311 STANDARD ELECTRICAL DICTIONARY.K.The symbol for electrostatic capacity.Kaolin.A product of decomposition of feldspar, consisting approximately ofsilica, 45, alumina, 40, water, 15. It was used in electric candles ofthe Jablochkoff type as a constituent of the insulating layer orcolombin. Later it was abandoned for another substance, as it was foundthat it melted and acted as a conductor.312 STANDARD ELECTRICAL DICTIONARY.Kapp Line of Force.A line of force proposed by Kapp. It is equal to 6,000 C. G. S. lines offorce, and the unit of area is the square inch. Unfortunately it hasbeen adopted by many manufacturers, but its use should be discouraged,as it is a departure from the uniform system of units.One Kapp line per square inch = 930 C. G. S. lines per squarecentimeter.Kathelectrotonus.A term used in medical electricity or electro-therapeutics to indicatethe increased functional activity induced in a nerve by the proximity ofthe kathode of an active circuit which is completed through the nerve.The converse of anelectrotonus.Kathode.The terminal of an electric circuit whence an electrolyzing currentpasses from a solution. It is the terminal connected to the zinc plateof a primary battery.Kathodic Closure Contraction.A term in electro-therapeutics; the contractions near where the kathodeof an active circuit is applied to the body, which are observed at theinstant when the circuit is closed.Kathodic Duration Contraction.A term in electro-therapeutics; the contraction near where the kathodeof an active circuit is applied to the body for a period of time.K. C. C.Abbreviation for Kathodic Closure Contraction, q. v.K. D. C.Abbreviation for Kathodic Duration Contraction, q. v.Keeper.A bar of soft iron used to connect the opposite poles of a horseshoemagnet or the opposite poles of two bar magnets placed side by side. Itis designed to prevent loss of magnetism. The armature of a horseshoemagnet is generally used as its keeper. For bar magnets a keeper is usedfor each end, the magnets being laid side by side, with their poles inopposite direction but not touching, and a keeper laid across at eachend connecting the opposite poles.Kerr Effect.The effect of an electrostatic field upon polarized light traversing adielectric contained within the field. (See Electrostatic Refraction.)Kerr's Experiment.Polarized light reflected from the polished face of a magnet pole hasits plane of polarization rotated; when it is reflected from the northpole the rotation is from left to right.313 STANDARD ELECTRICAL DICTIONARY.Key.A switch adapted for making and breaking contact easily when worked byhand, as a Morse telegraph key.Key Board.A board or tablet on which keys or switches are mounted.Key-board.(a) A switch board, q. v.(b) A set of lettered keys similar to those of a typewriter employed insome telegraph instruments. As each key is depressed it produces thecontact or break requisite for the sending of the signal correspondingto the letter marked upon the key. The signal in printing telegraphs, onwhich such key-boards are used, is the reprinting of the letter at thedistant end of the line.Key, Bridge.A key for use with a Wheatstone Bridge, q.v. It is desirable to firstsend a current through the four arms of the bridge in using it fortesting resistances and then through the galvanometer, because it takesa definite time for the current to reach its full strength. This isespecially the case if the element being measured has high staticcapacity, as a long ocean cable. If the galvanometer connections werecompleted simultaneously with the bridge connections a momentary swingwould be produced even if the arms bore the proper relation to eachother. This would cause delay in the testing. A bridge key avoids thisby first connecting the battery circuit through the arms of the bridge,and then as it is still further depressed the galvanometer circuit iscompleted.314 STANDARD ELECTRICAL DICTIONARY.Fig. 206. CHARGE AND DISCHARGE KEYKey, Charge and Discharge.A key for use in observing the discharge of a condenser immediatelyafter removing the battery. In one typical form it has two contacts, onebelow and one above, and being a spring in itself is pressed up againstthe upper one. Connections are so made that when in its upper positionit brings the two coatings of the condenser in circuit with thegalvanometer. When depressed it does the same for a battery. In use itis depressed and suddenly released when the galvanometer receives thefull charge, before there has been time for leakage. This is one methodof connection illustrating its principle.In the cut L is the spring-key proper. S2, is the upper contact screwagainst which the spring normally presses. In this position thegalvanometer G is in circuit with the opposite coatings of the condenserC. On depressing the contact S2, is broken and S1, is made. This bringsthe battery