2.70 A History of Electric Telegrapfiy
`
`As the result of all these observations the Bavarian
`
`philosopher concluded that “ electrical combinations,
`when not exhibiting their electric tension, were in
`
`a magnetic state; and that there existed a kind of
`electro—magnetic meridian depending on the electricity
`of the earth, and at right angles to the magnetic
`poles.“ These speculations are, as we see, suffi-
`ciently obscure, and, like those that we have hitherto
`described, failed to throw any light on the relation so
`
`anxiously sought after.
`Nor can we give Oersted credit at this period for
`any more distinct apprehensions.
`In a work which
`
`the
`It is curious to note that
`lviii. p. 43.
`" Phil. Mag, vol.
`English philosophers entirely neglected this study, being content to
`follow the brilliant lead of Sir Humphry Davy in another branch
`of the science.
`Indeed, it seems to have been the general opinion
`in this country, as late as the year 1818,
`that
`there was nothing
`' more to be discovered.
`Bostock,
`in his Account of Me History
`and Present State of Galvanim, published in London in that year,
`
`says :—
`“Although it may be somewhat hazardous to form predictions
`respecting the progress of science, I may remark that the impulse,
`which was given in the first instance by Galvani‘s original experiments,
`was revived by Volta's discovery of the pile, and was carried to the
`highest pitch by Sir H. Davy’s application of it to chemical decom-
`position, seems to have, in a great measure, subsided.
`It may be
`conjectured that we have carried the power of the instrument to the
`utmost extent of which it admits ; and it does not appear that we are
`at present in the way of making any important additions to our know-
`ledge of its effects, or of obtaining any new light upon the theory of
`its action” (p. 102).
`In the First Consul’s letter to
`Napoleon did not hold these views.
`the Minister, Chaptal, founding two prizes to encourage new researches
`in galvanism, he said :—“Galvanism, in my opinion, will lead to
`great discoveries."
`
`301
`
`301
`
`
`
`As the result of all these observations the Bavarian
`
`philosopher concluded that “ electrical combinations,
`when not exhibiting their electric tension, were in
`
`a magnetic state; and that there existed a kind of
`electro—magnetic meridian depending on the electricity
`of the earth, and at right angles to the magnetic
`poles.“ These speculations are, as we see, suffi-
`ciently obscure, and, like those that we have hitherto
`described, failed to throw any light on the relation so
`
`anxiously sought after.
`Nor can we give Oersted credit at this period for
`any more distinct apprehensions.
`In a work which
`
`the
`It is curious to note that
`lviii. p. 43.
`" Phil. Mag, vol.
`English philosophers entirely neglected this study, being content to
`follow the brilliant lead of Sir Humphry Davy in another branch
`of the science.
`Indeed, it seems to have been the general opinion
`in this country, as late as the year 1818,
`that
`there was nothing
`' more to be discovered.
`Bostock,
`in his Account of Me History
`and Present State of Galvanim, published in London in that year,
`
`says :—
`“Although it may be somewhat hazardous to form predictions
`respecting the progress of science, I may remark that the impulse,
`which was given in the first instance by Galvani‘s original experiments,
`was revived by Volta's discovery of the pile, and was carried to the
`highest pitch by Sir H. Davy’s application of it to chemical decom-
`position, seems to have, in a great measure, subsided.
`It may be
`conjectured that we have carried the power of the instrument to the
`utmost extent of which it admits ; and it does not appear that we are
`at present in the way of making any important additions to our know-
`ledge of its effects, or of obtaining any new light upon the theory of
`its action” (p. 102).
`In the First Consul’s letter to
`Napoleon did not hold these views.
`the Minister, Chaptal, founding two prizes to encourage new researches
`in galvanism, he said :—“Galvanism, in my opinion, will lead to
`great discoveries."
`
`301
`
`301
`
`
`
`to tlze Year 1837.
`
`271
`
`he published in German, in 1807, on the identity of
`chemical and electrical forces, he observes z“—
`
`“ When a plate. composed of several thin layers is
`electrified, and the layers afterwards separated, each
`is found to possess an electric polarity, just as each
`fragment of a magnet possesses a magnetic polarity.
`“ There is, however, one fact which would appear to
`be opposed to the theory of the identity of magnetism
`and electricity.
`It is that electrified bodies act upon
`magnetic bodies, as if they [? the magnetic bodies]
`were endowed with no force in particular.
