History of electromagnetic theory
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The history of electromagnetic theory begins with ancient measures to understand atmospheric electricity, in particular lightning.[1] People then had little understanding of electricity, and were unable to explain the phenomena.[2] Scientific understanding into the nature of electricity grew throughout the eighteenth and nineteenth centuries through the work of researchers such as Coulomb, Ampère, Faraday and Maxwell.
In the 19th century it had become clear that electricity and magnetism were related, and their theories were unified: wherever charges are in motion electric current results, and magnetism is due to electric current.[3] The source for electric field is electric charge, whereas that for magnetic field is electric current (charges in motion).
Ancient and classical history
The knowledge of static electricity dates back to the earliest civilizations, but for millennia it remained merely an interesting and mystifying phenomenon, without a theory to explain its behavior, and it was often confused with magnetism. The ancients were acquainted with rather curious properties possessed by two minerals, amber (Greek: ἤλεκτρον, ēlektron) and magnetic iron ore (μαγνῆτις λίθος magnētis lithos,[4] "the Magnesian stone,[5] lodestone"). Amber, when rubbed, attracts lightweight objects, such as feathers; magnetic iron ore has the power of attracting iron.[6]
Based on his find of an
Long before any knowledge of electromagnetism existed, people were aware of the effects of electricity. Lightning and other manifestations of electricity such as St. Elmo's fire were known in ancient times, but it was not understood that these phenomena had a common origin.[11] Ancient Egyptians were aware of shocks when interacting with electric fish (such as the electric catfish) or other animals (such as electric eels).[12] The shocks from animals were apparent to observers since pre-history by a variety of peoples that came into contact with them. Texts from 2750 BC by the ancient Egyptians referred to these fish as "thunderer of the Nile" and saw them as the "protectors" of all the other fish.[6] Another possible approach to the discovery of the identity of lightning and electricity from any other source, is to be attributed to the Arabs, who before the 15th century used the same Arabic word for lightning (barq) and the electric ray.[11]
These electrostatic phenomena were again reported millennia later by
A group of objects found in
Magnetic attraction was once accounted for by Aristotle and Thales as the working of a soul in the stone.[23]
Middle Ages and the Renaissance
The magnetic needle compass was developed in the 11th century and it improved the accuracy of navigation by employing the astronomical concept of true north (Dream Pool Essays, 1088). The Chinese scientist Shen Kuo (1031–1095) was the first person known to write about the magnetic needle compass and by the 12th century Chinese were known to use the lodestone compass for navigation. In Europe, the first description of the compass and its use for navigation are of Alexander Neckam (1187), although the use of compasses was already common. Its development, in European history, was due to Flavio Gioja from Amalfi.[24]
In the 13th century,
Archbishop
Italian physician Gerolamo Cardano wrote about electricity in De Subtilitate (1550) distinguishing, perhaps for the first time, between electrical and magnetic forces.
17th century
Toward the late 16th century, a physician of
Gilbert undertook a number of careful electrical experiments, in the course of which he discovered that many substances other than amber, such as sulphur, wax, glass, etc.,[28] were capable of manifesting electrical properties. Gilbert also discovered that a heated body lost its electricity and that moisture prevented the electrification of all bodies, due to the now well-known fact that moisture impaired the insulation of such bodies. He also noticed that electrified substances attracted all other substances indiscriminately, whereas a magnet only attracted iron. The many discoveries of this nature earned for Gilbert the title of founder of the electrical science.[11] By investigating the forces on a light metallic needle, balanced on a point, he extended the list of electric bodies, and found also that many substances, including metals and natural magnets, showed no attractive forces when rubbed. He noticed that dry weather with north or east wind was the most favourable atmospheric condition for exhibiting electric phenomena—an observation liable to misconception until the difference between conductor and insulator was understood.[29]
Gilbert's work was followed up by Robert Boyle (1627–1691), the famous natural philosopher who was once described as "father of Chemistry, and uncle of the Earl of Cork." Boyle was one of the founders of the Royal Society when it met privately in Oxford, and became a member of the council after the Society was incorporated by Charles II in 1663. He left a detailed account of his research under the title of Experiments on the Origin of Electricity.[29] He discovered electrified bodies attracted light substances in a vacuum, indicating the electrical effect did not depend upon the air as a medium. He also added resin, and other substances, to the then known list of electrics.[11][30][31][32]
In 1663 Otto von Guericke invented a device that is now recognized as an early (possibly the first) electrostatic generator, but he did not recognize it primarily as an electrical device or conduct electrical experiments with it.[33] By the end of the 17th century, researchers had developed practical means of generating electricity by friction with an electrostatic generator, but the development of electrostatic machines did not begin in earnest until the 18th century, when they became fundamental instruments in the studies about the new science of electricity.
The first usage of the word electricity is ascribed to Sir Thomas Browne in his 1646 work, Pseudodoxia Epidemica.
The first appearance of the term electromagnetism was in Magnes,[34] by the Jesuit luminary Athanasius Kircher, in 1641, which carries the provocative chapter-heading: "Elektro-magnetismos i.e. On the Magnetism of amber, or electrical attractions and their causes" (ἠλεκτρο-μαγνητισμός id est sive De Magnetismo electri, seu electricis attractionibus earumque causis).
18th century
Improving the electric machine
The electric machine was subsequently improved by
Electrics and non-electrics
In 1729, Stephen Gray conducted a series of experiments that demonstrated the difference between conductors and non-conductors (insulators), showing amongst other things that a metal wire and even packthread conducted electricity, whereas silk did not. In one of his experiments he sent an electric current through 800 feet of hempen thread which was suspended at intervals by loops of silk thread. When he tried to conduct the same experiment substituting the silk for finely spun brass wire, he found that the electric current was no longer carried throughout the hemp cord, but instead seemed to vanish into the brass wire. From this experiment he classified substances into two categories: "electrics" like glass, resin and silk and "non-electrics" like metal and water. "Non-electrics" conducted charges while "electrics" held the charge.[11][38]
Vitreous and resinous
Intrigued by Gray's results, in 1732, C. F. du Fay began to conduct several experiments. In his first experiment, Du Fay concluded that all objects except metals, animals, and liquids could be electrified by rubbing and that metals, animals and liquids could be electrified by means of an electric machine, thus discrediting Gray's "electrics" and "non-electrics" classification of substances.
In 1733 Du Fay discovered what he believed to be two kinds of frictional electricity; one generated from rubbing glass, the other from rubbing resin.[39] From this, Du Fay theorized that electricity consists of two electrical fluids, "vitreous" and "resinous", that are separated by friction and that neutralize each other when combined.[40] This picture of electricity was also supported by Christian Gottlieb Kratzenstein in his theoretical and experimental works. The two-fluid theory would later give rise to the concept of positive and negative electrical charges devised by Benjamin Franklin.[11]
Leyden jar
The Leyden jar, a type of capacitor for electrical energy in large quantities, was invented independently by Ewald Georg von Kleist on 11 October 1744 and by Pieter van Musschenbroek in 1745–1746 at Leiden University (the latter location giving the device its name).[39][41] William Watson, when experimenting with the Leyden jar, discovered in 1747 that a discharge of static electricity was equivalent to an electric current. Capacitance was first observed by Von Kleist of Leyden in 1754.[42] Von Kleist happened to hold, near his electric machine, a small bottle, in the neck of which there was an iron nail. Touching the iron nail accidentally with his other hand he received a severe electric shock. In much the same way Musschenbroeck assisted by Cunaens received a more severe shock from a somewhat similar glass bottle. Sir William Watson of England greatly improved this device, by covering the bottle, or jar, outside and in with tinfoil. This piece of electrical apparatus will be easily recognized as the well-known Leyden jar, so called by the Abbot Nollet of Paris, after the place of its discovery.[11]
In 1741, John Ellicott "proposed to measure the strength of electrification by its power to raise a weight in one scale of a balance while the other was held over the electrified body and pulled to it by its attractive power".