B in circuit with the condenser coatings. On releasing thekey it springs up and the galvanometer receives the effect of the chargeof the condenser as derived from the battery.Key, Double Contact.A key arranged to close two distinct circuits, holding the first closeduntil the second is completed. It is used for Wheatstone bridge work.Key, Double Tapper.A telegraph key giving contacts alternately for currents in oppositedirections, used in needle telegraphy.Key, Increment.A key for use in duplex and quadruplex telegraphy. Its action is toincrease the line current, not merely to suddenly turn current into it.315 STANDARD ELECTRICAL DICTIONARY.Fig. 207. KEMPE'S DISCHARGE KEY.Key, Kempe's Discharge.A key giving a charging, discharging and insulating connection, forstatic condenser work. Referring to the cut l is a lever or spring withupper discharging contact s, and lower charging contact s'. In use it ispressed down by the insulating handle or finger piece C, until caught bythe hook attached to the key I. This hook is lower down than that on thekey D, and holds it in contact with the charging contact piece S'. Onpressing the key I, marked or designated "Insulate," it springs up,breaks contact at S', and catching against the hook on D, which key isdesignated "Discharge," remains insulated from both contacts; next onpressing D it is released and springs up and closes the dischargecontact S. It is a form of charge and discharge key. (See Key, Chargeand Discharge.)Key, Magneto-electric.A telegraph key whose movements operate what is virtually a smallmagneto-generator, so as to produce currents of alternating direction,one impulse for each motion of the key. It is employed for telegraphingwithout a line battery, a polarized relay being used. In one very simpleform a key is mounted on a base with a permanent magnet and connected tothe armature, so that when the key is pressed downwards it draws thearmature away from the poles of the magnet. If the magnet or itsarmature is wound with insulated wire this action of the key will causeinstantaneous currents to go through a circuit connected to the magnetor armature coils.Fig. 208. SIEMENS' MAGNETO-ELECTRIC KEY.In Siemens & Halske's key an H armature E is pivoted between the poles NS, of a powerful compound horseshoe magnet, G G. It is wound with finewire and a key handle H is provided for working it. In its normalposition the handle is drawn upward, and the end S S of the armaturecore is in contact with the south pole S of the permanent magnet, andthe end D D with the north pole. This establishes the polarity of thearmature. On depressing the key the contacts are broken and in theirplace the end D D comes in contact with the south pole and the end S Swith the north pole. This suddenly reverses the polarity of the armatureand sends a momentary current through the armature coil which is incircuit with the line. The cut only shows the principle of the key,whose construction is quite complicated.316 STANDARD ELECTRICAL DICTIONARY.Key, Make and Break.An ordinary electric key, usually making a contact when depressed, andrising by spring action when released, and in its rise breaking thecontact.Fig. 209. PLUG KEYKey, Plug.An appliance for closing a circuit. Two brass blocks are connected tothe terminals, but are disconnected from each other. A brass plugslightly coned or with its end split so as to give it spring action isthrust between the blocks to complete the circuit. It is used inResistance coils and elsewhere. (See Coil, Resistance.) Grooves areformed in the blocks to receive the plug.Key, Reversing.(a) A double key, arranged so that by depressing one key a current flowsin one direction, and by depressing the other a current flows in theopposite direction. It is used in connection with a galvanometer inexperimental, testing or measuring operations.(b) A key effecting the same result used in quadruplex telegraphy.Key, Sliding-Contact.A name given to the key used for making instantaneous contacts with themetre wire of a metre bridge, q. v. The name is not strictly correct,because it is important that there should be no sliding contact made, asit would wear out the wire and make it of uneven resistance.It is a key which slides along over the wire and which, when depressed,presses a platinum tipped knife edge upon the wire. On being releasedfrom pressure the key handle springs up and takes the knife edge off thewire. This removal is essential to avoid wearing the wire, whoseresistance per unit of length must be absolutely uniform.Key, Telegraph.The key used in telegraphy for sending currents as desired over theline. It consists of a pivoted lever with finger piece, which lever whendepressed makes contact between a contact point on its end and astationary contact point on the base. This closes the circuit throughthe line. When released it springs up and opens