`It would be
`very interesting to science to explain away this diffi-
`culty; but the present state of physics will not enable
`us to do so.
`It is, meanwhile, only a difficulty, and
`not a fact absolutely Opposed to theory ; for we see in
`frictional electricity and in that of contact [galvanism]
`analogous phenomena. Thus, we can alter the tension
`of the electric pile by bringing near it an excited glass
`rod, and yet not affect in any way the chemical action.
`A long column of water, or a wetted thread of flax or
`wool, will also suffer a change in its electricity without
`experiencing any chemical changes.
`“ It would appear, then, that the forces can be super-
`posed without interfering with each other when they
`operate under forms of different activities.
`“ The form of galvanic activity holds a middle place
`
`between those of magnetism and [static] electricity.
`
`the French edition, RetMCM .mr
`" Chap. viii. pp. 23545 of
`l’ldmmé d'a Force: Ckmr’guc: d Ekan'guer, Paris, 1813.
`
`302
`
`302
`
`
`
`272 A History of Electric Telegrapky
`
`The force is in that form more latent than as electricity,
`and less so than as magnetism.
`It is, therefore, pro-
`bable that the electric force, when superposed, will
`exercise a less influence on magnetism than on gal-
`vanism.
`In the galvanic pile, it is the electric state
`
`[tension] which it acquires that is affected by the
`
`approach of an excited glass rod; more, it is not that
`
`interior distribution of forces constituting magnetism
`that we can change by electricity, but it is the electric
`state which belongs to the magnet as to bodies in
`
`general.
`“We do not pretend to decide anything in this
`
`matter; we only wish to clear up, as far as possible, a
`very obscure subject, and, in a question of such im-
`portance, we shall be very well satisfied if we have
`made it apparent that the principal objection to the
`identity of the forces which produce electricity and
`magnetism is rather a difliculty of reconciling facts
`than of the facts themselves.”
`
`And again, on p. 238, he says :—“ Steel when
`heated loses its magnetism, showing that it becomes
`a better conductor by the elevation of temperature,
`like electrical bodies. Magnetism, too, like electricity,
`exists in all bodies in nature, as Bruckmann and
`
`Coulomb have shown. From this it seems that the
`
`magnetic force is as general as the electric; and it
`remains to be seen whether electricity in its most
`latent state [i a, as galvanism] will not affect
`the
`magnetic needle a: sue/z.
`
`303
`
`303
`
`
`
`to the Year1837.
`
`273
`
`“This experiment will not be made without diffi-
`culty, for the electrical actions will blend and render
`the observations very complicated.
`In comparing
`the attractions on magnetic and non-magnetic bodies,
`some data will probably be obtained.”
`In trying experiments with a view to the illustration
`of these hazy notions Oersted is said to have succeeded
`in obtaining indications of the action of the conducting
`wires of the pile, during the passage of electricity, on
`the needle ; but the phenomena were, at first view, not
`a little perplexing ; and it was not till after repeated
`investigation that, in the winter of 1819-20, the real
`nature of the action was satisfactorily made out.’
`
`Even then Oersted seems not to have clearly under-
`
`stood the full significance of his own experiment.
`Unlike Davy, who, when he first saw the fiery drops
`
`of potassium flow under the action of his battery,
`recorded his triumph in a few glowing words in his
`laboratory journal,1' Oersted took no immediate steps,
`
`’ “ Professor Forchhammer, the pupil and friend of Oersted, states
`that. in 1818 and 1819, it was well known in Copenhagen that he was
`engaged in a special study of the connection of magnetism and elec-
`tricity. Yet we must ascribe it to a happy impulse—the result. no
`doubt, of much anxious thought-that, at a private lecture to a few
`advanced students in the winter of 1819—20, he made the observation
`that a wire uniting the ends of a voltaic battery in a state of activity
`afl'ected a magnet in its vicinity.”—Enc_y. Brit, 8th ed., Dissertation vi.
`
`P- 973-
`1' On 16th October, 1807, while investigating the compound nature
`of the alkalies. On seeing the globules of potassium burst through the
`crust of the potash, and take fire as they entered the atmosphere, he
`could not contain his joy, but danced about the room in wild delight,
`
`T
`
`304
`
`304
`
`
`
`274 A History of E[:26th Telegmpny
`
`to complete, or to publish, his discovery.