As early as 1746, Jean-Antoine Nollet (1700–1770) had performed experiments on the propagation speed of electricity. By involving 200 Carthusian monks connected from hand to hand by iron wires
About 1750, first experiments in
Late 18th century
Benjamin Franklin promoted his investigations of electricity and theories through the famous, though extremely dangerous, experiment of having his son fly a kite through a storm-threatened sky. A key attached to the kite string sparked and charged a Leyden jar, thus establishing the link between lightning and electricity.[50] Following these experiments, he invented a lightning rod. It is either Franklin (more frequently) or Ebenezer Kinnersley of Philadelphia (less frequently) who is considered to have established the convention of positive and negative electricity.
Theories regarding the nature of electricity were quite vague at this period, and those prevalent were more or less conflicting. Franklin considered that electricity was an
Up to the time of Franklin's historic
"At this key the phial (Leyden jar) may be charged; and from the electric fire thus obtained spirits may be kindled, and all the other electric experiments be formed which are usually done by the help of a rubbed glass globe or tube, and thereby the sameness of the electric matter with that of lightning be completely demonstrated."[56]
On 10 May 1742 Thomas-François Dalibard, at Marly (near Paris), using a vertical iron rod 40 feet long, obtained results corresponding to those recorded by Franklin and somewhat prior to the date of Franklin's experiment. Franklin's important demonstration of the sameness of frictional electricity and lightning added zest to the efforts of the many experimenters in this field in the last half of the 18th century, to advance the progress of the science.[11]
Franklin's observations aided later scientists [
Henry Elles was one of the first people to suggest links between electricity and magnetism. In 1757 he claimed that he had written to the Royal Society in 1755 about the links between electricity and magnetism, asserting that "there are some things in the power of magnetism very similar to those of electricity" but he did "not by any means think them the same". In 1760 he similarly claimed that in 1750 he had been the first "to think how the electric fire may be the cause of thunder".[57] Among the more important of the electrical research and experiments during this period were those of Franz Aepinus, a noted German scholar (1724–1802) and Henry Cavendish of London, England.[11]
Franz Aepinus is credited as the first to conceive of the view of the reciprocal relationship of electricity and magnetism. In his work Tentamen Theoria Electricitatis et Magnetism,[58] published in Saint Petersburg in 1759, he gives the following amplification of Franklin's theory, which in some of its features is measurably in accord with present-day views: "The particles of the electric fluid repel each other, attract and are attracted by the particles of all bodies with a force that decreases in proportion as the distance increases; the electric fluid exists in the pores of bodies; it moves unobstructedly through non-electric (conductors), but moves with difficulty in insulators; the manifestations of electricity are due to the unequal distribution of the fluid in a body, or to the approach of bodies unequally charged with the fluid." Aepinus formulated a corresponding theory of magnetism excepting that, in the case of magnetic phenomena, the fluids only acted on the particles of iron. He also made numerous electrical experiments apparently showing that, in order to manifest electrical effects, tourmaline must be heated to between 37.5 °C and 100 °C. In fact, tourmaline remains unelectrified when its temperature is uniform, but manifests electrical properties when its temperature is rising or falling. Crystals that manifest electrical properties in this way are termed pyroelectric; along with tourmaline, these include sulphate of quinine and quartz.[11]
Henry Cavendish independently conceived a theory of electricity nearly akin to that of Aepinus.[59] In 1784, he was perhaps the first to utilize an electric spark to produce an explosion of hydrogen and oxygen in the proper proportions that would create pure water. Cavendish also discovered the inductive capacity of dielectrics (insulators), and, as early as 1778, measured the specific inductive capacity for beeswax and other substances by comparison with an air condenser.
Around 1784
Through the experiments of William Watson and others proving that electricity could be transmitted to a distance, the idea of making practical use of this phenomenon began, around 1753, to engross the minds of inquisitive people. To this end, suggestions as to the employment of electricity in the transmission of intelligence were made. The first of the methods devised for this purpose was probably that of Georges Lesage in 1774.[60][61][62] This method consisted of 24 wires, insulated from one another and each having had a pith ball connected to its distant end. Each wire represented a letter of the alphabet. To send a message, a desired wire was charged momentarily with electricity from an electric machine, whereupon the pith ball connected to that wire would fly out. Other methods of telegraphing in which frictional electricity was employed were also tried, some of which are described in the history on the telegraph.[11]
The era of
The first mention of voltaic electricity, although not recognized as such at the time, was probably made by
To account for this phenomenon, Galvani assumed that electricity of opposite kinds existed in the nerves and muscles of the frog, the muscles and nerves constituting the charged coatings of a Leyden jar. Galvani published the results of his discoveries, together with his hypothesis, which engrossed the attention of the physicists of that time.
Even Faraday himself, however, did not settle the controversy, and while the views of the advocates on both sides of the question have undergone modifications, as subsequent investigations and discoveries demanded, up to 1918 diversity of opinion on these points continued to crop out. Volta made numerous experiments in support of his theory and ultimately developed the pile or battery,
19th century
Early 19th century
In 1800
Davy in 1806, employing a voltaic pile of approximately 250 cells, or couples, decomposed potash and soda, showing that these substances were respectively the oxides of potassium and sodium, metals which previously had been unknown. These experiments were the beginning of electrochemistry, the investigation of which Faraday took up, and concerning which in 1833 he announced his important law of electrochemical equivalents, viz.: "The same quantity of electricity — that is, the same electric current — decomposes chemically equivalent quantities of all the bodies which it traverses; hence the weights of elements separated in these electrolytes are to each other as their chemical equivalents." Employing a battery of 2,000 elements of a voltaic pile Humphry Davy in 1809 gave the first public demonstration of the electric arc light, using charcoal enclosed in a vacuum.[11]
Somewhat important to note, it was not until many years after the discovery of the voltaic pile that the sameness of animal and frictional electricity with voltaic electricity was clearly recognized and demonstrated. Thus as late as January 1833 we find Faraday writing[65] in a paper on the electricity of the electric ray. "After an examination of the experiments of Walsh,[66][67] Ingenhousz, Henry Cavendish, Sir H. Davy, and Dr. Davy, no doubt remains on my mind as to the identity of the electricity of the torpedo with common (frictional) and voltaic electricity; and I presume that so little will remain on the mind of others as to justify my refraining from entering at length into the philosophical proof of that identity. The doubts raised by Sir Humphry Davy have been removed by his brother, Dr. Davy; the results of the latter being the reverse of those of the former. ... The general conclusion which must, I think, be drawn from this collection of facts (a table showing the similarity, of properties of the diversely named electricities) is, that electricity, whatever may be its source, is identical in its nature."[11]
It is proper to state, however, that prior to Faraday's time the similarity of electricity derived from different sources was more than suspected. Thus, William Hyde Wollaston,[68] wrote in 1801:[69] "This similarity in the means by which both electricity and galvanism (voltaic electricity) appear to be excited in addition to the resemblance that has been traced between their effects shows that they are both essentially the same and confirm an opinion that has already been advanced by others, that all the differences discoverable in the effects of the latter may be owing to its being less intense, but produced in much larger quantity." In the same paper Wollaston describes certain experiments in which he uses very fine wire in a solution of sulphate of copper through which he passed electric currents from an electric machine. This is interesting in connection with the later day use of almost similarly arranged fine wires in electrolytic receivers in wireless, or radio-telegraphy.[11]
In the first half of the 19th century many very important additions were made to the world's knowledge concerning electricity and magnetism. For example, in 1820 Hans Christian Ørsted of Copenhagen discovered the deflecting effect of an electric current traversing a wire upon a suspended magnetic needle.[11]
This discovery gave a clue to the subsequently proved intimate relationship between electricity and magnetism which was promptly followed up by
- Two parallel portions of a circuit attract one another if the currents in them are flowing in the same direction, and repel one another if the currents flow in the opposite direction.
