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 A COMPENDIOUS VIEW 
 
 OP THE 
 
 REMARKABLE FACTS 
 
 RECENT DISCOVERIES 
 
 ELECTRO-MAGNETISM 
 
 MAGNETO -ELECTRICITY. 
 
 BY FREDERICK A. P. BARNARD, A. M. 
 
 I' 
 
 NEW- YORK : 
 
 GEORGE^EARBORN AND CO. 
 
 * NO. 38 GOLD STREET. 
 
 Scatchcrd and Adams, Printers. 
 
 1837 . 
 
B,us. 
 
 
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Digitized by the Internet Archive 
 in 2017 with funding from 
 
 University of Illinois Urbana-Champaign Alternates 
 
 https://archive.org/details/compendiousviewoOObarn 
 
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ELECTRO-MAGNETISM 
 
 What, in the entire range of nature and nature’s works, is so 
 wonderful as electricity ? What, rather, in the circle of natural 
 phenomena, is not, in one way or other, directly or indirectly, con- 
 nected with this mysterious, all-pervading, and fearfully energetic 
 principle 1 Above, around, beneath — nay, even within our very 
 selves — we find it ever present, ever active. Whether we contem- 
 plate its sublimely splendid coruscations blazing along the heavens, 
 or its more quiet, and often more gorgeous magnificence as it 
 streams upward from the pole, or its hidden agency in quickening to 
 life, and clothing with beauty the whole animal and vegetable 
 world, or regulating, in the deep caverns of the earth, the labora- 
 tories of nature — the ceaseless decompositions and recompositions 
 of matter ; whether we regard it in its power, and clothed in its 
 robe of terrors, speaking in thunders, shivering in splinters the 
 stoutest monarchs of the forest, and prostrating in the dust the 
 proudest fabrics of human art, or in its beauty and beneficence, 
 breathing vitality into all the myriad forms of sentient existence, 
 and scattering around them sources of enjoyment varied to infinity ; 
 in whatever light we view this wonderful emanation of creative power 
 — the handmaid of creation itself — new marvels ceaselessly dawn 
 - upon us, and our imaginations are borne away in loftier and loftier 
 flights, till we grow even giddy with our elevation, and almost 
 shudder as we gaze through the wide expanse it has revealed to us. 
 
 Nor is it among the least of our wonders, to reflect that we are 
 even yet upon the threshold of discovery. The science of elec- 
 tricity, stupendous as it is, is but an infant science still. A half 
 century has not yet passed away since the first detection of galvanic 
 currents. Never, perhaps, before nor since, was there made a dis- 
 covery productive to science of consequences so vast, so splendid. 
 
2 
 
 and so rapidly succeeding one another, as those which have flowed 
 from this. First in order came electro-chemistry, unlocking all the 
 secrets of matter, dissolving nature’s most curious compounds, and 
 reducing all things to their original elements — a science which has 
 more recently unravelled the laws of the composition, as well as of the 
 separation of elements, and revealed to us, doubtless, the agent first 
 employed by creative energy, to bring order and beauty out of the 
 primeval chaotic ocean. To this have succeeded electro-dyna- 
 mics, electro-magnetism, thermo-electricity, magneto-electricity, 
 and (if the term has not been used it should be) electro-physiology 
 — all new ramifications of a single science, growing up together, 
 and each unfolding to us its own peculiar catalogue of wonders. 
 Of the first two of these, and of magneto-electricity, we shall have 
 occasion to speak at large. The curious discovery by Professor 
 Seebeck, of the generation of electricity by heat, with the more re- 
 cent inquiries of Becquerel, Nobili, and Melloni, Cumming, Faraday, 
 and Andrews, renders it more than probable that we shall yet be 
 compelled to strike caloric, as we have done magnetism already, 
 from the list of distinct imponderable agents. Light, too, if the 
 observations of Morichini and Mrs. Somerville should be confirmed, 
 may yet be forced to add another braneh to electrical science, 
 which some future philosopher may denominate Photo-Electricity. 
 The wonderful discoveries of Becquerel, in animal and vegetable 
 electricity, are possibly about to throw a flood of illumination upon 
 the science of pathology, and the healing art, as well as upon the 
 culture of plants, to subserve the purposes, or to gratify the taste of 
 man. 
 
 Should the identity of light and heat with electricity be esta- 
 blished, what then of our imponderable agents will remain ? Gravi- 
 tation stands alone — and who shall say that even this, like the rest, 
 will not be ultimately swallowed up by electricity ; leaving but a 
 single essence in the universe, too ethereal to be matter, yet too 
 passive and too inert, if not too gross, to be spirit ? To this opi- 
 nion we confess ourselves inclined. Its correctness is a question, 
 which, if settled at all, will probably be settled in another age. 
 
 However fertile and animating a theme for speculation and de- 
 clamation is afforded us by the wonderful discoveries at which we 
 have just been glancing, we propose, in the present article, to re* 
 
3 
 
 strict ourselves to a series of simple statements of fact. The sci- 
 ence of electro-magnetism — a science of not yet twenty years* 
 growth, and one which has only acquired its importance within less 
 than ten, has become, in consequence of its practical applications, 
 a subject of general interest to mankind. Few have leisure for the 
 perusal of scientific treatises ; and, were it otherwise, they would 
 seek in vain for one which would exhibit to them the science under 
 consideration in its present state. The last five or six years have 
 added a world to the sum of preceding discoveries ; and the sub- 
 stance of this is still scattered through the scientific transactions 
 and journals. There are very many persons, nevertheless, who 
 would be gratified even with such a hasty outline of the subject, as 
 a few pages of a magazine devoted to literature will admit. They 
 wish to think of something more than a name, when the title of 
 this much talked of, but little understood, science, falls upon their 
 ears. To such, the following sketch will, without doubt, prove ac- 
 ceptable. 
 
 The first indication of the positive relation existing between 
 electricity and the magnetic power, was observed in 1819, by Pro- 
 fessor CErsted, of Copenhagen. This philosopher ascertained that 
 an electric current, passing along the wire used to connect the ex- 
 tremities of a galvanic battery, possesses power to deflect the mag- 
 netic needle in a remarkable manner. If this wire, conveying a 
 positive electric current from north to south, be placed horizontally 
 over the needle, and therefore parallel to it, the north pole of the 
 needle is turned toward the east. If it be placed in like manner 
 below, the same pole is carried toward the west. If it be removed 
 to the east side, the pole is depressed ; if the west, it is elevated. 
 The effects produced by a similar current on a south magnetic 
 pole, are precisely the reverse. Accordingly, since in the rotation 
 of a needle suspended by its centre, the two ends move always in 
 opposite directions, both forces conspire to increase the effect pro- 
 duced upon it by a single electric current. 
 
 These appearances, at first view, seem to be singularly anoma- 
 lous. They are dependent, nevertheless, on a simple law, which 
 may be illustrated by the following artifice. Suppose that, upon 
 the wire placed north and south as before, a small serrated wheel is 
 made to revolve constantly in the direction in which the sun passes 
 
4 
 
 over — that is, from east to west ; the lower part of this wheel 
 will, of course, return from west to east. If we bring down the 
 wire from above to the needle, so that the teeth of the wheel may 
 strike the north pole, that pole will be carried along with them to 
 the east. But if the wire be brought upward from below, then the 
 teeth of the wheel, moving in the direction of the sun, will carry 
 the pole toward the west. As the teeth descend on the left, and 
 ascend on the right, (we suppose ourselves facing the north,) the 
 elevation or depression of the pole, according as the wire is on the 
 west or the east side of the needle, admit of explanation with equal 
 facility. The phenomena are, therefore, precisely such as would 
 be produced by a rotary or circular force, referred to the wire as 
 an axis. As the magnetic pole, acted on by this force, is moved 
 in a tangent to the circle, the force has itself been called tangential . 
 
