Fig. 19. EXPERIMENTAL APPARATUS FOR PRODUCING THE VOLTAIC ARC.41 STANDARD ELECTRICAL DICTIONARY.Areometer.An instrument for determining the specific gravity of a fluid. Itconsists of an elongated body ballasted so as to float vertically andprovided with a mark or a scale. It floats deeper in a light than in aheavy liquid. If it carries but one mark weights are added until thatmark is reached, when the weights required give the specific gravity. Orthe scale may give the reading directly based upon the depth to which itsinks. Areometers are often made of glass, ballasted with shot ormercury enclosed in their bottom bulb as shown. They are used inregulating battery solutions, and in watching the charging anddischarging of storage batteries.Fig. 20. AREOMETERFig. 21. BEAD AREOMETERAreometer, Bead.A tube of glass containing beads of different specific gravities. It hasapertures at top and bottom. When immersed in a liquid, the same fillsit, and the specific gravity within certain limits, depending on thefactors of the beads, is shown by the beads which float and those whichsink. It is used for storage batteries and other purposes where acidsand solutions have to be tested.Argyrometry.The method of ascertaining the weight and inferentially the thickness ofan electroplater's deposit of silver. It is done by weighing the articlebefore and after plating.Arm.The four members of a Wheatstone bridge, q. v., are termed its arms.Referring to the diagram of a bridge, P, Q, R, S, are the arms.Fig. 22. DIAGRAM OF WHEATSTONE'S BRIDGE.Armature.(a.) A mass or piece of iron or steel, or a collection of pieces of irondesigned to be acted on by a magnet. While nickel or cobalt might beused, they rarely or never are except in experimental apparatus. Thearmature of a permanent horse shoe magnet is simply a little bar of softiron. When the magnet is not in use it is kept in contact with the poleswith the idea of retaining its magnetism. It is then said to be used asa keeper. A bar magnet does not generally have an armature. The armatureis also used to exhibit the attraction of the magnet.Sometimes an armature is made of steel and is permanently magnetized.Such an armature, termed a polarized armature, is repelled when its likepoles are opposed to like poles of the magnet and otherwise is attractedwith force due to the sums of the magnetism. If the magnet issufficiently powerful depolarization of the armature may ensue when likepoles are opposed to like poles. Polarized armatures are used in variousappliances, magneto generators, telegraphic instruments and others.(b) In a dynamo or Motor the mass of laminated iron or of wire whichcarries the coils of insulated wires which are caused to rotate in thefield of force of the field magnets in order to establish and maintainpotential difference with its accompanying current, or which rotatesunder the effects of a current in a motor. (See Dynamo ElectricGenerator.)The work of the armature core is twofold. It acts as a portion of themagnetic circuit, conducting the lines of force, and by virtue of itshigh permeability or multiplying power concentrating a number of thelines of force through its own substance. To enable it to act withefficiency in this direction it should be made of iron of the highestpermeability, and should approach as closely as possible to the armaturecores consistent with leaving space for the wire winding. It next actsas a support for the wires which are to be swept through the field offorce. Thus it acts both to establish a strong field and then acts as acarrier for the wires which are to be cut by the wires in question. Inconnection with this subject the different definitions under Armature,Dynamo, Commutator, Induction and similar topics may be consulted.(c) See Armature of Influence Machine.(d) See Armature of Leyden Jar or Static Condenser.42 STANDARD ELECTRICAL DICTIONARY.Armature, Bar.An armature in a dynamo or motor whose winding is made up of conductorsin the form of bars, round, rectangular and of other sections. This typeof armature conductor is objectionable as Foucault currents are producedin it. It is found best to laminate or subdivide low resistance armaturewindings.