Fig. 241. METHVEN SCREEN
376 STANDARD ELECTRICAL DICTIONARY.Mho.A unit of conductance, not in very general use. It is the reciprocal ofthe ohm. Thus a resistance of ten ohms is a conductance of one-tenthmho.Mica.A natural mineral, a silicate of several oxides; muscovite. It is usedas an insulator and dielectric. Its resistance per centimeter cube afterseveral minutes electrification at 20º C. (68º F.) is 8.4E13 ohms(Ayrton). Its specific inductive capacity is 5, air being taken at 1.Mica, Moulded.An insulating material, whose body is made of mica pulverized andcemented together with heat and pressure and some suitable cement.Shellac is often used as the cement.Micro.A prefix meaning "one-millionth of;" a micro-farad is one-millionth of afarad.Micrometer.An instrument for measuring small distances or small differences. Itgenerally is based upon an accurate screw which may have a worm wheelfor head, actuated by a worm or helix with graduated head, so thatexceedingly small advances of the screw may be produced. The pitch ofthe screw being known its actual advance is known.Micrometer, Arc.A micrometer for measuring the distance between voltaic arc electrodes.Micron.A unit of length. It is one-millionth of a meter or fourone-hundred-thousandths of an inch.377 STANDARD ELECTRICAL DICTIONARY.Microphone.An apparatus which includes a contact of variable resistance; suchresistance can be varied in amount by slight vibrations, such as thoseproduced by sound waves. The apparatus in use forms part of a circuitincluding a telephone and current generator. As the contact is variedthe resistance of the circuit and consequently the current intensitychanges and sounds are emitted by the telephone corresponding to suchchanges. If the microphone is spoken to, the telephone will emitcorresponding sounds, reproducing the voice.It has been found in practice that carbon gives the best microphonecontact. One of the simplest and earliest forms is shown in the cut. Ashort rod or pencil of carbon, A, such as used in batteries, issharpened at the ends and rests loosely in a vertical position betweentwo blocks of carbon, C C, in each of which a hole is drilled to receiveone of the points. The blocks are carried on a standard and base D. Theblocks are connected with two terminals x, y, of a circuit, including atelephone and battery. There are two contacts to be disturbed.If delicately adjusted a fly walking over the base-board will disturbthe contacts enough to produce sounds in the telephone. These sounds arepossibly not due only to sound waves, but in part to absolute mechanicaldisturbances.The various forms of telephone transmitter are generally microphones.Fig. 242. MICROPHONE.Microphone Relay.A combined microphone and telephone. A microphone is placed close to thediaphragm of a telephone. The slight sound waves emitted by thetelephone affect the microphone and are repeated in its circuit. Themicrophone circuit includes a local battery and telephone.Microtasimeter.An apparatus for indicating minute changes in temperature or atmosphericmoisture.378 STANDARD ELECTRICAL DICTIONARY.A button of compressed lampblack is placed in series with a battery andgalvanometer. A strip of some substance, affected in its length eitherby heat or by moisture, is held pressing against the button. A slightchange in length of the strip varies the resistance of the button andhence affects the galvanometer. In this way exceedingly slight changesin heat or moisture may be indicated.For heat indications vulcanite may be used. The heat of the hand heldnear it is enough to affect the galvanometer. For moisture a slip ofgelatine is used. The moisture of a damp slip of paper two or threeinches distant is sufficient to affect the galvanometer.In the cut, Fig. 2, shows the general distribution of the apparatus incircuit with a battery and galvanometer. C is the base of the apparatus,from which the standard, B, with adjusting screw, H, rises. The strip ofvulcanite is held between I and G. Within D is the carbon button (F inFig. 3) pressed between G and E; A is a standard to carry the parts lastdescribed. In Fig. I it is shown as part of a Wheatstone bridge, a, band c being resistance coils; l the tasimeter, and g the galvanometer.If a balance is secured, any variation in the resistance of thetasimeter will disturb the galvanometer.Synonym--Tasimeter.Fig. 243. MICROTASIMETER.379 STANDARD ELECTRICAL DICTIONARY.Mil.A unit of length; one-thousandth part of a lineal inch.It is equal to.025399 millimeter;.000083 foot;.001000 inch.Mil, Circular.A unit of area; employed in designating the cross-sectional area ofwires and other circular conductors.It is equal to.78540 square mil;.000507 square millimeter;7.8E-7 (.00000078) square inch.If the diameter of a wire is given in mils, the square of its diametergives its cross-sectional area in circular mils.Mil-foot.A unit of resistance. (See Resistance, Mil-foot, Unit of).Mil, Square.A unit of area; one-millionth of a square inch.It is equal to.000645 square millimeter;1.2733 circular mil;.000001 square inch.Milli.A prefix; one-thousandth. Thus a milligram is one-thousandth of a gram;a millimeter is one thousandth of a meter.Milligram.A unit of weight ; one-thousandth of a gram, q. v.It is equal to.015432 grain;.000032 troy ounce.Millimeter.A unit of length; one-thousandth of a meter.It is equal to39.37079 mils;.03937 inch;.00109 yard.380 STANDARD ELECTRICAL DICTIONARY.Milli-oerstedt.A proposed but not adopted unit of current; one-thousandth of anoerstedt. It is equal to one-thousandth of an ampere.[Transcriber's note: oersted: 1. CGS unit of magnetic intensity, equalto the magnetic pole of unit strength when undergoing a force of onedyne in a vacuum. 2. Formerly, the unit of magnetic reluctance equal tothe reluctance of a centimeter cube of vacuum between parallelsurfaces.]mm.Contraction for millimeters.Molar.Referring to phenomena of mass as gravitation. Mechanicsgenerally treats of molar laws and phenomena.