- Two portions of circuits crossing one another obliquely attract one another if both the currents flow either towards or from the point of crossing, and repel one another if one flows to and the other from that point.
- When an element of a circuit exerts a force on another element of a circuit, that force always tends to urge the second one in a direction at right angles to its own direction.
Ampere brought a multitude of phenomena into theory by his investigations of the mechanical forces between conductors supporting currents and magnets. James Clerk Maxwell, in his "A Treatise on Electricity and Magnetism", named Ampere “the Newton of electricity”.[citation needed]
The German physicist Seebeck discovered in 1821 that when heat is applied to the junction of two metals that had been soldered together an electric current is set up. This is termed thermoelectricity. Seebeck's device consists of a strip of copper bent at each end and soldered to a plate of bismuth. A magnetic needle is placed parallel with the copper strip. When the heat of a lamp is applied to the junction of the copper and bismuth an electric current is set up which deflects the needle.[11]
Around this time, Siméon Denis Poisson attacked the difficult problem of induced magnetization, and his results, though differently expressed, are still the theory, as a most important first approximation. It was in the application of mathematics to physics that his services to science were performed. Perhaps the most original, and certainly the most permanent in their influence, were his memoirs on the theory of electricity and magnetism, which virtually created a new branch of mathematical physics.
In 1822
Futile attempts were made by
He drew considerable inspiration from Fourier's work on heat conduction in the theoretical explanation of his work. For experiments, he initially used voltaic piles, but later used a thermocouple as this provided a more stable voltage source in terms of internal resistance and constant potential difference. He used a galvanometer to measure current, and knew that the voltage between the thermocouple terminals was proportional to the junction temperature. He then added test wires of varying length, diameter, and material to complete the circuit. He found that his data could be modeled through a simple equation with variable composed of the reading from a galvanometer, the length of the test conductor, thermocouple junction temperature, and a constant of the entire setup. From this, Ohm determined his law of proportionality and published his results. In 1827, he announced the now famous law that bears his name, that is:Ohm brought into order a host of puzzling facts connecting electromotive force and electric current in conductors, which all previous electricians had only succeeded in loosely binding together qualitatively under some rather vague statements. Ohm found that the results could be summed up in such a simple law and by Ohm's discovery a large part of the domain of electricity became annexed to theory.
Faraday and Henry
The discovery of electromagnetic induction was made almost simultaneously, although independently, by Michael Faraday, who was first to make the discovery in 1831, and Joseph Henry in 1832.[76][77] Henry's discovery of self-induction and his work on spiral conductors using a copper coil were made public in 1835, just before those of Faraday.[78][79][80]
In 1831 began the epoch-making researches of Michael Faraday, the famous pupil and successor of Humphry Davy at the head of the Royal Institution, London, relating to electric and electromagnetic induction. The remarkable researches of Faraday, the prince of experimentalists, on electrostatics and electrodynamics and the induction of currents. These were rather long in being brought from the crude experimental state to a compact system, expressing the real essence. Faraday was not a competent mathematician,[81][82][83] but had he been one, he would have been greatly assisted in his researches, have saved himself much useless speculation, and would have anticipated much later work. He would, for instance, knowing Ampere's theory, by his own results have readily been led to Neumann's theory, and the connected work of Helmholtz and Thomson. Faraday's studies and researches extended from 1831 to 1855 and a detailed description of his experiments, deductions and speculations are to be found in his compiled papers, entitled Experimental Researches in Electricity.' Faraday was by profession a chemist. He was not in the remotest degree a mathematician in the ordinary sense — indeed it is a question if in all his writings there is a single mathematical formula.[11]
The experiment which led Faraday to the discovery of electromagnetic induction was made as follows: He constructed what is now and was then termed an induction coil, the primary and secondary wires of which were wound on a wooden bobbin, side by side, and insulated from one another. In the circuit of the primary wire he placed a battery of approximately 100 cells. In the secondary wire he inserted a galvanometer. On making his first test he observed no results, the galvanometer remaining quiescent, but on increasing the length of the wires he noticed a deflection of the galvanometer in the secondary wire when the circuit of the primary wire was made and broken. This was the first observed instance of the development of electromotive force by electromagnetic induction.[11]
He also discovered that induced currents are established in a second closed circuit when the current strength is varied in the first wire, and that the direction of the current in the secondary circuit is opposite to that in the first circuit. Also that a current is induced in a secondary circuit when another circuit carrying a current is moved to and from the first circuit, and that the approach or withdrawal of a magnet to or from a closed circuit induces momentary currents in the latter. In short, within the space of a few months Faraday discovered by experiment virtually all the laws and facts now known concerning electro-magnetic induction and magneto-electric induction. Upon these discoveries, with scarcely an exception, depends the operation of the telephone, the
In his investigations of the peculiar manner in which iron filings arrange themselves on a cardboard or glass in proximity to the poles of a magnet, Faraday conceived the idea of
Brugans of Leyden in 1778 and Le Baillif and
The 25 years immediately following Faraday's discoveries of
The
Middle 19th century
The
electrostatic force, in a comprehensive ethereal dynamics."
Up to the middle of the 19th century, indeed up to about 1870, electrical science was, it may be said, a sealed book to the majority of electrical workers. Prior to this time a number of handbooks had been published on electricity and magnetism, notably
These books were departures from the beaten path. As Jenkin states in the preface to his work the science of the schools was so dissimilar from that of the practical electrician that it was quite impossible to give students sufficient, or even approximately sufficient, textbooks. A student he said might have mastered de la Rive's large and valuable treatise and yet feel as if in an unknown country and listening to an unknown tongue in the company of practical men. As another writer has said, with the coming of Jenkin's and Maxwell's books all impediments in the way of electrical students were removed, "the full meaning of Ohm's law becomes clear; electromotive force, difference of potential, resistance, current, capacity, lines of force, magnetization and chemical affinity were measurable, and could be reasoned about, and calculations could be made about them with as much certainty as calculations in dynamics".[11][104]
About 1850,
In 1853,
About 1876 the American physicist Henry Augustus Rowland of Baltimore demonstrated the important fact that a static charge carried around produces the same magnetic effects as an electric current.[109][110] The Importance of this discovery consists in that it may afford a plausible theory of magnetism, namely, that magnetism may be the result of directed motion of rows of molecules carrying static charges.[11]
After Faraday's discovery that electric currents could be developed in a wire by causing it to cut across the lines of force of a magnet, it was to be expected that attempts would be made to construct machines to avail of this fact in the development of voltaic currents.