[Transcriber's Note: Foucault currents are also called eddy currents.]Armature, Bipolar.An armature in which two poles are induced by the field. A bipolar fieldmagnet produces a bipolar armature.Armature Bore.The cylindrical space defined by the pole pieces of a dynamo or motorwithin which the armature rotates.Synonym--Armature Chamber.43 STANDARD ELECTRICAL DICTIONARY.Armature, Closed Coil.An armature for a motor or dynamo, the ends of all of whose coils areunited, so as to be in one closed circuit all the way around.Fig. 23. CLOSED COIL GRAMME RING ARMATURE.Armature Coil, or Coils.The insulated wire wound around the core of the armature of an electriccurrent generator or motor.Armature Core.The central mass of iron on which the insulated wire, to be rotated inthe field of an electric current generator or motor, is wound. (SeeDynamo-electric Machine and Motor, Electric.)Armature, Cylinder.An armature of the Gramme ring type, but longer in the axial direction,so that its core resembles a long hollow cylinder, the wire being woundinside and outside as in the Gramme ring. (See Gramme Ring.)Armature, Disc.(a) An armature of a dynamo electric machine or motor in which the coilsare wound so as to be flat and are carried on the face of a disc formingthe core or part of the core of the armature. S. P. Thompson treats itas a modified drum armature extended radially, the outer peripherycorresponding to the back end of the drum. The poles of the field aregenerally placed to face the side or sides of the disc.(b) Another type of disc armature has its wire wound on bobbins arrangedaround the periphery of a disc.In disc armatures there is often no iron core, their thinness enablingthis to be dispensed with.44 STANDARD ELECTRICAL DICTIONARY.Fig. 24. DISC ARMATURE OF FRITSCHE MACHINE.Fig. 25. PLAN OF WINDING PACINOTTI'S DISC ARMATURE.Armature, Discoidal Ring.In a dynamo an armature of the shape of a ring of considerable radialdepth of section as compared to its axial depth. It is generally made ofiron ribbon or thin band wound to the proper size.Synonym--Flat Ring Armature.45 STANDARD ELECTRICAL DICTIONARY.Armature, Drum.An armature for a dynamo or motor, consisting of a cylinder of ironpreferably made up of discs insulated from each other by thin shellackedpaper, or simply by their oxidized surfaces, and wound with wireparallel to the axis where it lies on the cylindrical periphery andcrossing the heads approximately parallel to the diameter. It operatespractically on the same principle as a Gramme Ring Armature. (See GrammeRing.)Synonym--Cylindrical Armature.Armature Factor.The number of conductors on an armature, counted or enumerated allaround its external periphery.Armature, Hinged.An armature pivoted to the end of one of the legs of an electro-magnetso as to be free to swing and bring its other end down upon the otherpole.Fig. 26. HINGED ARMATURES OF CLUB-FOOT ELECTRO MAGNETS.Armature, Hole.An armature whose core is perforated to secure cooling.Synonym--perforated Armature.Armature, Intensity.An armature wound for high electro-motive force. A term little used atthe present time.Armature Interference.A limit to the ampere turns permissible on a given armature is found inthe increase of cross magnetizing effect, q. v., the increased leadnecessitated, and the growth of the demagnetizing power. All suchperturbing effects are sometimes expressed as armature interference.46 STANDARD ELECTRICAL DICTIONARY.Armature, Load of.The circumflux, q. v., of the armature, or the ampere turns of the same.The maximum load which can be carried by an armature without sparking isdirectly proportional to the radial depth of core and to the length ofthe gap, and inversely proportional to the breadth of the polar span.Armature, Multipolar.An armature in which a number of poles greater than two is determined bythe field. A multipolar field is employed for its production.Armature, Neutral.An armature of a magnet or telegraph relay which is not polarized ormagnetized.Synonym--Non-polarized Armature--Neutral Relay Armature.Armature of Influence Machine.Pieces of paper pasted on the stationary plate of an electric machine ofthe Holtz type.Armature of Leyden Jar or Static Condenser.The inner and outer tin-foil coatings of a Leyden jar or othercondenser.Armature, Open Coil.An armature of a dynamo or motor on which the coils are not joined inone closed circuit, but have their ends or some of them separated, andconnected each to its own commutator bar