
+<div>*** START OF THE PROJECT GUTENBERG EBOOK 1225 ***</div>
+    <p>
+      <br /><br />
+    </p>
+    <h1>
+      FARADAY AS A DISCOVERER
+    </h1>
+    <p>
+      <br />
+    </p>
+    <h2>
+      by John Tyndall
+    </h2>
+    <p>
+      <br /> <br />
+    </p>
+    <hr />
+    <p>
+      <br /> <br />
+    </p>
+    <blockquote>
+      <p class="toc">
+        <big><b>CONTENTS</b></big>
+      </p>
+      <p>
+        <br />
+      </p>
+      <p class="toc">
+        <a href="#link2H_PREF"> Preface to the fifth edition. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2H_PREF2"> Preface to the fourth edition. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2H_PREF2"> Preface to the second edition. </a>
+      </p>
+      <p>
+        <br />
+      </p>
+      <p class="toc">
+        <a href="#link2H_4_0004"> <b>FARADAY AS A DISCOVERER.</b> </a>
+      </p>
+      <p>
+        <br />
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0001"> Chapter 1. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0002"> Chapter 2. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0003"> Chapter 3. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0004"> Chapter 4. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0005"> Chapter 5. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0006"> Chapter 6. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0007"> Chapter 7. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0008"> Chapter 8. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0009"> Chapter 9. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0010"> Chapter 10. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0011"> Chapter 11. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0012"> Chapter 12. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0013"> Chapter 13. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0014"> Chapter 14. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0015"> Chapter 15. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0016"> Chapter 16. </a>
+      </p>
+    </blockquote>
+    <p>
+      <br /> <br />
+    </p>
+    <hr />
+    <p>
+      <br /> <br /> <a name="link2H_PREF" id="link2H_PREF">
+      <!--  H2 anchor --> </a>
+    </p>
+    <h2>
+      Preface to the fifth edition.
+    </h2>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      John Tyndall. Hind Head, December, 1893.
+    </p>
+    <p>
+      [Note.&mdash;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.
+    </p>
+    <p>
+      Louisa C. Tyndall.]
+    </p>
+    <p>
+      <a name="link2H_PREF2" id="link2H_PREF2">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Preface to the fourth edition.
+    </h2>
+    <p>
+      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.
+    </p>
+    <p>
+      Royal Institution, February, 1884.
+    </p>
+    <p>
+      <a name="link2H_PREF3" id="link2H_PREF3">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Preface to the second edition.
+    </h2>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      John Tyndall. Royal Institution: December, 1869.
+    </p>
+    <p>
+      <a name="link2H_4_0004" id="link2H_4_0004">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      FARADAY AS A DISCOVERER.
+    </h2>
+    <p>
+      <a name="link2HCH0001" id="link2HCH0001">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 1.
+    </h2>
+<pre xml:space="preserve">
+     Parentage: introduction to the royal institution: earliest
+     experiments: first royal society paper: marriage.
+</pre>
+    <p>
+      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&mdash;however numerous the
+      illustrations which occur to me of the loftiness of Faraday's character
+      and the beauty of his life&mdash;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&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;sharing the opinion of Mr.
+      Carlyle, that 'a really able man never proceeded from entirely stupid
+      parents'&mdash;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.
+    </p>
+    <p>
+      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:&mdash;
+    </p>
+    <p>
+      'Clapham Common, Surrey,
+    </p>
+    <p>
+      'November 28, 1867.
+    </p>
+    <p>
+      'My Dear Tyndall,&mdash;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&mdash;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.
+    </p>
+    <p>
+      '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.
+    </p>
+    <p>
+      'Believe me, my dear Tyndall, yours truly,
+    </p>
+    <p>
+      'J. P. Gassiot.
+    </p>
+    <p>
+      'Dr. Tyndall.'
+    </p>
+    <p>
+      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:&mdash;
+    </p>
+    <p>
+      'London, Sept. 13, 1813.
+    </p>
+    <p>
+      '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:&mdash;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&mdash;about the end; and my absence from home will perhaps be as long
+      as three years. But as yet all is uncertain.'
+    </p>
+    <p>
+      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:&mdash;
+    </p>
+    <p>
+      'My Dear Friend,&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      '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&mdash;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.
+    </p>
+    <p>
+      '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.
+    </p>
+    <p>
+      '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.'
+    </p>
+    <p>
+      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&mdash;her
+      predecessor's name&mdash;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&mdash;that
+      it must be 'Sir Charles Faraday.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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:&mdash;
+    </p>
+    <p>
+      '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.
+    </p>
+    <p>
+      'M. Faraday.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 1
+    </h2>
+<pre xml:space="preserve">
+      (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:&mdash;
+
+     '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,&mdash;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.