[Transcriber's note: Molar, or mole, often refers to a quantity of asubstance containing an Avagadro number (6.02E23) of molecules--a weightequal to the atomic weight of the molecule. For example, a mole ofhydrogen (H2) is 2.015 grams; sodium chloride (NaCl) is 58.443 grams.]Molar Attraction.The attraction of mass for mass; gravitation. Synonyms--MassAttraction--Gravitation.Molecular Affinity.The attraction of molecules for each other as seen in the formation ofdouble salts, the combining of water of crystallization with a salt, andin other cases; a phase of affinity belonging to chemistry, althoughoutside of true atomic attraction.Molecular Attraction.The attraction of molecules; physical affinity. Cohesion, the attractionof similar molecules for each other, and adhesion, that of dissimilarmolecules, are examples. This should be distinguished from molecularaffinity, a phase of chemical force.Molecular Bombardment.When a gas contained in a vessel is brought to a sufficient state ofrarefaction the molecules cease to be subject to the laws of diffusion,but move back and forth in straight lines from side to side of thevessel. Their courses can be affected by electric discharge, which cancause them to all impinge upon one of the electrodes, the positive one,producing luminous effects. The path, if referred to the negativeelectrode, tends to be normal to its surface, so that the resultant pathmay be curved, as the stream of molecules go to the positive electrode.The fanciful name of molecular bombardment is given to the phenomenon,the luminous effect being attributed to the impinging of the moleculesagainst the positive electrode as they are projected from the positive.The course of the molecules is comparable to the stream of carbonparticles from the positive to the negative electrode in an arc lamp.(See Matter, Radiant.)Molecular Chain.The theoretical rows of molecules supposed to extend from anode tocathode in an electrolytic cell (see Cell, Electric--Grothüss'Hypothesis) are called molecular chains.381 STANDARD ELECTRICAL DICTIONARY.Molecular Rigidity.The tendency of the molecules of a mass to retain their position in amass in resistance to polarizing or depolarizing force, the first beingthe effect of a magnetic field. It is the theoretical cause of coerciveforce, q. v., and of residual magnetism. (See Magnetism, Residual.)Molecule.The smallest particle of matter that can exist alone. It is made up ofatoms, but an atom can never exist alone, but only, with one or twopossible exceptions, combined with one or more other atoms as amolecule. The molecules under present conditions are not in constantcontact with each other, but are perpetually vibrating through paths, insolids probably in defined paths, in liquids and gases in perpetuallynew paths. The molecules collide with each other and rebound. Thismotion is the kinetic motion termed heat. At the absolute zero--minus273.72° C. (-460.7° F.) the molecules would be in contact and quiescent.In the gaseous state the molecules of most substances occupy the samevolume; those of a few elements occupy one-half and of others twice thenormal volume. The mean free path of the molecule of hydrogen is about1/20,000 mm. (1/508,000 inch) (Maxwell) or twice this length (Crookes),the collisions in hydrogen are about 17,750 millions per second; thediameter is about 8/10,000,000 mm. (8/254,000,000 inch) ; A particle ofmatter 1/4,000 mm. (1/102,000 inch) contains, it is supposed, about40,000 molecules. The results of different authorities vary so widely asto deprive the subject of much of its interest. A Sprengel pump, such asused for exhausting Geissler tubes, or incandescent lamp bulbs, mayleave only one hundred-millionth (1/100,000,000,) of an atmospherepresent, giving the molecules a capability of an average free path ofvibration 33 feet long.Moment.When a force is applied so as to tend to produce rotation around apoint, the product of the force by the shortest distance from the pointof rotation to the extension of the line of the force. Such distance isthe perpendicular to the extension of the line through the point ofrotation.Mordey Effect.A phenomenon observed in dynamo armatures. At full loads the hysteresisdecreases. The effect is thus expressed by S. P. Thompson. "When anarmature core is rotated in a strong magnetic field, the magnetizationof the iron is being continually carried through a cycle, but in amanner quite different from that in which it is carried when themagnetizing force is periodically reversed, as in the core of atransformer. Mordey has found the losses by hysteresis to be somewhatsmaller in the former case than in the latter."Morse Receiver.The receiving instrument formerly universally used in the Morse system.It is now but little employed, the sounder having displaced it. Severaltypes were invented.It consists of machinery which carries a reel of paper ribbon arrangedto be fed over a roller by clockwork. A pencil, inking roller, orembossing stylus (for the latter the roller must have a groove) iscarried by an arm with restricted range of vibration just over the paperand roller. The armature of an electro-magnet is attached to the arm.When the magnet is excited the armature is attracted and the markingdevice is pressed on the paper. If the clockwork is in operation themarker will make a line as long as the armature is attracted. Whenreleased no mark will be produced. In this way the dots and dashes ofthe Morse code are made on a ribbon of paper.As an inking arrangement a small roller is carried by the end of thevibrating arm. The embosser, or dry point stylus, was very extensivelyused. The clockwork was generally driven by descending weights.Synonym--Morse Recorder.382 STANDARD ELECTRICAL DICTIONARY.Mortar, Electric.An electric toy which may have various modifications. In the cut awooden mortar with recess to receive a ball is shown. Two wires enterthe base but do not touch. On placing the ball in position and passing aspark from a Leyden jar across the interval between the wires, the heatand disturbance are enough to project the ball. Gunpowder may be used,the discharge being passed through a wet string to prolong the spark.Fig. 244. ELECTRIC