USA > Maine > York County > Parsonsfield > A history of the first century of the town of Parsonsfield, Maine > Part 12
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The deflection of the magnetic needle by the action of the current suggested to several inquirers its use as a means of measuring the strength of the current as has already been hinted. A great variety of instruments have been contrived dependent on this general principle, and the laws of their action have been de- termined with the greatest accuracy, both by mathematical calculations and by experiment. It is now the common practice with electrical engineers to measure electrical quantities by means of these instruments with as much certainty as characterizes any other measurements which they have to execute. And not only so, but complete systems of units have been devised which are very simply related to the common well known fundamental units of time (second), length (centimetre), and mass (gramme); and electricity is now bought and sold for lighting and manufacturing purposes with the same confidence as coins are ex- changed for ordinary commodities.
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Before leaving the matter of measurements, a word should be said respecting the remarkable investigations of Ohm already alluded to. These investigations resulted in the announcement of the law which is now known as Ohm's law. . This law points out the relations which exist in every case between the electro- motive force, or cause which sets the current in motion, the resistance of the circuit and the resulting current strength. The law asserts that the current is determined by the ratio of the electromotive force to the resistance.
The original observation leading to Galvani's research which opened up the field of current electricity has been described, but the immediate cause of the convulsions observed has not been considered. It was noticed soon after the invention of the Leyden jar, that when it is discharged through a long conduc- tor, the discharge is accompanied by a so-called " return stroke,"-that is, the electric equilibrium of conducting bodies in the neighborhood is disturbed and this is manifested under favorable conditions by the passage of sparks between them. As soon as the identity of the electricity produced by the battery with that produced by the electrical machine was established, it might have been expected that some similar disturbances would occur in the neighborhood of the conducting battery wires. Ampére was apparently the first to detect an action of this kind although he did not investigate it with his usual zeal. He hung a closed movable conductor in the presence of a wire conveying a current, and found that the closed conductor was attracted or repelled by a magnet, which he presented, on breaking or closing the circuit of the battery. In 1824, Arago found that if a magnet be suspended freely over a revolving copper disc, the magnet, is deflected from its proper position so as to follow the rotation; and he further observed that if the disc be at rest, and the needle be set in vibration, it sooner comes to rest than it would if the disc were removed. He at first referred this action to induce magnetism. But in 1826, he placed a revolving disc under a magnet which hung vertically from one arm of a balance and found that repulsion ensued, which he could not account for. Herschel and Babbage, in 1825, found that if the revolving disc be partially traversed by radial slits the effect already noticed is much diminished. But it was reserved for Faraday, in 1831, to give the true explanation of the phenomenon. Reflecting on the mutual reaction of two conductors which are conveying currents, he was led to conjec- ture that by the motion of one conductor conveying a current, in the neighbor- hood of a closed conductor, a current might be excited in the latter. He there- fore commenced a systematic inquiry to ascertain if this were possible. He placed two coils of insulated wire near each other, the terminals of one of which were connected with the galvanometer while those of the other were connected with the battery. No movement of the galvanometer needle could be observed so long as the current was passing steadily, but on opening the battery circuit, he noticed a slight deflection of the needle, and on closing it there was a similar deflection, but in the opposite direction. This was positive proof of the produc-
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tion of a current in the closed circuit, including the galvanometer, which had no direct connection with the battery, and he concluded that this secondary current, as he called it, depended on the changes in the intensity of the primary, or battery current, which must occur during the closing and the breaking of the circuit.
He next endeavored to produce a current in the wire connected with the galvanometer by suddenly magnetizing and demagnetizing a piece of iron. For this purpose, he employed an iron ring over a portion of which the battery wire was coiled, and over another portion of which the galvanometer wire was coiled, its two extremities being united with the galvanometer. When connection with the battery was made, there was a movement of the needle in one direction, and when the connection was broken there was a movement in the other direction. Thus, the magnetizing and the demagnetizing of the iron was found competent to produce the momentary currents in the secondary coil. When he joined the galvanometer coil to the instrument with no other coil near it, or with the battery removed, and merely made a permanent magnet approach the coil, there was a current of momentary duration, and another in the opposite direction when the magnet was withdrawn. These most important discoveries gave Faraday the explanation of the mutual actions of the magnet and the copper disc already spoken of. They were due to the attractions and repulsions of the Amperian currents which are in constant circulation about the molecules of the magnet and the induced currents in the metal of the disc in its vicinity, which are produced by the relative motion of the two. In pursuance of this view, he mounted a circular copper disc so that it could revolve with its edge between the poles of a powerful electromagnet. On the edge of the revolving disc he made a spring to rest which was in connection with one wire of the galvanometer, while the other galvanometer wire was in contact with the metallic axis of the disc. Now when the electromagnet was excited and the disc was put in motion, a current was produced!