 Professor CErsted’s discovery at once aroused the curiosity, and 
 stimulated to activity the ingenuity, of the whole philosophic world. 
 M. Arago and Sir Humphrey Davy soon discovered that the con. 
 necting wire of the battery, beside exerting this singular and ap- 
 parently repulsive power upon a magnetic pole, exhibited also, dur- 
 ing the passage of the current, the ordinary magnetic attraction 
 upon unmagnetized iron and steel, in a high degree. Thus, it would 
 sustain a mass of iron-filings of a dozen times its own diameter : 
 but these instantly fell away, on the cessation of the current. The 
 philosopher last mentioned found, moreover, that steel needles, 
 placed near the current transversely, or at right angles to its course, 
 became instantaneously and permanently magnetic ; while other 
 needles, placed parallel to the current, exhibited the same magnetic 
 properties as the conducting wire, but lost them, in like manner, 
 when the current ceased. The induction of magnetism by elec- 
 tricity was thus early demonstrated. In its practical consequences, 
 this discovery bids fair to rank among the first in importance, 
 ever made in philosophy. 
 
 From a consideration of the law of tangential force explained 
 above, it seemed obvious that a magnetic pole, free to move in any 
 direction, and prevented, at the same time, from so far obeying the 
 centrifugal force as to be thrown beyond the influence of the elec- 
 tric current, ought to revolve in a circle about the conducting wire. 
 This inference, first drawn by Dr. Wollaston, was practically con- 
 
6 
 
 firmed by Mr. Faraday, with the aid of a very simple apparatus. 
 One end of a bar magnet was attached by a thread to the bottom 
 of a vessel of mercury, in which the magnet floated almost upright. 
 An electrical current was then introduced into the centre of the 
 mercury, by means of a terminated wire, and carried off below by 
 another wire, passing through the bottom of the vessel. The mag- 
 net instantly began to revolve, and continued its motion while the 
 current lasted. Action and re-action in mechanics being equal, it 
 followed, of course, that the conducting wire might be made to re- 
 volve about a magnet. This effect was produced by an arrangement 
 nearly similar to the former, the magnet being fixed, and the wire 
 provided with a joint. By rendering both the magnet and the wire 
 moveable in the same apparatus, both phenomena were exhibited 
 at once. Fluid conductors, like mercury and water, contained be- 
 tween concentric glass cylinders, were also made to revolve about a 
 magnetic pole. Magnets and conductors were made to revolve 
 on their own axes ; and, finally, the galvanic battery employed to 
 generate the electric current, having been constructed very light 
 and suspended with delicacy, was itself forced to make the circuit. 
 This battery being composed of hollow cylinders with the magnet 
 in the centre, it was even found possible to produce, at the same 
 time, independent rotations of the zinc and copper plates, in con- 
 trary directions. It must be observed of all these rotations, that 
 their directions were reversed, by reversing that in which the elec- 
 tric current passed. 
 
 These phenomena are all curious and interesting. They demon- 
 strate a relation to exist between the principles of magnetism and 
 electricity ; but they afford little evidence of similarity — much less 
 of absolute identity — between them. It is otherwise with those we 
 are about to describe. 
 
 Let a piece of copper wire be bent into a circle of about an inch 
 in diameter, the extremities not being allowed to meet, but being 
 again bent so as to pass off a little distance in parallel lines, and 
 terminate in hooks. Through the wire suspended by these hooks 
 in the manner usually practised by experimenters in Volta-electri- 
 city, let an electric current be transmitted. The pole of a magnet 
 being then presented to the centre of the circle, an attraction will 
 be manifested on one side and a repulsion on the other. That is, 
 
6 
 
 the circle will approach the magnet so as to surround it, in the first 
 instance ; and will recede from it, in the second. If the other pole 
 of the magnet be presented, the effects will be severally reversed. 
 An explanation of this phenomenon may easily be found in the law 
 of tangential force. For, if we suppose this force to be visibly re- 
 presented by a number of toothed wheels revolving round the wire’ 
 we shall perceive that their effect on one side will be, to draw the 
 magnet into the circle ; and, on the other, to drive it out. 
 
 These phenomena of attraction and repulsion, correspond exactly 
 with those of magnetic polarity. And, indeed, the circle may be 
 considered to represent a magnet, having considerable breadth and 
 an exceedingly short axis. 
 
 Various devices have been contrived to render the resemblance 
 
 » 
 
 thus discovered, to a common magnet, more striking. M. A. De 
 La Rive attached a circle like that just described, to narrow slips 
 of zinc and copper, passing through a cork of sufficient buoyancy 
 to float the whole in an acid or saline bath. These slips of metal 
 thus immersed, constituted the battery : while the lightness of the 
 apparatus and its perfect freedom of motion, well adapted it to the 
 purpose intended. The power of this little apparatus was increased, 
 by causing the wire to make several complete circles, before at- 
 taching it to the battery ; the wire having been itself first insulated 
 by winding with silk, in order to force the electricity to traverse 
 its entire length. 
 
 A still nearer approach to the magnet is made, by separating to 
 a little distance from each other laterally, the coils of wire in this 
 improved apparatus of Mr. De La Rive, so as to produce a spiral 
 cylinder, or helix . The number of turns may be increased at plea- 
 sure. The ends of the coiled wire are carried back along the axis 
 of the helix, till they meet half-way ; and afterward at right angles 
 downward to the floating battery. This elongation of the coil se- 
 parates the poles, one being found at each end of the helix. The 
 whole, if constructed with delicacy, will obey the magnetic influence 
 of the earth, and settle itself with the axis of the helix in the mag- 
 netic meridian. 
 
 When this position has been spontaneously assumed, positive 
 electricity, if the helix be wound like the thread of a screw, will be 
 moving from south to north ; and, consequently, in the upper half of 
 
7 
 
 each coil of the spiral, from west to east : but, in a helix wound in 
 the opposite direction, the current will be from north to south ; that 
 is, in the several coils of the spiral, from west to east still. If, then, 
 instead of the helix, we had but a single circle of wire, in the cir- 
 cuit, theory would require that this should assume a position, under 
 the influence of terrestrial magnetism, at right angles to the mag- 
 netic meridian. Experiment with a circle of some size, delicately 
 suspended, confirms this inference. And not only that, but, with 
 suitable arrangements, a similar circle will be brought by the pow- 
 er of the earth’s magnetism, to stand with its plane precisely at 
 right angles to the line of the dip. 
 
 Helices constructed as above described, exhibit all the phenomena 
 of ordinary magnetism. Their similar poles repel each other, and 
 repel those of steel magnets ; and their dissimilar poles exert reci- 
 procal attraction, and attract the dissimilar poles of magnets. We 
 should be warranted, even here, in concluding the phenomena of 
 ordinary magnetism to be simple manifestations of electric energy. 
 On this supposition, the common magnet must be encircled by cur- 
 rents of electricity moving at right angles to its axis ; and the 
 earth itself must be traversed by similar currents, passing round it 
 from east to west. That the effect of such currents upon the mag- 
 netic needle, would be precisely such as we see to be actually produc- 
 ed by the influence of terrestrial magnetism, was experimentally de- 
 monstrated by Mr. Barlow, in 1831, by means of an artificial globe. 
 We may add, furthermore, that experiments made by Mr. Robert 
 Were Fox in the mines of Cornwall, seem to prove the actual ex- 
 istence of such currents in the earth. 
 
 The power of magnetic induction, that is, of exciting magnetism 
 in unmagnetized bodies, has already been mentioned as remarkably 
 belonging to electricity moving in currents. This power is won- 
 derfully increased by causing the current to pass through a heliacal 
 conductor, and placing the bar to be magnetized within the coil. 
 Hardly an instant is necessary to produce the effect. In soft iron, 
 the magnetism, as when excited by the common methods, is but 
 temporary : in steel, it is permanent. 
 
 The power developed by winding large bars of soft iron with 
 copper wire covered with silk or cotton, is in the highest degree 
 astonishing. In 1829 or 30, Professor Moll of Utrecht produced a 
 
8 
 
 horse-shoe magnet of this description, capable of sustaining more 
 than one hundred and fifty pounds. But Professor Henry and Dr. 
 Ten Eyck of our own country, who were carrying on a simultaneous 
 and independent series of experiments, accomplished wonders im- 
 mensely greater. Their most powerful magnets sustained about a 
 ton. 
 