A notable advance in the art of dynamo construction was made by Samuel Alfred Varley in 1866[112] and by Siemens and Charles Wheatstone,[113] who independently discovered that when a coil of wire, or armature, of the dynamo machine is rotated between the poles (or in the "field") of an electromagnet, a weak current is set up in the coil due to residual magnetism in the iron of the electromagnet, and that if the circuit of the armature be connected with the circuit of the electromagnet, the weak current developed in the armature increases the magnetism in the field. This further increases the magnetic lines of force in which the armature rotates, which still further increases the current in the electromagnet, thereby producing a corresponding increase in the field magnetism, and so on, until the maximum electromotive force which the machine is capable of developing is reached. By means of this principle the dynamo machine develops its own magnetic field, thereby much increasing its efficiency and economical operation. Not by any means, however, was the dynamo electric machine perfected at the time mentioned.[11]
In 1860 an important improvement had been made by Dr.
In 1872 the drum armature was devised by Hefner-Alteneck. This machine in a modified form was subsequently known as the Siemens dynamo. These machines were presently followed by the Schuckert, Gulcher,[114] Fein,[115][116][117] Brush, Hochhausen, Edison and the dynamo machines of numerous other inventors.[118] In the early days of dynamo machine construction the machines were mainly arranged as direct current generators, and perhaps the most important application of such machines at that time was in electro-plating, for which purpose machines of low voltage and large current strength were employed.[11][119]
Beginning about 1887 alternating current generators came into extensive operation and the commercial development of the transformer, by means of which currents of low voltage and high current strength are transformed to currents of high voltage and low current strength, and vice versa, in time revolutionized the transmission of electric power to long distances. Likewise the introduction of the rotary converter (in connection with the "step-down" transformer) which converts alternating currents into direct currents (and vice versa) has effected large economies in the operation of electric power systems.[11][120]
Before the introduction of dynamo electric machines, voltaic, or primary, batteries were extensively used for electro-plating and in telegraphy. There are two distinct types of voltaic cells, namely, the "open" and the "closed", or "constant", type. The open type in brief is that type which operated on closed circuit becomes, after a short time, polarized; that is, gases are liberated in the cell which settle on the negative plate and establish a resistance that reduces the current strength. After a brief interval of open circuit these gases are eliminated or absorbed and the cell is again ready for operation. Closed circuit cells are those in which the gases in the cells are absorbed as quickly as liberated and hence the output of the cell is practically uniform. The Leclanché and Daniell cells, respectively, are familiar examples of the "open" and "closed" type of voltaic cell. Batteries of the Daniell or "gravity" type were employed almost generally in the United States and Canada as the source of electromotive force in telegraphy before the dynamo machine became available.[11]
In the late 19th century, the term luminiferous aether, meaning light-bearing aether, was a conjectured medium for the propagation of light.[121] The word aether stems via Latin from the Greek αιθήρ, from a root meaning to kindle, burn, or shine. It signifies the substance which was thought in ancient times to fill the upper regions of space, beyond the clouds.
Maxwell
In 1864
Around 1862, while lecturing at King's College, Maxwell calculated that the speed of propagation of an electromagnetic field is approximately that of the speed of light. He considered this to be more than just a coincidence, and commented "We can scarcely avoid the conclusion that light consists in the transverse undulations of the same medium which is the cause of electric and magnetic phenomena."[127]
Working on the problem further, Maxwell showed that the equations predict the existence of waves of oscillating electric and magnetic fields that travel through empty space at a speed that could be predicted from simple electrical experiments; using the data available at the time, Maxwell obtained a velocity of 310,740,000 m/s. In his 1864 paper A Dynamical Theory of the Electromagnetic Field, Maxwell wrote, The agreement of the results seems to show that light and magnetism are affections of the same substance, and that light is an electromagnetic disturbance propagated through the field according to electromagnetic laws.[128]
As already noted herein Faraday, and before him, Ampère and others, had inklings that the luminiferous ether of space was also the medium for electric action. It was known by calculation and experiment that the velocity of electricity was approximately 186,000 miles per second; that is, equal to the velocity of light, which in itself suggests the idea of a relationship between -electricity and "light." A number of the earlier philosophers or mathematicians, as Maxwell terms them, of the 19th century, held the view that electromagnetic phenomena were explainable by action at a distance. Maxwell, following Faraday, contended that the seat of the phenomena was in the medium. The methods of the mathematicians in arriving at their results were synthetical while Faraday's methods were analytical. Faraday in his mind's eye saw lines of force traversing all space where the mathematicians saw centres of force attracting at a distance. Faraday sought the seat of the phenomena in real actions going on in the medium; they were satisfied that they had found it in a power of action at a distance on the electric fluids.[129]
Both of these methods, as Maxwell points out, had succeeded in explaining the propagation of light as an electromagnetic phenomenon while at the same time the fundamental conceptions of what the quantities concerned are, radically differed. The mathematicians assumed that insulators were barriers to electric currents; that, for instance, in a Leyden jar or electric condenser the electricity was accumulated at one plate and that by some occult action at a distance electricity of an opposite kind was attracted to the other plate.
Maxwell, looking further than Faraday, reasoned that if light is an electromagnetic phenomenon and is transmissible through dielectrics such as glass, the phenomenon must be in the nature of electromagnetic currents in the dielectrics. He therefore contended that in the charging of a condenser, for instance, the action did not stop at the insulator, but that some "displacement" currents are set up in the insulating medium, which currents continue until the resisting force of the medium equals that of the charging force. In a closed conductor circuit, an electric current is also a displacement of electricity.
The conductor offers a certain resistance, akin to friction, to the displacement of electricity, and heat is developed in the conductor, proportional to the square of the current (as already stated herein), which current flows as long as the impelling
Maxwell extended this view of displacement currents in dielectrics to the ether of free space. Assuming light to be the manifestation of alterations of electric currents in the ether, and vibrating at the rate of light vibrations, these vibrations by induction set up corresponding vibrations in adjoining portions of the ether, and in this way the undulations corresponding to those of light are propagated as an electromagnetic effect in the ether. Maxwell's electromagnetic theory of light obviously involved the existence of electric waves in free space, and his followers set themselves the task of experimentally demonstrating the truth of the theory. By 1871, Maxwell could already reflect on the philosophy of science.[131][132]: 214
End of the 19th century
In 1887, the German physicist
The
During the late 1890s a number of physicists proposed that electricity, as observed in studies of electrical conduction in conductors, electrolytes, and
Faraday, Weber, Helmholtz, Clifford and others had glimpses of this view; and the experimental works of Zeeman, Goldstein, Crookes, J. J. Thomson and others had greatly strengthened this view. Weber predicted that electrical phenomena were due to the existence of electrical atoms, the influence of which on one another depended on their position and relative accelerations and velocities. Helmholtz and others also contended that the existence of electrical atoms followed from Faraday's laws of electrolysis, and Johnstone Stoney, to whom is due the term "electron", showed that each chemical ion of the decomposed electrolyte carries a definite and constant quantity of electricity, and inasmuch as these charged ions are separated on the electrodes as neutral substances there must be an instant, however brief, when the charges must be capable of existing separately as electrical atoms; while in 1887, Clifford wrote: "There is great reason to believe that every material atom carries upon it a small electric current, if it does not wholly consist of this current."[11]
In 1896, J. J. Thomson performed experiments indicating that cathode rays really were particles, found an accurate value for their charge-to-mass ratio e/m, and found that e/m was independent of cathode material. He made good estimates of both the charge e and the mass m, finding that cathode ray particles, which he called "corpuscles", had perhaps one thousandth of the mass of the least massive ion known (hydrogen). He further showed that the negatively charged particles produced by radioactive materials, by heated materials, and by illuminated materials, were universal. The nature of the Crookes tube "cathode ray" matter was identified by Thomson in 1897.[137][non-primary source needed]
In the late 19th century, the Michelson–Morley experiment was performed by Albert A. Michelson and Edward W. Morley at what is now Case Western Reserve University. It is generally considered to be the evidence against the theory of a luminiferous aether. The experiment has also been referred to as "the kicking-off point for the theoretical aspects of the Second Scientific Revolution."[138] Primarily for this work, Michelson was awarded the Nobel Prize in 1907. Dayton Miller continued with experiments, conducting thousands of measurements and eventually developing the most accurate interferometer in the world at that time. Miller and others, such as Morley, continue observations and experiments dealing with the concepts.[139] A range of proposed aether-dragging theories could explain the null result but these were more complex, and tended to use arbitrary-looking coefficients and physical assumptions.[11]
By the end of the 19th century
William Stanley made the first public demonstration of a transformer that enabled commercial delivery of alternating current in 1886.[140] Large two-phase alternating current generators were built by a British electrician, J. E. H. Gordon,[141][non-primary source needed] in 1882. Lord Kelvin and Sebastian Ferranti also developed early alternators, producing frequencies between 100 and 300 hertz. After 1891, polyphase alternators were introduced to supply currents of multiple differing phases.[142] Later alternators were designed for varying alternating-current frequencies between sixteen and about one hundred hertz, for use with arc lighting, incandescent lighting and electric motors.[143]
The possibility of obtaining the electric current in large quantities, and economically, by means of dynamo electric machines gave impetus to the development of incandescent and arc lighting. Until these machines had attained a commercial basis voltaic batteries were the only available source of current for electric lighting and power. The cost of these batteries, however, and the difficulties of maintaining them in reliable operation were prohibitory of their use for practical lighting purposes. The date of the employment of arc and
Even in 1880, however, but little headway had been made toward the general use of these illuminants; the rapid subsequent growth of this industry is a matter of general knowledge.
