See also:manual or other power for transforming
See also:work into electric energy in the
See also:form of electrostatic charges of opposite sign delivered to
See also:separate conductors . Electrostatic
See also:machines are of two kinds: (I) Frictional, and (2) Influence machines . Frictional Machines.—A
See also:primitive form of frictional electrical machine was constructed about 1663 by
See also:Otto von Guericke (1602–1686) . It consisted of a globe of
See also:sulphur fixed on an
See also:axis and rotated by a winch, and it was electrically excited by the
See also:friction of warm hands held against it .
See also:Sir Isaac
See also:Newton appears to have been the first to use a
See also:glass globe instead of sulphur (
See also:Optics, 8th Query) . F . Hawksbee in 1709 also used a revolving glass globe . A
See also:metal chain resting on the globe served to collect the
See also:charge . Later G . M . Bose (1710–1761), of
See also:berg, added the
See also:prime conductor, an insulated
See also:tube or cylinder supported on
See also:silk strings, and J . H .
See also:professor of physics at
See also:Leipzig, substituted a
See also:cushion for the
See also:hand . Andreas
See also:Gordon (1712–1751) of
See also:Erfurt, a Scotch
See also:monk, first used a glass cylinder in place of a sphere . Jesse
See also:Ramsden (1735–1800) in 1768 constructed his well-known form of
See also:plate electrical machine (fig . I) . A glass plate fixed to a wooden or metal
See also:shaft is rotated by a winch . It passes between two rubbers made of leather, and is partly covered with two silk aprons which extend over quadrants of its
See also:surface . Just below the places where the aprons terminate, the glass is embraced by two insulated metal forks having the
See also:sharp points projecting towards the glass, but not quite touching it . The glass is excited positively by friction with the rubbers, and the charge is
See also:drawn off by the
See also:action of the points which, when acted upon inductively,
See also:discharge negative
See also:electricity against it . The insulated conductor to which the points are connected therefore becomes positively electri- fied . The cushions must be connected to
See also:earth to remove the negative elec- tricity which accumulates on them . It was found that the machine acted better if the rubbers were covered with bisulphide of tin or with F. von Kien- mayer's
See also:amalgam, consist-
See also:ing of one
See also:part of
See also:zinc, one of tin and two of mer- cury . The cushions were greased and the amalgam in a state of powder spread over them .
See also:Edward Nairne's electrical machine (1787) consisted of a glass cylinder with two insu- lated conductors, called prime conductors, on glass legs placed near it . One exacting cushions and the other the
See also:collecting metal points, a silk
See also:apron extending over the cylinder from the cushion almost to the points . The
See also:rubber was smeared with amalgam . The
See also:function of the apron is to prevent the
See also:escape of electrification from the glass during its passage from the rubber to the collecting points . Nairne's machine could give either
See also:positive or negative electricity, the first named being collected from the prime conductor carrying the collecting points and the second from the prime conductor carrying the cushion . Influence Machines.—Frictional machines are, however, now quite superseded by the second class of instrument mentioned above, namely, influence machines . These operate by electrostatic induction and convert mechanical work into electrostatic energy by the aid of a small initial charge which is continually being replenished or reinforced . The general principle of all the machines de-scribed below will be best understood by considering a
See also:simple ideal case . Imagine two
See also:Leyden jars with large brass knobs, A and B, to stand on the ground (fig . 2) . Let one
See also:jar be initially charged with positive electricity on its inner coating and the other with negative, and let both have their outsides connected to earth . Imagine two insulated balls A' and B' so held that A' is near A and B' is near B .
Then the positive charge on A induces two charges on A', viz.: a negative on theside nearest and a positive on the side most removed . Likewise the negative charge on B induces a positive charge on the side of B' nearest to it and repels negative electricity to the far side . Next let the balls A' and B' be connected together for a moment by a
See also:wire N called a neutralizing conductor which is subsequently removed . Then A' will be
See also:left negatively electrified and B' will be left positively electrified . Suppose that A' and B' are then made to
See also:change places . To do this we shall have to exert energy to remove A' against the attraction of A and B' against the attraction of B . Finally let A' be brought in contact with B and B' with A . The
See also:ball A' will give up its charge of negative electricity to the Leyden jar B, and the ball B' will give up its positive charge to the Leyden jar A . This transfer will take place because the inner coatings of the Leyden jars have greater capacity with respect to the earth than the balls . Hence the charges of the jars will be increased . The balls A' and B' are then practically discharged, and the above cycle of operations may be repeated . Hence, however small may be the initial charges of the Leyden jars, by a principle of accumulation resembling that of compound
See also:interest, they can be increased as above shown to any degree .