MORTAR.Motor, Compound or Compound Wound.A motor which has two windings on the field magnets, one in parallelwith that on the armature, the other in series therewith, exactly as ina compound dynamo. (See Dynamo, Compound.)Motor, Differential.A differentially wound motor; with a compound wound field, whose seriescoil and shunt coil are wound in opposition to each other. It isvirtually a compound wound dynamo. (See Dynamo, Compound Wound.)Motor, Electric.A machine or apparatus for converting electric energy into mechanicalkinetic energy. The electric energy is generally of the dynamic orcurrent type, that is to say, of comparatively low potential andcontinuous or virtually continuous flow. Some electrostatic motors have,however, been made, and an influence machine can often be operated as astatic motor.Electric motors of the current type may be divided into twoclasses--direct current and alternating current motors.Direct current motors are generally based on the same lines ofconstruction as dynamos. One of the great discoveries in modernelectricity was that if a current is passed through a dynamo, thearmature will rotate. This fact constitutes the principle of thereversibility of the dynamo.383 STANDARD ELECTRICAL DICTIONARY.Motors built on the dynamo model may be series wound, shunt wound, orcompound wound, or of the magneto type, in the latter case having afixed field irrespective of any current sent through them. The field maybe produced by an electro-magnet separately excited and unaffected bythe current sent through the motor.A current passed through a magneto or motor with separately excitedfield will turn it in the direction opposite to that required to producethe same current from it were it worked as a generator.A current passed through a series wound motor acts exactly as above.Both these facts follow from Lenz's law, q. v.A current passed through a shunt wound motor acts oppositely to theabove. The direction of rotation is the same as that required to producea current of the same direction. This is because the field being inparallel with the armature the motor current goes through the magnetcoils in the direction the reverse of that of the current produced inthe armature when it is used as a dynamo. Hence this also carries outLenz's law.The compound wound motor acts one way or the other according as itsshunt or series winding preponderates. The two may exactly balance eachother, when there will be no motion at all. The series connections of acompound wound dynamo should therefore be reversed, making both seriesand shunt work in unison, if the dynamo is to be used as a motor.The general principles of the electric motor of the dynamo, orcontinuous rotation type, can only be outlined here. The current passingthrough the field magnets polarizes them and creates a field. Enteringthe armature by the brushes and commutators it polarizes its core, butin such a way that the north pole is away from the south pole of thefield magnet, and the same for the south pole. Hence the armaturerotates. As it does this the brushes connect with other commutatorsections, and the poles of the armature are shifted back. This actioncontinues indefinitely.Another class of motors is of the reciprocating type. These are now verylittle used. (See Motor, Reciprocating.)One valuable feature of continuous rotation electric motors is the factthat they absorb energy, to a great extent proportional in amount to thework they have to do. The rotation of the armature in the field of themotor involves the cutting of lines of force by its coils. Thisgenerates an electro-motive force contrary in direction to thatproducing the actuating current. The more rapid the rotation the greateris this counter-electro-motive force. The motor armature naturallyrevolves faster with diminished resistance to the motion of thearmature. This increases the counter-electromotive force, so that lessenergy is absorbed. When the motor is called on to do work, the armaturerotates more slowly, and the counter-electro-motive force diminishes, sothat the machine absorbs more energy. (See Jacobi's Law.)384 STANDARD ELECTRICAL DICTIONARY.Motor Electro-motive Force.The counter-electro-motive force of a motor. (F. J. Sprague.)A motor rotates in virtue of the pull of the field magnet upon the polesof the core of its armature. In responding to this pull the windings ofthe armature cuts lines of force and hence generates acounter-electro-motive force, for which the above term was suggested.Motor-Generator.A combined motor and generator used to lower the potential difference ina portion of a circuit, e. g., that part within a building.A motor-generator is a dynamo whose armature carries two commutators,with two separate windings, one of fine wire of many turns, the other ofcoarse wire of few turns. If the potential of the system is to belowered, the main current is passed through the fine winding. Thiscauses the armature to turn motor-fashion, and a potential difference isgenerated by the rotation of the large coils in the field. Thispotential difference is comparatively low and by properly proportioningthe windings may be lowered to as great a degree as required.The same apparatus may be inverted so as to raise potential difference.It acts for continuous current systems as the induction coil transformerdoes for alternating current systems.Synonym--Continuous Current Transformer.Motor, Multiphase.A motor driven by multiphase currents. It is arranged in general termsfor distribution of the multi phase currents in coils symmetricallyarranged around the circle of the field. These coils are wound on coresof soft iron. A rotating field is thus produced, and a permanent magnetor a polarized armature pivoted in such a field will rotate with thefield, its poles following the poles of the rotatory field.The cut, Fig. 245, illustrates the principles of action of a four phasecurrent motor, connected to a four phase current dynamo or generator.The generator is shown on the left hand of the cut and the motor on theright hand. In the generator the armature N S is supposed to be