For the 1893 World's Columbian International Exposition in Chicago, General Electric proposed to power the entire fair with direct current. Westinghouse slightly undercut GE's bid and used the fair to debut their alternating current based system, showing how their system could power poly-phase motors and all the other AC and DC exhibits at the fair.[145][146][147]
Second Industrial Revolution
The Second Industrial Revolution, also known as the Technological Revolution, was a phase of rapid
The 1880s saw the spread of large scale commercial electric power systems, first used for lighting and eventually for electro-motive power and heating. Systems early on used alternating current and direct current. Large centralized power generation became possible when it was recognized that alternating current electric power lines could use transformers to take advantage of the fact that each doubling of the voltage would allow the same size cable to transmit the same amount of power four times the distance. Transformer were used to raise voltage at the point of generation (a representative number is a generator voltage in the low kilovolt range) to a much higher voltage (tens of thousands to several hundred thousand volts) for primary transmission, followed to several downward transformations, for commercial and residential domestic use.[11] Between 1885 and 1890 poly-phase currents combined with electromagnetic induction and practical AC induction motors were developed.[148]
The
Much was done in the direction in the improvement of railroad terminal facilities, and it is difficult to find one steam railroad engineer who would have denied that all the important steam railroads of this country were not to be operated electrically. In other directions the progress of events as to the utilization of electric power was expected to be equally rapid. In every part of the world the power of falling water, nature's perpetual motion machine, which has been going to waste since the world began, is now being converted into electricity and transmitted by wire hundreds of miles to points where it is usefully and economically employed.[11][149]
The first windmill for electricity production was built in
20th century
Various units of electricity and magnetism have been adopted and named by representatives of the electrical engineering institutes of the world, which units and names have been confirmed and legalized by the governments of the United States and other countries. Thus the volt, from the Italian Volta, has been adopted as the practical unit of electromotive force, the ohm, from the enunciator of Ohm's law, as the practical unit of resistance; the ampere, after the eminent French scientist of that name, as the practical unit of current strength, the henry as the practical unit of inductance, after Joseph Henry and in recognition of his early and important experimental work in mutual induction.[154]
Dewar and
In 1900,
Lorentz and Poincaré
Between 1900 and 1910, many scientists like Wilhelm Wien, Max Abraham, Hermann Minkowski, or Gustav Mie believed that all forces of nature are of electromagnetic origin (the so-called "electromagnetic world view"). This was connected with the electron theory developed between 1892 and 1904 by Hendrik Lorentz. Lorentz introduced a strict separation between matter (electrons) and the aether, whereby in his model the ether is completely motionless, and it won't be set in motion in the neighborhood of ponderable matter. Contrary to other electron models before, the electromagnetic field of the ether appears as a mediator between the electrons, and changes in this field can propagate not faster than the speed of light.
In 1896, three years after submitting his thesis on the
Continuing the work of Lorentz,
Einstein's Annus Mirabilis
In 1905, while he was working in the patent office,
- His paper on the particulate nature of light put forward the idea that certain experimental results, notably the photoelectric effect, could be simply understood from the postulate that light interacts with matter as discrete "packets" (quanta) of energy, an idea that had been introduced by Max Planck in 1900 as a purely mathematical manipulation, and which seemed to contradict contemporary wave theories of light (Einstein 1905a). This was the only work of Einstein's that he himself called "revolutionary."
- His paper on atomic theory. (Einstein 1905b)
- His paper on the electrodynamics of moving bodies introduced the radical theory of special relativity, which showed that the observed independence of the speed of light on the observer's state of motion required fundamental changes to the notion of simultaneity. Consequences of this include the time-space frame of a moving body slowing down and contracting (in the direction of motion) relative to the frame of the observer. This paper also argued that the idea of a luminiferous aether—one of the leading theoretical entities in physics at the time—was superfluous. (Einstein 1905c)
- In his paper on mass–energy equivalence (previously considered to be distinct concepts), Einstein deduced from his equations of special relativity what later became the well-known expression: , suggesting that tiny amounts of mass could be converted into huge amounts of energy. (Einstein 1905d)
All four papers are today recognized as tremendous achievements—and hence 1905 is known as Einstein's "Wonderful Year". At the time, however, they were not noticed by most physicists as being important, and many of those who did notice them rejected them outright. Some of this work—such as the theory of light quanta—remained controversial for years.[165][166]
Mid-20th century
The first formulation of a
In December 1938, the German chemists
Difficulties with the quantum theory increased through the end of 1940. Improvements in
Shortly after the end of the war in 1945, Bell Labs formed a Solid State Physics Group, led by
As to the problems in the electron experiments, a path to a solution was given by Hans Bethe. In 1947, while he was traveling by train to reach Schenectady from New York,[181] after giving a talk at the conference at Shelter Island on the subject, Bethe completed the first non-relativistic computation of the shift of the lines of the hydrogen atom as measured by Lamb and Retherford.[182] Despite the limitations of the computation, agreement was excellent. The idea was simply to attach infinities to corrections at mass and charge that were actually fixed to a finite value by experiments. In this way, the infinities get absorbed in those constants and yield a finite result in good agreement with experiments. This procedure was named renormalization.
Based on Bethe's intuition and fundamental papers on the subject by
Robert Noyce credited Kurt Lehovec for the principle of p–n junction isolation caused by the action of a biased p-n junction (the diode) as a key concept behind the integrated circuit.[193] Jack Kilby recorded his initial ideas concerning the integrated circuit in July 1958 and successfully demonstrated the first working integrated circuit on September 12, 1958.[194] In his patent application of February 6, 1959, Kilby described his new device as "a body of semiconductor material ... wherein all the components of the electronic circuit are completely integrated."[195] Kilby won the 2000 Nobel Prize in Physics for his part of the invention of the integrated circuit.[196] Robert Noyce also came up with his own idea of an integrated circuit half a year later than Kilby. Noyce's chip solved many practical problems that Kilby's had not. Noyce's chip, made at Fairchild Semiconductor, was made of silicon, whereas Kilby's chip was made of germanium.