`either
`“ Although,” he says, “ the effect was unquestionable,
`it appeared to me, nevertheless, so confused that I
`deferred a minute examination of it to a period at
`which I hoped for more leisure.” ' And when he had
`made this minute examination and published the
`
`results, he could not explain the phenomena by a
`better hypothesis than that negative electricity acts
`only on the northern pole, and positive only on the
`southern pole of the needle.1'
`This most important discovery may be thus briefly
`defined :—Supposing the electric current to pass from
`north to south through a wire, placed horizontally in
`the magnetic meridian, then a compass needle sus-
`pended above it will have its north end turned to-
`wards the west;
`if below the wire, to the east;
`if
`
`on the east side of it, the north end will be raised;
`
`and if on the west side, depressed. These results
`Oersted first published in a Latin tract, dated the
`fist July, 1820, a copy of which (with translation in
`English), will be found in the yonrnal of the 506120
`of Teiegrap/z Engineers, vol. v. pp. 459-69.
`
`and some time elapsed before he could sufliciently compose himself to
`continue his experiments.—Bakewell‘s Manual q/ Electria'ol, London,
`1857. p- 34-
`’ Tyndall’s Lectures on Voltaic Electricity at the Royal Institution,
`1876.
`1 See concluding paragraph of his paper in the 7mm! of“: Sat.
`12/ T:1. Eng:., vol. v. p. 468.
`
`305
`
`305
`
`
`
`to fire Year 1837.
`
`275
`
`CHAPTER X.
`
`ELECTROMAGNETISM AND MAGNETO-ELECTRICITY
`
`-—HISTORY IN RELATION TO TELEGRAPHY
`
`(continued).
`
`THE effect of Oersted’s pamphlet was most wonderful.
`The enthusiasm, says Lardner,“ which had been
`lighted up by the great discovery of Volta twenty
`years before, and which time had moderated, was
`relumined, and the experimental resources of every
`cabinet and laboratory were brought to bear on the
`pursuit of the consequences of this new relation be-
`tween sciences so long suspected of closer ties. The
`inquiry was taken up, more particularly, by Ampere
`and Arago, in France; by Davy, Faraday, Cumming,
`and Sturgeon, in England ; and by Seebeck, Schweig-
`ger, De la Rive, Henry, and numerous other philoso-
`phers in all parts of Europe and America.
`Among these, Ampere has assumed the first and
`highest place. No sooner was the fact discovered
`by Oersted made known, than that philosopher com-
`menced the beautiful series of researches which has
`
`surrounded his name with so much lustre, and
`
`" Elxlria'ly, Mogudirm, and Menorah”, vol. i. p. 205.
`
`T 2
`
`306
`
`306
`
`
`
`276 A History qf Electrz'c Telegraph};
`
`brought electro-dynamics within the pale of mathe-
`matical physics. On the 18th of September, 1820,
`within less than two months of the publication of
`Oersted’s experiments, he communicated his
`first
`memoir on electro-magnetism to the Academy of
`
`Sciences.
`
`In this paper was explained the law which deter-
`mined the position of the magnetic needle in relation
`to the electric current.
`In order to illustrate this, he
`
`proposed that a man should imagine the current to
`be transmitted through his body,
`the positive pole
`being applied to his feet, and the negative pole to
`his head, so that the current shall pass upwards from
`the feet to the head. This being premised, a magnetic
`needle, freely supported on its centre of gravity, and
`placed before him, will throw itself at right angles to
`him ; the north pole pointing towards his left, and the
`south pole towards his right.
`If the person through whose body the current thus
`passes turn round, so as to present his face in different
`directions, a magnetic needle, still placed before him,
`will have its direction determined by the same con-
`dition; the north pole pointing always to the left, and
`the south to the right.
`In the same memoir were described several instru-
`
`ments intended to be constructed ; especially spiral, or
`
`helical, wires, through which it was proposed to trans-
`mit the electric currents, and which, it was expected,
`would thereby acquire the properties of magnets, and
`
`307
`
`307
`
`
`
`(0 Me Year 1837.
`
`277
`
`_
`
`retain these properties so long as the current might
`be transmitted through them. The author also ex-
`plained his theory of magnets, ascribing their attrac-
`tive and directive powers to currents of electricity
`circulating constantly round their molecules, in planes
`at right angles to the line joining their poles; the
`position of the poles, on the one side or the other
`of these planes,‘ depending on the direction of the
`revolving current.