turnedby power in the direction shown by the arrow. Each one of the pair ofcoils is wound in the reverse sense of the one opposite to it, and thetwo are connected in series with each other, and with a correspondingpair in the motor. The connection can be readily traced by the letters AA', a a' for one set of coils and B B' b b' for the other set.385 STANDARD ELECTRICAL DICTIONARY.For each rotation of the armature two currents, each in oppositedirection, are produced in A A', and the same is the case for B B'.These currents which have an absolutely constant relation of phase, andwhich it will be seen alternate four times for each rotation of thearmature, regulate the polarity of the field of the motor. The resultantof their action is to keep the poles of the field magnet of the motorconstantly traveling around its circle. Hence the armature N S of themotor, seen on the right hand of the cut, tends to travel around alsoits north and south poles, following the south and north poles of therotatory field respectively.Fig. 245. FOUR-PHASE CURRENT GENERATOR AND MOTOR.It is not essential that the armature should be a magnet or polarized.Any mass of soft iron will by induction be polarized and will berotated, although not necessarily synchronously, with the rotatoryfield. Any mass of copper, such as a disc or cylinder, will haveFoucault currents induced in it and will also rotate. The onlycomponents of such currents which are useful in driving the motor arethose which are at right angles to the lines of force and to thedirection of motion. A very good type of armature based on theseconsiderations is a core of soft iron wound with insulated copper wirein one or more closed coils; and so wound as to develop the currents ofproper direction.Such an armature is used in the Tesla alternating current motor. Anefficiency of 85 per cent. has been attained with some of the Teslamotors.Motor, Prime.A machine used for producing mechanical motion against resistance. Itmay operate by converting heat or any other form of kinetic or potentialenergy into mechanical energy of the moving type. A steam-engine and awater-wheel are examples of prime motors.Motor, Reciprocating.The early type of motor depending upon reciprocating motion, such as themotion of a coil in a solenoid. These were based upon the lines of asteam engine, and have been abandoned except for special purposes wherereciprocating motion is especially required, as in the case of rockdrills.386 STANDARD ELECTRICAL DICTIONARY.Fig. 246. RICORDON'S RECIPROCATING MOTOR.In the cut, B is an electro-magnet; A is an armature; E a pole piece.The current enters by the springs, b b, and by commutation is suppliedand cut off alternately, thus maintaining a reciprocating movement ofthe armature and rotation of the fly-wheel.Synonym--Pulsating Motor.Motor, Series.A motor whose winding on the armature is in series with the winding onthe field. It is similar to a series dynamo. (See Dynamo, Series.)Motor, Shunt.A motor whose winding on the armature is in parallel with the winding onthe field magnets. It is similar to a shunt wound dynamo. (See Dynamo,Shunt.)Fig. 247. MULTIPLE ARC CONNECTION.Multiple.A term expressing connection of electric apparatus such as batterycouples, or lamps in parallel with each other. In the ordinaryincandescent lamp circuits the lamps are connected in multiple.Synonym--Multiple Arc.387 STANDARD ELECTRICAL DICTIONARY.Multiple Arc Box.A resistance box arranged so that the coils may be plugged in multipleinstead of in series. Such can be used as a rheostat, as the resistancecan be very gradually changed by putting the coils one by one intoparallel with each other. Thus by adding in parallel with a 10 ohm coila 10,000 ohm coil the resistance is decreased to 9.999001 ohms, and thusthe resistance can be very slowly changed without sudden stops or abruptchanges.[Transcriber's note: The correct value is 9.99001]Multiple Series.Arrangements of electric apparatus in a circuit in a number of series,which minor series are then arranged in parallel. The term may be usedas a noun, as "arranged in multiple-series," or as an adjective, as "amultiple-series circuit."Fig. 248. MULTIPLE SERIES CONNECTION.Multiple Switch Board.A switch board on whose face connecting spring jacks or other devicesare repeated for the same circuits, so that different operators haveeach the entire set of connections repeated on the section of the boardimmediately in front of and within their reach. This multiplication ofthe same set of connections, giving one complete set to each operator,gives the title "multiple" to the type of switch board in question. Thetypical multiple switch board used in telephone exchanges is the bestexample of this construction. The calling annunciators of thesubscribers are distributed along the bottom of the board extending itsfull length. To each operator a given number is assigned, all withinreach of the right or left hand. This gives five or six feet length ofboard to each, and an operator only responds to those subscribers withinhis range. But anyone of his subscribers may want to connect with any ofthe others in the entire central station. Accordingly in front of eachoperator spring jacks are arranged, one for each of the entire set ofsubscribers connected in that office. The operator connects as requiredany of the calling subscribers, who are comparatively few, to any one ofthe large number served by the central station. Thus the entire set ofsubscribers' spring jacks are multiplied over and over again so as togive one set to each operator.388 STANDARD ELECTRICAL DICTIONARY.Multiple Wire Method for Working Electro-magnets.A method for suppressing sparking in working electro-magnetsintermittently. The magnet core is wound with a number (from four totwenty) of separate layers of fine wire. A separate wire is taken foreach layer and all are wound in the same direction, from one end to theother of the space or bobbin without returning. The ends are then joinedso as to bring all the wires in parallel. The effect of this is that asthe coils vary in diameter the