Part 15
We have now to notice a discovery, which forms the basis of those modern telegraphs in which the principle of electro magnetism is adopted. The following is an extract from the “Library of Useful Knowledge,” in relation to the discovery:
“The real discoverer of the magnetic properties of electric currents M. Oersted, Professor of Natural Philosophy, and Secretary of the Royal Society of Copenhagen. In a work which he published in the German, about the year 1813, on the identity of chemical and electrical forces, he had thrown out conjectures concerning the relations subsisting between the electric, galvanic and magnetic fluids, which he conceived might differ from one another only in their respective degrees of tension. If galvanism, he argued, be merely a more latent form of electricity, so magnetism may possibly be nothing more than electricity in a still more latent form; and he, therefore, proposed it as a subject worthy of inquiry, whether electricity employed in this, its most latent form, might not be found to have a sensible effect upon a magnet. It is difficult clearly to understand what he meant by the expression of _latent states_, as applied to electricity, but it may be sufficient for us to know, that in the various endeavours he subsequently made to verify his conjectures, he was led to such forms of experiment as afforded decisive indications of the influence of Voltaic currents on the magnetized needle. Yet, even after he had succeeded thus far, it was a matter of extreme difficulty to determine the real direction of this action, and it was not till the close of the year 1819, that his perseverance was at length rewarded by complete success.
“The first account of his discovery that appeared in England is contained in a paper, which he himself communicated, in Thompson’s Annals of Philosophy, for October, 1820, vol. 16, page 273; and in which the following experiments are described. The two poles of a powerful Voltaic battery were connected by a metallic wire, so as to complete the galvanic circuit. The wire which performs this office he called the _uniting_ wire; and the effect, whatever it may be, which takes place in this conductor, and in the space surrounding it, during the passage of the electricity, he designates by the term _electric_ conflict, from an idea that there takes place some continued collision and neutralization of the two species of electric fluids, while circulating in opposite currents in the apparatus. Then taking a magnetic needle, properly balanced on its pivot, as in the mariner’s compass, and allowing it to assume its natural position in the magnetic meridian, he placed a straight portion of the uniting wire horizontally above the needle, and in a direction parallel to it; and then completed the circuit, so that the electric current passed through the wire. The moment this was done, the needle changed its position, its ends deviating from the north and south towards the east and west, according to the direction in which the electric current flowed, so that by reversing the direction of the current the motion of the needle was also reversed. The general law he expressed as follows: ‘That end of the needle which is situated next to the negative side of the battery, or towards which the current of positive electricity is following, immediately moves to the westward.’
“The deviation of the needle is the same, whether the uniting wire, instead of being immediately above the needle, be placed somewhat to the east or west of it, provided it continue parallel to and also above it. This shows that the effect is not the result of a simple attractive or repulsive influence, for the same pole of the magnetic needle which approaches the uniting wire, when placed on its east side, recedes from it when placed on its west side.”
[20]“Soon after this important discovery of Oersted’s was made, M. Ampère established the second fundamental law of electro magnetism, that the two conducting wires from the poles of the battery, when conveniently suspended, _attracts each other when they transmit electrical currents moving in the same direction, and repel each other when the currents which they transmit have opposite directions_.
[20] Encyclopedia Britannica, vol. 21, p. 686.
“On the 25th Sept. 1820, M. Arago communicated to the French Institute the important discovery that the electrical current possesses, in a very high degree the power of developing magnetism in iron or steel. Sir H. Davy communicated a similar fact to Dr. Wollaston on the 12th of November, 1820, and Dr. Seebeck laid before the Royal Academy of Berlin a series of experiments on the same subject.
“M. Arago found that the uniting wires of a powerful Voltaic battery attracts iron filings often with such force as to form a coating around the wire ten or twelve times thicker than itself. This attraction, as he found, did not originate in any magnetism previously possessed by the iron filing, which he ascertained would not adhere to iron, and that it was not a case of common electrical attraction, was evident from the fact that copper and brass filings were not attracted by the uniting wire. M. Arago likewise found, that the iron filings began to rise before they came in contact with the uniting wire; and hence he drew the conclusion, that the electric currents converted each small piece of iron into a temporary magnet. In following out this view, the French philosopher converted large pieces of iron into temporary magnets and also small steel needles into permanent ones, (by employing the helix.) Sir H. Davy and Dr. Seebeck obtained analogous results without knowing what had been previously done in France.
“A galvanometer was first constructed by Professor Schweigger, of Halle, very soon after the first discovery of electro magnetism, and by him called an _electro_ magnetic multiplier.”