If thisseries of operations be made to depend upon the continuous rotation of a winch or handle, the arrangement constitutes an electrostatic influence machine . The principle therefore somewhat resembles that of the self-exciting dynamo . The first
See also:suggestion for a machine of the above kind seems to have grown out of the invention of Volta's
See also:electrophorus . Abraham Bennet, the inventor of the gold
See also:leaf electro- Kennet's
See also:scope, described a doubler or machine for multiplying Doubler. electric charges (Phil . Trans., 1787) . The principle of this apparatus may be explained thus . Let A and C be two fixed disks, and B a disk which can be brought at will within a very
See also:short distance of either A or C . Let us suppose all the plates to be equal, and let the capacities of A and C in presence of B be each equal to p, and the coefficient of induction between A and B, or C and B, be q . Let us also suppose that the plates A and C are so distant from each other that there is no mutual influence, and that p' is the capacity of one of the disks when it stands alone . A small charge Q is communicated to A, and A is insulated, and B, uninsulated, is brought up to it; the charge on B will be—(q/p)Q . B is now uninsulated and brought to
See also:face C, which is uninsulated; the charge on C will be (q/p)'Q . C is now insulated and connected with A, which is always insulated .
B is then brought to face A and uninsulated, so that the charge on A becomes rQ, where r p+ p c,2 p'(I+p2 A is now disconnected from C, and here the first operation ends . It is obvious that at the end of n such operations the charge on A will be r"Q, so that the charge goes on increasing in geometrical progression . If the distance between the disks could be made infinitely small each
See also:time, then the multiplier r would be 2, and the charge would be doubled each time . Hence the name of the apparatus .
See also:Erasmus Darwin, B .
See also:Wilson, G . C . Bohnenberger and J . C . E . Peclet devised various modifications of Bennet's instrument (see S . P .
See also:Thompson, " The Influence Machine from 1788 to 1888," Journ .
See also:Soc . Tel . Eng., 1888, 17, p . 569) . Bennet's doubler appears to have given a suggestion to
See also:Nicholson (Phil . Trans., 1788, p . 403) of " an instrument which by turning a winch produced the two states of electricity without friction or communication with the earth." This " revolving doubler," according to the description of Professor S . P . Thompson (loc. cit.), consists of two fixed plates of brass A and C (fig . 3), each two inches in diameter and separately supported on insulating arms in the same
See also:plane, so that a third revolving plate B may pass very near them without touching . A brass ball D two inches in diameter is fixed on the end of the axis that carries the plate B, and is loaded within at one side, so as to
See also:act as a counterpoise to the revolving plate B .
The axis P N is made of varnished glass, and so are the axes that join the three plates with the brass axis N O . The axis N 0 passes through the brass piece M, which stands on an insulatingpillar of glass, and supports the plates A and C . At one extremity of this axis is the ball D, and the other is connected with a
See also:rod of glass, N P, upon which is fixed the handle L, and also the piece G H, which is separately insulated . The pins E, F rise out of the back of the fixed plates A and C, at unequal distances from the axis . The piece K is parallel to G H, and both of them are furnished at their ends with small pieces of flexible wire that they may
See also:touch the pins E, F in certain points of their revolution . From the brass piece M there stands out a
See also:pin I, to touch against a small flexible wire or
See also:spring which projects C sideways from the rotating plate B when it comes op- posite A . The wires are so ad- justed by bending that B, at the moment when it is opposite A, com- municates with the ball D, and A communicates with C through GH; and
See also:half a revolution later C, when B comes opposite to it, communicates with the ball D through the contact of K with F . In all other positions A, B, C and D are completely disconnected from each other . Nicholson thus described the operation of his machine: " When the plates A and B are opposite each other, the two fixed plates A and C may be considered as one mass, and the revolving plate B, together with the ball D, will constitute another mass . All the experiments yet made concur to prove that these two masses will not possess the same electric state . . . .The redundant electricities in the masses under
See also:consideration will be unequally distributed; the plate A will have about ninety-nine parts, and the plate C one; and, for the same reason, the revolving plate B will have ninety-nine parts of the opposite electricity, and the ball D one .