+</pre>
+    <p>
+      <a name="link2HCH0002" id="link2HCH0002">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 2.
+    </h2>
+<pre xml:space="preserve">
+     Early researches: magnetic rotations: liquefaction of gases:
+     heavy glass: Charles Anderson: contributions to physics.
+</pre>
+    <p>
+      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&mdash;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.
+    </p>
+    <p>
+      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:&mdash;
+    </p>
+    <p>
+      'Dear Sir,&mdash;The oil you noticed yesterday turns out to be liquid
+      chlorine.
+    </p>
+    <p>
+      'Yours faithfully,
+    </p>
+    <p>
+      'M. Faraday.' (2)
+    </p>
+    <p>
+      The gas had been liquefied by its own pressure. Faraday then tried
+      compression with a syringe, and succeeded thus in liquefying the gas.
+    </p>
+    <p>
+      To the published account of this experiment Davy added the following note:&mdash;'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.
+    </p>
+    <p>
+      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?
+    </p>
+    <p>
+      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)
+    </p>
+    <p>
+      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)
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT_">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 2
+    </h2>
+<pre xml:space="preserve">
+      (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:&mdash;'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:&mdash;'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.&mdash;M. F.' (Exp.
+     Researches, vol. iii. p. 3, footnote.)
+</pre>
+    <p>
+      <a name="link2HCH0003" id="link2HCH0003">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 3.
+    </h2>
+<pre xml:space="preserve">
+     Discovery of Magneto-electricity: Explanation of Argo's
+     magnetism of rotation: Terrestrial magneto-electric
+     induction: The extra current.
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      'During its flow,' and this was the time when an effect was expected&mdash;but
+      here Faraday's power of lateral vision, separating, as it were, from the
+      line of expectation, came into play&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      At the suggestion of a mind fruitful in suggestions of a profound and
+      philosophic character&mdash;I mean that of Sir John Herschel&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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)
+    </p>
+    <p>
+      Three years subsequent to the publication of these researches&mdash;that
+      is to say, on January 29, 1835&mdash;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.
+    </p>
+    <p>
+      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'&mdash;this was his term&mdash;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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      Footnote to Chapter 3
+    </p>
+<pre xml:space="preserve">
+      (1) I am indebted to a friend for the following exquisite
+     morsel:&mdash;'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."'
+</pre>
+    <p>
+      <a name="link2HCH0004" id="link2HCH0004">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 4.
+    </h2>
+<pre xml:space="preserve">
+     Points of Character.
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      As already intimated, Faraday had contributed many of his minor papers&mdash;including
+      his first analysis of caustic lime&mdash;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:&mdash;
+    </p>
+    <p>
+      'PAPERS, NOTES, NOTICES, &amp;c., &amp;c.,published in octavo, up to 1832.
+      M. Faraday.'
+    </p>
+    <p>
+      '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.
+    </p>
+    <p>
+      '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&mdash;and none more than the bad&mdash;in pointing out to me in
+      future, or rather, after times, the faults it became me to watch and to
+      avoid.
+    </p>
+    <p>
+      '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.
+    </p>
+    <p>
+      'M. Faraday.
+    </p>
+    <p>
+      'Aug. 18, 1832.'
+    </p>
+    <p>
+      '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.
+    </p>
+    <p>
+      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:&mdash;
+    </p>
+    <p>
+      'Sydenham, Oct. 6, 1855.
+    </p>
+    <p>
+      'My Dear Tyndall,&mdash;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)
+    </p>
+    <p>
+      'Yours, very truly,
+    </p>
+    <p>
+      'M. Faraday.'
+    </p>
+    <p>
+      Footnote to Chapter 4
+    </p>
+<pre xml:space="preserve">
+      (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.
+</pre>
+    <p>
+      <a name="link2HCH0005" id="link2HCH0005">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 5.
+    </h2>
+<pre xml:space="preserve">
+     Identity of electricities; first researches on
+     electro-chemistry.
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;a favourite test of his&mdash;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.
+    </p>
+    <p>
+      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)
+    </p>
+    <p>
+      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:&mdash;'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.
+    </p>
+    <p>
+      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:&mdash;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&mdash;and this exception he thought might be apparent
+      only&mdash;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)
+    </p>
+    <p>
+      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?&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT__">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 5
+    </h2>
+<pre xml:space="preserve">
+      (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.
+</pre>
+    <p>
+      <a name="link2HCH0006" id="link2HCH0006">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 6.
+    </h2>
+<pre xml:space="preserve">
+     Laws of electro-chemical decomposition.
+</pre>
+    <p>
+      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)
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT___">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 6
+    </h2>
+<pre xml:space="preserve">
+      (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!'&mdash;Proceedings of the Royal Institution, vol.
+     ii. p. 132.