In the year 1820, Ampère predicted the possibility of making the deflection of the magnetic needle, by the agency of the galvanic fluid, serve the purposes of transmitting intelligence. In page 19 of his memoir, he thus resolves the problem:
“As many magnetic needles as there are letters of the alphabet,” he says, “which may be put in action by conductors; which may be made to communicate successively with the battery by means of keys; which may be pressed down at pleasure, might give place to a telegraphic correspondence which would surmount all distance and would be as prompt as writing speech to transmit thought.”
“The next step in the progress of discovery, was that of making magnets of extraordinary power by means of a galvanic battery. This seems to have been first accomplished by Prof. Moll, of Utrecht, and Professor Henry, of Princeton, who was able to lift thousands of pounds weight by his apparatus.”
_The following Extract is taken from a Work on Electro Magnetism published by Jacob Green, M. D. Professor of Chemistry in Jefferson Medical College, 1827._
“In the very early stage of electro magnetic experiments, it had been suggested, that an instantaneous telegraph might be constructed by means of conjunctive wires, and magnetic needles. The details of this contrivance are so obvious, and the principles on which it is founded so well understood, that there was only one question which could render the result doubtful. This was, whether by lengthening the conjunctive wires, there would be any diminution in the electrical effect upon the needle. It is the general opinion, that the electrical fluid, from a common electrical battery, may be transmitted, without any sensible diminution, instantaneously, through a wire three or four miles in length. At the philosophical dinner, as it has been called, got up a number of years ago by some gentlemen of Philadelphia, on the banks of the Schuylkill, it may be recollected that Dr. Franklin killed a turkey with the electric shock, transmitted across the river, a distance of more than half a mile; and Dr. Watson, who was also at the pains of making some experiments of this kind, asserts that the electric shock was transmitted, instantaneously, through the length of 12,276 feet. Had it been found true that the galvanic fluid could be transmitted in a moment through a great extent of conducting wire, without diminishing its magnetic effect then no question could have been entertained as to the practicability and importance of the suggestion adverted to above, with regard to the telegraph. Mr. Barlow, of the Royal Military Academy, who has made a number of successful experiments and investigations in electro magnetism, fully ascertained that there was so sensible a diminution with only 200 feet of wire, as to convince him at once of the impracticability of the scheme.
_Triboaillet’s Proposition._
[21]“In 1828, M. Victor Triboaillet de Saint Amand proposed to establish a correspondence from Paris to Brussels, by placing along the highway, and at some feet deep, a metallic wire, about a line or a line and a half diameter. He recommended to cover the wire with shellac, upon which was to be wound silk, very dry, which should be covered in their turn with a coating of resin. The whole was then to be put into glass tubes carefully luted up with a resinous substance and secured by a last envelope in the earth, then varnished over and hermetically sealed. Then, by means of a powerful battery, he would communicate the electricity to the conducting wire, which would transmit the current to the opposite point to an electroscope, destined to render sensible the slightest influence, and left to each one to adopt at pleasure the number of motions to express the words or letters which they might need.”
[21] Report of Academy of Industry, Paris.
_Fechner’s Suggestion._[22]
“Fechner, in his manual of galvanism, (Voss, 1829, page 269,) remarked, that the electro magnetic effects of the galvanic current would be far more appropriate for the giving of signs than Soemmering’s plan by the decomposition of water.”
He suggested that wires, having twenty-four multiplicators should be extended between Leipsic and Dresden, and there connected, alternately, with a galvanic column, for telegraphic purposes. Indeed, he ventured to prophecy, that probably hereafter such a connection between the central point of a kingdom, and different provinces might be arranged as there was existing in animal bodies, between the central point of organic structure of particular members and nerves.
[22] Polytechnic Central Journal, 1838.
_Magneto Electricity._
We come now to give an account of a new branch in the science of electricity, viz. _magneto electricity_; which Dr. Faraday was the first to discover in the year 1831. As this species of electricity has been applied to several of the plans of electric telegraphs, which we shall describe, it is desirable that some account should be given of its discovery, and of the instrument by which it is generated.
The following is an extract from “Daniell’s Introduction to Chemical Philosophy” 2d edition, London, 1843.
“The phenomena of electro magnetism are produced by _electricity in motion_; accumulated electricity, when _not in motion_, exerts no magnetic effects. Dr. Faraday early felt convinced that “as every electric current is accompanied by a corresponding intensity of magnetic action at right angles to the current, good conductors of electricity, when placed within the sphere of this action, should have a current induced through them, or some sensible effect produced, equivalent in force to such a current.” These considerations, with their consequence, the hope of obtaining electricity from ordinary magnetism, stimulated him to investigate the subject experimentally, and he was rewarded by an affirmative answer to the question proposed. He thus became, like Oersted, the founder of an entirely new branch of natural philosophy.