Philo Farnsworth developed the Farnsworth–Hirsch Fusor, or simply fusor, an apparatus designed by Farnsworth to create nuclear fusion. Unlike most controlled fusion systems, which slowly heat a magnetically confined plasma, the fusor injects high temperature ions directly into a reaction chamber, thereby avoiding a considerable amount of complexity. When the Farnsworth-Hirsch Fusor was first introduced to the fusion research world in the late 1960s, the Fusor was the first device that could clearly demonstrate it was producing fusion reactions at all. Hopes at the time were high that it could be quickly developed into a practical power source. However, as with other fusion experiments, development into a power source has proven difficult. Nevertheless, the fusor has since become a practical neutron source and is produced commercially for this role.[197]
Parity violation
The mirror image of an electromagnet produces a field with the opposite polarity. Thus the north and south poles of a magnet have the same symmetry as left and right. Prior to 1956, it was believed that this symmetry was perfect, and that a technician would be unable to distinguish the north and south poles of a magnet except by reference to left and right. In that year, T. D. Lee and C. N. Yang predicted the nonconservation of parity in the weak interaction. To the surprise of many physicists, in 1957 C. S. Wu and collaborators at the U.S. National Bureau of Standards demonstrated that under suitable conditions for polarization of nuclei, the beta decay of cobalt-60 preferentially releases electrons toward the south pole of an external magnetic field, and a somewhat higher number of gamma rays toward the north pole. As a result, the experimental apparatus does not behave comparably with its mirror image.[198][199][200]
Electroweak theory
The first step towards the
Z
boson exchange were discovered at CERN in 1973,[207][208][209][210] the electroweak theory became widely accepted and Glashow, Salam, and Weinberg shared the 1979 Nobel Prize in Physics for discovering it. The W and Z bosons were discovered experimentally in 1981, and their masses were found to be as the Standard Model predicted. The theory of the strong interaction, to which many contributed, acquired its modern form around 1973–74, when experiments confirmed that the hadrons were composed of fractionally charged quarks. With the establishment of quantum chromodynamics in the 1970s finalized a set of fundamental and exchange particles, which allowed for the establishment of a "standard model" based on the mathematics of gauge invariance
The 'standard model' groups the electroweak interaction theory and quantum chromodynamics into a structure denoted by the gauge group SU(3)×SU(2)×U(1). The formulation of the unification of the electromagnetic and weak interactions in the standard model is due to Abdus Salam, Steven Weinberg and, subsequently, Sheldon Glashow. After the discovery, made at CERN, of the existence of neutral weak currents,[211][212][213][214] mediated by the
Z
boson foreseen in the standard model, the physicists Salam, Glashow and Weinberg received the 1979 Nobel Prize in Physics for their electroweak theory.[215] Since then, discoveries of the bottom quark (1977), the top quark (1995), tau neutrino (2000) and the Higgs boson (2012) have given credence to the Standard Model.
21st century
Electromagnetic technologies
There are a range of
Magnetic resonance
Reflecting the fundamental importance and applicability of
Wireless electricity
Wireless electricity is a form of
Unified theories
A Grand Unified Theory (GUT) is a model in particle physics in which, at high energy, the electromagnetic force is merged with the other two
Open problems
The
After more than twenty years of intensive research, the origin of
See also
- Histories
- History of electromagnetic spectrum, History of electrical engineering, History of Maxwell's equations, History of radio, History of optics, History of physics
- General
- ampere hours, Transverse waves, Longitudinal waves, Plane waves, Refractive index, torque, Revolutions per minute, Photosphere, Vortex, vortex rings,
- Theory
- standard candle
- Technology
- Western Electric Company,
- Lists
- Outline of energy development
- Timelines
- Timeline of electromagnetism, Timeline of luminiferous aether
References
- Citations and notes
- ^ Bruno Kolbe, Francis ed Legge, Joseph Skellon, tr., "An Introduction to Electricity". Kegan Paul, Trench, Trübner, 1908. 429 pages. Page 391. (cf. "[...] high poles covered with copper plates and with gilded tops were erected 'to break the stones coming from on high'. J. Dümichen, Baugeschichte des Dendera-Tempels, Strassburg, 1877")
- ^ Urbanitzky, A. v., & Wormell, R. (1886). Electricity in the service of man: a popular and practical treatise on the applications of electricity in modern life. London: Cassell &.
- ^ Lyons, T. A. (1901). A treatise on electromagnetic phenomena, and on the compass and its deviations aboard ship. Mathematical, theoretical, and practical. New York: J. Wiley & Sons.
- ^ Platonis Opera, Meyer and Zeller, 1839, p. 989.
- ^ The location of Magnesia is debated; it could be the region in mainland Greece or Magnesia ad Sipylum. See, for example, "Magnet". Language Hat blog. 28 May 2005. Retrieved 22 March 2013.
- ^ a b c Whittaker, E. T. (1910). A history of the theories of aether and electricity from the age of Descartes to the close of the 19th century. Dublin University Press series. London: Longmans, Green and Co.; [etc.].
- S2CID 33186517.
- S2CID 33186517.
- ^ Li Shu-hua, p. 175
- ^ "Early Chinese Compass – 400 BC". Magnet Academy. National High Magnetic Field Laboratory. Retrieved 21 April 2018.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc bd Maver, William, Jr.: "Electricity, its History and Progress", The Encyclopedia Americana; a library of universal knowledge, vol. X, pp. 172ff. (1918). New York: Encyclopedia Americana Corp.
- ^ Heinrich Karl Brugsch-Bey and Henry Danby Seymour, "A History of Egypt Under the Pharaohs". J. Murray, 1881. Page 422. (cf. [... the symbol of a] 'serpent' is rather a fish, which still serves, in the Coptic language, to designate the electric fish [...])
- ISBN 978-0-313-33358-3
- ISBN 9-8102-4471-1
- JSTOR 1311732
- ISBN 0-387-23192-7
- ISBN 0-521-82704-3
- ^ Riddle of 'Baghdad's batteries'. BBC News.
- current production by a reconstruction of the inferred battery design when filled with grape juice. W. Jansen experimented with 1,4-Benzoquinone (some beetles produce quinones) and vinegar in a cell and got satisfactory performance.
- ^ An alternative, but still electrical explanation was offered by Paul Keyser. It was suggested that a priest or healer, using an iron spatula to compound a vinegar based potion in a copper vessel, may have felt an electrical tingle and used the phenomenon either for electro-acupuncture, or to amaze supplicants by electrifying a metal statue.
- batteriesof these "cells".
- ^ Corder, Gregory, "Using an Unconventional History of the Battery to engage students and explore the importance of evidence", Virginia Journal of Science Education 1
- ^ A history of electricity. By Park Benjamin. Pg 33
- ^ Gargano, Giuseppe. Storia della Bussola.
- ^ Schmidl, Petra G. (1996–1997). "Two Early Arabic Sources On The Magnetic Compass". Journal of Arabic and Islamic Studies. 1: 81–132.
- ^ Lane, Frederic C. (1963) "The Economic Meaning of the Invention of the Compass", The American Historical Review, 68 (3: April), p. 605–617
- ISBN 978-1-313-10605-4
- ^ consult ' Priestley's 'History of Electricity,' London 1757
- ^ a b Dampier, W. C. D. (1905). The theory of experimental electricity. Cambridge physical series. Cambridge [Eng.: University Press.