the line circuit.Kilo.A prefix to the names of units; it indicates one thousand times, askilogram, one thousand grams. A few such units are given below.Kilodyne.A compound unit; one thousand dynes. (See Dyne.)Kilogram.A compound unit; one thousand grams; 2.2046 pounds avds.317 STANDARD ELECTRICAL DICTIONARY.Kilojoule.A compound unit; one thousand joules, q. v.Kilometer.A compound unit; one thousand meters; 3280.899 feet; 0.621382 statutemiles. (See Meter.)Kilowatt.A compound unit; one thousand watts, q. v.Kine.An absolute or C. G. S. unit of velocity or rate of motion; onecentimeter per second; proposed by the British Association.Kirchoff's Laws.These relate to divided circuits.I. When a steady current branches, the quantity of electricity arrivingby the single wire is equal to the quantity leaving the junction by thebranches. The algebraical sum of the intensities of the currents passingtowards (or passing from) the junction is equal to zero; Summation(C) =0 (Daniell.) In the last sentence currents flowing towards the point areconsidered of one sign and those flowing away from it of the other.II. In a metallic circuit comprising within it a source of permanentdifference of potential, E, the products of the intensity of the currentwithin each part of the circuit into the corresponding resistance are,if the elements of current be all taken in cyclical order together,equal to E; Summation(C * r) =E. In a metallic circuit in which there isno source of permanent difference of potential E = 0, and Summation(C *r) = 0.This law applies to each several mesh of a wire network as well as to asingle metallic loop, and it holds good even when an extraneous currentis passed through the loop. (Daniell.)In this statement of the two laws E stands for electro-motive force, Cfor current intensity; and r for resistance of a single member of thecircuit.[Transcriber's note: These laws may be restated as: At any point in ansteady-state electrical circuit, the directed sum of currents flowingtowards that point is zero. The directed sum of the electrical potentialdifferences around any closed circuit is zero.]Knife-edge Suspension.The suspension of an object on a sharp edge of steel or agate. The knifeedge should abut against a plane. The knife edge is generally carried bythe poised object. Its edge then faces downward and on the support oneor more plane or approximately plane surfaces are provided on which itrests. In the ordinary balance this suspension can be seen. It issometimes used in the dipping needle.It is applied in cases where vertical oscillations are to be providedfor.Knot.The geographical mile; a term derived from the knots on the log line,used by navigators. It is equal to 6,087 feet.Synonyms--Nautical Mile--Geographical Mile.[Transcriber's note: A knot is a velocity, 1 nautical mile per hour, nota distance. The contemporary definition is: 1 international knot = 1nautical mile per hour = 1.852 kilometres per hour = 1.1507794 miles perhour = 0.51444444 meters per second = 6076.1152 feet per hour.]318 STANDARD ELECTRICAL DICTIONARY.Kohlrausch's Law.A law of the rate of travel of the elements and radicals in solutionsunder the effects of electrolysis. It states that each element under theeffects of electrolysis has a rate of travel for a given liquid, whichis independent of the element with which it was combined. The rates oftravel are stated for different elements in centimeters per hour for apotential difference of one or more volts per centimeter of path.[Friedrich Wilhelm Georg Kohlrausch (1840-1910)]Kookogey's Solution.An acid exciting and depolarizing solution for a zinc-carbon couple,such as a Bunsen battery. Its formula is: Potassium bichromate, 227parts; water, boiling, 1,134 parts; while boiling add very carefully andslowly 1,558 parts concentrated sulphuric acid. All parts are by weight.Use cold.Krizik's Cores.Cores of iron for use with magnetizing coils, q. v. They are so shaped,the metal increasing in quantity per unit of length, as the centre isapproached, that the pull of the excited coil upon them will as far aspossible be equal in all positions. A uniform cylinder is attracted withvarying force according to its position; the Krizik bars or cores areattracted approximately uniformly through a considerable range.