`'
`While Ampere was proceeding with these researches,
`Arago directed his inquiries to the state of the wire
`through which the current was transmitted, so as to
`determine whether every part of its surface was en-
`dowed with the same magnetic properties. With
`this view, he placed iron filings around the wire, and
`found that they adhered to it so long as the current
`flowed, and fell away immediately the connection
`with the battery was broken. He also found that
`on placing small
`steel needles
`across
`the wire
`through which a current from a voltaic pile, or a
`discharge from a Leyden jar, was sent, they were
`attracted, and, on removal, were found to be perma-
`nently magnetised. Acting upon Ampere’s theory
`of magnetism, he placed in a glass tube an ordinary
`sewing needle, and wound round the tube a copper
`wire. On sending a current through this wire the
`needle was magnetised, its polarity depending on the
`
`' Annie: 4': Cfir'mr'e e! d: Pfiyrz’gue, Paris, 1820, vol. xv. pp. 59
`and 170.
`
`308
`
`308
`
`
`
`278 A History of Electric Telegraph}:
`
`If the helix were right-
`direction of the current.
`handed, the north pole was found at the end at which
`
`the current entered; and if left-handed,
`
`the same
`
`In the same way he was
`end was a south pole.
`able to impart a temporary magnetism to soft iron
`wires.‘
`
`Another important discovery, which followed fast
`on the heels of Oersted’s experiments, was that of
`Schweigger, of Halle, announced on the 16th Sep-
`tember, 1820. Observing that
`the deflection pro-
`duced by the outward current of a battery flowing
`over the needle was the same as that of the return
`
`current under the needle, he made the wire pro-
`ceed from and to his battery above and beneath
`
`twice
`the needle, and obtained, as he expected,
`the effect; by giving the wire another turn round
`the needle the effect was again doubled; a third
`
`turn produced six times the original deviation; a
`fourth, eight times, and so on. This effect may be
`thus formulatedz—If a magnetised needle, free to
`
`move, be surrounded by a number of convolutions
`
`of insulated wire, the power of the current to deflect
`it will increase in proportion to the number of con-
`
`’ Annie: 4': Ch'nu'c at de Pfiyu‘grm, vol. xv. p. 93. Soon after,
`and before any knowledge of Arago's experiments had reached England,
`Davy also succeeded in magnetising needles by the voltaie current, as
`well as by ordinary frictional electricity, and showed the effect of the
`conducting wire on iron filings.
`See his letter to Wollaston, dated
`November 12, 1820, in the Plu'l. 75mm, for 1821. About the same
`time Seebeck communicated a paper to the Berlin Academy on the
`same subject.
`
`309
`
`309
`
`
`
`to the Year 1837.
`
`279
`
`In this way the effect of a very feeble
`volutions.’
`current may be so multiplied as to produce as great
`a deviation of the magnetic needle as would other-
`
`wise be produced by a very strong current.
`On this principle are constructed instruments for
`indicating and measuring currents of electricity, called
`
`clean-magnetic multzflz’ers, or, more commonly, gal-
`nanometers T—the former being the name originally
`given to the arrangement by Schweigger. His first
`contrivance was a very humble affair, consisting of a
`small compass-box, round which were coiled several
`turns of copper wire in a direction parallel
`to the
`meridian line of the card: Yet this was the pro-
`totype of the beautiful
`instruments of Du Bois-
`Reymond and Sir William Thomson,
`in the former
`
`' The practical reader is, of course, aware that this definition is not
`strictly true,—for three reasons : tst, as the convolutions increase, the
`strength of the current decreases, by reason of the increased resistance
`in the circuit; and, each convolution has less and less effect, as it is
`farther and farther removed from the needle; and, 3rd, the current
`exerts less and less force on the needle, as it is deflected farther and
`farther from the plane of the current.
`1 In the early part of the century this name was applied to measuring
`instruments based on the chemical and calorific properties of the cur-
`rent; but
`these are now denominated wltamterr, and the name
`guhanmder is reserved exclusively for the class of apparatus described
`in the text.
`I Schweigger’s yourudfl'ir Cfimz’e and Pfiyu'b, vol. xxxi. pp. 1-17.
`A galvanometer of different form, called a. galactic-magma“: conden-
`ralor, with vertical coils and unmagnetised needle, was shortly after,
`but
`independently, devised by the celebrated Poggendorfl', then a
`student at Berlin. As the paths/ad description of his apparatus pre-
`ceded that of Schweigger’s, he is sometimes regarded as the first
`inventor (Gilbert's Annals» Jar Playrib, vol. lxvii. pp. 422-29).