 In the construction of magnets of this description, it is found that 
 the power acquired is not in exact proportion to the number of coils 
 made by the surrounding wire. Were it so, nothing could impede 
 the attainment of any proposed power, even with a battery of mode- 
 rate size, by the mere multiplication of the number of coils. The 
 current appears to become enfeebled in traversing a long circuit. 
 Thus, Professor Henry found that, after having wound his great 
 magnet in such a manner that he could, at pleasure, either send the 
 electricity in a single current through the whole length of the en- 
 circling wire, or in divided portions, passing each through a part of 
 the wire disconnected from the rest, the power of the magnet was 
 immensely greater in the latter case than in the former, though the 
 battery remained unchanged. 
 
 From a consideration of such phenomena, it appeared probable 
 to Professor Emmet of Virginia, that the power of an electro-mag- 
 net could not be dependent on the number of circuits made by the 
 electric fluid around the bar, but rather upon the collected volume 
 of the whole. By inference, therefore, there is no necessity for 
 using wire in the construction of these magnets ; but, in its stead, 
 we may employ metallic sheets in which to roll the iron to be mag- 
 netized — these sheets being, of course, insulated from the iron and 
 from their own convolutions, by interposed silk. His experiments 
 seemed to corroborate the truth of his supposition, very powerful 
 electro-magnets having been constructed by him, by the use of sheet 
 copper. 
 
 The length of the magnetized bar seems to have much to do with 
 the power attained. From some experiments detailed to the Royal 
 Society in 1833, by Dr. Ritchie, it would appear that short bars, 
 with a given quantity of enveloping wire, have much the advantage. 
 Of two horse-shoe magnets, having lengths as one to four, wound 
 with the same quantity of wire each, and magnetized by the same 
 battery, the result was in favor of the short one in the ratio of two 
 
9 
 
 to one. Having afterward, as he says, prepared a horse-shoe mag- 
 net with great pains, according to the American method, and found 
 its power to be about one hundred and forty pounds, he simply 
 rolled twelve feet of copper ribbon about the lifter, (the piece of 
 iron laid across the poles of a horse-shoe magnet) and, employing 
 that as the magnet, made the horse-shoe itself serve as a lifter in 
 turn. The lifter proved the more powerful magnet of the two. 
 “ All that is necessary, then,’’ he says, “ to make a powerful electro- 
 magnet, is simply to roll a ribbon of copper about a short bar of 
 iron, and use a horse-shoe lifter.” 
 
 Wonderful as the immense power thus instantaneously called into 
 action, by means the most simple, appears to us, our astonishment 
 becomes still greater, when we consider, not only that it may just as 
 instantaneously be reduced to nothing, but, that what was just now 
 attraction, may be converted, in the twinkling of an eye, into the 
 most powerful repulsion. This arises from the fact that the direc- 
 tion of the induced magnetic poles depends on that of the electric 
 current. This current may be reversed in a space of time too mi- 
 nute even for conception, and the poles are reversed along with it. 
 In late years, more than one experimenter has essayed to turn this 
 principle to account for the generation of motion. Professor Henry, 
 of this country, succeeded, so early as the year 18.31, in producing a 
 reciprocating motion in a horizontal electro-magnetic bar. Early 
 in 1833, Dr. Ritchie, of London, obtained a rapid rotation of a si- 
 milar bar, at first under the influence of a horse-shoe magnet wide 
 between the poles, and afterward by the power of terrestrial mag- 
 netism alone. The account of this invention was read to the Royal 
 Society on the 21st of March, 1833, and published in their Trans- 
 actions for that year. From the paper referred to, we extract the 
 following : — 
 
 “ But the most beautiful result I have obtained from changing the 
 poles of an electro-magnet, is the rapid rotation of such a magnet 
 about its centre. The following short description of the first actu- 
 ally constructed, will be sufficient to show how others of greater 
 power may easily be formed.” 
 
 [The description being connected with a diagram, we alter its 
 phraseology so far as is necessary to render it independently in- 
 telligible.] 
 
 2 
 
10 
 
 “ A circular sole of wood is taken, having a groove turned in it 
 for the purpose of holding mercury. The groove is divided into two 
 compartments by thin slips of wood. These divisions are to be 
 connected with the poles of a battery. An electro-magnet is form- 
 ed by a piece of soft iron wound with copper wire, and so balanced 
 on its centre, that the ends of the wire shall touch the mercury in 
 the two divisions of the groove. These ends are so adjusted as to 
 clear the two small divisions of wood, the surface of the mercury 
 rising a little above the divisions. If a horse-shoe magnet having a 
 considerable distance between the poles, be "placed above the tempo- 
 rary magnet, the poles of the permanent magnet being directly 
 above the slips of wood which divide the groove into two compart- 
 ments, whilst the soft iron is converted into a magnet by means of 
 the battery, a powerful and rapid rotation of the electro-magnet will 
 take place ; for the electro-magnet being put in motion by the at- 
 traction of the poles of the other, will have its poles reversed the 
 moment the wires pass the two divisions. At that moment attrac- 
 tion will be changed into repulsion, &c. * * * 
 
 “By a slight modification of the apparatus, horse-shoe magnets 
 may be made to revolve with considerable force. I have fitted up a 
 revolving apparatus of this kind, which has a power sufficient to 
 raise several ounces over a pulley. When the apparatus is placed 
 so that the change of poles of the electro-magnet may take place 
 in the magnetic meridian, the action of the earth is sufficient to 
 make the magnet revolve, without the aid of exterior magnets. By 
 fitting it up so as to revolve in the plane of the magnetic meridian, 
 and to change its poles at the point to which the needle dips, a dip- 
 ping needle might be made to revolve in a vertical plane.” 
 
 In July, 1834, our countryman, Mr. Davenport, with no know- 
 ledge of Dr. Ritchie’s previous success, obtained a rotary motion 
 upon identically the same principle. Since that time he has de- 
 voted himself perseveringly to the perfection of his machine, till at 
 length his triumphant results seem about to produce an entire revo- 
 lution in mechanics. As Americans, we are proud of the man, who, 
 under the weight of a thousand disheartening embarrassments, has 
 at last demonstrated to the world the practicability of employing 
 the tremendous energy of electro-magnetism, as a moving power. 
 Mr. Davenport has associated his name imperishably with the his- 
 tory of the science he has espoused, and with the progress of im- 
 provement in the entire range of the arts ; to which his labors will 
 be found hereafter to have contributed in a thousand ways. To him 
 also is no doubt due all the credit of having independently devised 
 the mode of producing rotary motion, on which, as recently pub- 
 lished, the history of his machine informs us, his patent rests. 
 
 But let us not on this account indulge ourselves too freely in ex* 
 
11 
 
 elusive laudation of American ingenuity, nor decry in too wholesale 
 terms the importance of attending to the past labors of scientific 
 men. After all, as a Persian would say, the philosophers are some- 
 body. We are quite too apt in this country to make ourselves ri- 
 diculous in the eyes of foreigners, by our extravagant and some- 
 times ignorant self-complacency. Mr. Davenport was, no doubt, an 
 original discoverer, but he was not the first discoverer of the princi- 
 ple of his machine. We have for some months been looking for the 
 circumstantial statement of this fact in the English journals. In 
 the mean time, we have seen, in our own, commendations lavished 
 upon our ingenious fellow-citizen, strictly for his inattention to the 
 writings of the great discoverers in this department of science ; on 
 the ground, forsooth, that, by reading, he might have bound down 
 his genius for ever to the less aspiring notions of the philosophers, or 
 have been led away wandering, in the hopeless mazes in which they 
 had lost themselves. Had Mr. Davenport read, however, he would 
 have found that the rotary motion he was seeking for, had been pro- 
 duced, in precisely the manner in which he has since produced it, 
 even before the period when, as we are informed, he “ saw a galva- 
 nic magnet for the first time.” We have no wish to detract from 
 the credit justly due to perseverance and successful ingenuity. But, 
 first or last, Dr. Ritchie will claim the priority of this discovery, and 
 the world will admit the justice of his claim. Mr. Davenport him- 
 self, we are confident, on a comparison of dates, would not hesitate 
 to do the same. 
 