- ^ Robert Boyle (1675). Experiments and notes about the mechanical origin or production of particular qualities.
- ^ Benjamin, P. (1895). A history of electricity: (The intellectual rise in electricity) from antiquity to the days of Benjamin Franklin. New York: J. Wiley & Sons.
- ^ Consult Boyle's 'Experiments on the Origin of Electricity,'" and Priestley's 'History of Electricity'.
- ISBN 0-520-03478-3.
- ^ The Magnet, or Concerning Magnetic Science (Magnes sive de arte magnetica)
- ^ From Physico-Mechanical Experiments, 2nd Ed., London 1719
- ^ Consult Dr. Carpue's 'Introduction to Electricity and Galvanism', London 1803.
- ISBN 0-486-27472-1.
- ISBN 0-313-32015-2
- ^ S2CID 34246664.
- ISBN 0-7803-1193-0
- ^ Biography, Pieter (Petrus) van Musschenbroek Archived 2009-03-26 at the Wayback Machine
- ^ According to Priestley ('History of Electricity,' 3d ed., Vol. I, p. 102)
- ^ Electricity in the 17th and 18th centuries : a study of early modern physics, by John L. Heilbron; published 1979 by University of California Press
- ISBN 978-1-57859-058-2.
- S2CID 207023221.
- ^ Priestley's 'History of Electricity,' p. 138
- ^ Catholic churchmen in science. (Second series) by James Joseph Wals. Pg 172.
- ^ The History and Present State of Electricity with Original Experiments By Joseph Priestle. Pg 173.
- ^ Cheney Hart: "Part of a letter from Cheney Hart, M.D. to William Watson, F.R.S. giving Account of the Effects of Electricity in the County Hospital at Shrewsbury", Phil. Trans. 1753:48, pp. 786–788. Read on November 14, 1754.
- IEEEGlobal History Network.
- ^ see atmospheric electricity
- .
- ^ Physico-mechanical experiments, on various subjects; with, explanations of all the machines engraved on copper
- ^ Vail, A. (1845). The American electro magnetic telegraph: With the reports of Congress, and a description of all telegraphs known, employing electricity or galvanism. Philadelphia: Lea & Blanchard
- ^ Hutton, C., Shaw, G., Pearson, R., & Royal Society (Great Britain). (1665). Philosophical transactions of the Royal Society of London: From their commencement, in 1665 to the year 1800. London: C. and R. Baldwin. PaGE 345.
- ^ Franklin, 'Experiments and Observations on Electricity'
- ^ Royal Society Papers, vol. IX (BL. Add MS 4440): Henry Elles, from Lismore, Ireland, to the Royal Society, London, 9 August 1757, f.12b; 9 August 1757, f.166.
- ^ Tr., Test Theory of Electricity and Magnetism
- ^ Philosophical Transactions 1771
- ^ Electric Telegraph, apparatus by wh. signals may be transmitted to a distance by voltaic currents propagated on metallic wires; fnded. on experimts. of Gray 1729, Nollet, Watson 1745, Lesage 1774, Lamond 1787, Reusserl794, Cavallo 1795, Betancourt 1795, Soemmering 1811, Gauss & Weber 1834, &c. Telegraphs constructed by Wheatstone & Independently by Steinheil 1837, improved by Morse, Cooke, Woolaston, &c.
- ^ Cassell's miniature cyclopaedia By Sir William Laird Clowes. Page 288.
- ^ Die Geschichte Der Physik in Grundzügen: th. In den letzten hundert jahren (1780–1880) 1887–90 (tr. The history of physics in broad terms: th. In the last hundred years (1780–1880) 1887–90) by Ferdinand Rosenberger. F. Vieweg und sohn, 1890. Page 288.
- ^ S2CID 39105914.
- ^ See Voltaic pile
- ^ 'Philosophical Transactions,' 1833
- ^ Of Torpedos Found on the Coast of England. In a Letter from John Walsh, Esq; F. R. S. to Thomas Pennant, Esq; F. R. S. John Walsh Philosophical Transactions Vol. 64, (1774), pp. 464-473
- ^ The works of Benjamin Franklin: containing several political and historical tracts not included in any former ed., and many letters official and private, not hitherto published; with notes and a life of the author, Volume 6 Page 348.
- ^ another noted and careful experimenter in electricity and the discoverer of palladium and rhodium
- ^ Philosophical Magazine, Vol. Ill, p. 211
- ^ 'Trans. Society of Arts,1 1825
- ^ Meteorological essays By François Arago, Sir Edward Sabine. Page 290. "On Rotation Magnetism. Proces verbal, Academy of Sciences, 22 November 1824."
- ^ For more, see Rotating magnetic field.
- The galvanic Circuit investigated mathematically".
- ^ G. S. Ohm (1827). Die galvanische Kette, mathematisch bearbeitet (PDF). Berlin: T. H. Riemann. Archived from the original (PDF) on 2009-03-26. Retrieved 2010-12-20.
- ^ The Encyclopedia Americana: a library of universal knowledge, 1918.
- ^ "A Brief History of Electromagnetism" (PDF).
- ^ "Electromagnetism". Smithsonian Institution Archives.
- ^ Tsverava, G. K. 1981. "FARADEI, GENRI, I OTKRYTIE INDUKTIROVANNYKH TOKOV." Voprosy Istorii Estestvoznaniia i Tekhniki no. 3: 99-106. Historical Abstracts, EBSCOhost . Retrieved October 17, 2009.
- ^ Bowers, Brian. 2004. "Barking Up the Wrong (Electric Motor) Tree." Proceedings of the IEEE 92, no. 2: 388-392. Computers & Applied Sciences Complete, EBSCOhost . Retrieved October 17, 2009.
- ^ 1998. "Joseph Henry." Issues in Science & Technology 14, no. 3: 96. Associates Programs Source, EBSCOhost . Retrieved October 17, 2009.
- ^ According to Oliver Heaviside
- ^ Oliver Heaviside, Electromagnetic theory: Complete and unabridged ed. of v.1, no.2, and: Volume 3. 1950.
- ^ Oliver Heaviside, Electromagnetic theory, v.1. "The Electrician" printing and publishing company, limited, 1893.
- ^ A treatise on electricity, in theory and practice, Volume 1 By Auguste de La Rive. Page 139.
- ^ 'Phil. Trans.,' 1845.
- ^ Elementary Lessons in Electricity and Magnetism By Silvanus Phillips Thompson. Page 363.
- ^ Phil. Mag-., March 1854
- ISBN 978-1-78326-917-4.
- S2CID 113256632.
- ^ For more, see Counter-electromotive force.
- ^ Philosophical Magazine, 1849.
- ^ Ruhmkorff's version coil was such a success that in 1858 he was awarded a 50,000-franc prize by Napoleon III for the most important discovery in the application of electricity.
- ^ American Academy of Arts and Sciences, Proceedings of the American Academy of Arts and Sciences, Vol. XXIII, May 1895 – May 1896, Boston: University Press, John Wilson and Son (1896), pp. 359-360: Ritchie's most powerful version of his induction coil, using staged windings, achieved electrical bolts 2 inches (5.1 cm) or longer in length.