318 STANDARD ELECTRICAL DICTIONARY.L.Symbol for length and also for the unit of inductance or coefficient ofinduction, because the dimensions of inductance are length.Lag, Angle of.(a) The angle of displacement of the magnetic axis of an armature of adynamo, due to its magnetic lag. The axis of magnetism is displaced inthe direction of rotation. (See Magnetic Lag.)(b) The angle expressing the lag of alternating current andelectro-motive force phases.Laminated. adj.Made up of thin plates, as a laminated armature core or converter core.Lamination.The building up of an armature core or other thing out of plates. Thecores of dynamo armatures or of alternating current converters are oftenlaminated. Thus a drum armature core may consist of a quantity of thiniron discs, strung upon a rod and rigidly secured, either with orwithout paper insulation between the discs. If no paper is used the filmof oxide on the iron is relied on for insulation. The object oflamination is to break up the electrical continuity of the core, so asto avoid Foucault currents. (See Currents, Foucault.) The laminationsshould be at right angles to the direction of the Foucault currentswhich would be produced, or in most cases should be at right angles tothe active parts of the wire windings.319 STANDARD ELECTRICAL DICTIONARY.Lamination of Armature Conductors.These are sometimes laminated to prevent the formation of eddy currents.The lamination should be radial, and the strips composing it should beinsulated from each other by superficial oxidation, oiling orenamelling, and should be united only at their ends.Fig. 210. PILSEN ARC LAMP.Lamp, Arc.A lamp in which the light is produced by a voltaic arc. Carbonelectrodes are almost universally employed. Special mechanism, operatingpartly by spring or gravity and partly by electricity, is employed toregulate the distance apart of the carbons, to let them touch when nocurrent passes, and to separate them when current is first turned on.The most varied constructions have been employed, examples of which willbe found in their places. Lamps may in general be divided into classesas follows, according to their regulating mechanism and other features:(a) Single light regulators or monophotes. Lamps through whoseregulating mechanism the whole current passes. These are only adapted towork singly; if several are placed in series on the same circuit, theaction of one regulator interferes with that of the next one.(b) Multiple light regulators or polyphotes. In these the regulatingmechanism and the carbons with their arc are in parallel; the regulatingdevice may be a single magnet or solenoid constituting a derived orshunt-circuit lamp, or it may include two magnets working differentiallyagainst or in opposition to each other constituting a differential lamp.320 STANDARD ELECTRICAL DICTIONARY.(c) Lamps with fixed parallel carbons termed candles (q. v., of varioustypes).(d) Lamps without regulating mechanism. These include lamps withconverging carbons, whose object was to dispense with the regulatingmechanism, but which in some cases have about as much regulatingmechanism as any of the ordinary arc lamps.Lamp, Contact.A lamp depending for its action on loose contact between two carbonelectrodes. At the contact a species of incandescence with incipientarcs is produced. One of the electrodes is usually flat or nearly so,and the other one of pencil shape rests upon it.Lamp, Differential Arc.An arc lamp, the regulation of the distance between whose carbonsdepends on the differential action of two separate electrical coils. Thediagram illustrates the principle. The two carbons are seen in black;the upper one is movable, The current arrives at A. It divides, and thegreater part goes through the low resistance coil M to a contact rollerr, and thence by the frame to the upper carbon, and through the arc andlower carbon to B, where it leaves the lamp. A smaller portion of thecurrent goes through the coil M1 of higher resistance and leaves thelamp also at B. A double conical iron core is seen, to which the uppercarbon holder is attached. This is attracted in opposite directions bythe two coils. If the arc grows too long its resistance increases andthe coil M1 receiving more current draws it down and thus shortens thearc. If the arc grows too short, its resistance falls, and the coil Mreceives more current and draws the core upwards, thus lengthening thearc. This differential action of the two cores gives the lamp its name.R is a pulley over which a cord passes, one end attached to the core andthe other to a counterpoise weight, W.Fig. 211. DIAGRAM OF THE PILSEN DIFFERENTIAL ARC LAMP.321 STANDARD ELECTRICAL DICTIONARY.Lamp, Holophote.A lamp designed for use alone upon its own circuit. These have theregulating mechanism in series with the carbon and arc, so that thewhole current goes through both. (See Lamp, Arc.)Synonym--Monophote Lamp.Lamp-hour.A unit of commercial supply of electric energy; the volt-coulombsrequired to maintain an electric lamp for one hour. A sixteen-candlepower incandescent lamp is practically the lamp alluded to, and requiresabout half an ampere current at 110 volts, making a lamp-hour equal toabout 198,000 volt-coulombs.