time constants of each is different fromthat of the others, the coefficient of self-induction being less, andthe resistance being greater for the coils farthest from the centralaxis. Thus the extra currents run differently in the different coils,and only a comparatively small spark can be produced owing to thedivision of forces thus brought about.Fig. 249. DIAGRAM ILLUSTRATING MULTIPLE WIRE WORKING.Multiplex Telegraphy.Any system of telegraphy transmitting more than four messagessimultaneously over a single wire. Properly it should apply to alltransmitting more than one, but conventionally has the above restrictedmeaning, distinguishing it from duplex and quadruplex telegraphy.Multiplying Power of a Shunt.When a resistance is placed in parallel with a galvanometer on a circuitthe following relation obtains. Let s and g equal the resistances of theshunt and galvanometer respectively, S and G the currents in amperespassing through them, V the potential difference between their commonterminals, and A the whole current in amperes. Then we haveA = ( (s + g ) / s ) * Gand ( (s + g ) / s ) is termed the multiplying power of the shunt, as itis the factor by which the current passing through the galvanometer mustbe multiplied by to produce the total current.Muscular Pile.A species of voltaic battery, often termed Matteueci's pile, made up ofalternate pieces of muscle cut longitudinally and transverselyrespectively. The different pieces represent the elements of a battery,and their difference of potential is naturally possessed by the pieces.Myria.A prefix; one million times. Thus myriavolt means one million volts.[Transcriber's note: Contemporary usage is mega, as in megavolt.]
389 STANDARD ELECTRICAL DICTIONARY.N.(a) Symbol for north pole or north-seeking pole of a magnet.(b) Symbol for the number of lines of force in a magnetic circuit.Nairne's Electrical Machine.The cylinder electrical machine, q.v.Napierian Logarithms.A series of logarithms the base of whose system is 2.72818. They arealso called hyperbolic logarithms.Nascent State.An element just separating from a combination possesses at that timehigher affinities than after separation, and can effect more powerfulchemical changes.It is sometimes attributed to a differential time of existence in theatomic modification, before the freed atoms have united to formmolecules.Natural Currents.A term for earth currents. (See Current, Earth.)Needle.(a) A term applied to a bar magnet poised horizontally upon a verticalpoint, or suspended in a horizontal position by a filament. Thus themagnet in a mariner's compass, which may be a substantial bar magnet, iscalled a magnetic needle.(b) An indicator in general shape like the hand of a clock. (SecAnnunciator, Needle- Telegraph, Needle.)Needle of Oscillation.The magnetic needle poised horizontally, and used for measuring theintensity of the earth's magnetic field, or of an artificial magneticfield, by the method of oscillations. The intensities of the field isinversely as the square of the number of oscillations performed in agiven time.Needle, Telegraphic.The index in needle telegraphy (see Telegraph, Needle), whose motionsindicate the characters it is desired to transmit.Negative Charge.One of the two kinds of electric charges. The other is the positive.By the double fluid hypothesis this is assumed to be a charge of aparticular kind of electricity--negative electricity.By the single fluid hypothesis it is supposed to be caused by theabsence of part of the normal electricity of a surface. The reverse isheld by some theorists.The subject is so purely theoretical that neither of the two hypothesesis accepted as final.[Transcriber's note: Current is a wire is the motion of negativeelectrons. Current in a electrolyte is the motion of positive ions andnegative ions. Current in a plasma is the motion of electrons andpositive ions.]390 STANDARD ELECTRICAL DICTIONARY.Negative Electricity.The kind of electricity with which a piece of amber is charged byfriction with flannel; resinous electricity. (See Electrostatic Series.)In a galvanic battery the surface of the zinc plate is charged withnegative electricity.According to the single fluid theory negative electrification consistsin a deficiency of electricity.[Transcriber's note: Negative electrification is an excess ofelectrons.]Negative Element.In a voltaic cell the plate not dissolved by the solution; the one whichis positively charged; the copper, platinum, or carbon plate in theusual type of battery.The current is assumed to flow from negative element to positive element(the zinc plate) through the wire or other external conductor.Nerve Currents.Currents of electricity obtained from nerves. They are much more feeblethan those obtained from muscle, but are produced in the same generalways.Network.Conductors in parallel and crossing each other, with connections at thejunctions.The term is sometimes so loosely applied as to include parallelconductors.Neutral Line of Commutator.The diameter of a commutator which connects its Neutral Points, q. v.;sometimes termed the diameter of commutation; the diameter approximatelyat right angles with the lines of force. The commutator brushes areapplied at the extremities of this diameter.Neutral Point of a Commutator.The points of a commutator at which no lines of force are cut; thepoints at the extremities of a diameter which, except for the lag, wouldbe at right angles to the lines of force; the points at which thebrushes touch the commutator.Neutral Point, Thermo-electric.A temperature marking a point of no thermo-electric difference ofpotential. If the junctions of a thermo-electric couple are attemperatures, one a little over and the other an equal amount under theneutral point, no current will be developed. At the neutral point thethermo-electric polarities are reversed. Differences of temperatureabove it give currents of reverse direction to those given bycorresponding differences below it. For an iron-copper couple theneutral point is 274.5° C. (526° F.)Synonym--Neutral Temperature.Neutral Relay Armature.An unpolarizable