+
+      (2) In 1838 he expresses himself thus:&mdash;'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.'&mdash;Exp. Resear., vol. i. p. 515. ($
+     1617.)
+
+      (3) This conclusion needs qualification.  Faraday overlooked
+     the part played by ozone.
+</pre>
+    <p>
+      <a name="link2HCH0007" id="link2HCH0007">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 7.
+    </h2>
+<pre xml:space="preserve">
+     Origin of power in the voltaic pile.
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;competent therefore to allow the electricity of
+      contact to flow through them if it were able to form a current&mdash;were
+      absolutely powerless when chemically inactive.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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:&mdash;'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)
+    </p>
+    <p>
+      Footnote to Chapter 7
+    </p>
+<pre xml:space="preserve">
+      (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.
+</pre>
+    <p>
+      <a name="link2HCH0008" id="link2HCH0008">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 8.
+    </h2>
+<pre xml:space="preserve">
+     Researches on frictional electricity: induction: conduction:
+     specific inductive capacity: theory of contiguous particles.
+</pre>
+    <p>
+      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.'
+    </p>
+    <p>
+      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,&mdash;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)
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;even the earth itself&mdash;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.
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT____">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 8
+    </h2>
+<pre xml:space="preserve">
+      (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.
+</pre>
+    <p>
+      <a name="link2HCH0009" id="link2HCH0009">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 9.
+    </h2>
+<pre xml:space="preserve">
+     Rest needed&mdash;visit to Switzerland.
+</pre>
+    <p>
+      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
+    </p>
+<pre xml:space="preserve">
+          'Nature never did betray
+           The heart that loved her.'
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      'August 2, 1841.&mdash;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.'
+    </p>
+    <p>
+      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:&mdash;
+    </p>
+    <p>
+      'August 12, 1841.&mdash;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,&mdash;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.'
+    </p>
+    <p>
+      Footnote to Chapter 9
+    </p>
+<pre xml:space="preserve">
+      (1) See note, p. 77.
+</pre>
+    <p>
+      <a name="link2HCH0010" id="link2HCH0010">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 10.
+    </h2>
+<pre xml:space="preserve">
+     Magnetization of light.
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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:&mdash;'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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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)
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT_____">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 10
+    </h2>
+<pre xml:space="preserve">
+      (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.
+</pre>
+    <p>
+      <a name="link2HCH0011" id="link2HCH0011">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 11.
+    </h2>
+<pre xml:space="preserve">
+     Discovery of diamagnetism&mdash;researches on magne-crystallic
+     action.
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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:&mdash;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&mdash;though it contains iron&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      '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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      And here follows one of those expressions which characterize the
+      conceptions of Faraday in regard to force generally:&mdash;'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&mdash;'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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      Supplementary remarks
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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,&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT______">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 11
+    </h2>
+<pre xml:space="preserve">
+      (1) See Heat as a Mode of Motion, ninth edition, p. 75.
+
+      (2) See Sir Wm. Thomson on Magne-crystallic Action. Phil.
+     Mag., 1851.
+</pre>
+    <p>
+      <a name="link2HCH0012" id="link2HCH0012">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 12.
+    </h2>
+<pre xml:space="preserve">
+     Magnetism of flame and gases&mdash;atmospheric magnetism
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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,&mdash;'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.'
+    </p>
+    <p>
+      On observing this deportment the question immediately occurs to him,&mdash;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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;perhaps
+      too much&mdash;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.
+    </p>
+    <p>
+      Footnote to Chapter 12
+    </p>
+<pre xml:space="preserve">
+      (1) This persuasion has been greatly strengthened by the
+     recent perusal of a paper by Mr. Baxendell.
+</pre>
+    <p>
+      <a name="link2HCH0013" id="link2HCH0013">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 13.
+    </h2>
+<pre xml:space="preserve">
+     Speculations: nature of matter: lines of force
+</pre>
+    <p>
+      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:&mdash;'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,
+      &amp;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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      The letter to Mr. Phillips winds up with this beautiful conclusion:&mdash;
+    </p>
+    <p>
+      '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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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:&mdash;'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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT_______">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 13
+    </h2>
+<pre xml:space="preserve">
+      (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.
+</pre>
+    <p>
+      <a name="link2HCH0014" id="link2HCH0014">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 14.
+    </h2>
+<pre xml:space="preserve">
+     Unity and convertibility of natural forces: theory of the
+     electric current.
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;a separating force&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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)
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT________">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 14
+    </h2>
+<pre xml:space="preserve">
+      (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.
+</pre>
+    <p>
+      <a name="link2HCH0015" id="link2HCH0015">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 15.
+    </h2>
+<pre xml:space="preserve">
+     Summary.