“If a wire connecting the two ends of a delicate galvanometer be placed parallel and close to the wire connecting the poles of a Voltaic battery, no effect will be produced upon the needle, however powerful the current may be. If the points opposed in the two wires be multiplied by coiling the one, as a helix, _within the convolutions_ of the other, coiled in the same way, both being covered with silk to prevent metallic contact, still no effect will be discernible so long as the current is _uninterrupted_. When, however, the current of the battery is stopped by breaking the circuit, the needle is momentarily deflected, as by a wave of electricity passing in the same direction as that of the main current. Upon allowing the needle to come to a state of rest, and then renewing the contact, a similar impulse will be given to it in the contrary direction. While the current continues, the needle returns to its state of rest, again to be deflected in the first direction by stopping the current. Motion may be accumulated to a considerable amount in the needle, by making and breaking the contacts with the battery in correspondence with its swing. The same effects are produced when, the current being uninterrupted, the conducting wire is made suddenly to approach or recede from the wire of the galvanometer. As the wires approximate, there will be a momentary current induced in the direction contrary to the inducing current; and as the wires recede, an induced current in the same direction as the inducing current.
“As this _Volta electric induction_ is obviously produced by the transverse action of the Voltaic current, in one case, by the _mechanical_ motion of the wire, and in the other at the moments of _generation_ and _annihilation_ of the current, Dr. Faraday thought that the sudden induction and cessation of the same magnetic force in soft iron, either by the agency of a Voltaic current, or by that of a common magnet, ought to produce the same results. He constructed a combination of helices (8) upon a hollow cylinder of pasteboard: they consisted of lengths of copper wire, containing, altogether, 220 feet; four of these were connected end to end, and then with the galvanometer. The other intervening four were also connected end to end, and then with the Voltaic battery. In this form a slight effect was produced upon the needle by making and breaking contact. But when a soft iron cylinder, seven-eighths of an inch thick and twelve inches long, was introduced into the pasteboard tube, surrounded by the helices, the induced current affected the galvanometer powerfully. When the iron cylinder was replaced by an equal cylinder of copper, no effect beyond that of the helices alone was produced.
“Similar effects were then produced by _ordinary magnets_. The hollow helix had all its elementary helices connected with the galvanometer, and the soft iron cylinder having been introduced into its axis, a couple of bar magnets were arranged with their opposite poles in contact, so as to resemble a horse-shoe magnet, and contact was then made between the other poles and the ends of the iron cylinder, by which it was converted, for the time, into a magnet; by breaking the magnetic contacts, or reversing them, the magnetism of the iron cylinder could be destroyed or reversed at pleasure. Upon making magnetic contact, the needle was deflected; continuing the contact, the needle became indifferent, and resumed its first position; on breaking contact, it was again deflected, but in the opposite direction to the first effect, and then it again became indifferent. When the magnetic contacts were reversed, the deflections were reversed. The actual contacts of the magnets with the soft iron is not essential to the success of these experiments, for their near approximation induces sufficient magnetism in the cylinder to generate the electric current, which affects the needle. The first rise of the magnetic force induces the electric wave in one direction; its sudden decline, in the opposite. Mechanical motion of a permanent magnetic pole in one direction, across the coils of the helix, will produce the same effect as the sudden induction of the magnetism in the soft iron, and its motion in the opposite direction will cause a corresponding effect with its annihilation, when the soft iron cylinder is removed from the helix, and one end of a cylindrical magnet thrust into it, the needle is deflected in the same way as if the magnet had been formed, by either of the two preceding processes. Being left in, the needle will resume its first position, and then being withdrawn, the needle will be deflected in the opposite direction. On substituting a small hollow helix, formed round a glass tube, for the galvanometer, in these experiments, and introducing a steel needle, it will be converted into a magnet, provided care be taken not to expose it to the opposite action of the reverse current; and if the continuity of the conducting wire be broken, at the moment when the secondary electric wave is passing through it, a bright spark may be obtained.
“The connection of electro magnetical and magneto electrical phenomena may be exhibited in a very striking way, by employing any of the apparatus, by which the rotary motions of the _magnet_ or _conducting wire_, are produced by a current of electricity, to generate electric currents by the mechanical rotations of the magnet or wire. For this purpose, the galvanometer may be substituted for the battery, and when the wire is made to turn round the pole of the magnet, or the pole of the magnet round the wire, in one direction, the needle will be deflected to one side; and to the other by the opposite rotation. Nothing can be better shown that _magneto electric_ is the _converse_ of _electro_ magnetic action.
“Dr. Faraday by rotating a copper disc between the poles of a horse-shoe magnet, produced a constant current of electricity in one direction, and deflected the needle of the galvanometer; one wire being connected with the disc, and the other with the arbour. By turning the disc in one direction, the circuit will pass from the axis to the circumference; by turning it in the opposite direction, the current will flow from the circumference to the axis.”