or each set to their own bar.Fig. 27. OPEN COIL RING ARMATURE.47 STANDARD ELECTRICAL DICTIONARY.Armature, Pivoted.An armature for an electro-magnet mounted on a pivot, which is at rightangles to the yoke or parallel with the legs of the magnet, so as to befree to rotate. When the magnet is excited the armature is drawn intoline or approximately so with its base or yoke. The system is used insome telegraph apparatus.Armature Pockets.Spaces or recesses in armatures provided for the reception of the coils.Armature, Polarized.An armature made of steel or having a steel core to which permanentmagnetism has been imparted. Such are used in some forms of magnetocurrent generators, and in telegraphic instruments. (See Relay,Polarized.)Armature, Pole.An armature having coils wound on separate poles projecting radially allaround the periphery of its central hub or disc, or projectinginternally from a ring-like frame, their ends facing the field magnet.Synonym--Radial Armature.Armature, Quantity.An armature of a dynamo or motor wound for current of large quantity.The term is now but little used.Armature-Reactions.When an armature is running in an active dynamo a series ofreactions is established, the more important of which are:I. A tendency to cross-magnetize the armature.II. A tendency to spark at the brushes.III. A tendency for the armature current to demagnetize on account ofthe lead which has to be given to the brushes.IV. Variations in the neutral points as more or less current is takenfrom the machine.V. Heating of armature, both core and conductors, and of pole pieces,which heating is due to Foucault currents.Armature, Revolving, Page's.An early form of motor. The field is produced by a permanent magnet.Above its poles is a soft iron armature wound with a coil of insulatedwire. A two-part commutator with contact springs conveys the current tothe coil. The whole is so arranged that the polarity of the armature, asinduced by the coil, through which a current is passed, is reversed asits ends sweep by the poles of the magnet. Then it is repelled from thepoles and swings through 180° to have its polarity reversed and to gothrough the next 180°, and so on. Thus it rotates at a very high rate ofspeed.In the cut showing the elevation A, B, is the armature; f, g, thesprings or brushes; h, the commutator with its sections o, i. In thesection of the commutator W, W, designate the springs or brushes, A, thevertical spindle carrying the armature and commutator, and S, S, thecommutator sections.48 STANDARD ELECTRICAL DICTIONARY.Fig. 28. PAGE'S REVOLVING ARMATURE.Fig. 29. SECTION OF COMMUTATOR OF PAGE'S REVOLVING ARMATURE.W, W, Brushes; A, Spindle; S, S, Armature Segments.Armature, Ring.An armature whose core is in the shape of a ring, as the Gramme RingArmature. (See Figs. 23 & 27.)49 STANDARD ELECTRICAL DICTIONARY.Armature, Rolling.(a) An armature for a permanent horseshoe magnet consisting of astraight cylinder of soft iron on which a heavy wheel is mounted. Whenthe legs of the magnet are inclined downward and the bar is laid acrossthem it rolls down to the poles, across their ends, and back up theunder side. It is merely a magnetic toy or illustrative experiment.Synonym--Wheel Armature.(b) Another form consists of little bars of iron with brass discsattached to the ends. On placing two of these together and bringing thepoles of a magnet near them, as shown, they become magnetized with likepolarity by induction and repel each other, rolling away in oppositedirections.Fig. 30. ROLLING OR WHEEL ARMATURE.Fig. 31. ROLLING ARMATURES.Armature, Shuttle.The original Siemens' armature, now discarded. The core was long andnarrow, and its cross section was nearly of the section of an H. Thegrooves were wound full of wire, so that the whole formed almost aperfect cylinder, long and narrow comparatively. (See Winding Shuttle.)Synonym--Siemens' Old Armature--Girder Armature--H Armature.Fig. 32. SHUTTLE OR H ARMATURE.Armature, Spherical.An armature of a dynamo which is wound on a spherical core, so as to bealmost a sphere. It is employed in the Thomson-Houston dynamo, beingenclosed in a cavity nearly fitting it, formed by the pole pieces.Armature, Stranded Conductor.A substitute for bar-armatures in which stranded copper wire conductorsare substituted for the solid bar conductors, to avoid