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      His third great discovery is the Magnetization of Light, which I should
+      liken to the Weisshorn among mountains&mdash;high, beautiful, and alone.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      <a name="link2HCH0016" id="link2HCH0016">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 16.
+    </h2>
+<pre xml:space="preserve">
+    Illustrations of Character.
+</pre>
+    <p>
+      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&mdash;namely, with the general human
+      heart.
+    </p>
+    <p>
+      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:&mdash;'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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      Letters of his, covering a period of sixteen years, are before me, each
+      one of which contains some characteristic utterance;&mdash;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&mdash;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:&mdash;'Dear Tyndall,&mdash;I was looking for you, because we
+      were at tea&mdash;we have not yet done&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      'Royal Institution. ( this is crossed out by Faraday )
+    </p>
+    <p>
+      'Ventnor, Isle of Wight, June 28, 1854.
+    </p>
+    <p>
+      'My Dear Tyndall,&mdash;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.
+    </p>
+    <p>
+      '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.
+    </p>
+    <p>
+      'Good-bye for the present.
+    </p>
+    <p>
+      'Ever, my dear Tyndall,
+    </p>
+    <p>
+      'Yours truly,
+    </p>
+    <p>
+      'M. Faraday.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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:&mdash;'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.
+    </p>
+    <p>
+      'Brighton, December 9, 1857.
+    </p>
+    <p>
+      'My Dear Tyndall,&mdash;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.
+    </p>
+    <p>
+      'We return on Friday, when I will return you the paper.
+    </p>
+    <p>
+      'Ever truly yours,
+    </p>
+    <p>
+      'M. Faraday.'
+    </p>
+    <p>
+      The third letter will come in its proper place towards the end.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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:&mdash;'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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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:&mdash;
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      T. But I do not wish to accept it.
+    </p>
+    <p>
+      F. Then you know what the consequence of sending that letter will be?
+    </p>
+    <p>
+      T. I do.
+    </p>
+    <p>
+      F. They will dismiss you.
+    </p>
+    <p>
+      T. I know it.
+    </p>
+    <p>
+      F. Then send the letter!
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;for unhappily for them and us, Ministers
+      of State in England are only too often ignorant of great Englishmen&mdash;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&mdash;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.
+    </p>
+    <p>
+      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&mdash;one of many priceless
+      letters now before me&mdash;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.
+    </p>
+    <p>
+      'Hampton Court, August 1, 1864.
+    </p>
+    <p>
+      'My Dear Tyndall,&mdash;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.
+    </p>
+    <hr />
+    <p>
+      '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.
+    </p>
+    <p>
+      'My dear wife and Jane desire their kindest remembrances: I hear them in
+      the next room:... I forget&mdash;but not you, my dear Tyndall, for I am
+    </p>
+    <p>
+      'Ever yours,
+    </p>
+    <p>
+      'M. Faraday.'
+    </p>
+    <p>
+      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&mdash;shall I not say
+      of glory?&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      It was my wish and aspiration to play the part of Schiller to this Goethe:
+      and he was at times so strong and joyful&mdash;his body so active, and his
+      intellect so clear&mdash;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?&mdash;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.
+    </p>
+    <p>
+      But it is time that I should end these weak words, and lay my poor garland
+      on the grave of this
+    </p>
+<pre xml:space="preserve">
+         Just and faithful knight of God.
+</pre>
+    <p>
+      <br /><br /><br /><br />
+    </p>
+  <div>*** END OF THE PROJECT GUTENBERG EBOOK 1225 ***</div>
+</body>
+</html>
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+Project Gutenberg (https://www.gutenberg.org) public repository for
+eBook #1225 (https://www.gutenberg.org/ebooks/1225)
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+  <head>
+    <title>
+      Faraday As a Discoverer, by John Tyndall
+    </title>
+    <style type="text/css" xml:space="preserve">
+
+    body { margin:5%; background:#faebd0; text-align:justify}
+    P { text-indent: 1em; margin-top: .25em; margin-bottom: .25em; }
+    H1,H2,H3,H4,H5,H6 { text-align: center; margin-left: 15%; margin-right: 15%; }
+    hr  { width: 50%; text-align: center;}
+    .foot { margin-left: 20%; margin-right: 20%; text-align: justify; text-indent: -3em; font-size: 90%; }
+    blockquote {font-size: 97%; font-style: italic; margin-left: 10%; margin-right: 10%;}
+    .mynote    {background-color: #DDE; color: #000; padding: .5em; margin-left: 10%; margin-right: 10%; font-family: sans-serif; font-size: 95%;}
+    .toc       { margin-left: 10%; margin-bottom: .75em;}
+    .toc2      { margin-left: 20%;}
+    div.fig    { display:block; margin:0 auto; text-align:center; }
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+    pre        { font-style: italic; font-size: 90%; margin-left: 10%;}