 Beside the attempts already noticed, to turn the power of electro- 
 magnetism to practical account, there have been one or two others 
 deserving of a passing mention. Mr. Sturgeon, of Woolwich, con- 
 structed a machine of considerable power, by means of two magnetic 
 steel bars revolving horizontally, surrounded by four fixed upright 
 electro-magnets. Mr. McGauly, of Ireland, a year or two since, 
 reported an electro-magnetic machine to the British Association ; 
 but the volume of reports containing his statements is not at hand 
 at present, and we can give no account of the form of his machine. 
 
 We have heard, moreover, of one or two recent inventions in 
 this country, but are not aware that they rest on any new prin- 
 ciple. 
 
 In the preceding pages, we have given a cursory outline of the 
 
12 
 
 most important facts in the science of electro-magnetism. This 
 term, electro-magnetism, so long as the phenomena of magnetism 
 and electricity were supposed to be dependent on distinct invisible 
 agents, possessed a significancy, which it has now in a measure lost. 
 Magnetism, which, for such a length of time, has occupied an inde- 
 pendent rank among the physical sciences, is, by common consent, 
 transferred to a subordinate place in the more comprehensive sci- 
 ence of electricity ; and its phenomena, with those of the particu- 
 lar branch we are considering, are to be referred to the laws of that 
 division of the general subject, denominated Electro-Dynamics . 
 
 This term is opposed to Electro-Statics ; the one science treating 
 of electricity in motion through conductors, and the reciprocal action 
 of its currents ; and the other, of common electricity, called by 
 Faraday electricity of tension, or electricity in equilibrio. The 
 phenomena characteristic of these two states are widely different, 
 as will be evident from the consideration, that two bodies charged 
 with similar electricity of tension repel each other, and with dis- 
 similar electricity, attract ; while, on the other hand, two con- 
 ductors carrying similar currents in the same direction, attract, and 
 carrying dissimilar, repel. This last-mentioned fact is at the basis 
 of the science of electro-dynamics. It was a discovery of Am- 
 pere, a celebrated French philosopher, made soon after the publica- 
 tion of (Ersted’s experiments. For our present purpose, it will be 
 sufficient to show in what manner this simple law may serve, instead 
 of the supposition of a tangential force, to explain the phenomena 
 of electro-magnetism. Let us suppose two small floating batteries, 
 like the apparatus of De La Rive already described, to be brought 
 near to each other, with the zinc ends in the same direction. It is 
 not to be supposed that an apparatus of so little power and so great 
 comparative inertia, would actually manifest the phenomena we are 
 about to infer ; but its construction is favorable to the illustration 
 of the theory. In the situation described, similar electrical cur- 
 rents will be passing in the same direction in both the parallel 
 circles, and the two should accordingly approach each other. Let 
 one be turned half a revolution ; then, as the currents will be mov- 
 ing in contrary directions, separation ought to take place. If each 
 circle be extended as above described, into a helix, (an electro- 
 dynamic cylinder, in the language of M. Ampere) their extremities 
 
13 
 
 will severally manifest contrary polarities, attracting and repelling 
 one another, according as the cylinders are so arranged that the cur- 
 rents move similarly in both, or the contrary. 
 
 From this rude method of illustration, we are not, it is true, at 
 liberty to conclude, at once, that these cylinders will manifest all the 
 phenomena of ordinary magnetism ; nor even that they will con- 
 tinue to attract and repel each other in all positions, precisely as 
 magnets would do. But it would here be out of place to adduce the 
 mathematical reasoning by which all the observed magnetic pheno- 
 mena are legitimately derived from the one fundamental law of 
 electro-dynamics. As general rules, we may say that the effect, 
 according to this law, of the mutual action of electric cross cur- 
 rents, is to create a tendency to parallelism ; and that, when cur- 
 rents inclined to each other, are both approaching toward, or both 
 receding from, the angle of their inclination, they exert a reciprocal 
 attraction ; but, when otherwise, repel. 
 
 The application of these principles, and of some others which it 
 is unnecessary to state, is sufficient to account for the attraction 
 and repulsion of electro-dynamic cylinders, and for rotations per- 
 formed by them, and by conductors in their vicinity, like those 
 produced by the use of magnets ; as well as for additional pheno- 
 mena somewhat similar. But all this will not enable us to explain 
 the phenomena of electro-magnetism without supposing the exist- 
 ence of a tangential force, unless, with M. Ampere, we regard the 
 common magnet as an electro-dynamic instrument. 
 
 Indeed, in view of all the wonderful developements of modern 
 science, we can hardly escape from the conclusion, that the polarity 
 of the needle is owing to the circulation of electric currents in its 
 substance. M. Ampere supposes each particle of a magnetic bar 
 to be encircled by such a current. All these currents moving in 
 the same direction, (that is, from west to east on the upper surface, 
 when the bar assumes the position to which it is impelled by the 
 action of terrestrial magnetism) those in the interior will counteract 
 one another’s effects ; precisely as the two wheels on the same side 
 of a carriage, would, if in immediate contact, obstruct each other’s 
 motion. There is nothing, however, to oppose the exterior cur- 
 rents, and these must exert an influence on bodies around them, 
 equivalent to that of a single current encircling the entire magnet. 
 
14 
 
 This is, in few words, M. Ampere’s electro-dynamic theory of mag- 
 netism. Not only has it the merit of simplifying a hitherto myste- 
 rious class of phenomena, but it explains, much more satisfactorily, 
 many of the remarkable rotations we have described, than the sup- 
 position of the singular force denominated tangential, could possibly 
 do ; to say nothing of the contradiction to all the analogies of na- 
 ture, implied in the supposition of a force so altogether unique. 
 
 But notwithstanding the general disposition to admit Ampere’s 
 solution of the mystery of magnetism, it was felt that the production 
 of some phenomenon decidedly electric, by the agency of magnetism 
 alone, would be an important corroboration of the theory. To Mr. 
 Faraday must be ascribed the honor due to the accomplishment of 
 an object so desirable, and the developement of a new series of won- 
 ders in the world of science. Toward the close of the year 1831, 
 after a very laborious series of experiments, that philosopher suc- 
 ceeded in producing momentary electrical effects from a common 
 magnet. He found that when a helix of copper wire is brought 
 near the poles of a powerful magnet, electrical currents are excited 
 in it. These are increased by the presence of a bar of soft iron 
 within the helix. Similar currents are generated by the introduc- 
 tion of a bar already magnetised, within the helix, or by removing 
 it after it has been so introduced. These are observed to continue 
 only during the motion of the bar or helix ; and cease with the ces- 
 sation of the motion, though the parts of the apparatus maintain 
 their relative situations. The first indication of their existence 
 was afforded by the galvanometer ; but they became subsequently 
 much more obvious, producing convulsions in the limbs of a frog, 
 and magnetising steel needles. 
 
 With the new light thus afforded him, Mr. Faraday next directed 
 his attention to a class of phenomena previously altogether inexpli- 
 cable. M. Arago had observed something very like magnetic at- 
 traction to take place between disks of various substances in rapid 
 rotation, and magnets in their vicinity. Sir John Herschell and 
 Mr. Babbage had attributed this to a temporary magnetism induced 
 in the disks by the magnet. But it was remarkable, that, with the 
 cessation of the motion, the magnetism, if it had existed, was wholly 
 lost. Mr. Faraday did not hesitate to ascribe it to electrical cur- 
 rents produced by magnetism ; since his previous experiments had 
 
15 
 
 proved motion to be essential to their developement. To determine 
 the correctness of his supposition, he caused a disk of copper to re- 
 volve, with its edge between the poles of a horse-shoe magnet. 
 Conductors of electricity having been applied to the centre and cir- 
 cumference of the disk, and connected with a galvanometer, his con- 
 jecture was completely corroborated. 
 