Thus, the first magneto-electric machine had its origin. The reason which justifies giving this matter so much space it obvious when it is remembered to what this simple device has grown, and what a place it fills in the production of the electric light, the transfer of power from one place to another, its use in telegraphy, etc. Faraday's genius did not stop here. He rightly concluded that since the earth is a great magnet, it would be easy to produce an electric current, by merely causing a coil of wire to revolve about one of its diameters. Experi- ment justified his previsions. Faraday called the currents thus excited in closed conductors, by the change of intensity in neighboring currents, or by the relative motion of the conductors conveying these currents, or by the motion of magnets, " induction currents," or " induced currents," and as just seen, he determined, experimentally, the conditions of their production as respects direction and intensity.
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The whole matter was very beautifully stated, however, by Lenz, in 1834, in a form which is now known as Lenz's law. "The motion of a magnet or of a con- ductor conveying a current, in the neighborhood of a closed conductor induces, ' in the latter, a current which of itself, would produce an opposite movement." This law is of universal application where magnets or electrical currents are made to move in the presence of conducting bodies.
In 1832, Henry observed that when a short wire is used to join the mercury terminals of a small battery, no spark is produced either on making or breaking the connection, but if a wire thirty or forty feet in length be used, though no spark is visible on making the connection, there is a brilliant one when it is broken. He found the effect somewhat increased when the wire was coiled on itself. This is the first notice of the phenomenon of self induction in an electric discharge. In 1834, Jenkins observed that this spark, due to induction, is greatly increased if a core of iron be inserted in the spiral coil. Faraday referred these phenomena to the mutual influence of the separate turns of the wire constituting the spiral, and he showed that on making the current to pass through the spiral there is set up, in consequence of this mutual influence, an electromotive force opposite that of the battery, which prevents the current of the battery rising at once to its full value, and also, that on breaking the circuit the effect is to strengthen the battery current momentarily, by inducing an electromotive force in the same direction with that of the battery. In 1849, Edlund, in Stockholm, showed that these " extra" currents are equal in intensity, and proportional to the strength of the primary.
The mathematical theories of Neumann, Fechner, Weber, Kirchhoff, Helm- holtz, Clausius, Maxwell, and others must here be omitted.
It was regretted by Franklin, that the results of electrical research had not, in his time, been turned to more practical use in the service of man. The discov- eries of Faraday, that in various ways electrical currents can be maintained by the expenditure of mechanical energy made it possible to remove this reproach more completely than the invention of the battery had done. Faraday, himself, pointed out this fact, but pushing on with all zeal in the path of discovery, he left the practical applications to others.
In 1832, Pixi constructed a magneto-electric engine consisting of a U shaped electro-magnet in front of the poles of which a U shaped permanent magnet could revolve about a vertical axis. The two free ends of the coils of the electro- magnet were connected with a pole changer, which could reverse the direction of the current through the electro-magnet twice for every revolution of the perma- nent magnet. Ritchie constructed a machine in which the electro-magnets were made to revolve while the heavier permanent ones remained fixed. Other im- provements followed along the same general line. Machines for converting a current into mechanical energy were constructed, having great numbers of magnets, and some of these could be operated by mechanical power, so as to
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produce powerful currents, which could be employed for electric lighting, electro- plating, etc.
The next important step was taken by Siemens, in Berlin, in 1857. Several · steel magnets were placed parallel with each other, and a portion of their polar regions was cut away so as to form a nearly cylindrical opening in which an armature of special construction could revolve. This armature was a cylinder of iron having longitudinal grooves cut along opposite sides. These were filled by winding with insulated copper wire, the extremities of which were to a pole-chang- ing device, so as to turn the currents produced by revolution, in the same direc- tion, and so give a nearly continuous flow.
In 1860, Pacinotti, in Florence, constructed an apparatus designed to convert the energy of a battery into mechanical power. It consisted of two electro- magnets near the poles of which an iron ring on which, at equal distances, were wound several coils of insulated copper wire continuously. Upon loops of the wire, carried to an insulating hub, on the revolving axis were placed two springs, one opposite the other. When this apparatus was joined up in circuit with a battery so that the current could traverse the electro-magnets, the coils of the iron ring and the springs, the ring was set in rotation by the attractive and repulsive action of the magnetic poles developed. It was subsequently found that the battery could be removed, and that then a current could be set up by simply making the iron ring to revolve by mechanical energy. As thus used, the arrangement embodies the principle of the dynamo-machine subsequently pointed out by Siemens.