Foucaultcurrents. (See Armature, Bar.)50 STANDARD ELECTRICAL DICTIONARY.Armature, Unipolar.An armature of a unipolar dynamo. (See Dynamo Unipolar.)Armor of Cable.The metal covering, often of heavy wire, surrounding a telegraph orelectric cable subjected to severe usage, as in submarine cables.Synonym--Armature of Cable.Arm, Rocker.An arm extending from a rocker of a dynamo or motor, to which arm one ofthe brushes is attached. (See Rocker.) Ordinarily there are two arms,one for each brush.Articulate Speech.Speech involving the sounds of words. It is a definition which hasacquired importance in the Bell telephone litigations, one contention,concerning the Bell telephone patent, holding that the patentee did notintend his telephone to transmit articulations, but only sound andmusic.Astatic. adj.Having no magnetic directive tendency due to the earth's magnetism.Examples are given under Astatic Needle; Circuit, Astatic; andGalvanometer Astatic.Fig. 33. NOBILI'S PAIR.FIG. 34. VERTICAL PAIR ASTATIC COMBINATION.Astatic Needle.A combination of two magnetic needles so adjusted as tohave as slight directive tendency as possible. Such a pair of needleswhen poised or suspended will hardly tend to turn more to one point ofthe compass than another. The combination is generally made up of twoneedles arranged one above the other, with their poles in oppositedirections. This combination is usually called Nobili's pair. If ofequal strength and with parallel magnetic axes of equal length theywould be astatic. In practice this is very rarely the case. A resultantaxis is generally to be found which may even be at right angles to thelong axis of the magnets, causing them to point east and west. Such acompound needle requires very little force to turn it one way or theother. If one of the needles is placed within a coil of insulated wire afeeble current will act almost as strongly to deflect the system as ifthe other was absent, and the deflection will only be resisted by theslight directive tendency of the pair of needles. This is the basis ofconstruction of the astatic galvanometer. Sometimes coils wound inopposite directions and connected in series, or one following the other,surround both needles, thus producing a still greater effect ofdeflection.Other astatic needles are shown in the cuts below. [Figures 33 to 35.]51 STANDARD ELECTRICAL DICTIONARY.FIG. 35. SIMPLE ASTATIC NEEDLE.Asymptote.A line continuously approached by a curve, but which the curve, owing toits construction or nature of curvature, can never touch, be tangent to,or intersect.Atmosphere.(a) A term applied to the atmospheric pressure as a practical unit ofpressure equal to 15 lbs. to the square inch as generally taken. It isreally about 14.7 lbs. per square inch, or 1,033 grams per squarecentimeter.(b) Air, q. v.Atmosphere Residual.The atmosphere left in a vessel after exhaustion. The term may beapplied to any gas. In an incandescent lamp after flashing the residualatmosphere consists of hydro-carbons.Atmospheric Electricity.The electricity of the atmosphere, rarely absent, but often changing inamount and sign. Benjamin Franklin, in a memoir published in 1749,indicated the method of drawing electricity from the clouds by pointedconductors. In June, 1752, he flew a kite and by its moistened cord drewan electric spark from the clouds, confirming his hypothesis thatlightning was identical with the disruptive discharge of electricity. Toobserve electricity in fine weather a gold-leaf or other electroscopemay be connected to the end of a long pointed insulated conductor. Theelectricity during thunderstorms can be shown by a similar arrangement,or burning alcohol or tinder gives an ascending current of warm air thatacts as a conductor. Quite elaborate apparatus for observing andrecording it have been devised. Atmospheric electricity is usuallypositive, but occasionally negative. When the sky is cloudless it isalways positive, increasing with the elevation and isolation of theplace. In houses, streets, and under trees no positive electricity canbe found. In the Isle of Arran, Scotland, a rise of 24 to 48 volts perfoot of increase in elevation was found by Sir William Thomson. Atsunrise the electrification of the air is feeble, it increases towardsnoon and decreases again to reach a second maximum a few hours aftersunset. It increases