 Mr. Faraday soon demonstrated that the circular form of the 
 moving body was by no means an essential condition. Even a sin- 
 gle wire, moved in the vicinity of a magnetic pole, was sufficient to 
 deflect the needle of the galvanometer. He ascertained the general 
 fact, that any conductor of electricity so moved as to cut the mag- 
 netic curves, (curves into which iron filings are observed to arrange 
 themselves, under the influence of a magnet) was invariably tra- 
 versed by electrical currents at right angles to the line of its own 
 motion. 
 
 Proceeding in the career of discovery, he found that terrestrial 
 magnetism alone was sufficient to excite similar currents. “ It is a 
 consequence,” says he, “ which appears very extraordinary to the 
 mind, that scarcely any piece of metal can be moved in contact 
 with others, either at rest, or in motion with different velocities, or 
 in other directions, without currents of electricity existing within 
 them.” Mr. Faraday further ascertained, that, when a body itself 
 magnetic is made to rotate, electrical currents are excited on its 
 own surface ; and that these are independent of the currents, which, 
 4 according to M. Ampere’s theory, give it polarity. 
 
 A copper disk rotating in any direction, in which its plane did 
 not pass through the line of the dip, was found to constitute an elec- 
 * trical machine, capable of sustaining a constant current, passing 
 
 through conductors connecting its centre and circumference. The 
 effect was greatest at right angles to the dip. Currents occurred in 
 a brass globe, in whatever direction rotated. The axis of the globe 
 being made parallel to the dipping needle, and the revolution caused 
 to take place from west to east, the effects of the earth’s diurnal 
 motion, in producing electrical currents within itself, were exem- 
 plified. These currents were found to proceed from the equator to- 
 ward both poles. There is not a little plausibility in the theory 
 respecting the Aurora Borealis, which he thus modestly sug- 
 gests : — 
 
16 
 
 “ I hardly dare, even in the most hypothetical form, to ask whe- 
 ther the Aurora Borealis and Australis may not be the discharge of 
 electricity thus urged toward the poles of the earth, from whence it is 
 endeavoring to return, by natural and appointed means, above the 
 earth to the equatorial regions. The non-occurrence of it in very 
 high latitudes is not at all against this supposition ; and it is re- 
 markable, that Mr. Fox, who observed the deflection of the needle 
 at Falmouth, gives that direction of it which perfectly agrees with 
 the present view.” 
 
 To the new department thus added by Mr. Faraday to the 
 science of Electricity, he has given the name of Magneto* Elec- 
 tricity. 
 
 The progressive manner in which he approached these brilliant 
 discoveries, is worthy of attention. Though stimulated, doubtless, 
 by the hope of ultimately obtaining electricity from ordinary mag- 
 netism, his first experiments were instituted simply with a design to 
 ascertain the inductive effect of electric currents ; the effect, in other 
 words, if any such existed, of one current already in motion, to excite 
 another in a neighboring conductor of electricity. Upon a wooden 
 cylinder, he wound twelve helices, containing on an average twenty- 
 seven feet of copper wire each, one above another, and insulated by 
 calico interposed. By soldering corresponding ends of the wires, 
 the first, third, fifth, seventh, ninth, and eleventh of these helices 
 were combined into a single helix ; and the alternate ones, in like 
 manner, into another. The two compound helices, of about one 
 hundred and sixty feet each in length, were thus interlocked through- 
 out, and brought into close vicinity in every part of their course. 
 Through one of them Mr. Faraday caused a current of electricity 
 to pass, while the extremities of the other were connected with a 
 galvanometer. The effect anticipated was, that the current from 
 the battery circulating through one helix, would occasion another 
 current in the other ; but no indication of such an effect could be 
 detected. In order to obtain a nearer approach to contact, a new 
 double helix was formed, by winding two hundred and three feet of 
 wire upon a wooden cylinder, and the same quantity again between 
 the coils of the first, twine being interposed between. A much 
 more powerful battery being now used to transmit a current through 
 one of the spirals, while the other was connected with the galva- 
 nometer, a momentary and very slight effect was perceptible at the 
 instant of either making or breaking the connexion with the bat- 
 
17 
 
 tery ; these two effects being of contrary kinds. But during the 
 passage of the battery current, however long continued or intense, 
 nothing like an induced current could be perceived in the other 
 wire, but the galvanometer needle, from its momentary disturbance 
 in the beginning, returned quietly to its ordinary position, where it 
 remained at rest till the moment when the voltaic current was sus- 
 pended. Then occurred the other momentary disturbance, in a 
 direction contrary to the former. 
 
 These momentary currents produced by induction, were in a di- 
 rection contrary to that of the inducing current, when the battery 
 contact was made ; and in the same direction, when this contact 
 was broken. They were found sufficiently energetic, when passed 
 through spiral conductors, to magnetise steel needles ; but the suc- 
 cessive currents, being in opposite directions, produced in such 
 needles contrary polarities. The same needle being allowed, there- 
 fore, to remain in the helix during the first passage and subsequent 
 return of the induced current, was found scarcely magnetised at 
 all ; but when subjected to the single action of either, exhibited de- 
 cided polarity. 
 
 To avoid the possibility of error from any unobserved peculiarity 
 of circumstances attendant upon making or breaking contact with 
 the battery, the induction was then produced in a different mode. 
 Upon two separate boards, two similar zig-zags of wire were fas- 
 tened, so that they could be brought into mutual contact in every 
 part, except that a sheet of paper was interposed between. Being 
 separated, one of the zig-zags was connected with the battery, and 
 the other with the galvanometer. They were then made to approach 
 t each other, and at this moment the galvanometer indicated elec- 
 
 tricity. On being again separated, electricity of the opposite kind 
 was developed. With the cessation of the motion, these currents 
 ceased. 
 
 The fact of Yolta-electric induction having been thus demon- 
 strated in the case of conductors contiguous to a current of elec- 
 tricity, Mr. Faraday proceeded to ascertain whether the same effect 
 would be produced at a greater distance, provided a communication 
 were formed by means of iron rendered magnetic by the current. 
 Two helices of insulated copper wire were wound upon the opposite 
 semicircles of an iron ring of about six inches in external diameter. 
 
 3 
 
18 
 
 An electric current having been passed through one of these, the 
 other was traversed by momentary currents, precisely as with the 
 former arrangement, but much more powerful. When passed 
 through dry charcoal points, they exhibited a faint spark. 
 
 Two helices were then intertwined with each other upon a hol- 
 low pasteboard cylinder, into which was introduced a bar of iron. 
 The presence of the iron added remarkably to the energy of the 
 induced currents : but this arrangement was inferior in power to 
 that of the ring. A copper cylinder, substituted for the iron, pro- 
 duced no effect ; but a single iron wire materially increased the 
 power of the apparatus. 
 
 The Voltaic battery was then entirely disused, and the iron cy- 
 linder in the helix, magnetised, by applying to its extremities the 
 contrary poles of two common bar magnets, each two feet in length, 
 brought together at the other extremities, in imitation of a horse- 
 shoe magnet. Currents were still excited in the helix, precisely as 
 when the battery was used. Their first direction, or that which 
 occurred on making contact, was contrary to the direction of the 
 currents supposed, by M. Ampere’s theory, to exist in the magne- 
 tised cylinder ; but their returning direction, of course, corresponded 
 with that of these. 
 
 Instead of the soft iron cylinder, a bar, already magnetised, was 
 then employed alone. W T hen introduced into the helix, it excited 
 currents opposite to those supposed to exist within itself ; and 
 when withdrawn, it produced others, corresponding with the same. 
 It was a matter of no consequence, as it regarded these directions, 
 at which end of the helix the magnet was first inserted, nor, of 
 course, which pole first entered, nor which way it was moved ; 
 provided the same ends of the magnet and helix continued to cor- 
 respond in direction — that is, provided they were not relatively 
 reversed. 
 