In 1866, Wilde, in England, combined in one construction a magneto-machine with steel magnets and an electro-magneto-machine. The office of the former was to furnish a current of electricity to magnetize the electro-magnets of the latter to a high degree. This resulted in producing a very powerful current. In 1867, Siemens showed that the same result as Wild had reached could be pro- duced, by making the current, generated by the revolution of the armature in the presence of a very feeble electro-magnet, to traverse the coils of the electro- magnet, and thereby develope a more intense magnetism. Thus, a current could be built up from the smallest beginnings to any required strength, by the expen- diture of sufficient mechanical energy. This, in fact, is what the Pacinotti machine, just spoken of, could do when properly regulated. The principle is called the " dynamo " principle, and is employed in the construction of most of the powerful machines now used for electric lighting, such as the Siemens, the the Brush, the Edison, the Weston, the Thompson and Houston and others. These machines, generally, are capable of transforming mechanical energy into electrical energy with very little loss, so that we have at command the means of producing the electrical current for practical purposes with the greatest economy.
Not only are we able, by means of these machines, to transform mechanical energy into electrical energy, but we can also reconvert the energy of the electri-
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cal current into mechanical work. It is only necessary to connect two dynamo- machines by means of metallic or other good conductors, and apply power to one of them to produce the current which will then traverse the coils of the other, 1 and set it in motion by means of the magnetic actions consequent thereon. Bat- # tery currents as we have seen, were used by Pacinotti, for the purpose of con- verting the electric current into work. The commencement, on this plan of pro- curing power, was made early. In the year 1830, Salvastro del Negro, and at about the same time, Prof. Henry, constructed reciprocating engines to be actuated by the energy of the battery which was made to energize an electro- magnet, first in one direction and then in the other alternately, by means of an automatic pole-changer, which could reverse the current with every stroke of the engine.
Several persons in different countries, made many trials and experiments with the hope that some cheap motive power might be secured by the use of electrici- ty, but it was early seen, and by none clearer than by Professor Henry, that all such hopes were delusive until some means of producing the current at less cost than can be done by the battery, should be discovered.
It remains to speak of a very important apparatus for transforming the electri- cal current of one potential into that of another. This apparatus is called the induction coil, or the "inductorium." Pohl, in 1835, was the first to take advantage of Faraday's discoveries in order to produce, by means of the inductive action of a current suddenly established and broken, in one coil, a momentary current, in another coil, of much higher potential. Various devices were em- ployed to effect this closing and breaking of the' circuit. In 1839, Wagner de- vised a self-acting hammer by means of which the current was alternately inter- rupted and renewed. The whole apparatus then consisted of a thick, insulated wire coil, surrounded by a coil of many turns of thin insulated wire, the interior coil having within it a bundle of iron wires, and having its extremities joined to the circuit breaking hammer. When this apparatus is included in a battery circuit, the current begins to flow in the interior coil, but is immediately inter- rupted by the action of the hammer, and the iron wires at the same time lose their magnetism, thereby inducing a momentary current of high potential in the secondary coil. This operation is repeated with the successive blows of the hammer, and so a series of interrupted currents is produced which can be util- ized in any way desired. By the use of a condenser the terminals of which are joined to the extremities of the thick wire coil the effect is much increased. The condenser was added by Fizeau. Ritchie, in Boston, Rhumkorff and others, have made important improvements in the methods of winding the second, or fine wire, coil. The inductorium finds many applications in the physical' laboratory, and the smaller ones are somewhat used in medicine. A modified form of the apparatus has lately been introduced into some systems of electric lighting.
Mention has been made of the early attempts to use the electricity produced by
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the friction machine for the purposes of telegraphy ; not long after the invention of the pile by Volta, it was proposed by Salva, at a meeting of the " Academy of Sciences," at Barcelona, to employ "Galvanism " for the same purpose. In his experiments, which he cites, he employed long wires stretched on insulators, and as means of making the signals he used frogs' legs. He even used a combination of frogs' legs for his battery, for he had not yet heard of the invention of the metallic pile by Volta. He, however, read another paper before the same body, in 1804, in which he makes reference to the pile of Volta as being better suited to his purpose. By the use of six wires and of decomposing cells containing water for his receiver, he shows how it may be possible to so make combinations of signals as to enable one to carry on telegraphic correspondence between two stations.
Between the years 1809 and 1812, Sommerring devised and successfully exe- cuted an apparatus similar in principle to that of Salva. The system, however, was too complicated for practical use, inasmuch as there were as many wires as there are signals to be made. Schweigger, in 1811, reduced the number of wires to two and employed two batteries differing in strength, so as to be able to com- bine a succession of effects to produce any required signals. Other plans involving the same general principles must be passed over without mention.
