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FOURTH PERIOD
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See also:FOURTH See also:PERIOD
.—With the publication of Clerk See also:Maxwell's See also:treatise in 1873, we enter fully upon the See also:fourth and See also:modern See also:period of See also:electrical See also:research
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On the technical See also:side the invention of a new See also:form of See also:armature for See also:dynamo electric See also:machines by Z
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T
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Gramme (1826-19o1) inaugurated a departure from which we may date modern electrical See also:engineering
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It will be convenient to See also:deal with technical development first
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Technical Development.—As far back as 1841 large magneto-electric machines driven by See also:steam See also:power had been constructed, and in 1856 F
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H
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See also:Holmes had made a magneto See also:machine with multiple permanent magnets which was installed in 1862 in See also:Dungeness lighthouse
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Further progress was made in 1867 when H
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See also:Wilde introduced the use of electromagnets for the See also:
Gramme dynamos were then soon made on the self-exciting principle
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In 1873 at See also:Vienna the fact was discovered that a dynamo machine of the Gramme type could also See also:act as an electric motor and' was set in rotation when a current was passed into it from another similar machine
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Henceforth the electric transmission of power came within the possibilities of engineering
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Electric See also:Lighting.—In 1876, See also:Paul See also:Jablochkov (1847-1894), a See also:Russian officer, passing through See also:Paris, invented his famous electric See also:candle, consisting of two rods of See also:carbon placed side by side and separated from one another by an insulating material
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This invention in See also:conjunction with an alternating current dynamo provided a new and See also:simple form of electric arc lighting
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Two years afterwards C
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F
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See also:Brush, in the See also:United States, produced another efficient form of dynamo and electric arc See also:lamp suitable for working in See also:series (see LIGHTING: Electric), and these inventions of Brush and Jablochkov inaugurated commercial arc lighting
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The so-called subdivision of electric See also:light by incandescent lighting lamps then engaged See also:attention
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E
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A
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See also: E . Staite in 1848 had made incandescent electric lamps of an elementary form, and T . A . See also:Edison in 1878 again attacked the problem of producing light by the incandescence of See also:platinum . It had by that See also:time become clear that the most suitable material for an incandescent lamp was carbon contained in a See also:good vacuum, and St G . See also:Lane See also:Fox and See also:Sir J . W . See also:Swan in See also:England, and T . A . Edison in the United States, were engaged in struggling with the difficulties of producing a suitable carbon incandescence electric lamp . Edison constructed in 1879 a successful lamp of this type consisting of a See also:vessel wholly of See also:glass containing a carbon filament made by carbonizing See also:paper or some other carbonizable material, the vessel being exhausted and the current led into the filament through platinum wires . In 1879 and 188o, Edison in the United States, and Swan in conjunction with C .
H
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Stearn in England, succeeded in completely solving the See also:practical problems
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From and after that date incandescent electric lighting became commercially possible, and was brought to public notice chiefly by an electrical See also:exhibition held at the Crystal See also:Palace, near See also:London, in 1882
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Edison, moreover, as well as Lane-Fox, had realized the See also:idea of a public electric See also:supply station, and the former proceeded to establish in See also:Pearl See also:Street, New See also:York, in 1881, the first public electric supply station
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A similar station in England was opened in the See also:basement of a See also:house in See also:Holborn Viaduct, London, in See also:
In 1882, numerous electric lighting companies were formed for the conduct of public and private lighting, but an electric lighting act passed in that See also:year greatly hindered commercial progress in See also:Great See also:Britain
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Nevertheless the delay was utilized in the completion of inventions necessary for the safe and economical See also:distribution of electric current for the purpose of electric lighting
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See also:Telephone.—Going back a few years we find the technical applications of electrical invention had developed themselves in other directions
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See also: Edison, See also:Leo Daft, E . M . See also:Bentley and W . H . See also:Knight, F . J . Sprague, C . J . See also:Van Depoele and others between 188o and 1884 were the pioneers of electric See also:traction . One of the earliest electric tram cars was exhibited by E . W. and W . See also:Siemens in Paris in 1881 .