 Experiments were then made with a soft iron cylinder, and a 
 compound steel magnet, of such power, that, when the cylinder was 
 laid across the poles, nearly one hundred pounds were required to 
 break the contact. When this cylinder, surrounded by the helix, 
 was applied to the poles, the needle of the galvanometer was caused 
 to spin violently jound : but it returned at length to its quiescent 
 state, if the parts of the apparatus were kept motionless, though 
 
19 
 
 the contact still continued. But when this contact was broken, a 
 disturbance quite as violent took place in the other direction. The 
 amount of effect produced, seemed much to depend upon the sudden- 
 ness of making or breaking contact. When the separation was 
 accomplished by a blow, the currents were most remarkably de- 
 veloped. 
 
 Mr. Faraday had not yet obtained the electric spark from a 
 permanent steel magnet alone, when he announced his discoveries, 
 in a private letter, to M. Hachette of Paris. Imperfect statements 
 of them were soon made public ; and the experiments were, conse- 
 quently, at once repeated and varied by numerous individuals. 
 Messrs. Nobili and Antenori of Florence, by a simple arrangement, 
 elicited sparks from magnets of a comparatively low power. A 
 coil of insulated wire was wound upon the middle of the lifter (or 
 keeper ) of a horse-shoe magnet, the ends resting upon the poles of 
 the horse-shoe beyond the extremities of the lifter, which was made 
 short for the purpose. On suddenly breaking contact with the 
 poles, sparks made their appearance at the extremities of the wire. 
 Professor Emmet, of Virginia, has essentially improved this appa- 
 ratus. 
 
 In March, 1832, Mr. J. D. Forbes obtained the electric spark 
 from a natural magnet, or loadstone, of great power ; the loadstone 
 being capable of sustaining one hundred and seventy pounds. His 
 mode of exciting the currents was similar to that of Faraday, with 
 the large compound steel magnet above-mentioned. 
 
 In October of the same year, Mr. Faraday contrived a mode of 
 eliciting the spark, without the aid of the soft iron cylinder, or lifter, 
 intervening between the magnet itself and the conductor carrying 
 the induced current, which had hitherto been found necessary to 
 produce that phenomenon. He fixed a helix horizontally to a firm 
 support, and bent the two ends of the wire to meet, one of them 
 passing before the end of the helix, or crossing the line of its axis 
 continued. This end pressed with a spring against a little disk 
 soldered to the other. It was, of course, impossible for a solid body 
 to pass through the helix without striking the wire which crossed 
 its axis, and thus breaking the contact of that wire with the disk. 
 If the solid body were a magnet, an electric current would be ex- 
 
20 
 
 cited in the helix by its passage, and the interruption of the contact 
 as above, would cause the spark to appear. 
 
 By a particular arrangement, the electrical shock may be obtained 
 even more directly from the permanent magnet, than the spark, as 
 just described. It is known that if a steel ring be magnetised in 
 the ordinary way, by carrying round it repeatedly one of the poles 
 of a common bar-magnet, it will, while it remains whole, exhibit no 
 polarity. If, then, an insulated wire be wound on a part of the 
 ring, and the latter be suddenly fractured, a momentary current 
 will, at the moment of the fracture, be induced in the wire, of suf- 
 ficient intensity to produce a sensible shock. This is accounted 
 for, by supposing that the electricity of the magnet is obliged to 
 seek a new distribution, when the continuity of the ring is inter- 
 rupted. 
 
 The first successful experiment of effecting chemical decompo- 
 sition by magneto-electricity, was communicated anonymously to 
 Mr. Faraday, in July, 1832. It was accomplished by means of an 
 ingenious magneto-electric machine, contrived for the double pur- 
 pose of rendering available the joint power of many comparatively 
 feeble horse-shoe magnets, and of increasing the facility of produc- 
 ing the spark, by a sudden reversal of poles. The horse-shoe mag- 
 nets were fixed equidistant in the circumference of a revolving 
 wheel, so that their poles should be even with the surface of its 
 plane, and stand severally in the lines of its radii. They were 
 placed with their north and south poles alternately outward, or at 
 the extreme edge. A number of lifters equal to that of the mag- 
 nets, were fixed in like manner in another disk of wood of equal 
 size, placed motionless, in full contact, surface to surface, with the 
 wheel. Thus all the magnets were, at the same time, in contact 
 with their respective lifters. A single long wire was wound round 
 the middle of each lifter, sucessively, alternately from left to right 
 and from right to left, in order that the magneto-electric currents 
 excited by the whole might be in the same direction, though the 
 poles of the magnets succeeded each other in contrary order. In 
 passing from lifter to lifter, the wire was wound round an iron ring 
 on the outside of the fixed disk ; this being found to increase the 
 power. Let us call one of the magnets A, and its next neighbor 
 
21 
 
 B. If, then, A has its north pole outward, B will have its south 
 pole outward at the same time. The magnet A produces a cer- 
 tain polarity in its lifters ; but, as the wheel turns, B takes the place 
 of A over the same lifter, and reverses that polarity, because its 
 poles stand in a contrary direction. A similar change, from a simi- 
 lar cause, occurs, of course, throughout the whole apparatus at 
 the same moment. Thus, if the wheel turns rapidly, a rapid succes- 
 sion of changes is constantly going on. If a little projection be 
 placed over each magnet, to break, by a suitable arrangement, the 
 continuity of the circuit formed by the wire, at the exact moment 
 of the change of poles, the spark becomes visible. The currents 
 thus excited are found sufficient to decompose water ; and this, ac- 
 cording to Mr. Faraday, was the first arrangement by which that 
 object was accomplished. 
 
 In October of the same year, Professor Botto, of Turin, succeeded 
 in effecting many decompositions, and in producing the spark, with 
 the aid of a magnet capable of lifting no more than six pounds. 
 Water, sulphate of copper, and acetate of lead, were among the sub- 
 stances decomposed. His magnet was placed in a box, with a soft 
 iron cylinder wound with wire fixed before its poles. By means 
 of a handle, contact between the poles and the cylinder could be 
 very quickly made and broken, and a current of electricity, almost 
 constant, kept up. 
 
 Professor Dal Negro, of Padua, contrived, early in 1832, a very 
 ingenious magneto-electrical battery. A series of parallel spirals, 
 wound alternately from right to left and from left to right, and 
 formed all of one wire, were placed opposite to the poles of a num- 
 ber of horse-shoe magnets fixed to a little carriage, which was so 
 constructed, that, in moving, the poles should be made to pass se- 
 verally within the spirals. All the currents thus generated would 
 conspire to move in the same general direction along the wire, and 
 by the facility with which the carriage could be advanced or with- 
 drawn, they could be kept up as long as desired. ^ 
 
 But a magneto-electrical machine, much more efficient than 
 any that had been previously constructed, was that invented in 
 1833 by our countryman, Mr. Joseph Saxton, resident in London, 
 and denominated by him a revolving-keeper-magnet. A simple 
 drawing would serve to convey a better idea of its construction 
 
22 
 
 than many words. We will, nevertheless, attempt a brief descrip, 
 tion. A horse-shoe magnet is fixed firmly in a horizontal position. 
 Through the upper part, or curve, of the horse-shoe, a horizontal axis 
 passes longitudinally to the keeper, which last is wound with a 
 quantity of wire. Beyond the keeper, on the same axis, is a ver- 
 tical and parallel disk of copper, and farther still, a light cross- 
 bar, all insulated from each other, and the disk and cross-bar dip- 
 ping, as the whole revolves, into a basin of mercury. One end of 
 the wire coiled upon the keeper, touches the copper disk, and the 
 other is carried along the middle of the wooden axis, through the 
 centre of the disk, without touching, to the cross-bar. Rapid rota- 
 tion is then given to the axis, carrying the keeper, the disk, and 
 the cross-bar, by means of a wheel and band ; and as often as the 
 point of the cross-bar leaves the surface of the mercury, a spark ap- 
 pears. By placing other conductors in contact with the disk and 
 cross-bar, the circuit may be lengthened, and made to include an 
 apparatus for the purpose of effecting decompositions. 
 