Figure 39 represents a side view of the instrument. B shows the copper disc permanently secured upon its axis, and which is turned by means of the crank, E. G represents one of the standards which support the axis. H is the platform upon which the various parts are arranged. The edge, C, of the copper disc, is amalgamated so as to make a perfect connection with the amalgamated segment, _a_, to which is soldered a wire, I, leading to the galvanometer. That portion of the disc, B, which is shaded, is not amalgamated. J is the other wire proceeding from the galvanometer, and both it and the axis are amalgamated, at the points of connection. A is the permanent magnet, with its poles on each side of the copper disc, B, opposite the amalgamated portion of the rim.
Figure 40, represents a top view of the instrument, H is the platform; C the disc; _a_ the segment; A the permanent magnet; J the wire attached to the axis, P; G and G are the two standards. E the crank; and I the wire attached to the segment _a_.
Mr. Saxton,[23] in a letter to Mr. Lukens, dated, London, April 14th, 1832, after describing Dr. Faraday’s rotating disc, figures 39 and 40, says, “I have made this experiment in a different way, and succeeded satisfactorily. The method was as follows: A coil of wire wrapped with silk, similar to that used in the galvanometer, was attached, by the ends, to the wires of the galvanometer. On passing this roll, backward and forward, upon one of the poles of a horse-shoe (permanent) magnet, or placing it upon and removing it from either pole, I have made the needle of the galvanometer to spin round rapidly.” Figure 41, represents Mr. Saxton’s plan.
[23] We here introduce to the reader our ingenious and scientific country man, Mr. Joseph Saxton, formerly of the United States mint, Philadelphia, but now connected with the Department of weights and measures, at Washington, who invented the first Rotary Magneto Electric Machine, and which has now been extensively adopted.
N and S represent the north and south poles of the horse-shoe permanent magnet. C is the coil of wire, wound round a spool of an oblong shape, through the centre of which there is an opening sufficiently large to admit either of the prongs of the magnet through it. A and B are the ends of the wire leaving the coil, and are connected with the galvanometer.
Mr. Saxton on the 2d of May, 1832, obtained the spark by the following arrangement of the permanent magnet and the helix of wire round the armature. In relation to this instrument, he thus writes to Mr. Lukens, of Philadelphia, dated, London, May 11th, 1832. Jour. Frank. Int. vol. 13, p. 67. “Since my last I have heard of a method of producing a spark from a magnet, discovered I think by an Italian.[24] This experiment I made at once upon a large horse-shoe magnet, which I am making for Mr. Perkins and his partners. One of your large magnets will answer the same purpose. Make a cylinder of soft iron of an inch, or three-fourths of an inch, in diameter, and of the usual length of the keeper; place two discs of brass or wood upon this cylinder, and at such a distance apart that they will conveniently pass between the poles of the magnet; between these wind, say fifty feet of bobbin wire, which may be of iron covered with cotton; let the ends of this coil be bent over the ends of the cylinder and brought down until they touch the poles of the magnet. The ends should be of such a length, that on bringing the cylinder to the magnet, one of the ends will touch, when the cylinder is about half an inch from the magnet, and the other at one-fourth of an inch. The cylinder being thus arranged, and in contact with the magnet, on drawing it suddenly away a spark will pass between the end of the wire, and the pole of the magnet.”
[24] M. M. Nobili and Antinori.
Figure 42 represents the instrument as first constructed by Mr. Saxton, in London.[25] A and B are the ends of the helix, surrounding the cylindrical bar of soft iron between E and F, filling the cavity which has been formed out of the solid iron. The size of bar between the collars E and F, thus formed, is the same as the projections H and G. The wire, _a_, proceeds from the outside of the coil and makes a suitable contact upon the prong, A, of the magnet: _b_ proceeds from the bottom of the coil, where the winding commenced and makes a similar contact upon the prong, B, of the permanent magnet. One wire extends a little further upon the magnet than the other, so that the shorter one may break its connection sooner than the longer. H and G are projections from the sides of the armature, to which the handle, D, is secured. Let the armature, with its helix, be held up against the ends of the prongs of the permanent magnet; and the wires _a_ and _b_, in perfect contact with their respective prongs, as shown in the figure; if, while in this condition, the keeper is suddenly withdrawn, a spark will appear at the end of the short wire, as it breaks its contact with the prong of the magnet.
[25] Mr. Saxton on the 3d of May exhibited his apparatus, and the mode of obtaining the spark to Dr. Ritchie, Messrs. Thomas Gill, John Isaac Hawkens and Steadman Whitwell. On the 8th of May he loaned it to Dr. Ritchie, who publicly exhibited it at a lecture, at the London University, and also at the London Institution, Finsbury.