The rotation, by destroying the contacts, preserves this unequaldistribution, and carries B from A to C at the same time that the tail K connects the ball with the plate C . In this situation, the electricity in B acts upon that in C, and produces the contrary state, by virtue of the communication between C and the ball; which last must therefore acquire an electricity of the same kind with that of the revolving plate . But the rotation again destroys the contact and restores B to its first situation opposite A . Here, if we attend to the effect of the whole revolution, we shall find that the electric states of the respective masses have been greatly increased; for the ninety-nine parts in A and B remain, and the one part of electricity in C has been increased so as nearly to compensate ninety-nine parts of the opposite electricity in the revolving plate B, while the communication produced an opposite mutation in the electricity of the ball . A second rotation will, of course, produce a proportional
See also:augmentation of these increased quantities; and a continuance ofturning will soon bring the intensities to their maximum, which is limited by an
See also:explosion between the plates" (Phil . Trans., 1788, p . 405) . Nicholson described also another apparatus, the "
See also:condenser," which worked on the same principle . Bennet and Nicholson were followed by T .
See also:John Read, Belle's Bohnenberger, C . B . Desormes and J .
N . P .
See also:Hachette doubler. and others in the invention of various forms of rotating doubler . A simple and typical form of doubler, devised in 1831 by G . Belli (fig . 4), consisted of two curved metal plates between which revolved a pair of balls carried on an insulating
See also:stem . Following the nomenclature usual in connexion with dynamos we may speak of the conductors which carry the initial charges as the
See also:field plates, and of the moving conductors on which are induced the charges which are subsequently added to those on the field plates, as the
See also:carriers . The wire which connects two armature plates for a moment is the neutralizing conductor . The two curved metal plates constitute the field plates and must have
See also:original charges imparted to them of opposite sign . The rotating balls are the carriers, and are connected together for a moment by a wire when in a position to be acted upon inductively by the field plates, thus acquiring charges of opposite sign . The moment after they are separated again . The rotation continuing the ball thus negatively charged is made to give up this charge to that negatively electrified field plate, and the ball positively charged its charge to the positively electrified field plate, by touching little contact springs .
In this manner the field plates accumulate charges of opposite sign .
See also:Modern types of influence machine may be said to date from 186o when C . F . Varley patented a type of influence machine which has been the
See also:parent of numerous subsequent forms (Brit . Pat . Spec . No . 206 of 186o) . In it the
See also:vane machchine . field plates were sheets of tin-
See also:foil attached to a glass plate (fig . 5) . In front of them a disk of ebonite or glass, having carriers of metal fixed to its edge, was rotated by a winch .
In the course of their rotation two diametrically opposite carriers touched against the ends of a neutralizing conductor so as to form for a moment one conductor, and the moment afterwards these two carriers were insulated, one carrying away a positive charge and the other a negative . Continuing their rotation, the positively chargedcarrier gave up its positive charge by touching a little knob attached to the positive field plate, and similarly for the negative charge carrier . In this way the charges on the field plates were continually replenished and reinforced . Varley also constructed a multiple form of influence machine having six rotating disks, each having a number of carriers and rotating between field plates . With this apparatus he obtained
See also:sparks 6 in. long, the initial source of electrification being a single Daniell
See also:cell . Varley was followed by A . J . I . Toepler, who in 1865 constructed an influence machine consisting of FRG . 5.-Varley's machine. two disks fixed on the same shaft and rotating in the same direction . Each disk carried two strips of tin-foil extending nearly over a semi-circle, and there were two field plates, one behind each disk; one of the plates was positively and the other negatively electrified . The carriers which were touched under the influence of the positive field plate passed on and gave up a portion of their negative charge to increase that of the negative field plate; in the same
See also:Nichol-son's doubler .