 Soon after the announcement of Mr. Saxton’s invention, the great 
 magnet belonging to the Philadelphia Museum, capable of sustaining 
 a weight of 134 pounds, was fitted up into a magneto-electrical 
 machine by Mr. Isaiah Lukens of that city. The “ Journal of the 
 Franklin Institute,” vol. 13, contains an account of some experi- 
 ments made with that apparatus, by Professor Green of Jefferson 
 Medical College. Professor Green remarks, that the effects produced 
 were by no means proportional to the power of the magnet ; but it is 
 probable that the quantity of enveloping wire, used to surround the 
 keeper, was altogether too small, since it was not more than one 
 third as much in length as is now employed by Mr. Saxton, with 
 magnets of greatly inferior power. In his experiments on the 
 spark, Professor Green dispensed with the use of the basin of mer- 
 cury, substituting strips of different metals, bent into the form of 
 an arc, so as to present flat surfaces to the wheel and the cross- 
 bar, or a second wheel substituted in its place. When a steel arc 
 was employed, brilliant coruscations and scintillations were pro- 
 duced, resembling those of the same metal burning in oxygen gas. 
 By sending the current through a helix surrounding a bar of iron, 
 electro-magnetic effects were also produced, but less powerful than 
 had been anticipated. 
 
23 
 
 A contrivance somewhat similar in principle to that of Mr. Sax- 
 ton, but much simpler in construction, and less powerful, was in- 
 vented by M. Pixii, of Paris. In this, the magnet was made to 
 rotate, poles downward, over a fixed keeper. 
 
 In the year 1836, an account was published by Mr. E. M. Clarke 
 of London, of a magneto-electrical machine constructed by him, 
 possessing, as he claimed, important advantages over that of Mr. 
 Saxton, and, indeed, every other. In principle, however, it seemed 
 to differ so little from the contrivance of our ingenious countryman, 
 that the latter, not without a show of justice, complained of the 
 appropriation of his labors. In the apparatus of Mr. Clark, the mag- 
 net employed is fixed perpendicularly, poles downward ; and the 
 keeper revolves against its lateral surface. The vessel of mercury 
 is inclosed in a box, the wheel and cross-bar are dispensed with, 
 and the communication is made by means of wires proceeding from 
 the box, and pressing on the revolving axis with a spring. In the 
 construction of his later machines, Mr. Clarke has dispensed, 
 moreover, entirely with the use of the mercury — a part of the ap- 
 paratus which is always troublesome, and not at all essential to the 
 production of the effects. 
 
 Mr. Clarke states that the intensity of the magneto-electric 
 shock is increased by employing a very long and fine enveloping 
 wire ; but that the spark is more brilliant when the wire is of less 
 length and greater diameter. Few persons, he says, can endure 
 the intense agony produced by his machine, when a small wire is 
 used, fifteen hundred feet in length : but the brightness of the spark 
 is vastly superior, when only one hundred and twenty feet of a 
 coarse wire are substituted in its place. 
 
 In regard to the magneto-electrical spark, Mr. Faraday has made 
 a curious observation ; that when a very long wire is employed, 
 the brilliancy is greater on breaking than on making contact, 
 while no difference is perceived when the wire is short. He con- 
 siders this circumstance to be, not improbably, due to the inductive 
 action of the current upon itself ; that is, of each portion of the 
 current upon the rest ; an action which, very naturally, takes place 
 when the fluid is passing through the parallel coils of an extended 
 helix, and not impossibly, when the conductor is perfectly straight. 
 The effect must, of course, be proportional to the length of the cir- 
 
24 
 
 cuit, and may become imperceptible when the circuit is short. 
 There are many phenomena analogous to this, observable in elec- 
 tricity and magnetism. We know, for example, that when, by ex- 
 periment, the weight which a single pole of a magnet will sustain 
 has been determined, the application of a bar of unmagnetized iron 
 to the other pole, will so increase the power of the first, that a much 
 greater weight may be suspended from it than before. This can only 
 be accounted for by supposing that the induced magnetism of the iron 
 bar re-acts, by an opposite induction, upon the inducing magnet 
 itself, to increase its magnetic energy. 
 
 The magneto- electrical machines of Messrs. Saxton and Clarke, 
 operate, it will be observed, by a change of polarity at every semi- 
 revolution of the keeper. The direction of the induced electric 
 current is, of course, reversed just as often. An ingenious con- 
 trivance of Dr. Ritchie is described in the Philosophical Transac- 
 tions for 1833, for producing an almost uninterrupted flow of mag- 
 neto-electricity in the same direction. A horse-shoe magnet is 
 fixed firmly, poles upright, beneath a wooden axis having four arms 
 like those of a wind-mill, the ends of which, as the axis revolves, 
 pass by the poles of the magnet. To the end of each arm is fixed 
 transversely a soft iron cylinder, wound in the usual manner with 
 wire. The extremities of each wire are carried along the arm, to 
 the axis, and so to one of the fixed supports in which the axis turns. 
 To the inside and the outside of this support are fixed metallic 
 disks, or portions of disks, the axis passing through the centres of 
 both. Against the inside disk one end of each wire presses, so as 
 to remain in contact while the revolution goes on. The other end 
 passes along the interior of the axis to the outside of the support, 
 and is there re-curved so as to press, in like manner, on the outside 
 disk. The disks are connected severally with wires, which pass 
 off to form a circuit for the ordinary purposes. As the revolution 
 proceeds, and each bar with its coil approaches the magnet, a flow 
 of electricity commences from it, which, as it declines in one coil, 
 is renewed in that which succeeds, and so on indefinitely. 
 
 We have already observed that a flow of electricity, perfectly 
 continuous, is excited by the magnetic action of the earth upon a 
 circular metallic plate, revolving at right angles to the line of the 
 dip. Mr. Faraday, in 1832, suggested the construction of a mag- 
 
25 
 
 neto-electrical machine of considerable power, on this simple prin- 
 ciple alone. When the rotation of the plate is made to correspond 
 in direction with that of the earth, that is from west to east, the 
 electrical currents excited, tend toward the axis, from the circum- 
 ference ; and the reverse, when the direction of rotation is reversed. 
 Mr. Faraday would, accordingly, have had a number of parallel 
 disks to revolve about a common axis of motion, and in contact 
 with one another only at the centres and circumferences alternately, 
 the alternate disks revolving in contrary directions. The effect of 
 such an arrangement will be obvious to a little thought. If we 
 suppose the currents to be proceeding outward, on the surface of 
 the first disk, they will, on arriving at the circumference, pass to 
 the next disk, where the currents are at the same time flowing in- 
 ward ; making the volume of those inward currents two-fold. On 
 reaching the centre, they will pass to the third disk, and flow outward 
 again, with a volume a second time augmented. The electricity 
 will thus continue to accumulate to the end of the series. 
 
 We are not aware that any machine has ever been actually con- 
 structed on this principle. In making the suggestion, Mr, Faraday 
 remarks, as a reason for not having carried it out in practice, that he 
 has chosen rather to busy himself in seeking for new modes of 
 evolving this mysterious agent, than in endeavoring, by improved 
 mechanical arrangements, which must follow of course in due time, 
 to render more striking the effects of those already known. Such 
 seems to have been the spirit by which all the great discoverers in 
 this novel and brilliant department of natural science have been 
 actuated. New and beautiful facts have been coming to light in so 
 rapid succession, within the past ten years, that every philosophic 
 investigator has felt himself excited to emulation by the hope of 
 being first to announce to the world each additional extraordinary 
 discovery ; and of thus more surely linking his name forever to 
 the history of the science. This may, in part, account for the 
 comparatively little attention which the philosophers have given to 
 the subject of employing electro-magnetism as a moving power. 
 Motion, they have from time to time produced, with feeble apparatus ; 
 but they have, in very few instances, applied themselves to the task 
 of testing, in practice, how great might be the possible energy of 
 more perfect arrangements. Dr. Ritchie, it is true, in some of his 
 4 
 
26 
 
 later publications, has pronounced his rotating invention to be 
 practically useless ; assigning its inutility as a reason for having 
 laid it aside : but he has never devoted that patient industry to its 
 improvement, which he has been ever ready to contribute to the 
 advancement of science. Mr. Sturgeon also laid aside his ma- 
 chine, but only because he thought it might be improved ; yet no 
 gentleman has been more indefatigable than he in the field of phi- 
 losophical inquiry. 
 