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+
+The Project Gutenberg EBook of Faraday As A Discoverer, by John Tyndall
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Faraday As A Discoverer
+
+Author: John Tyndall
+
+Release Date: August 20, 2008 [EBook #1225]
+Last Updated: February 7, 2013
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK FARADAY AS A DISCOVERER ***
+
+
+
+
+Produced by An Anonymous Volunteer, and David Widger
+
+
+
+
+
+</pre>
+    <p>
+      <br /><br />
+    </p>
+    <h1>
+      FARADAY AS A DISCOVERER
+    </h1>
+    <p>
+      <br />
+    </p>
+    <h2>
+      by John Tyndall
+    </h2>
+    <p>
+      <br /> <br />
+    </p>
+    <hr />
+    <p>
+      <br /> <br />
+    </p>
+    <blockquote>
+      <p class="toc">
+        <big><b>CONTENTS</b></big>
+      </p>
+      <p>
+        <br />
+      </p>
+      <p class="toc">
+        <a href="#link2H_PREF"> Preface to the fifth edition. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2H_PREF2"> Preface to the fourth edition. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2H_PREF2"> Preface to the second edition. </a>
+      </p>
+      <p>
+        <br />
+      </p>
+      <p class="toc">
+        <a href="#link2H_4_0004"> <b>FARADAY AS A DISCOVERER.</b> </a>
+      </p>
+      <p>
+        <br />
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0001"> Chapter 1. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0002"> Chapter 2. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0003"> Chapter 3. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0004"> Chapter 4. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0005"> Chapter 5. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0006"> Chapter 6. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0007"> Chapter 7. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0008"> Chapter 8. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0009"> Chapter 9. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0010"> Chapter 10. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0011"> Chapter 11. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0012"> Chapter 12. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0013"> Chapter 13. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0014"> Chapter 14. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0015"> Chapter 15. </a>
+      </p>
+      <p class="toc">
+        <a href="#link2HCH0016"> Chapter 16. </a>
+      </p>
+    </blockquote>
+    <p>
+      <br /> <br />
+    </p>
+    <hr />
+    <p>
+      <br /> <br /> <a name="link2H_PREF" id="link2H_PREF">
+      <!--  H2 anchor --> </a>
+    </p>
+    <h2>
+      Preface to the fifth edition.
+    </h2>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      John Tyndall. Hind Head, December, 1893.
+    </p>
+    <p>
+      [Note.&mdash;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.
+    </p>
+    <p>
+      Louisa C. Tyndall.]
+    </p>
+    <p>
+      <a name="link2H_PREF2" id="link2H_PREF2">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Preface to the fourth edition.
+    </h2>
+    <p>
+      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.
+    </p>
+    <p>
+      Royal Institution, February, 1884.
+    </p>
+    <p>
+      <a name="link2H_PREF3" id="link2H_PREF3">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Preface to the second edition.
+    </h2>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      John Tyndall. Royal Institution: December, 1869.
+    </p>
+    <p>
+      <a name="link2H_4_0004" id="link2H_4_0004">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      FARADAY AS A DISCOVERER.
+    </h2>
+    <p>
+      <a name="link2HCH0001" id="link2HCH0001">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 1.
+    </h2>
+<pre xml:space="preserve">
+     Parentage: introduction to the royal institution: earliest
+     experiments: first royal society paper: marriage.
+</pre>
+    <p>
+      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&mdash;however numerous the
+      illustrations which occur to me of the loftiness of Faraday's character
+      and the beauty of his life&mdash;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&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;sharing the opinion of Mr.
+      Carlyle, that 'a really able man never proceeded from entirely stupid
+      parents'&mdash;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.
+    </p>
+    <p>
+      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:&mdash;
+    </p>
+    <p>
+      'Clapham Common, Surrey,
+    </p>
+    <p>
+      'November 28, 1867.
+    </p>
+    <p>
+      'My Dear Tyndall,&mdash;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&mdash;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.
+    </p>
+    <p>
+      '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.
+    </p>
+    <p>
+      'Believe me, my dear Tyndall, yours truly,
+    </p>
+    <p>
+      'J. P. Gassiot.
+    </p>
+    <p>
+      'Dr. Tyndall.'
+    </p>
+    <p>
+      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:&mdash;
+    </p>
+    <p>
+      'London, Sept. 13, 1813.
+    </p>
+    <p>
+      '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:&mdash;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&mdash;about the end; and my absence from home will perhaps be as long
+      as three years. But as yet all is uncertain.'
+    </p>
+    <p>
+      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:&mdash;
+    </p>
+    <p>
+      'My Dear Friend,&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      '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&mdash;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.
+    </p>
+    <p>
+      '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.
+    </p>
+    <p>
+      '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.'