In 1883 Lucien Gaulard, following a See also:line of thought opened by Jablochkov, proposed to employ high pressure alternating currents for electric distributions over wide areas by means of See also:transformers
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His ideas were improved by Carl Zipernowsky and O
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T
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Blathy in See also:Hungary and by S
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Z. de Ferranti in England, and the alternating current transformer (see TRANSFORMERS) came into existence
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Polyphase alternators were first exhibited at the See also:Frankfort electrical exhibition in 1891, developed as a consequence of scientific researches by Galileo Ferraris (1847—1897) ,Nikola Tesla,M
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O.von Dolivo-Dobrowolsky and C
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E
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L
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See also:
E
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B
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See also:Crompton, Elihu See also:Thomson, See also:Rudolf Eickemeyer, See also: Z. de Ferranti and Messrs Ganz of See also:Budapest . Thus in twenty years from the invention of the Gramme dynamo, electrical engineering had developed from small beginnings into a vast See also:industry . The See also:amendment, in 1888, of the Electric Lighting Act of 1882, before long caused a huge development of public electric lighting in Great Britain . By the end of the 19th See also:century every large See also:city in See also:Europe and in See also:North and See also:South See also:America was provided with a public electric supply fcr the purposes of electric lighting . The various improvements in electric illuminants, such as the Nernst See also:oxide lamp, the See also:tantalum and See also:osmium incandescent lamps, and improved forms189 of arc lamp, enclosed, inverted and See also:flame arcs, are described under LIGHTING: Electric . Between 1890 and 1900, electric traction advanced rapidly in the United States of America but more slowly in England . In r902 the success of deep See also:tube electric See also:railways in Great Britain was assured, and in 1904 See also:main line railways began to abandon, at least experimentally, the steam See also:locomotive and substitute for it the electric transmission of power . Long distance electrical transmission had been before that time exemplified in the great See also:scheme of utilizing the falls of See also:Niagara . The first projects were discussed in 1891 and 1892 and completed practically some ten years later . In this scheme large turbines were placed at the bottom of See also:hydraulic fall tubes 150 ft. deep, the turbines being coupled by long shafts with 5000 H.P. alternating current dynamos on the See also:surface . By these electric current was generated and transmitted to towns and factories around, being sent overhead as far as See also:Buffalo, a distance of 18 m . At the end of the 19th century electrochemical See also:industries began to be developed which depended on the See also:possession of cheap electric See also:energy . The See also:production of See also:aluminium in See also:Switzerland and See also:Scotland, See also:carborundum and See also:calcium See also:carbide in the United States, and soda by the Castner-Kellner See also:process, began to be conducted on an immense See also:scale . The early See also:work of Sir W . Siemens on the electric See also:furnace was continued and greatly extended by See also:Henri See also:Moissan and others on its scientific side, and electro-See also:chemistry took, its See also:place as one of the most promising departments of technical research and invention . It was stimulated and assisted by improvements in the construction of large dynamos and increased knowledge concerning the See also:control of powerful electric currents . In the early See also:part of the 20th century the distribution in bulk of electric energy for power purposes in Great Britain began to assume important proportions . It was seen to be uneconomical for each city and See also:town to manufacture its own supply since, owing to the intermittent nature of the demand for current for lighting, the See also:price had to be kept up to 4d. and 6d. per unit . It was found that by the manufacture in bulk, even by steam engines, at See also:primary centres the cost could be considerably reduced, and in numerous districts in England large power stations began to be erected between 1903 and 1905 for the supply of current for power purposes . This involved almost a revolution in the nature of the tools used, and in the methods of working, and may ultimately even greatly affect the factory See also:system and the concentration of See also:population in large towns which was brought about in the early part of the loth century by the invention of the steam See also:engine . Development of Electric Theory . Turning now to the theory of See also:electricity, we may See also:note the equally remarkable progress made in 300 years in scientific insight into the nature of the agency which has so recast the See also:face of human society . There is no need to dwell upon the early crude theories of the action of See also:amber and lodestone . In a true scientific sense no See also:hypothesis was possible, because few facts had been accumulated .
The discoveries of See also:Stephen Gray and C
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F. de C. du See also:Fay on the conductivity of some bodies for the electric agency and the dual See also:character of electrification gave rise to the first notions of electricity as an imponderable fluid, or non-gravitative subtile'See also:matter, of a more refined and penetrating See also:kind than See also:ordinary liquids and gases
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Its duplex character, and the fact that the electricity produced by rubbing glass and vitreous substances was different from that produced by rubbing sealing-See also:wax and resinous substances, seemed to necessitate the See also:assumption of two kinds of electric fluid; hence there arose the conception of See also:positive and negative electricity, and the two-fluid theory came into existence
.