with the barometric pressure generally. In cloudyweather it is sometimes negative and the sign often changes severaltimes in the same day. In a thunderstorm the changes in sign andpotential are very rapid. The cause of atmospheric electricity is farfrom clear. Tait attributes it to a contact effect between air and watervapor, Solmeke to friction of water vesicles against ice particles inthe upper atmosphere, he first showing that the two may coexist. Thecause of the enormous increase of potential producing lightning isattributed to the decreased capacity due to the change of water fromcloud vesicles to drops, thus diminishing the electrostatic capacity ofthe water in question. (See Lightning.)52 STANDARD ELECTRICAL DICTIONARY.Atom.The ultimate particle or division of an elementary substance; thesmallest part that can exist in combination, and one which cannot existalone. An elementary substance is composed of molecules just as truly asa compound one, but the atoms in the molecule of an elementary substanceare all precisely alike. Hence atoms are the units of chemistry, theyhave to do with combinations, but the physical unit, the smallestparticle of matter that can have an independent existence, is themolecule. The two are often confounded, especially by writers of a fewyears ago, so that by "atom" the molecule is often meant. There isnothing to be said of their size or mass. All such calculations refer tothe molecule, q. v., often spoken of and called the atom.[Transcriber's note: Yet to be discovered: electron--1897 (5 years),proton--1920 (28 years), neutron--1932 (30 years), quark--1961 (69 years).]Atomic Attraction.The attraction of atoms for each other, in virtue of which they combineinto molecules; chemical affinity, q. v., treats principally of this,although molecular attraction also plays a part in it.Atomic Heat.The product of the atomic weight of a substance by its specific heat.This product is approximately the same, 6.4; this approximation is soclose that it is of use in determining the valency and atomic weights ofsubstances. The atomic weight of a substance therefore represents theapproximate number of gram-calories required to raise one gram-atom, q.v., of such substance through 1° C. (1.8° F.)Atomicity.The quantivalence or valency of the atoms; the number of combinationbonds, or bonds of affinity, possessed by the atoms of any substance.Thus two atoms of hydrogen combine with one atom of oxygen, and three ofoxygen with one of sulphur, forming saturated compounds. Therefore,taking hydrogen as of single atomicity or a monad, oxygen is of doubleatomicity or a dyad, and sulphur is of six-fold atomicity, or a hexad.The elements are thus classified into seven orders of atomicities, thus:1, Monads or Univalent elements, Hydrogen, etc.2, Dyads or Bivalent " Oxygen, etc.3, Triads or Trivalent " Nitrogen, etc.4, Tetrads or Quadrivalent " Lead, etc.5, Pentads or Quinquivalent " Phosphorous, etc.6, Hexads or Sexivalent " Chromium, etc.7, Heptads or Septivalent " Chromium, etc.The same element often possesses several atomicities. Barium isgenerally a dyad, sometimes a tetrad; nitrogen acts as a monad, dyad,triad, tetrad and pentad. The familiar electrolysis of water, giving twovolumes of hydrogen to one of oxygen, is one of the illustrations of thetheory indicating that two atoms of hydrogen are combined with one ofoxygen.53 STANDARD ELECTRICAL DICTIONARY.Atomic Weight.The number expressing the relative weight of the atom of any substance,that of hydrogen being generally taken as unity. This is the universalsystem, although any other element might be taken as the basis of thesystem. The whole theory of atomic weights is based on theindivisibility of the atom and on the theory of atomicity, q. v. (SeeEquivalents.)