The first suggestion of a telegraph in which the current should be made to cause the deflection of a magnetic needle was made by Laplace, the mathema- tician, to Ampère who read a paper before the Academy of Sciences, in October 1820, setting forth a plan for carrying this idea into practice. There were to be as many pairs of conducting wires reaching from one station to the other, as there are characters to be used in correspondence, and at the receiving station, the wires were to be placed parallel to the magnetic meridian, with a freely suspended magnetic needle near each of them, so as to avail of the deflection ob- served by Oersted for manifesting the signal intended in any given case. On the 16th of Sept. preceding, Schweigger had read a paper at Halle, in which he de- scribed his " multiplier," - a simple device for increasing the amount of deflec- tion caused by a current acting on a magnet. It consisted in carrying the wire several times around in a coil so that the needle could be placed in the coil and freely suspended. In 1829, Fechner, of Leipsic, proposed to employ this device in the construction of the receiving instrument for the telegraph. In 1830, Ritchie, of the Royal Institution, London, carried this plan into effect, and showed in a paper the great probability that it could be employed for long dis- tances notwithstanding the general scepticism among men of science concerning this point. Somewhere about 1825, Baron Schilling, of Canstadt, exhibited to the emperor Alexander, his incomplete inventions. His plan employed the deflections of a needle by the action of a current which could be reversed at pleasure. The needle carried a disc of paper, white on one side and black on the other. When the current was sent in the one direction one side of the disc
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presented, and when it was sent in the other direction the other side of the disc presented. By combinations of these elementary signals an alphabet could be made to serve all purposes. There was nothing new in the use of such combina- tions, for they were employed by the Greeks and Romans for military purposes, by means of flags. Some of Schilling's apparatus was on exhibition by the Russian Government, at the Paris Exhibition of 1881.
In 1833, Gauss and Weber, at Goettingen, constructed a practical telegraph which depended for its action on the deflection of a magnet by a current which passes near it. They employed two wires which were supported on posts and extended about a mile and a quarter. At first, the current was produced by a battery, but finally it was produced by a magneto-engine. This consisted of an upright permanent magnet which was encircled by a coil of insulated wire, hav- ing in the final form, 7,000 turns. This coil could be lifted by depressing a lever on which it was mounted, when a momentary current was induced in it. On allowing the lever to resume its natural position the coil would rise, thereby inducing a current in the opposite direction. The ends of the coil were con- nected with the line wires which led to the receiving station, there traversing a second coil having about 3,000 turns of insulated wire. In this coil was freely suspended a bar magnet weighing about 100 lbs. To the axis of revolution was fixed a small mirror in which the reflected image of a divided scale could be seen by means of a telescope. The alternate currents just spoken of caused devia- tions of the magnet to the right or left according to their direction, and suitable combinations of these deflections constituted the alphabet with which correspon- dence could be carried on. This telegraph was in practical operation down to 1838. In 1836, Steinheil, of Munich, at the request of Gauss, greatly improved this form of telegraplı. In 1838, he accidentally found that the earth could be used as a return conductor, thus making it possible to dispense with one wire between the sending and the receiving stations. This plan had, however, been unconsciously acted on by those who had attempted to employ static electricity in telegraphy.
The current used by Steinheil, was produced by the rotation of wire coils near the poles of fixed steel magnets, as in Clark's magneto-electric machine. The indicator consisted of a wire coil in which could freely turn two magnets. These could be made to move at will by means of the induced currents just spoken of. Each magnet carried a small cup the bottom of which was drawn out into a small point with a very minute opening. These cups were filled with ink, and beneath them passed a strip of paper carried continuously by means of clock work. As the points could be brought into printing contact with the paper it is clear that the operator .. could produce any required signals. Instead of the printing device just explained, he also used two small bells which could be struck by the magnets as they were deflected. The pitch of the two bells being different, it was easy to interpret the message sent in signals produced by the successions of their tones ..
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In 1837, Edward Davy exhibited in London, a telegraphic apparatus which had much to recommend it. The development of his ideas commenced with the use of static electricity. He subsequently recommended the use of Danniell's bat- tery. At first he proposed to have a wire and a coil for each of the elementary signals employed, but he afterward showed how the number of the wires might be greatly reduced by the use of double deflections. He also added a "relay " by means of which he could employ the deflections of the needle in one circuit to close another circuit including a fresh battery, and so extend the action of his telegraph as far as might be required. As has been well said, "the air was full of invention at that time," and Davy had vigorous competitors in Wheatstone and Cooke, Morse and others, and failed to reap the rewards of his labors.
In 1832, Professor Morse conceived the idea of an electro-magnetic telegraph which eventuated in the apparatus which is generally known as the Morse tele- graph. As remarked on a former page, the principle of this device had been developed by Professor Henry, and to him must belong the credit of the inven- tion, so far as scientific principles are concerned. In 1843, the first telegraph line in this country was constructed between Baltimore and Washington, an appropriation having been made by Congress for that purpose. The instruments used were those of Morse, and the whole constituted a telegraph in the strict sense of the word, since the messages were written by a registering device. We need not describe it in detail since its general form and operation is familiar to all. The registering apparatus is, however, at the present time very generally discarded, since it is entirely practicable to recognize the several elementary signals by the ear alone.
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