+    </p>
+    <p>
+      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&mdash;her
+      predecessor's name&mdash;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&mdash;that
+      it must be 'Sir Charles Faraday.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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:&mdash;
+    </p>
+    <p>
+      '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.
+    </p>
+    <p>
+      'M. Faraday.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 1
+    </h2>
+<pre xml:space="preserve">
+      (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:&mdash;
+
+     '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,&mdash;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.
+</pre>
+    <p>
+      <a name="link2HCH0002" id="link2HCH0002">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 2.
+    </h2>
+<pre xml:space="preserve">
+     Early researches: magnetic rotations: liquefaction of gases:
+     heavy glass: Charles Anderson: contributions to physics.
+</pre>
+    <p>
+      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&mdash;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.
+    </p>
+    <p>
+      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:&mdash;
+    </p>
+    <p>
+      'Dear Sir,&mdash;The oil you noticed yesterday turns out to be liquid
+      chlorine.
+    </p>
+    <p>
+      'Yours faithfully,
+    </p>
+    <p>
+      'M. Faraday.' (2)
+    </p>
+    <p>
+      The gas had been liquefied by its own pressure. Faraday then tried
+      compression with a syringe, and succeeded thus in liquefying the gas.
+    </p>
+    <p>
+      To the published account of this experiment Davy added the following note:&mdash;'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.
+    </p>
+    <p>
+      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?
+    </p>
+    <p>
+      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)
+    </p>
+    <p>
+      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)
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT_">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 2
+    </h2>
+<pre xml:space="preserve">
+      (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:&mdash;'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:&mdash;'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.&mdash;M. F.' (Exp.
+     Researches, vol. iii. p. 3, footnote.)
+</pre>
+    <p>
+      <a name="link2HCH0003" id="link2HCH0003">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 3.
+    </h2>
+<pre xml:space="preserve">
+     Discovery of Magneto-electricity: Explanation of Argo's
+     magnetism of rotation: Terrestrial magneto-electric
+     induction: The extra current.
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      'During its flow,' and this was the time when an effect was expected&mdash;but
+      here Faraday's power of lateral vision, separating, as it were, from the
+      line of expectation, came into play&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      At the suggestion of a mind fruitful in suggestions of a profound and
+      philosophic character&mdash;I mean that of Sir John Herschel&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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)
+    </p>
+    <p>
+      Three years subsequent to the publication of these researches&mdash;that
+      is to say, on January 29, 1835&mdash;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.
+    </p>
+    <p>
+      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'&mdash;this was his term&mdash;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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      Footnote to Chapter 3
+    </p>
+<pre xml:space="preserve">
+      (1) I am indebted to a friend for the following exquisite
+     morsel:&mdash;'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."'
+</pre>
+    <p>
+      <a name="link2HCH0004" id="link2HCH0004">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 4.
+    </h2>
+<pre xml:space="preserve">
+     Points of Character.
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      As already intimated, Faraday had contributed many of his minor papers&mdash;including
+      his first analysis of caustic lime&mdash;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:&mdash;
+    </p>
+    <p>
+      'PAPERS, NOTES, NOTICES, &amp;c., &amp;c.,published in octavo, up to 1832.
+      M. Faraday.'
+    </p>
+    <p>
+      '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.
+    </p>
+    <p>
+      '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&mdash;and none more than the bad&mdash;in pointing out to me in
+      future, or rather, after times, the faults it became me to watch and to
+      avoid.
+    </p>
+    <p>
+      '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.
+    </p>
+    <p>
+      'M. Faraday.
+    </p>
+    <p>
+      'Aug. 18, 1832.'
+    </p>
+    <p>
+      '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.
+    </p>
+    <p>
+      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:&mdash;
+    </p>
+    <p>
+      'Sydenham, Oct. 6, 1855.
+    </p>
+    <p>
+      'My Dear Tyndall,&mdash;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)
+    </p>
+    <p>
+      'Yours, very truly,
+    </p>
+    <p>
+      'M. Faraday.'
+    </p>
+    <p>
+      Footnote to Chapter 4
+    </p>
+<pre xml:space="preserve">
+      (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.
+</pre>
+    <p>
+      <a name="link2HCH0005" id="link2HCH0005">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 5.
+    </h2>
+<pre xml:space="preserve">
+     Identity of electricities; first researches on
+     electro-chemistry.
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;a favourite test of his&mdash;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.
+    </p>
+    <p>
+      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)
+    </p>
+    <p>
+      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:&mdash;'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.
+    </p>
+    <p>
+      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:&mdash;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&mdash;and this exception he thought might be apparent
+      only&mdash;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)
+    </p>
+    <p>
+      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?&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT__">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 5
+    </h2>
+<pre xml:space="preserve">
+      (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.
+</pre>
+    <p>
+      <a name="link2HCH0006" id="link2HCH0006">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 6.