[Transcriber's note: 0.55 KW hours.]Lamp, Incandescent.An electric lamp in which the light is produced by heating to whitenessa refractory conductor by the passage of a current of electricity. It isdistinguished from an arc lamp (which etymologically is also anincandescent lamp) by the absence of any break in the continuity of itsrefractory conductor. Many different forms and methods of constructionhave been tried, but now all have settled into approximately the sametype.The incandescent lamp consists of a small glass bulb, called thelamp-chamber, which is exhausted of air and hermetically sealed. Itcontains a filament of carbon, bent into a loop of more or less simpleshape. This shape prevents any tensile strain upon the loop and alsoapproximates to the outline of a regular flame.Fig. 212. INCANDESCENT ELECTRIC LAMP.322 STANDARD ELECTRICAL DICTIONARY.The loop is attached at its ends to two short pieces of platinum wire,which pass through the glass of the bulb and around which the glass isfused. As platinum has almost exactly the same coefficient ofheat-expansion as glass, the wires do not cause the glass to crack.The process of manufacture includes the preparation of the filament.This is made from paper, silk, bamboo fibre, tamidine, q. v., or othermaterial. After shaping into the form of the filament the material iscarbonized at a high heat, while embedded in charcoal, or otherwiseprotected from the air. The flashing process (see Flashing ofincandescent Lamp Carbons) may also be applied. The attachment to theplatinum wires is effected by a minute clamp or by electric soldering.The loop is inserted and secured within the open globe, which the glassblower nearly closes, leaving one opening for exhaustion.The air is pumped out, perhaps first by a piston pump, but always at theend by a mercurial air pump. (See Pump, Geissler--and others.) As theexhaustion becomes high a current is passed through the carbons heatingthem eventually to white heat so as to expel occluded gas. The occludedgases are exhausted by the pump and the lamp is sealed by melting theglass with a blowpipe or blast-lamp flame. For the exhaustion severallamps are usually fastened together by branching glass tubes, and aresealed off one by one.The incandescent lamps require about 3.5 watts to the candle power, orgive about 12 sixteen-candle lamps to the horse power expended on them.Generally incandescent lamps are run in parallel or on multiple arccircuits. All that is necessary in such distribution systems is tomaintain a proper potential difference between the two leads acrosswhich the lamps are connected. In the manufacture of lamps they arebrought to an even resistance and the proper voltage at which theyshould be run is often marked upon them. This may be fifty volts andupward. One hundred and ten volts is a very usual figure. As current oneampere for a fifty-volt, or about one-half an ampere for a one hundredand ten volt lamp is employed.Lamp, Incandescent, Three Filament.A three filament lamp is used for three phase currents. It has threefilaments whose inner ends are connected, and each of which has oneleading-in wire. The three wires are connected to the three wires of thecircuit. Each filament receives a current varying in intensity, so thatthere is always one filament passing a current equal to the sum of thecurrents in the other two filaments.Lamp, Lighthouse.A special type of arc light. It is adapted for use in a lighthousedioptric lantern, and hence its arc has to be maintained in the sameposition, in the focus of the lenses. The lamps are so constructed as tofeed both carbons instead of only one, thereby securing the aboveobject.323 STANDARD ELECTRICAL DICTIONARY.Lamp, Pilot.A lamp connected to a dynamo, and used by its degree of illumination toshow when the dynamo on starting becomes excited, or builds itself up.Lamp, Polyphote.An arc lamp adapted to be used, a number in series, upon the samecircuit. The electric regulating mechanism is placed in shunt or inparallel with the carbons and arc. (See Lamp, Arc.)Lamps, Bank of.A number of lamps mounted on a board or other base, and connected toserve as voltage indicator or to show the existence of grounds, or forother purposes.Lamp, Semi-incandescent.A lamp partaking of the characteristics of both arc and incandescence; alamp in which the imperfect contact of two carbon electrodes produces apart of or all of the resistance to the current which causesincandescence.The usual type of these lamps includes a thin carbon rod which restsagainst a block of carbon. The species of arc formed at the junction ofthe two heats the carbons. Sometimes the upper carbon or at least itsend is heated also by true incandescence, the current being conveyednear to its end before entering it.Semi-incandescent lamps are not used to any extent now.Lamp Socket.A receptacle for an incandescent lamp; the lamp being inserted thenecessary connections with the two leads are automatically made in mostsockets. The lamps may be screwed or simply thrust into the socket anddifferent ones are constructed for different types of lamps. A