armature for use with a relay; an armature of soft ironor iron wire; as distinguished from a polarized armature.391 STANDARD ELECTRICAL DICTIONARY.Neutral Wire.The central wire in the three wire system, q. v., of electricdistribution; the wire connected to a point between the two dynamos, orotherwise to the central point of the current generator.Fig. 250. DIAGRAM OF THREE WIRE SYSTEM SHOWING NEUTRAL WIRE.Neutral Wire Ampere Meter.An ampere meter connected in the circuit of the neutral wire todetermine the current passing through it. Such determination is for thepurpose of ascertaining how much more work is being done by one of thelateral leads than by the other.Synonym--Balance Ampere Meter.N. H. P.Symbol or contraction for "nominal horse power." This is a basis forrating the size of an engine.Nickel.A metal; one of the elements; atomic weight, 58.8 ; equivalent, 29.4;valency, 2; specific gravity, 8.8. It is a conductor of electricity.Relative resistance, annealed (Silver = 1), 8.285Specific Resistance, 12.47 microhms.Resistance of a wire(a) 1 foot long, weighing 1 grain, 15.206 ohms.(b) 1 foot long, 1/1000 inch thick, 74.963 "(c) 1 meter long, weighing 1 gram, 1.060 "(d) 1 meter long, 1 millimeter thick, .1587 "Resistance of a 1-inch cube, 4.907 microhms.Electro-chemical equivalent, (Hydrogen = .0105) .3087 mgs.It is strongly paramagnetic, but loses this quality at 350º C. (662º F.)It is important as a constituent of German silver, an alloy much usedfor resistance coils.Nickel, Bath.A bath for the electro-deposition of nickel. A great manyformulae have been given. Metallic nickel is dissolved in 1 vol.sulphuric acid mixed with 2 vols. water. Neutralize with ammonia, andadd of ammonium sulphate one-half the weight of metallic nickeloriginally used; 135 parts of nickel will be enough for a bath of 10,000parts.392 STANDARD ELECTRICAL DICTIONARY.Other formulae are as follows:Double nickel-ammonium sulphate, 4 parts.Ammonium carbonate, 3 "Water 100 "Nickel sulphate, nitrate or chloride, 1 "Sodium bisulphate, 1 "Water, 20 "Nickel anodes are used in the bath to maintain the strength. Too muchcare cannot be exercised in the absolute cleanliness of the articles tobe plated. A too alkaline bath gives a disagreeable yellow color to thedeposit; too acid a bath gives badly adhering deposits.Night Bell.An alarm bell in a telegraph office, which bell is connected at night togive a loud signal to attract the operator's attention. It is used intelephone exchanges and is connected so as to ring as long as asubscriber remains unanswered after calling.Nobili's Rings.When a dilute solution of copper acetate is placed on a bright silverplate and a strip of zinc is touched to the silver beneath the copper, aseries of rings of copper are formed by electrolysis around the zinc.These are Nobili's rings.If for the copper acetate a solution of lead oxide in potassium hydratesolution is substituted, and if the polished plate which may be Germansilver is connected to the positive electrode of a battery, and aplatinum wire connected to the negative pole is immersed in the liquid,it determines the formation of beautiful iridescent rings of leadbinoxide. The platinum wire is sometimes sealed in glass so that onlyits point projects.The colors are due to interference of light, the layers of lead oxidebeing extremely thin.The lead binoxide is formed by secondary reaction. Metallic lead isfirst deposited on the negative pole. The oxygen which goes to thepositive pole formed by the polished plate produces lead binoxide whichis deposited there in rings. The reaction is comparable to that of astorage battery.Synonyms--Metallochromes--Electric Rings.Nodular Deposit.A deposit obtained in electroplating, characterized by irregularthickness; due to too low density of current.Non-conductor.A material that does not conduct electricity except with greatdifficulty; a substance of very high resistance.Synonym--Insulator--Dielectric.North Pole.(a) The north-seeking pole of a magnet; the pole of a magnet which tendsto point to the north, and whence lines of force are assumed to issue ontheir course to the other pole of the magnet.(b) The North Pole of the earth. Treating the earth as a magnet, andaccepting the above nomenclature the north pole should be termed thesouth pole. (See Austral Pole--Boreal Pole.)393 STANDARD ELECTRICAL DICTIONARY.North-seeking Pole.The pole of a magnet which tends to point to the north; the north poleof a magnet.Null Method.Any method of obtaining measurements or comparisons, in which themeasurement is correct when the deflection of the galvanometer or otherindicator is zero, nought or null. The Wheatstone Bridge (see Bridge,Wheatstone) is an example of a null method.Two obvious advantages attach to null methods in electric galvanometerwork. One is that an uncalibrated galvanometer can be employed. Theother is that a galvanometer of any high degree of sensitiveness can beemployed, there being no restriction as to its fineness of winding orhighness of resistance.
393 STANDARD ELECTRICAL DICTIONARY."Upper case Omega Graphic".(Greek capital" Omega") symbol for megohm.[Transcriber's note: Now used for ohms.]"Lower case Omega Graphic".(Greek omega) symbol for ohm.[Transcriber's note: Now used for angular velocity, 2*PI*frequency.]Occlusion.An absorption of gases by metals. Palladium will, if used as thehydrogen evolving electrode in decomposing water, absorb 980 times itsvolume of hydrogen, which is said to be occluded. The metal may also beheated in hydrogen and allowed to cool therein, when occlusion occurs.Platinum will occlude 4 times its volume of hydrogen; iron, 4.15 timesits volume of carbon-monoxide; silver, 7 times its volume of oxygen.Metals with occluded gases may serve as elements in a galvanic couple.