`
`310
`
`310
`
`
`
`280 A History qf Electric Telegrap/zy
`
`of which as many as 30,000 convolutions are some-
`
`times employed.
`There was, however, still wanting another discovery
`to bring the galvanometer to its present perfection,
`and this want was soon supplied.
`In deflecting a
`magnetic needle the current acts against the direc-
`tive force of terrestrial magnetism; hence it is clear
`that if this force could be neutralised the deflection
`
`would be greater; in other words, a galvanometer, in
`which the needle is freed from the controlling action
`
`of the earth’s magnetism, would be more sensitive
`than the same galvanometer when its needle was
`not so freed. Ampere suspended a single needle
`so that the earth’s magnetism acted perpendicularly
`to it, and had, therefore, no directive force upon it;
`and he found that it set accurately at right angles to
`
`the current.
`
`This led him to the invention of the double, or
`
`astatz'c, needles, which he thus describes in his memoir
`
`of 1821 :—
`
`“When a magnetic needle is withdrawn from the
`directive action of the earth,
`it sets itself, by the
`
`action of a voltaic conductor,
`in a direction which
`makes a right angle with the direction of the con-
`ductor, and has its south pole to the left of the
`current against which it
`is placed; so that
`if M.
`Oersted,
`in the experiments which he published in
`1820, only obtained deviations of the needle which
`were less than a right angle, on placing it above or
`
`311
`
`311
`
`
`
`to the Year 1837.
`
`281
`
`below a conducting wire parallel to its direction, it
`was solely because the needle which he subjected to
`the action of the current was not withdrawn from that
`
`of the earth, and took consequently an intermediate
`position between the directions which the two forces
`tended to-give it. There are several means of with-
`drawing a magnetic needle from the earth’s action.
`A very simple one consists in attaching to a stout
`brass wire, which has its upper part curved and fitted
`with a steel point of suspension, two magnetic needles
`of equal strength, in such a manner that their poles
`are in opposite directions, so that the directive force
`of the earth upon one is destroyed by the action in
`the opposite direction which it exercises on the other.
`The needles are so arranged that the lower one is just
`below the conducting wires, and the upper one close
`above them. On sending a current through the con-
`volutions the needles turn, until they take a direction
`at right angles with the conducting wire." '
`Having oscillated a magnetised needle, freely sus-
`pended in a circular copper cage, the bottom and sides
`
`In Professor
`* Annals: d: Chim'e d (It Péyrfgue, vol. xviii. p. 320.
`Cnmming's paper 0n the connection qf Galvanirm and Magnum,
`read before the Cambridge Philosophical Society on April 2, 182;, he
`described a near approach to the astatic needle.
`In order to neutralise
`the terrestrial magnetism he placed a small magnetised needle under
`the galvnnometer needle—Trans. Cam. Phil. Son, vol.
`i. p. 279.
`The credit of Ampere's discovery is usually attributed to Nobili. As
`in Noad's Manual qf Emmi-fly, London, 1859, p. 327; also Roget’s
`Elatra-Magndfim, in Library of Useful Knowledge, London, I832,
`p. 42.
`
`312
`
`312
`
`
`
`282 A Histmy of Electric Telegrap/zy
`
`of which were very near the needle, Arago, in 1824,
`noticed that
`the oscillations rapidly diminished in
`extent, and very quickly ceased, as if the medium in
`which they were being produced had become more
`and more resistant. The proximity of the copper,
`while thus checking the amplitude of the oscillations,
`was observed to have no effect on their duration, they
`
`being accomplished in exactly the same time as in
`free air. By making the needle oscillate at different
`distances above discs of different materials, Arago
`found that distance considerably diminished the effect ;
`and that metals acted with more energy than wood,
`
`glass, &c.’
`Arago now conceived the idea of trying whether the
`disc which possessed this remarkable property would
`not draw the needle with it if itself rotated. The
`
`experiment was tried and resulted in the discovery of
`a new class of phenomena to which its author gave the
`name of magnetism by rotation.