key forturning the current on and off is often a part of the socket.Latent Electricity.The bound charge of static electricity. (See Charge, Bound.)Law of Intermediate Metals.A law of thermo-electricity. The electro-motive force between any twometals is equal to the sum of electro-motive forces between each of thetwo metals and any intermediate metal in the thermo-electric series, orthe electro-motive force between any two metals is equal to the sum ofthe electromotive forces between all the intermediate ones and theoriginal two metals; it is the analogue of Volta's Law, q. v.Law of Inverse Squares.When force is exercised through space from a point, its intensity variesinversely with the square of the distance. Thus the intensity of lightradiated by a luminous point at twice a given distance therefrom is ofone-fourth the intensity it had at the distance in question.Gravitation, electric and magnetic attraction and repulsion and otherradiant forces are subject to the same law.324 STANDARD ELECTRICAL DICTIONARY.Law of Successive Temperatures.A law of thermo-electricity. The electro-motive force due to a givendifference of temperature between the opposite junctions of the metalsis equal to the sum of the electro-motive forces produced by fractionaldifferences of temperature, whose sum is equal to the given differenceand whose sum exactly fills the given range of temperature.Law, Right-handed Screw.This rather crude name is given by Emtage to a law expressing therelation of direction of current in a circuit to the positive directionof the axis of a magnet acted on by such current. It is thus expressed:A right-handed screw placed along the axis of the magnet and turned inthe direction of the current will move in the positive direction, i. e.,towards the north pole of the axis of the magnet.Lead.A metal; one of the elements; symbol Pb. Atomic weight, 207;equivalent, 103-1/2; valency, 2.Lead may also be a tetrad, when its equivalent is 51.75.The following data are at 0º C. (32º F.) with compressed metal:Relative Resistance, (Silver = l) 13.05Specific Resistance, 19.63 microhms.Resistance of a wire,(a) 1 ft. long, weighing 1 grain, 3.200 ohms.(b) 1 meter long, weighing 1 gram, 2.232 "(c) 1 meter long, 1 millimeter thick, .2498 "Resistance of 1 inch cube, 7.728 microhms.Electro-Chemical Equivalent (Hydrogen = .0105) 1.086 mgs.Leading Horns.The tips of pole pieces in a dynamo, which extend in the direction ofmovement of the armature.Leading-in Wires.The platinum wires passing through the glass of an incandescentlamp-chamber, to effect the connection of the carbon filament with thewires of the circuit.Lead of Brushes, Negative.In a motor the brushes are set backwards from their normal position, orin a position towards the direction of armature rotation or given anegative lead instead of a positive one, such as is given to dynamobrushes.Leak.A loss or escape of electricity by accidental connection either with theground or with some conductor. There are various kinds of leak to whichdescriptive terms are applied.Leakage.The loss of current from conductors; due to grounding at least at twoplaces, or to very slight grounding at a great many places, or all alonga line owing to poor insulation. In aerial or pole telegraph lines inwet weather there is often a very large leakage down the wet poles fromthe wire. (See Surface Leakage--Magnetic Leakage.)325 STANDARD ELECTRICAL DICTIONARY.Leakage Conductor.A conductor placed on telegraph poles to conduct directly to earth anyleakage from a wire and thus prevent any but a very small portionfinding its way into the other wires on the same pole. It presents achoice of evils, as it increases the electrostatic capacity of the line,and thus does harm as well as good. It consists simply of a wiregrounded and secured to the pole.Leg of Circuit.One lead or side of a complete metallic circuit.Lenz's Law.A law expressing the relations of direction of an inducing current orfield of force to the current induced by any disturbance in therelations between such field and any closed conductor within itsinfluence. It may be variously expressed.(a) If the relative position of two conductors, A and B, be changed, ofwhich A is traversed by a current, a current is induced in B in such adirection that, by its electro-dynamic action on the current in A, itwould have imparted to the conductors a motion of the contrary kind tothat by which the inducing action was produced. (Ganot.)(b) The new (induced) current will increase the already existingresistances, or develop new resistance to that disturbance of the fieldwhich is the cause of induction. (Daniell.)(c) When a conductor is moving in a magnetic field a current is inducedin the conductor in such a direction as by its mechanical action tooppose the motion. (Emtage.)