Toepler machine . way the carriers which were touched under the influence of the negative field plate sent a part of their charge to
See also:augment that of the positive field plate . In this apparatus one of the charging rods communicated with one of the field plates, but the other with the neutralizing
See also:brush opposite to the other field plate . Hence one of the field plates would always remain charged when a spark was taken at the transmitting terminals . Between 1864 and 188o, W . T . B . Holtz constructed and described a large number of influence machines which were for a long time considered the most advanced development of this type of electrostatic machine . In one form the Holtz machine consisted of a glass disk mounted on a
See also:horizontal axis F (fig . 6) which could be made to rotate at a considerable
See also:speed by a multiplying
See also:gear, part of which is seen at X . Close behind this disk was fixed another vertical disk of glass in which were cut two windows B, B . On the side of the fixed disk next the rotating disk were pasted two sectors of paper A, A, with short blunt points attached to them which projected out into the windows on the side away from the rotating disk .
On the other side of the rotating disk were placed two metal combs C, C, which consisted of sharp points set in metal rods and were each connected to one of a pair of discharge balls E, D, the distance between which could be varied . To start the machine the balls were brought in contact, one of the paper armatures electrified, say, with positive electricity, and the disk set inmotion . Thereupon very shortly a hissing sound was heard and the machine became harder to turn as if the disk were moving through a resisting
See also:medium . After that the discharge balls might be separated a little and a continuous series of sparks or brush discharges would take place between them . If two Leyden jars L, L were hung upon the conductors which supported the combs, with their
See also:outer coatings put in connexion with one another by M, a series of strong spark discharges passed between the discharge balls . The action of the machine is as follows: Suppose one paper armature to be charged positively, it acts by induction on the right hand
See also:comb, causing negative electricity to issue from the comb points upon the glass revolving disk; at the same time the positive electricity passes through the closed discharge circuit to the left comb and issues from its teeth upon the part of the glass disk at the opposite end of the diameter . This positive electricity electrifies the left paper armature by induction, positive electricity issuing from the blunt point upon the side farthest from the rotating disk . The charges thus deposited on the glass disk are carried
See also:round so that the upper half is electrified negatively on both sides and the
See also:lower half positively on both sides, the sign of the electrification being reversed as the disk passes between the combs and the armature by discharges issuing from them respectively . If it were not for leakage in various ways, the electrification would go on every-where increasing, but in practice a stationary state is soon attained . Holtz's machine is very uncertain in its action in a moist
See also:climate, and has generally to be enclosed in a chamber in which the air is kept artificially dry . Robert Voss, a Berlin instrument maker, in 188o devised a form of machine in which he claimed that the principles of Toepler and Holtz were combined . On a rotating glass or ebonite disk were placed carriers of tin-foil or metal buttons m Voss's achine .
against which neutralizing brushes touched . This armature plate revolved in front of a field plate carrying two pieces of tin-foil backed up by larger pieces of varnished paper . The studs on the armature plate were charged inductively by being connected for a moment by a neutralizing wire as they passed in front of the field plates, and then gave up their charges partly to renew the field charges and partly to collecting combs connected to discharge balls . In generaldesign and construction, the manner of moving the rotating plate and in the use of the two Leyden jars in connexion with the discharge balls, Voss borrowed his ideas from Holtz . All the above described machines, however, have been thrown into the shade by the invention of a greatly improved type of influence machine first constructed by
See also:James Wimshurst about 1878 . Two glass disks are mounted on two shafts win's-in such a manner that, by means of two belts and pulleys burst machine . worked from a winch shaft, the disks can be rotated rapidly in opposite directions close to each other (fig . 7) . These glass disks carry on them a certain number (not less than 16 or 2o) tin-foil carriers which may or may not have brass buttons upon them . The glass plates are well varnished, and the carriers are placed on the outer sides of the two glass plates . As therefore the disks revolve, these carriers travel in opposite directions, coming at intervals in opposition to each other . Each upright bearing carrying the shafts of the revolving disks also carries a neutralizing conductor or wire ending in a little brush of gilt
See also:thread .