Single fluid Theory.—The study of the phenomena of the See also:Leyden See also:jar and of the fact that the inside and outside coatings possessed opposite electricities, so that in charging the jar as much positive electricity is added to one side as negative to the other, led See also:Franklin about 1750 to suggest a modification called the single fluid theory, in which the two states of electrification
were regarded as not the results of two entirely different fluids but of the addition or subtraction of one electric fluid from matter, so that positive electrification was to be looked upon; as the result of increase or addition of something to ordinary matter and negative as a subtraction
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The positive and negative electrifications of the two coatings of the Leyden jar were therefore to be regarded as the result of a transformation of something called electricity from one coating to the other, by which process a certain measurable quantity became so much less on one side by the same amount by which it became more on the other
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A modification of this single fluid theory was put forward by F
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U
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T
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See also:Aepinus which was explained and illustrated in his Tentamen theoriae electricitatis et magnetismi, 'published in St See also:Petersburg in 1759
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This theory was founded on the following principles:—(I) the particles of the electric fluid repel each other with a force decreasing as the distance increases; (2) the particles of the electric fluid attract the atoms of all bodies and are attracted by them with a force obeying the same See also:law; (3) the electric fluid exists in the pores of all bodies, and while it moves without any obstruction in conductors such as metals, See also:water, &c., it moves with extreme difficulty in so-called non-conductors such as glass, See also:resin, &c.; (4) electrical phenomena are produced either by the transference of the electric fluid of a See also:body containing more to one containing less, or from its attraction and repulsion when no transference takes place
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Electric attractions and repulsions were, however, regarded as See also:differential actions in which the mutual repulsion of the particles of electricity operated, so to speak, in antagonism to the mutual attraction of particles of matter for one another and of particles of electricity for matter
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Independently of Aepinus, See also: Trans., 1771, 61, p . 584), in which he considered it in more precise detail . Two fluid Theory.—In the elucidation of electrical phenomena, however, towards the end of the 18th century, a modification of the two-fluid theory seems to have been generally preferred . The notion then formed of the nature of electrification was something as follows:—All bodies were assumed to contain a certain quantity of a so-called neutral fluid made up of equal quantities of positive and negative electricity, which when in this See also:state of See also:combination neutralized one another's properties . The neutral fluid could, however, be divided up or separated into its two constituents, and these could be accumulated on See also:separate conductors or non-conductors . This view followed from the discovery of the facts of electric See also:induction of J . See also:Canton (1753, 1754) . When, for instance, a positively electrified body was found to induce upon another insulated conductor a See also:charge of negative electricity on the side nearest to it, and a charge of positive electricity on the side farthest from it, this was explained by saying that the particles of each of the two electric fluids repelled one another but attracted those of the positive fluid . Hence the operation of the positive charge upon the neutral fluid was to draw towards the positive the negative constituent of the neutral charge and repel to the distant parts of the conductor the positive constituent . C . A . See also:Coulomb experimentally proved that the law of attraction and repulsion of simple electrified bodies was that the force between them varied inversely as the square of the distance and thus gave mathematical definiteness to the two-fluid hypo-thesis . It was then assumed that each of the two constituents of the neutral fluid had an atomic structure and that the so-called particles of one of the electric fluids, say positive, repelled similar particles with a force varying inversely as a square of the distance and attracted those of the opposite fluid according to the same law . This fact and hypothesis brought electrical phenomena within the domain of mathematical See also:analysis and, as already mentioned, See also:Laplace, See also:Biot, See also:Poisson, G . A . A . Plana (1781-1846), and later See also:Robert See also:Murphy (1806-1843), made them the subject of their investigations on the mode in which electricity distributes itself on conductors when in See also:equilibrium . See also:Faraday's Views.—The two-fluid theory may be said to have held the field until the time when Faraday began his researcheson electricity . After he had educated himself by the study of the phenomena of lines of magnetic force in his discoveries on electromagnetic induction, he applied the same conception to electrostatic phenomena, and thus created the notion of lines of electrostatic force and of the important See also:function of the di-electric or non-conductor in sustaining them . Faraday's notion as to the nature of electrification, therefore, about the See also:middle of the 19th century came to be something as follows:—He considered that the so-called charge of electricity on a conductor was in reality nothing on the conductor or in the conductor itself, but consisted in a state of See also:strain or polarization, or a See also:physical See also:change of some kind in the particles of the See also:dielectric surrounding the conductor, and that it was this physical state in the dielectric which constituted electrification . Since Faraday was well aware that even a good vacuum can act as a dielectric, he recognized that the state he called dielectric polarization could not be wholly dependent upon the presence of gravitative matter, but that there must be an electromagnetic See also:medium of a supermaterial nature . In the 13th series of his Experimental Researches on Electricity he discussed the relation of a vacuum to electricity . Furthermore his electrochemical investigations, and particularly his discovery of the important law of See also:electrolysis, that the See also:movement of a certain quantity of electricity through an electrolyte is always accompanied by the See also:transfer of a certain definite quantity of matter from one electrode to another and the liberation at these electrodes of an See also:equivalent See also:weight