(d) The induced currents are such as to develop resistance to the changebrought about.Letter Boxes, Electric.Letter boxes with electrical connections to a bell or indicator of somesort, which is caused to act by putting a letter into the box.Leyden Jar.A form of static condenser.In its usual form it consists of a glass jar. Tinfoil is pasted aroundthe lower portions of its exterior and interior surfaces, covering fromone-quarter to three-quarters of the walls in ordinary examples. Therest of the glass is preferably shellacked or painted over withinsulating varnish, q. v. The mouth is closed with a wooden or corkstopper and through its centre a brass rod passes which by a short chainor wire is in connection with the interior coating of the jar. The topof the rod carries a brass knob or ball.If such a jar is held by the tinfoil-covered surface in one hand and itsknob is held against the excited prime conductor of a static machine itsinterior becomes charged; an equivalent quantity of the same electricityis repelled through the person of the experimenter to the earth and whenremoved from the conductor it will be found to hold a bound charge. Ifthe outer coating and knob are both touched or nearly touched by aconductor a disruptive discharge through it takes place.326 STANDARD ELECTRICAL DICTIONARY.Fig. 213. LEYDEN JAR WITH DISCHARGER.If one or more persons act as discharging conductors they will receive ashock. This is done by their joining hands, a person at one end touchingthe outer coating and another person at the other end touching the knob.From an influence machine a charge can be taken by connecting thecoating to one electrode and the knob to the other.Fig. 214. SULPHURIC ACID LEYDEN JAR.327 STANDARD ELECTRICAL DICTIONARY.Leyden Jar, Sir William Thomson's.An especially efficient form of Leyden jar. It consists of a jar withouter tinfoil coating only. For the interior coating is substituted aquantity of concentrated sulphuric acid. The central rod is of lead witha foot, which is immersed in the acid and from which the rod rises. Awooden cover partly closes the jar, as the central tube through whichthe rod passes is so large as not to allow the wood to touch it. Thusany leakage from inner to outer coating has to pass over the inside andoutside glass surfaces. In the common form of jar the wooden cover mayshort circuit the uncoated portion of the inner glass surface. In thecut a simplified form of Thomson's Leyden jar is shown, adapted forscientific work.Lichtenberg's Figures.If the knob of a Leyden jar or other exited electrode is rubbed over thesurface of ebonite, shellac, resin or other non-conducting surface itleaves it electrified in the path of the knob. If fine powder such asflowers of sulphur or lycopodium is dusted over the surface and theexcess is blown away, the powder will adhere where the surface waselectrified, forming what are called Lichtenberg's Figures, Lycopodiumand sulphur show both positive and negative figures, that is to say,figures produced by a positively or negatively charged conductor. Redlead adheres only to negative figures. If both positive and negativefigures are made and the surface is sprinkled with both red lead andflowers of sulphur each picks out its own figure, the sulphur goingprincipally to the positive one.The red lead takes the form of small circular heaps, the sulphurarranges itself in tufts with numerous diverging branches. Thisindicates the difference in the two electricities. The figures have beendescribed as "a very sensitive electrosope for investigating thedistribution of electricity on an insulating surface." (Ganot.)Life of Incandescent Lamps.The period of time a lamp remains in action before the carbon filamentis destroyed. The cause of a lamp failing may be the volatilization ofthe carbon of the filament, causing it to become thin and to break; orthe chamber may leak. The life of the lamp varies; 600 hours is a fairestimate. Sometimes they last several times this period.The higher the intensity at which they are used the shorter is theirlife. From their prime cost and the cost of current the most economicalway to run them can be approximately calculated.[Transcriber's note: Contemporary incandecent buls are rated for 1000hours; flourescent bulbs up to 24000 hours; LED lamps up to 100000 hours.]Lightning.The electrostatic discharge to the earth or among themselves of cloudsfloating in the atmosphere. The discharge is accompanied by a spark orother luminous effect, which may be very bright and the effects, thermaland mechanical, are often of enormous intensity.The lightning flash is white near the earth, but in the upper regionswhere the air is rarefied it is of a blue tint, like the spark of theelectric machine. The flashes are often over a mile in length, andsometimes are four or five miles long. They have sometimes a curioussinuous and often a branching shape, which has been determined byphotography