[Transcriber's note: The standard is now the isotope carbon-12 asexactly 12.]Attraction.The tendency to approach and adhere or cohere, shown by all forms ofmatter. It includes gravitation, cohesion, adhesion, chemical affinityand other forms, and is opposed by repulsion, and is sometimes overcomeby it, although it may be assumed to be always present. See thedifferent kinds of attractions under their titles: Atomic Attraction,Electro-magnetic Attraction and Repulsion, Electro Static Attraction andRepulsion, Electro-dynamic Attraction and Repulsion; Magnetic Attractionand Repulsion; Molar Attraction.Audiometer.An apparatus for obtaining a balance of induction from two coils actingupon a third. The third is placed between the other two and is free tomove towards either. A scale is provided to show the extent of itsmovement. A varying or interrupted current being passed through the twoouter coils, the preponderating current will produce the most inductionif the central coil is equidistant. It can always be moved to such apoint that there will be no inductive effect, one counteracting theother. Thus its position measures the relative induction. A telephone isin circuit with the intermediate coil and is used to determine when itsposition is such that no current is induced in it. It is sometimes usedas a direct test of hearing. (See Hughes' Induction Balance.)Synonym--Acoutemeter.Aura, Electrical.The blast of air produced at highly electrified points.Aurora.A luminous display seen in the northern heavens in the northernhemisphere, where it is the Aurora Borealis, and seen in the southernheavens in the southern hemisphere, where it is called Aurora Australis,or indifferently for either, the Aurora Polaris. It takes the form ofpale luminous bands, rays and curtains varying in color. Near the polesthey are very numerous. A French commission observed 150 auroras in 200days. Their height is variously estimated at from 90 to 460 miles; theyare most frequent at the equinoxes and least so at the solstices. Thereis a secular variation also, they attain a maximum of occurrence every11 years together with sun spots, with a minimum 5 or 6 years after themaximum. There is also a period of 60 years, coincident withdisturbances in the earth's magnetism. Various attempts have been madeto account for them. They have a constant direction of arc withreference to the magnetic meridian (q. v.) and act upon the magneticneedle; in high latitudes they affect telegraph circuits violently.There is a strong probability that they represent electric currents ordischarges. De la Rive considers them due to electric discharges betweenthe earth and atmosphere, which electricities are separated by theaction of the sun in equatorial regions. According to Balfour Stewart,auroras and earth currents.(q. v.) may be regarded as secondary currentsdue to small but rapid changes in the earth's magnetism. The subject isvery obscure. Stewart treats the earth as representing the magnetic coreof an induction coil, the lower air is the dielectric, and the upperrarefied and therefore conducting atmosphere is the secondary coil. Thismakes the aurora a phenomenon of induced currents. Then the sun may beregarded as the instigator of the primary changes in the earth's linesof force representing the primary of an induction coil.[Transcriber's note: Solar wind, streams of electrons and protons,interacting with the earth's magnetic field causes aurora. Neitherelectrons (1897) nor protons (1920) were known in 1892. The Sovietsatellite Luna first measured the solar wind in 1959. Even todayincreased understanding of solar and auroral phenomenon continues.]54 STANDARD ELECTRICAL DICTIONARY.Austral Pole.The north pole of the magnet is thus called sometimes in France; theaustral pole of a magnet is the one which points towards the north polarregions As unlike magnetic poles attract each other, it is but rationalto call the north-seeking pole of the magnet the south or Austral Pole.In the same nomenclature the south pole of a magnet, or thesouth-seeking pole, is called the Boreal Pole.A. W. G.Abbreviation for American Wire Gauge, q. v.Axis, Electric.The electric axis of a pyroelectric crystal, such as a tourmalinecrystal; the line connecting the points of greatest pyroelectricexcitability.Axis of Abscissa.In a system of rectilinear, or right angle co-ordinates, the horizontalaxis. (See Co-ordinates.)Synonym--Axis of X.Axis of Ordinates.In a system of rectilinear right angle co-ordinates, the vertical axis.(See Co-ordinates.)Synonym--Axis of Y.Azimuth.The angle between the plane of the meridian and the plane of an azimuthcircle, q. v.Azimuth Circle.A great circle, whose plane passes through the zenith or point of theheavens directly overhead; any great circle in whose plane the verticalat the point of observation is included.Each celestial body has or determines an azimuth circle.