- ^ Page, Charles G., History of Induction: The American Claim to the Induction Coil and Its Electrostatic Developments, Boston: Harvard University, Intelligencer Printing house (1867), pp. 104-106
- ^ American Academy, pp. 359-360
- ^ Lyons, T. A. (1901). A treatise on electromagnetic phenomena, and on the compass and its deviations aboard ship. Mathematical, theoretical, and practical. New York: J. Wiley & Sons. Page 500.
- ^ La, R. A. (1853). A treatise on electricity: In theory and practice. London: Longman, Brown, Green, and Longmans.
- ^ tr., Introduction to electrostatics, the study of magnetism and electrodynamics
- ^ May be Johann Philipp Reis, of Friedrichsdorf, Germany
- ^ "On a permanent Deflection of the Galvanometer-needle under the influence of a rapid series of equal and opposite induced Currents". By Lord Rayleigh, F.R.S.. Philosophical magazine, 1877. Page 44.
- ^ Annales de chimie et de physique, Page 385. "Sur l'aimantation par les courants" (tr. "On the magnetization by currents").
- ^ 'Ann. de Chimie III,' i, 385.
- ^ Jenkin, F. (1873). Electricity and magnetism. Text-books of science. London: Longmans, Green, and Co
- ^ Introduction to 'Electricity in the Service of Man'.
- ^ 'Poggendorf Ann.1 1851.
- ^ Proc. Am. Philos. Soc., Vol. II, pp. 193
- ^ Annalen der Physik, Volume 103. Contributions to the acquaintance with the electric spark, B. W. Feddersen. Page 69+.
- ^ Special information on method and apparatus can be found in Feddersen's Inaugural Dissertation, Kiel 1857th (In the Commission der Schwers'sehen Buchhandl Handl. In Kiel.)
- ^ Rowland, H. A. (1902). The physical papers of Henry Augustus Rowland: Johns Hopkins University, 1876–1901. Baltimore: The Johns Hopkins Press.
- ^ LII. On the electromagnetic effect of convection-currents Henry A. Rowland; Cary T. Hutchinson Philosophical Magazine Series 5, 1941-5990, Volume 27, Issue 169, Pages 445 – 460
- electrical generators.
- ^ consult his British patent of that year
- ^ consult 'Royal Society Proceedings, 1867 VOL. 10—12
- ^ RJ Gulcher, of Biala, near Bielitz, Austria.
- ^ "Fein's Dynamo Electric Machine Illustrated". The Electrical Journal. 7: 117–120. 1881.
- ^ ETA: Electrical magazine: A. Ed, Volume 1
- ISBN 978-1-108-07063-8.
- ISBN 978-1-108-02687-1.
- electric direct current.
- ^ See Electric alternating current machinery.
- ^ The 19th century science book A Guide to the Scientific Knowledge of Things Familiar provides a brief summary of scientific thinking in this field at the time.
- ^ Consult Maxwell's 'Electricity and Magnetism,1 Vol. II, Chap. xx
- ^ "On Faraday's Lines of Force' byJames Clerk Maxwell 1855" (PDF). Archived from the original (PDF) on 2010-12-15. Retrieved 2010-12-28.
- ^ James Clerk Maxwell, On Physical Lines of Force, Philosophical Magazine, 1861
- ^ In November 1847, Clerk Maxwell entered the University of Edinburgh, learning mathematics from Kelland, natural philosophy from J. D. Forbes, and logic from Sir W. R. Hamilton.
- ^ Glazebrook, R. (1896). James Clerk Maxwell and modern physics. New York: Macmillan.Pg. 190
- ^ J J O'Connor and E F Robertson, James Clerk Maxwell Archived 2011-01-28 at the Wayback Machine, School of Mathematics and Statistics, University of St Andrews, Scotland, November 1997
- ^ James Clerk Maxwell, A Dynamical Theory of the Electromagnetic Field, Philosophical Transactions of the Royal Society of London 155, 459-512 (1865).
- ^ Maxwell's 'Electricity and Magnetism,' preface
- oscillating current, telegraphy, wireless.
- ^ Clerk‐Maxwell, J. "Remarks on the mathematical classification of physical quantities." Proceedings of the London Mathematical Society 1.1 (1869): 224-233.
- ISBN 978-94-010-2524-9.
- ^ Heinrich Hertz (1893). Electric Waves: Being Researches on the Propagation of Electric Action with Finite Velocity Through Space. Dover Publications.
- S2CID 9232535.
- ^ consult 'Proc. British Association,' 1879
- ^ Announced in his evening lecture to the Royal Institution on Friday, 30 April 1897, and published in Philosophical Magazine, 44, 293 [3]
- ^ Earl R. Hoover, Cradle of Greatness: National and World Achievements of Ohio's Western Reserve (Cleveland: Shaker Savings Association, 1977).
- ^ Dayton C. Miller, "Ether-drift Experiments at Mount Wilson Solar Observatory", Physical Review, S2, V19, N4, pp. 407-408 (April 1922).
- ^ Blalock, Thomas J. (31 December 2015). "Alternating Current Electrification, 1886". Engineering and Technology History Wiki. United Engineering Foundation. Retrieved 22 April 2018."Stanley Transformer – 1886". Magnet Academy. National High Magnetic Field Laboratory. 10 December 2014. Retrieved 22 April 2018.
- ^ Gordon gave four lectures on static electric induction (S. Low, Marston, Searle, and Rivington, 1879). In 1891, he also published "A treatise on electricity and magnetism]). Vol 1. Vol 2. (S. Low, Marston, Searle & Rivington, limited).
- ^ Thompson, Silvanus P., Dynamo-Electric Machinery. pp. 17
- ^ Thompson, Silvanus P., Dynamo-Electric Machinery. pp. 16
- electric lighting
- ^ Richard Moran, Executioner's Current: Thomas Edison, George Westinghouse, and the Invention of the Electric Chair, Knopf Doubleday Publishing Group – 2007, p. 222
- ^ America at the Fair: Chicago's 1893 World's Columbian Exposition (Google eBook) Chaim M. Rosenberg Arcadia Publishing, 20 February 2008
- ISBN 978-0-313-26644-7. Retrieved 10 September 2012.
- ^ Giovanni Dosi, David J. Teece, Josef Chytry, Understanding Industrial and Corporate Change, Oxford University Press, 2004, page 336. Google Books.
- Electric transmission of energy.
- ^ 'James Blyth – Britain's first modern wind power pioneer', by Trevor Price, 2003, Wind Engineering, vol 29 no. 3, pp 191-200
- ^ [Anon, 1890, 'Mr. Brush's Windmill Dynamo', Scientific American, vol 63 no. 25, 20 December, p. 54]
- ^ A Wind Energy Pioneer: Charles F. Brush Archived 2008-09-08 at the Wayback Machine, Danish Wind Industry Association. Retrieved 2007-05-02.
- ISBN 978-1-60119-433-6, 2007, pp. 421-422
- electrical terms.
- ^ a b Miller 1981, Ch. 1
- ^ a b Pais 1982, Ch. 6b
- ^ a b c Janssen, 2007
- doi:10.1086/143148
- ^ Galison 2002
- ^ Darrigol 2005
- ^ Katzir 2005
- ^ Miller 1981, Ch. 1.7 & 1.14
- ^ Pais 1982, Ch. 6 & 8
- ISBN 90-277-2498-9.
- ISBN 0-19-520438-7
- .
- .
- .
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External links
- Electrickery, BBC Radio 4 discussion with Simon Schaffer, Patricia Fara & Iwan Morus (In Our Time, Nov. 4, 2004)
- Magnetism, BBC Radio 4 discussion with Stephen Pumphrey, John Heilbron & Lisa Jardine (In Our Time, Sep. 29, 2005)