of the ions, gave See also:foundation for the idea of a definite atomic charge of electricity . In fact, long previously to Faraday's electrochemical researches, Sir H . See also:Davy and J . J . See also:Berzelius early in the 19th century had advanced the hypothesis that chemical combination was due to electric attractions between the electric charges carried by chemical atoms . The notion, however, that electricity is atomic in structure was definitely put forward by See also:Hermann von See also:Helmholtz in a well-known Faraday lecture . Helmholtz says: " If we accept the hypothesis that elementary substances are composed of atoms, we cannot well avoid concluding that electricity also is divided into elementary portions which behave like atoms of electricity."' Clerk Maxwell had already used in 1873 the phrase, " a See also:molecule of electricity."2 Towards the end of the third See also:quarter of the 19th century it therefore became clear that electricity, whatever be its nature, was associated with atoms of matter in the form of exact multiples of an in-divisible minimum electric charge which may be considered to be " Nature's unit of electricity." This ultimate unit of electric quantity See also:Professor See also:Johnstone Stoney called an See also:electron .3 The formulation of electrical theory as far as regards operations in space See also:free from matter was immensely assisted by Maxwell's mathematical theory . See also:Oliver Heaviside after 188o rendered much assistance by reducing Maxwell's mathematical analysis to more compact form and by introducing greater precision into terminology (see his Electrical Papers, 1892) . This is perhaps the place to refer also to the great services of See also:Lord See also:Rayleigh to electrical See also:science . Succeeding Maxwell as Cavendish professor of physics at See also:Cambridge in 188o, he soon devoted himself especially to the exact redetermination of the practical electrical See also:units in See also:absolute measure . He followed up the early work of the See also:British Association See also:Committee on electrical units by a fresh determination of the See also:ohm in absolute measure, and in conjunction with other work on the electrochemical equivalent of See also:silver and the absolute electromotive force of the See also:Clark See also:cell may be said to have placed exact electrical measurement on a new basis . He also made great additions to the theory of alternating electric currents, and provided fresh appliances for other electrical measurements (see his Collected Scientific Papers, Cambridge, 190o) . See also:Electra-See also:optics.—For a long time Faraday's observation on the rotation of the See also:plane of polarized light by heavy glass in a 1 H. von Helmholtz, " On the Modern Development of Faraday's Conception of Electricity," Journ . Chem . See also:Soc., 1881, 39, p . 277 . 2 See Maxwell's Electricity and See also:Magnetism, vol. i. p . 350 (2nd ed., 1881) . " On the Physical Units of Nature," Phil . Mag., 1881, fs1, II, p . 381 . Also Trans, Rey . Soc . (See also:Dublin, 1891), 4, P . 583 . magnetic field remained an isolated fact in electro-optics . Then M . E . Verdet (1824-186o) made a study of the subject and discovered that a See also:solution of ferric perchloride in methyl See also:alcohol rotated the plane of polarization in an opposite direction to heavy glass (See also:Ann . Chico . Phys., 1854, 41, p . 370; 1855, 43, p . 37; See also:Corn . Rend., 1854, 39, p . 548) . Later A . A . E .
E
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See also:Kundt prepared metallic films of iron, See also:nickel and See also:cobalt, and obtained powerful
negative See also:optical rotation with them (Wied
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Ann., 1884, 23, p
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228; 1886, 27, p
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191)
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See also: See also:Perkin for an immense range of inorganic and organic bodies.3 Kerr also discovered that when certain homogeneous dielectrics were submitted to electric strain, they became birefringent (Phil . Meg., 1875, 50, pp . 337 and 446) . The theory of electro-optics received great attention from Kelvin, Maxwell, Rayleigh, G . F . See also:Fitzgerald, A . Righi and P . K . L . Drude, and experimental contributions from innumerable workers, such as F . T . Trouton, O . 
J
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See also:Lodge and J
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L
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See also:Howard,
and many others
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Electric Waves.—In the See also:decade 188o-189o, the most important
advance in electrical physics was, however, that which originated with the astonishing researches of Heinrich Rudolf See also:Hertz (1857-1894)
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This illustrious investigator was stimulated, by a certain problem brought to his notice by H. von Helmholtz, to undertake investigations which had for their See also:object a demonstration of the truth of Maxwell's principle that a variation in electric displacement was in fact an electric current and had magnetic effects
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It is impossible to describe here the details of these elaborate experiments; the reader must be referred to Hertz's own papers, or the See also:English See also:translation of them by Prof
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D
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E
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See also:
Fitzgerald (1851-1901) in 1883 as to a method of producing electric waves in space
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He invented for this purpose a radiator consisting of two See also:metal rods placed in one line, their inner ends being provided with poles nearly touching and their See also:outer ends with metal plates
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Such an arrangement constitutes in effect a See also:condenser, and when the two plates respectively are connected to the secondary terminals of an induction coil in operation, the plates are rapidly and alternately charged, and discharged across the spark See also:gap with electrical oscillations (see See also:ELECTROKINETICS)
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Hertz then devised a See also:wave detecting apparatus called a resonator
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This in its simplest form consisted of a ring of wire nearly closed terminating in spark balls very See also:close together, adjustable as to distance by a See also:micrometer See also:screw
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He found that when the resonator was placed in certain positions with regard to the oscillator, small See also:sparks were seen between the micrometer balls, and when the oscillator was placed at one end of a See also:room having a See also:sheet of See also: |