`Ifwe fix to a rotation
`apparatus, such as a table made for experiments on
`centrifugal force, a copper disc, about twelve inches
`diameter, and one-tenth inch thick, and just above it
`suspend, by a silk fibre, a magnetic needle, in such a
`manner that its point of suspension is exactly above
`the centre of the disc (care being taken to interpose a
`
`" Annaler de Chm. et de Pfiyu'que, vol. xxvii. p. 363. Seebeck, of
`Berlin, on repeating these experiments two years later, obtained analo-
`gous results. See Peg. Ann, vol. vii. We shall see further on, pp. 32!.
`and 336-7, the use that has been made of this fact in the telegraph: of
`Gauss and Weber, and Steinheil.
`
`313
`
`313
`
`
`
`to the Year 1837.
`
`283
`
`screen of glass or paper, so that the agitation of the
`air resulting from the motion impressed upon the disc
`
`may have no effect upon the needle), and then put the
`disc in rotation, the needle is seen to deviate in the
`
`direction of this rotation, and to make with the mag-
`netic meridian a greater or less angle according to
`the velocity with which the disc is revolved.
`If this
`movement be very rapid, the needle is deflected more
`and more, until finally it rotates with the disc.
`The effect diminishes very rapidly with the distance
`of the needle from the disc ; and is still further lessened
`
`by cutting slits in the latter in the direction of rays—
`a fact which, as our practical readers know, is of the
`highest
`importance in the construction of electro-
`
`magnets.
`Whilst Arago was analysing the force that he had
`discovered, Babbage and Herschel, Barlow, Harris,‘
`and others, undertook an investigation of the causes
`that may vary its intensity. Messrs. Babbage and
`Herschel repeated Arago’s experiment by inverting it.
`They found that discs, of copper, Or other substances,
`when freely suspended over a rotating horse-shoe
`magnet, turned in the same direction as the magnet,
`with a movement at first slow, but which gradually
`increased in rapidity. The interposition of plates of
`glass and of non-magnetic metallic bodies in no degree
`
`“ For researches of the three first-named philosophers, see Phlo-
`xopha’cal flour-action, for I825 ; for those of Sir W. Snow Harris, see
`same {or 1831.
`
`314
`
`314
`
`
`
`284 A History of Electric Telegraph);
`
`affected the results; but it was not the same with
`plates of iron. The action was then greatly reduced,
`or even entirely annihilated.
`These two philosophers confirmed the accuracy of
`Arago’s observations on the influence of solutions of
`continuity, either partial or total, in the discs subjected
`to experiment. Thus, a light disc of copper, suspended
`at‘ a given distance above a magnet, executed its (6)
`revolutions in 55”. When cut in eight places, in the
`direction of radii near the centre, it required 12!" to
`
`execute the same number ; but, on the parts cut out
`being again soldered in with tin, the original effect
`was almost attained, the disc performing its revolu-
`tions in 57". The same efi‘ects were obtained with
`
`other metals.
`
`Sir W. Snow Harris, who made a great number of
`experiments on this subject, 'not only found great
`differences between bodies with regard to their power
`of drawing the needle after them when rotating, but
`also with regard to the property they possess of inter-
`cepting this action. He observed that iron, and mag-
`netic substances generally, are not the only ones that
`are thus able to arrest the effect of magnetism by
`
`rotation. Plates of non-magnetic substances, such as
`copper, silver, zinc, will do the same, provided only
`they be sufficiently thick, as from three to five inches.
`From a study of all
`these experiments Christie
`deduced the law that the force with which different
`
`substances draw along the magnetic needle in their
`
`315
`
`315
`
`
`
`to Ike Year 1837.
`
`285
`
`rotatory movement is proportional to their conducting
`power for electricity. But a full explanation of these
`phenomena could not be given until after Faraday’s
`discoveries in 1831, when it was seen that they were,
`one and all, the result of the electric currents induced
`
`in the disc by its rotation in the field of the magnet.
`In the case of those discs in which slits, or rays, were
`cut, the free circulation of these currents was pre-
`vented, and, consequently, there was no effect on the
`
`needle.“
`
`In November 182 5, a great advance was made on
`Arago’s experiment of magnetising soft iron, by the
`invention of the electro-rnagnet—an instrument which,
`
`in one form or another, has become the basis of nearly
`' every system of electric telegraphy. We owe this
`most important contrivance to Sturgeon, a well-known
`electrician of Woolwich, who had worked in his earlier
`
`days at the cobbler's last,T as Franklin had done at the
`printing stick, and Faraday at bookbinding. Fig. 10
`shows the earliest form of the instrument—a piece of
`
`stout iron wire, bent
`
`into the form of a horse-shoe,
`
`‘ See Faraday’s Experimental Researcher, :83! ; also Henry's clas-
`sical paper on Ekctra-dynamk Induction,
`in Tram. Amer. Phi.