(See Gas Battery.) A metal expands in occluding a gas.In the storage battery it is believed that occlusion plays a part,hydrogen and oxygen being respectively absorbed by the two sets ofplates, and acting as they do in Groves' gas battery.Oerstedt.Name proposed for the unit of current strength, but not adopted. Theampere is the accepted name.394 STANDARD ELECTRICAL DICTIONARY.Oerstedt's Discovery.Oerstedt discovered in 1820 that a magnetic needle tended to placeitself at right angles to a current of electricity. This fundamentalexperiment is the basis of the galvanometer.Fig. 251. OERSTEDT'S DISCOVERY.Ohm.The practical unit of resistance; 1E9 C. G. S. electro-magnetic units.The legal ohm is the resistance of a mercury column 1 square millimeterin cross-sectional area and 106 centimeters in length. There has beenconsiderable confusion, owing to inaccuracy in early determinations, inthe valuation of the ohm. In this work the legal ohm is used. Thedifferent ohms will be found defined in their place. Resistance units ofvarious names may also be consulted.The following table gives the relative values of the different ohms.Length ofMercury Board ofColumn in True B. A. Trade LegalCentimetre. Ohm. Ohm. Ohm. Ohm.True Ohm, 106.24 1. 1.0128 .9994 1.0022B. A. Ohm, 104.9 .9874 1. .9868 .9889Board of Trade Ohm 106.3 1.00050 1.0133 1. 1.0028Legal Ohm, 106.0 .9977 1.0112 .9971 1.Ohmage.The Resistance of a circuit expressed in ohms.Ohm, B. A.The British Association unit of resistance; the resistance of a columnof mercury 1 square millimeter in cross sectional area and 104.9centimeters long; the B. A. Unit of Resistance.Ohm, Board of Trade.The approximate ohm as recommended by the British Board of Trade on theadvice of a committee (Sir W. Thomson, Dr. J. Hopkinson, Lord Rayleighand others). It is the resistance of a mercury column one squaremillimeter in section, and 106.3 centimeters long at 0º C. (32º F.)Synonym--New Ohm.395 STANDARD ELECTRICAL DICTIONARY.Ohmic Resistance.True resistance as distinguished from spurious resistance, orcounter-electro-motive force.Ohm, Legal.The practical unit of resistance. The resistance of a column of mercuryone square millimeter in cross-sectional area and 106 centimetres longat 0º C. (32º F.) The ohm used previously to 1884 is the B. A. Unit ofResistance, q. v.One legal ohm = 1.0112 B. A. Units, and I B. A. Unit = 0.9889 legal ohm.The resistance of a copper wire 1 foot long and 1/1000 inch in diameteris about 10 ohms. The resistance of 1 mile of iron wire 1/3 inch indiameter is about 10 ohms.Synonym--Congress Ohm.396 STANDARD ELECTRICAL DICTIONARY.Fig. 252. THEORY OF OHMMETER.Fig. 253. OHMMETER.Ohmmeter.An instrument for measuring directly the resistance of a conductor or ofany part of a circuit through which a strong current is passing. It isthe invention of Prof. W. E. Ayrton.It contains two fixed coils at right angles to each other acting on thesame needle of soft iron. One coil is of thick wire and is placed inseries with the resistance to be measured. The other is of very thinwire and is placed in parallel with the same resistance. One wire actsby the total current, the other by the potential difference between theends of the resistance. The action on the soft iron needle is due to theratio of potential difference to total currents, or to the resistanceitself. By properly designing and proportioning the coils the angulardeflections of the needle are made proportional to the resistance.In use the thick wire may be kept permanently in circuit. On connectingthe binding posts of the thin wire coil to any two parts of the circuitits resistance is at once given by the deflection of the needle.When no current is passing the needle rests in any position. A currentin the thick coil brings it to zero. A current simultaneously passingthrough the thin high resistance coil brings about the deflection.The instrument is a commercial rather than a scientific one.Ohm's Law.The fundamental law expressing the relations between current,electro-motive force and resistance in an active electric circuit. Itmay be expressed thus:(a) The current strength is equal to the electro-motive force divided bythe resistance.(b) The electro-motive force is equal to the current strength multipliedby the resistance.(c) The resistance is equal to the electro-motive force divided by thecurrent strength. All these are different forms of the same statement.Algebraically the law is usually expressed thus, (a) C = E/R. It mayalso be expressed thus: (b) E = C*R and (c) R= E/C, in which R denotesresistance, C denotes current strength, and E denotes electro-motiveforce.Ohm, True.The true ohm is the resistance of a column of mercury 1 squaremillimeter in cross-sectional area, and 106.24 centimeters long. (SeeOhm.)Synonym-Rayleigh Ohm.Oil Insulation.Oil insulation has received several applications in electrical work. Ithas been proposed for use in underground conduits. These it was proposedto fill with oil after the insertion of the conductors, the latterproperly wrapped with cotton or other covering. For induction coils ithas been very successfully used. Its principal utility depends on thefact that it is liquid, so that if pierced by a spark it at once closesagain. A solid insulator if pierced is permanently injured. It is alsoused in telegraph insulators (see Insulator, Liquid) to prevent surfaceleakage.397 STANDARD ELECTRICAL DICTIONARY.Olefiant Gas.A compound gas; C2H4; composed of carbon, 24; hydrogen, 4; molecularweight, 28; specific gravity, .981.It is a dielectric of about the resistance of air. Its specificinductive capacity at atmospheric pressure is 1.000722 (Boltzman.)Synonym--Ethene; heavy carburetted hydrogen.