 Having proposed to ourselves merely a popular sketch of this 
 interesting science, we must here draw our remarks to a close. It 
 is proper to observe, however, that the question, long esteemed 
 doubtful, whether electricity, under all the various forms in which 
 it manifests itself to us, or by whatever mode excited from its latent 
 state, is in fact, or not, always identically the same, is admitted to 
 have been set at rest by the masterly investigations of Mr. Faraday. 
 The various forms alluded to, are Volta-Electricity, Magneto-Elec- 
 tricity, Thermo-Electricity, Animal Electricity, and common Elec- 
 tricity of tension. Since Mr. Faraday’s experiments on this subject, 
 the march of ^science has furnished additional corroborations of his 
 conclusions. Among these may be mentioned the production of the 
 electric spark from the torpedo, and from thermo-electrical apparatus. 
 
 It would be aside from our purpose, however, to follow out in 
 detail the interesting discoveries made, in late years, in any other 
 department of electrical science, than that to which we have given 
 particular consideration in this cursory view. That alone is full of 
 wonders ; and of these, if we have succeeded in imperfectly describ- 
 ing some of the most remarkable, our object is accomplished. 
 
 NOTE. 
 
 Since the commencement of the present sketch was put in type 
 as an article in the American Monthly Magazine, the October 
 number of Professor Silliman’s Journal of Science has made its 
 appearance, containing an account of an Electro-Magnetic machine, 
 constructed by Dr. Benjamin Rush McConnell, of Mauch Chunk, 
 Pennsylvania. This machine is, in principle, entirely different 
 from any previous contrivance of the kind ; and yet it can hardly 
 be called a new invention, since it is only a copy, on a large scale, 
 of an electro-magnetic trifle long known to experimenters. That 
 it may be understood, it will be necessary to recal the phenomena 
 
27 
 
 of the rotation of conductors around magnetic poles, mentioned in 
 the beginning of this outline. Suppose a magnet to be fixed in a 
 basin of mercury, the south pole upward, and a jointed wire to con- 
 vey a current of electricity downward to the mercury. The wire 
 will immediate^ commence a rotation in what is called the unscrew 
 direction : that is, from right to left. If a north pole be employed, 
 the rotation will take place in the opposite, or screw direction ; that 
 is, from left to right. If then, a horse-shoe magnet, with both poles 
 upward, be employed, the wire descending between the poles will, 
 in the first instant, be impelled by both in the same direction ; but, 
 immediately afterward, will be urged by one to deviate to the right, 
 and by the other, to the left ; so that, between the two, it will pro. 
 ceed in a straight line till it is carried out of the mercury. If the 
 wire be replaced by a wheel, the edge just touching the mercury, it 
 is obvious that the wheel will revolve, so long as the current con- 
 tinues. A current going upward from the mercury, the position of 
 the magnet remaining the same, will reverse the motion of the 
 wheel. This motion may also be reversed by causing the poles of 
 the magnet to exchange places. The little apparatus alluded to 
 above, consists of two disks, turning in separate channels of mercury, 
 and attached to the ends of a common metallic axis. The channels 
 of mercury severally communicate witn the opposite ends of a vol- 
 taic battery. Thus a current of electricity passes upward in one 
 wheel, then along the axis, and finally downward in 4he other. Two 
 horse-shoe magnets are laid, one to embrace each ^eel, in such a 
 manner that they may act unitedly to produce rotati^l in the same 
 direction. ^ 
 
 This piece of apparatus is the model of Mr. McConnell’s ma- 
 chine. He takes advantage of no change of poles, but derives his 
 available force wholly from an enlargement of the disks, and an in- 
 crease in the energy of the magnets (electro-magnets) employed. 
 He dispenses, also, with the use of the mercury. He employs hollow 
 electro-magnets, and says he has succeeded equally well with them, 
 whether made of bar iron, tinned iron, or copper. Their diameter 
 is one inch ; their length five and a half inches ; distance between 
 the poles, one and a half inches ; quantity of wire (iron wire) 
 surrounding each, one hundred and fifty feet. His battery is an 
 external copper cube of seven inches ; the zinc, six and a half 
 inches edge, by seven deep, with another interior copper surface ; 
 entire galvanic surface of zinc, about two square feet. The 
 copper disks are nine inches each in diameter ; and, on the middle 
 of the axis, is a band-wheel to communicate motion to machinery, 
 sixteen inches in diameter. The shaft is of iron, three-eighths of an 
 inch in diameter, by five inches long. The machine moves a car- 
 riage on which it is fixed. When not attached to its load, it makes 
 two hundred revolutions per minute. Loaded with forty pounds, it 
 revolves seventy times per minute, and moves over a space of two 
 hundred and eighty feet in the same time. It has been in opera- 
 tion more than a year. Dr. McConnell has not constructed any 
 other similar machine on a larger scale ; his professional duties in- 
 terfering, as he says, with the prosecution of his experiments. 
 
28 
 
 3 0112 072884932 
 
 We have been more particular in the description of this machine, 
 because its performances, as stated, astonish us, when we consider 
 that the power employed is only that of a single current of electri- 
 city, re-acting, by its tangential force, upon the poles of magnets ; 
 the parts of the apparatus not being, either, in very close juxtapo- 
 sition. It is to be desired that a careful series of experiments 
 should be instituted, to ascertain how far this principle may be use- 
 ful. 
 
 Electro-magnetic machines are coming into existence every- 
 where. We hear that Professor Dal Negro, of Padua, has produc- 
 ed an invention of the kind ; and that the same power has been suc- 
 cessfully applied so far off as Calcutta. It is more than eighteen 
 months since we heard of a magnetic loco-motive, set in operation 
 by M. Lemaire of Brussels. M. Lemaire was probably less suc- 
 cessful than he had hoped to be, for he has been already forgotten. 
 The Emperor of Russia is said to have directed a grand series of 
 experiments to be instituted, for the sake of settling the question 
 how far electro-magnetism can be employed as a moving power. 
 Our countrymen, Messrs. Davenport and Cooke, are preparing to 
 set in operation a Napier press, with a working wheel of thirty 
 inches diameter, and two oriiree horse power. 
 
 In the mean time, there ajre not wanting sceptics, who expect to 
 see these laudable enterprises abandoned for want of success. 
 They expect, ail most, onljf that electro-magnetism will be applied 
 to those opera^&ns in the arts which require but a trifling motive 
 power ; whiljReam is, in their opinion, destined for ever to perform, 
 without a ri/*al, those gigantic labors, which have already wrought 
 so complete a social, mechanical, and commercial revolution 
 throughout the civilized world. No great improvement in science 
 or the arts w r as ever yet received with hearty welcome or regarded 
 with undoubting confidence in the outset, by those whom it was 
 destined to benefit. Such things must f rce their own way to cele- 
 brity. Prejudice must be demolished, distrust overthrown, ridi- 
 cule rendered ridiculous, and opposition cc^ifounded, by the straight- 
 forward logic of facts. Let the humble but sagacious experimen- 
 ter, in the solitude of his laboratory, estimate at what it is worth, 
 the profundity that would demonstrate iq advance the folly of his 
 undertaking, or the shallowness that would pretend to pity or des- 
 pise, because incapable of comprehending ; he knows that in the 
 hour in which he shall announce his triumph, the reasoners and 
 the sneerers will alike be put to silence, by an argument to which they 
 must, as it is the only argument to which tihey ever will, submit. It 
 is a very just remark of a German writer, that, “ though it requires 
 but little wit to be of an opinion now, which all the world arrived 
 at twenty years ago ; it bespeaks no slight superiority of mind to 
 entertain already an opinion, in which all the world will not be 
 prepared to concur for twenty years to come.”