`Said], {or 1839, vol. vi. p. 318.
`1’ He was apprenticed to a shoemaker, and disliking the employ-
`ment, at the age of nineteen entered the Westmoreland Militia, and
`two years later enlisted in the Royal Artillery. While in this corps
`he devoted his leisure to scientific studies, and made himself familiar
`with all the great facts of electricity and magnetism, which were then
`opening on the world. His subsequent career has created for him an
`undying name in the annals of electricity.
`
`316
`
`316
`
`
`
`286 A History of Elam}: Telegrap/zy
`
`coated with an insulating varnish, and then bound
`round loosely with bare copper wire, the turns (of which
`there were sixteen) being, of course, separated from
`each other. This electro-magnet, when excited by a
`
`
`
`_.=E!;'-l'l|lE!“a|H1?filiall.|§i1|]'.il':nl'||n|IHHH
`
`single voltaic pair of large (1 30 square inches) surface,
`was capable of supporting a weight of nine pounds, a
`wonderful performance in those days.’
`Some of the further steps in the perfection of the
`electro-magnet as used in telegraphy were made by
`Professor Henry in America, between the years 1828
`and 1831, and it will be interesting to retrace them
`here, if only to see how little learned professors, fifty
`years ago, understood the conditions underlying the
`conversion of voltaic into magnetic force, and conse-
`quently how much groping in the dark, and stumbling
`to conclusions, where now Ohm’s celebrated law makes
`
`everything so clear.
`Henry was led to his first improvements in electro-
`magnets by a study of Schweigger’s galvanometer,
`
`‘ Tramachbm Society ofArh, 1825, vol. xliii. pp. 38-52.
`
`317
`
`317
`
`
`
`to the Year 1837.
`
`287
`
`which resulted in the idea that a much nearer approxi-
`mation to the requirements of Ampere’s theory could
`be attained by insulating the conducting wire itself,
`instead of the rod to be magnetised, and by covering
`the whole surface of the iron with a series of coils in
`
`close contact.
`In June 1828, he exhibited at the Albany Institute
`of New York, of which he was then professor, his
`electro-magnet, constructed on this principle.
`It con-
`sisted of a piece of soft iron, bent in the form of a
`horse-shoe, and closely wound with silk-covered copper
`wire, one-thirtieth of an inch in diameter.
`In this
`way he was able to employ a much larger number of
`convolutions, while each turn was more nearly at
`right angles with the magnetic axis of the bar. The
`lifting power of this magnet was, conforrnably to
`Henry's anticipations, much greater, cateris parz'bus,
`than that of Sturgeon.
`In March 1829, he exhibited, at the same place, a
`somewhat larger magnet of the same character. A
`round piece of iron, about one quarter inch diameter,
`was bent into the usual horse-shoe form, and tightly
`wound with thirty-five feet of silk-covered wire,
`in
`about four hundred turns, with silk ribbon between.
`A pair of small battery plates, which could be dipped
`into a tumbler of dilute acid, were soldered, one to
`
`each end of the wire, and the whole mounted on a
`stand. With this small battery the magnet could be
`much more powerfully excited than another of the
`
`318
`
`318
`
`
`
`288 A 112':on ofElectn'c Telegrafi/zy
`
`same sized core, wound according to the method of
`Sturgeon and excited by a battery of twenty-eight
`plates of copper and zinc, each plate eight inches
`square.’
`“In the arrangement,” says Henry, “of Arago and
`Sturgeon, the several turns of wire were not precisely
`at right angles to the axis of the rod, as they should
`be to produce the effect required by the theory, but
`slightly oblique, and, therefore, each tended to develop
`a separate magnetism not coincident with the axis of
`the bar. But
`in winding the wire over itself, the
`obliquity of the several turns compensated each other,
`and the resultant action was at the required right
`angles. The arrangement, then, introduced by myself
`was superior to those of Arago and Sturgeon, first, in
`the greater multiplicity of turns of wire, and second,
`in the better application of these turns to the develop-
`ment of magnetism.‘|'
`“ The maximum effect, however, with this arrange-
`ment and a single battery was not yet obtained.