+    </h2>
+<pre xml:space="preserve">
+     Laws of electro-chemical decomposition.
+</pre>
+    <p>
+      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)
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT___">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 6
+    </h2>
+<pre xml:space="preserve">
+      (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!'&mdash;Proceedings of the Royal Institution, vol.
+     ii. p. 132.
+
+      (2) In 1838 he expresses himself thus:&mdash;'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.'&mdash;Exp. Resear., vol. i. p. 515. ($
+     1617.)
+
+      (3) This conclusion needs qualification.  Faraday overlooked
+     the part played by ozone.
+</pre>
+    <p>
+      <a name="link2HCH0007" id="link2HCH0007">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 7.
+    </h2>
+<pre xml:space="preserve">
+     Origin of power in the voltaic pile.
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;competent therefore to allow the electricity of
+      contact to flow through them if it were able to form a current&mdash;were
+      absolutely powerless when chemically inactive.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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:&mdash;'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)
+    </p>
+    <p>
+      Footnote to Chapter 7
+    </p>
+<pre xml:space="preserve">
+      (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.
+</pre>
+    <p>
+      <a name="link2HCH0008" id="link2HCH0008">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 8.
+    </h2>
+<pre xml:space="preserve">
+     Researches on frictional electricity: induction: conduction:
+     specific inductive capacity: theory of contiguous particles.
+</pre>
+    <p>
+      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.'
+    </p>
+    <p>
+      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,&mdash;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)
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;even the earth itself&mdash;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.
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT____">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 8
+    </h2>
+<pre xml:space="preserve">
+      (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.
+</pre>
+    <p>
+      <a name="link2HCH0009" id="link2HCH0009">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 9.
+    </h2>
+<pre xml:space="preserve">
+     Rest needed&mdash;visit to Switzerland.
+</pre>
+    <p>
+      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
+    </p>
+<pre xml:space="preserve">
+          'Nature never did betray
+           The heart that loved her.'
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      'August 2, 1841.&mdash;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.'
+    </p>
+    <p>
+      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:&mdash;
+    </p>
+    <p>
+      'August 12, 1841.&mdash;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,&mdash;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.'
+    </p>
+    <p>
+      Footnote to Chapter 9
+    </p>
+<pre xml:space="preserve">
+      (1) See note, p. 77.
+</pre>
+    <p>
+      <a name="link2HCH0010" id="link2HCH0010">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 10.
+    </h2>
+<pre xml:space="preserve">
+     Magnetization of light.
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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:&mdash;'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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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)
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT_____">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 10
+    </h2>
+<pre xml:space="preserve">
+      (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.
+</pre>
+    <p>
+      <a name="link2HCH0011" id="link2HCH0011">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 11.
+    </h2>
+<pre xml:space="preserve">
+     Discovery of diamagnetism&mdash;researches on magne-crystallic
+     action.
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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:&mdash;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&mdash;though it contains iron&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      '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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      And here follows one of those expressions which characterize the
+      conceptions of Faraday in regard to force generally:&mdash;'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&mdash;'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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      Supplementary remarks
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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,&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT______">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 11
+    </h2>
+<pre xml:space="preserve">
+      (1) See Heat as a Mode of Motion, ninth edition, p. 75.
+
+      (2) See Sir Wm. Thomson on Magne-crystallic Action. Phil.
+     Mag., 1851.
+</pre>
+    <p>
+      <a name="link2HCH0012" id="link2HCH0012">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 12.
+    </h2>
+<pre xml:space="preserve">
+     Magnetism of flame and gases&mdash;atmospheric magnetism
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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,&mdash;'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.'
+    </p>
+    <p>
+      On observing this deportment the question immediately occurs to him,&mdash;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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;perhaps
+      too much&mdash;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.
+    </p>
+    <p>
+      Footnote to Chapter 12
+    </p>
+<pre xml:space="preserve">
+      (1) This persuasion has been greatly strengthened by the
+     recent perusal of a paper by Mr. Baxendell.
+</pre>
+    <p>
+      <a name="link2HCH0013" id="link2HCH0013">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 13.
+    </h2>
+<pre xml:space="preserve">
+     Speculations: nature of matter: lines of force
+</pre>
+    <p>
+      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:&mdash;'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,
+      &amp;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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      The letter to Mr. Phillips winds up with this beautiful conclusion:&mdash;
+    </p>
+    <p>
+      '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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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:&mdash;'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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT_______">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 13
+    </h2>
+<pre xml:space="preserve">
+      (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.
+</pre>
+    <p>
+      <a name="link2HCH0014" id="link2HCH0014">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 14.
+    </h2>
+<pre xml:space="preserve">
+     Unity and convertibility of natural forces: theory of the
+     electric current.