The neutralizing conductors for each disk are placed at right angles to each other . In addition there are collecting combs which occupy an intermediate position and have sharp points projecting inwards, and coming near to but not touching the carriers . These combs on opposite sides are connected respectively to the inner coatings of two Leyden jars whose outer coatings are in connexion with one another . The operation of the machine is as follows: Let us suppose that one of the studs on the back plate is positively electrified and one at the opposite end of a diameter is negatively electrified, and that at that moment two corresponding studs on the front plate passing opposite to these back studs are momentarily connected together by the neutralizing wire belonging to the front plate . The positive
See also:stud on the back plate will act inductively on the front stud and charge it negatively, and similarly for the other stud, and as the rotation continues these charged studs will pass round and give up most of their charge through the combs to the Leyden jars . The moment, however, a pair of studs on the front plate are charged, they act as field plates to studs on the back plate which are passing at the moment, provided these last are connected by the back neutralizing wire . After a few revolutions of the disks half the studs on the front plate at any moment are charged negatively and half positively and the same on the back plate, the neutralizing wires forming the boundary between the positively and negatively charged studs . The
See also:diagram in fig . 8, taken by permission from S . P . Thompson's paper (loc. cit.), represents a view of the distribution of these charges on the front and back plates respectively . It will be Holtz machine .
seen that each stud is in turn both a field plate and a carrier having a charge induced on it, and then passing on in turn induces further charges on other studs . Wimshurst constructed numerous very powerful machines of this type, some of them with multiple plates, which operate in almost any climate, and rarely fail to charge themselves and deliver a torrent of sparks between the dis-11 LI charge balls whenever the winch is t turned . He also devised an alternating current electrical machine in which the discharge balls were alternately positive and negative . Large Wimshurst multiple plate influence machines are often used instead of induction coils for ex-citingRontgen ray tubes in medical work . They give very steady
See also:illumination on fluorescent screens . In 1900 it was found by F . Tudsbury that if an influence machine is enclosed in a metallic chamber containing compressed air, or better,
See also:carbon dioxide, the insulating properties of compressed gases enable a greatly improved effect to be obtained owing to the diminution of the leakage across the plates and from the supports . Hence sparks can be obtained of more than
See also:double the length at ordinary atmospheric pressure . In one case a machine with plates 8 in. in diameter which could give sparks 2.5 in. at ordinary pressure gave sparks of 5, 7, and 8 in. as the pressure was raised to 15, 30 and 45 It above the normal atmosphere . The action of
See also:Lord Kelvin's replenisher (fig . 9) used by him in connexion with his electrometers for maintaining their charge, closely resembles that of Belli's doubler and will be understood from fig . 9 .
Lord Kelvin also devised an influence machine, commonly called a "
See also:mill," for electrifying the
See also:ink in connexion with his siphon recorder . It was an electrostatic and electromagnetic machine combined, driven by an electric current and producing in turn electrostatic charges of electricity . C, C, Metal carriers, fixed to a, a, Receiving springs . ebonite
See also:arm. n, n, Connecting springs or F, F, Brass field-plates or
See also:con- neutralizing brushes . ductors . In connexion with this subject mention must also be made of the
See also:water dropping influence machine of the same inventor.' The action and efficiency of influence machines have been investigated by F . Rossetti, A . Righi and F . W . G . Kohlrausch . The electromotive force is practically
See also:constant no
See also:matter what the velocity of the disks, but according to some observers the
See also:internal resistance decreases as the velocity increases .
Kohlrausch, using a Holtz machine with a plate 16 in. in diameter, found that the current given by it could only electrolyse acidulated water in 40
See also:hours sufficient to liberate one cubic centimetre of mixed gases . E . E . N . Mascart, A . Roiti, and E . Bouchotte have ' See Lord Kelvin, Reprint of Papers on
See also:Electrostatics and Magnet-ism (1872); " Electrophoric Apparatus and Illustrations of Voltaic Theory," p . 319; " On Electric Machines Founded on Induction and Convection," p . 330; " The Reciprocal Electrophorus," P . 337.179 also examined the efficiency and current producing power of influence machines .
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