`After a certain length of wire had been coiled upon
`the iron, the power diminished with a further increase
`of the number of turns. This was due to the increased
`
`resistance which the longer wire offered to the con-
`
`' Smithom'an Rtporl, 1878, p. 282.
`1' “When this conception," said Henry, “came into my brain, I
`was so pleased with it that I could not help rising to my feet and
`giving it my hearty approbation.”
`It was his first discovery.
`See
`Professor Mayer’s Eulogy of Henry, before the American Association
`for the Advancement of Science, 1880.
`
`319
`
`319
`
`
`
`to flu Year 1837.
`
`289
`
`duction of electricity. Two methods of improvement,
`therefore, suggested themselves. The first consisted,
`not in increasing the length of the coil, but in using a
`number of separate coils on the same piece of iron.
`By this arrangement the resistance to the conduction
`of the electricity was diminished, and a greater quan-
`tity made to circulate around the iron from the same
`battery. The second method of producing a similar
`result consisted in increasing the number of elements
`
`of the battery, or, in other words, the projectile force
`of the electricity, which enabled it to pass through an
`
`increased number of turns of wire, and thus to develop
`the maximum power of theiron.” '
`Employing a horse-shoe, formed from a cylindrical
`bar of iron, half an inch in diameter, and about ten
`inches long, and wound with thirty feet of fine copper
`wire, he found that, with a current from only 2} square
`inches of zinc, the magnet held I41bs.1' Winding upon
`its arms a second wire of the same length (30 feet)
`whose ends were similarly joined to the same galvanic
`pair, the magnet lifted 28 lbs. On these results Henry
`remarks :—
`
`“ These experiments conclusively proved that a great
`development of magnetism could be effected by a
`very small galvanic pair, and also that the power of
`the coil was materially increased by multiplying the
`
`* Smilhrom'an Report, for 1857, p. 102.
`f It must not be forgotten that at the time when this experimental
`magnet was made, the strongest electro-magnet in Europe was that of
`Sturgeon mentioned on p. 285, and then considered a prodigy.
`U
`
`320
`
`320
`
`
`
`290 A History qf Electric Telegrap/zy
`
`increasing the length of
`number of wires, without
`each. The multiplication of the wires increases the
`power in two ways: first, by conducting a greater
`quantity of galvanism, and secondly, by giving it a
`more prOper direction ; for, since the action of a gal-
`vanic current is directly at right angles to the axis of
`a magnetic needle, by using several shorter wires we
`
`can wind one on each inch of the length of the bar to
`be magnetised, so that the magnetism of each inch
`will be developed by a separate wire.
`In this way the
`
`action of each particular coil becomes directed very
`
`nearly at right angles to the axis of the bar, and con-
`sequently the effect
`is the greatest possible. This
`
`principle is of much greater importance when large
`bars are used. The advantage of a greater conducting
`
`power from using several wires might, in a less degree,
`be obtained by substituting for them one large wire of
`
`equal sectional area ; but in this case the obliquity of
`
`the spiral would be much greater, and
Accessing this document will incur an additional charge of $.
After purchase, you can access this document again without charge.
Accept $ Charge
Still Working On It
This document is taking longer than usual to download. This can happen if we need to contact the court directly to obtain the document and their servers are running slowly.
Give it another minute or two to complete, and then try the refresh button.
A few More Minutes ... Still Working
It can take up to 5 minutes for us to download a document if the court servers are running slowly.
Thank you for your continued patience.
This document could not be displayed.
We could not find this document within its docket. Please go back to the docket page and check the link. If that does not work, go back to the docket and refresh it to pull the newest information.
Your account does not support viewing this document.
You need a Paid Account to view this document. Click here to change your account type.
Your account does not support viewing this document.
Set your membership
status to view this document.
With a Docket Alarm membership, you'll
get a whole lot more, including:
- Up-to-date information for this case.
- Email alerts whenever there is an update.
- Full text search for other cases.
- Get email alerts whenever a new case matches your search.
One Moment Please
The filing “” is large (MB) and is being downloaded.
Please refresh this page in a few minutes to see if the filing has been downloaded. The filing will also be emailed to you when the download completes.
Your document is on its way!
If you do not receive the document in five minutes, contact support at support@docketalarm.com.
Sealed Document
We are unable to display this document, it may be under a court ordered seal.
If you have proper credentials to access the file, you may proceed directly to the court's system using your government issued username and password.
Access Government Site