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;a separating force&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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)
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      <a name="link2H_FOOT" id="link2H_FOOT________">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Footnotes to Chapter 14
+    </h2>
+<pre xml:space="preserve">
+      (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.
+</pre>
+    <p>
+      <a name="link2HCH0015" id="link2HCH0015">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 15.
+    </h2>
+<pre xml:space="preserve">
+     Summary.
+</pre>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      His third great discovery is the Magnetization of Light, which I should
+      liken to the Weisshorn among mountains&mdash;high, beautiful, and alone.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      <a name="link2HCH0016" id="link2HCH0016">
+      <!--  H2 anchor --> </a>
+    </p>
+    <div style="height: 4em;">
+      <br /><br /><br /><br />
+    </div>
+    <h2>
+      Chapter 16.
+    </h2>
+<pre xml:space="preserve">
+    Illustrations of Character.
+</pre>
+    <p>
+      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&mdash;namely, with the general human
+      heart.
+    </p>
+    <p>
+      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:&mdash;'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.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      Letters of his, covering a period of sixteen years, are before me, each
+      one of which contains some characteristic utterance;&mdash;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&mdash;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:&mdash;'Dear Tyndall,&mdash;I was looking for you, because we
+      were at tea&mdash;we have not yet done&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      'Royal Institution. ( this is crossed out by Faraday )
+    </p>
+    <p>
+      'Ventnor, Isle of Wight, June 28, 1854.
+    </p>
+    <p>
+      'My Dear Tyndall,&mdash;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.
+    </p>
+    <p>
+      '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.
+    </p>
+    <p>
+      'Good-bye for the present.
+    </p>
+    <p>
+      'Ever, my dear Tyndall,
+    </p>
+    <p>
+      'Yours truly,
+    </p>
+    <p>
+      'M. Faraday.'
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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:&mdash;'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.
+    </p>
+    <p>
+      'Brighton, December 9, 1857.
+    </p>
+    <p>
+      'My Dear Tyndall,&mdash;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.
+    </p>
+    <p>
+      'We return on Friday, when I will return you the paper.
+    </p>
+    <p>
+      'Ever truly yours,
+    </p>
+    <p>
+      'M. Faraday.'
+    </p>
+    <p>
+      The third letter will come in its proper place towards the end.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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:&mdash;'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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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:&mdash;
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      T. But I do not wish to accept it.
+    </p>
+    <p>
+      F. Then you know what the consequence of sending that letter will be?
+    </p>
+    <p>
+      T. I do.
+    </p>
+    <p>
+      F. They will dismiss you.
+    </p>
+    <p>
+      T. I know it.
+    </p>
+    <p>
+      F. Then send the letter!
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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&mdash;for unhappily for them and us, Ministers
+      of State in England are only too often ignorant of great Englishmen&mdash;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&mdash;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.
+    </p>
+    <p>
+      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&mdash;one of many priceless
+      letters now before me&mdash;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.
+    </p>
+    <p>
+      'Hampton Court, August 1, 1864.
+    </p>
+    <p>
+      'My Dear Tyndall,&mdash;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.
+    </p>
+    <hr />
+    <p>
+      '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.
+    </p>
+    <p>
+      'My dear wife and Jane desire their kindest remembrances: I hear them in
+      the next room:... I forget&mdash;but not you, my dear Tyndall, for I am
+    </p>
+    <p>
+      'Ever yours,
+    </p>
+    <p>
+      'M. Faraday.'
+    </p>
+    <p>
+      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&mdash;shall I not say
+      of glory?&mdash;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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      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.
+    </p>
+    <p>
+      It was my wish and aspiration to play the part of Schiller to this Goethe:
+      and he was at times so strong and joyful&mdash;his body so active, and his
+      intellect so clear&mdash;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?&mdash;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.
+    </p>
+    <p>
+      But it is time that I should end these weak words, and lay my poor garland
+      on the grave of this
+    </p>
+<pre xml:space="preserve">
+         Just and faithful knight of God.
+</pre>
+    <p>
+      <br /><br /><br /><br />
+    </p>
+<pre xml:space="preserve">
+
+
+
+
+
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+The Project Gutenberg EBook of Faraday As A Discoverer, by John Tyndall
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Faraday As A Discoverer
+
+Author: John Tyndall
+
+Posting Date: August 20, 2008 [EBook #1225]
+Release Date: March, 1998
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK FARADAY AS A DISCOVERER ***
+
+
+
+
+Produced by An Anonymous Volunteer
+
+
+
+
+
+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.
+
+
+
+
+
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+*Project Gutenberg Etext of Faraday As A Discoverer, by Tyndall*
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+Faraday As A Discoverer
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+
+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 Project Gutenberg Etext of Faraday As A Discoverer, by Tyndall
+
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