[Transcriber's note: Also called ethylene. A primary use is polyethyleneplastic.]Open. adj.An electric circuit is said to be open when it is cut or broken so thatno current can pass through it. The term may be recollected by thinkingof a switch; when open no current can pass through it. The sameadjective is applied to magnetic circuits, an air gap implying an opencircuit.Open Circuit Oscillation.An oscillation of current in open circuit so that a spark dischargeaccompanies it. It is produced by electric resonance in a simple circleor loop of wire with ends placed near together but not touching, if thecircuit is of such size that its period of oscillation corresponds withthat of the inducing discharge. (See Resonance, Electric.) Its perioddepends entirely on the self-induction of the circuit.Ordinate.In a system of plane co-ordinates (see Co-ordinates), the distance ofany point from the axis of abscissas measured parallel to the axis ofordinates.Ordinates, Axis of.The vertical axis in a system of co-ordinates, q. v.Synonym--Axis of Y.Organ, Electric.An organ in which the air blast is admitted or excluded from thedifferent pipes by electric mechanism.The outlines of the system are a series of contacts worked by the keysand stops, which cause, when operated by the organist, a current to passthrough electro-magnets, opening the valves of the different pipes. Thusthe manual may be at any distance from the organ, and a number of organsmay be worked upon the same manual. As many as five in a singlecathedral are thus connected to a manual in the chancel.Orientation of a Magnetic Needle.The acquirement by a magnetic needle of its position of rest, with itsmagnetic axis in the magnetic meridian.Origin of Co-ordinates.In a system of linear co-ordinates the point of intersection of theaxes; the point whose co-ordinates are both zero.398 STANDARD ELECTRICAL DICTIONARY.Oscillating Needle.A small light bar magnet suspended by a filament and employed indetermining the intensity of a magnetic field by the oscillations itcompletes in a given time after a given disturbance.Oscillations, Electric.In static electricity the sudden and very rapid alternations in thedischarge of a static condenser. This discharge of the disruptive orderseems a single one, but is really composed of a number of dischargesalternating in direction and producing electro-magnetic ether waves,probably identical with light waves except that they are longer and farless rapid.Oscillatory Electro-motive Force.Electro-motive force rapidly changing in sense or in direction, so thatit presents an oscillatory character. The alternating current and thetelephone current as used in practice are actuated by this type ofelectro-motive force.Osmose, Electric.When two liquids are separated by a porous diaphragm, and a strongcurrent of electricity is passed through from the liquid on one side,through the diaphragm, to the liquid on the other side, the liquid onthe side towards which the current is passing rises in level. Theprocess is termed electric osmose. When a liquid is forced through adiaphragm a current is produced; in other words electric osmose isreversible. The current thus produced is termed a diaphragm current.Oscillation, Electric.The phase of discharge of a static condenser in one direction. It isusually followed by a discharge in the opposite direction constituting asecond oscillation, and so on, so that a great number of exceedinglyshort oscillations are comprised. Thus, in the discharge of the Leydenjar a large number of oscillations of current back and forth areproduced, the current alternating like the swings of a pendulum.These oscillations are supposed to affect the ether, producing waves init identical with light waves, except that we have not been able yet toproduce them short enough to affect the visual organs. The waves thusproduced can be reflected or refracted; some substances are transparentfor them and others opaque. There is a possibility that man may yetsucceed in producing electric oscillations of sufficient frequency tobring about the direct production of light.Oscillatory Displacement.Hypothetical displacement currents of rapidly alternating directionproduced in the oscillatory discharge of a Leyden jar or staticcondenser.Oscillatory Induction.Induction produced by sympathetic action of an oscillatory discharge orby electric resonance. (See Oscillations, Electric--Resonance,Electric--Resonator, Electric.)399 STANDARD ELECTRICAL DICTIONARY.Outlet.The part of an electrolier or electric light fixture out of which thewires are led for attachment of an incandescent light socket.Output.The rate of energy delivered or of work done by a machine. In the caseof a current generator it is the volt-coulombs per given second, orbetter the volt-amperes delivered at its outer circuit terminals.Output, Magnetic.The analogue in a magnetic circuit of the output of an electric circuit.It is the product of the magnetizing force by the induced magnetism.Output, Unit of.As a unit of output of a dynamo Prof. Sylvanus P. Thompson has proposed1,000 watts, or one kilowatt. This unit is now frequently used. Tocompletely define the dynamo, however, the amperage or the voltage mustalso be given, as a 10 kilowatt--110 volt machine, or a 10 kilowatt--99ampere machine.[Transcriber's note: 10 kilowatt at 110 volts is 91 amperes.]Over-Compounding.A proportioning of the series and shunt windings of a compound dynamo,so that the voltage of the terminals rises with the load or outputenough to allow for the drop in mains, thus maintaining the potentialfor full load at distant points in a district. It is carried out by anincrease of ampere-turns in the series winding.Overload.In an electric motor a mechanical load put upon it so great as toprevent economical working. One effect of such a load is to make thearmature run so slowly as to unduly reduce the counter-electro-motiveforce and hence to permit so much current to pass through the coils asto heat them, perhaps injuriously. In this case the production of heatimplies the waste of energy.Overtype Dynamo or Motor.A dynamo or motor whose armature is placed above or in the upper part ofthe field magnets, the yoke piece of the magnets being in or restingupon the base of the machine.Ozone.An allotropic form of oxygen. It possesses much more energetic chemicalproperties than oxygen. It is supposed to contain three atoms of oxygenin its molecule, represented thus:O/ \O---OIt is produced by electric discharges and it is its peculiar odor whichis noticed about an electric machine, and sometimes in a thunderstormnear the path of a lightning flash.In the electrolysis of water some ozone may be produced, thusdiminishing the volume of the oxygen or of the mixed gases given off.This is a source of inaccuracy in a gas voltameter.