only recently. To the eye the shape seems zigzag.328 STANDARD ELECTRICAL DICTIONARY.In the case of a mile-long flash it has been estimated that 3,516,480 Dela Rue cells, q. v., would be required for the development of thepotential, giving the flash over three and one-half millions of volts.But as it is uncertain how far the discharge is helped on its course bythe rain drops this estimate may be too high.There are two general types of flash. The so-called zigzag flashresembles the spark of an electric machine, and is undoubtedly due tothe disruptive discharge from cloud to earth. Sheet lightning has noshape, simply is a sudden glow, and from examination of the spectrumappears to be brush discharges (see Discharge, Brush) between clouds.Heat lightning is attributed to flashes below the horizon whose lightonly is seen by us. Globe or ball lightning takes the form of globes offire, sometimes visible for ten seconds, descending from the clouds. Onreaching the earth they sometimes rebound, and sometimes explode with aloud detonation. No adequate explanation has been found for them.The flash does not exceed one-millionth of a second in duration; itsabsolute light is believed to be comparable to that of the sun, but itsbrief duration makes its total light far less than that of the sun forany period of time.If the disruptive discharge passes through a living animal it is oftenfatal. As it reaches the earth it often has power enough to fuse sand,producing fulgurites, q. v. (See also Back Shock or Stroke ofLightning.)Volcanic lightning, which accompanies the eruptions of volcanoes, isattributed to friction of the volcanic dust and to vapor condensation.[Transcriber's note: The origin of lightning is still (2008) not fullyunderstood, but is thought to relate to charge separation in thevertical motion of water droplets and ice crystals in cloud updrafts. Alightning bolt carries a current of 40,000 to 120,000 amperes, andtransfers a charge of about five coulombs. Nearby air is heated to about10,000 °C (18,000 °F), almost twice the temperature of the Sun’ssurface.]Lightning Arrester.An apparatus for use with electric lines to carry off to earth anylightning discharge such lines may pick up. Such discharge would imperillife as well as property in telegraph offices and the like.Arresters are generally constructed on the following lines. The linewires have connected to them a plate with teeth; a second similar plateis placed near this with its teeth opposite to those of the first plateand nearly touching it. The second plate is connected by a lowresistance conductor to ground. Any lightning discharge is apt to jumpacross the interval, of a small fraction of an inch, between theoppositely placed points and go to earth.Another type consists of two plates, placed face to face, and pressingbetween them a piece of paper or mica. The lightning is supposed toperforate this and go to earth. One plate is connected to the line, theother one is grounded.The lightning arrester is placed near the end of the line before itreaches any instrument. (See Alternative Paths.)329 STANDARD ELECTRICAL DICTIONARY.Fig. 215. COMB OR TOOTHED LIGHTNING ARRESTER.Fig. 216. FILM OR PLATE LIGHTNING ARRESTER.Lightning Arrester, Counter-electro-motive Force.An invention of Prof. Elihu Thompson. A lightning arrester in which thelightning discharge sets up a counter-electro-motive force opposed toits own. This it does by an induction coil. If a discharge to earthtakes place it selects the primary of the coil as it has lowself-induction. In its discharge it induces in the secondary a reverseelectro-motive force which protects the line.Lightning Arrester Plates.The toothed plates nearly in contact, tooth for tooth, or the flatplates of a film lightning arrester, which constitute a lightningarrester. Some advocate restricting the term to the plate connected tothe line.Lightning Arrester, Vacuum.A glass tube, almost completely exhausted, into which the line wire isfused, while a wire leading to an earth connection has its end fused inalso.A high tension discharge, such as that of lightning, goes to earthacross the partial vacuum in preference to going through the line, whichby its capacity and self-induction opposes the passage through it of alightning discharge.It is especially adapted for underground and submarine lines.330 STANDARD ELECTRICAL DICTIONARY.Lightning, Ascending.Lightning is sometimes observed which seems to ascend. It is thoughtthat this may be due to positive electrification of the earth andnegative electrification of the clouds.Lightning, Globe or Globular.A very unusual form of lightning discharge, in which the flashes appearas globes or balls of light. They are sometimes visible for ten seconds,moving so slowly that the eye can follow them. They often rebound onstriking the ground, and sometimes explode with a noise like a cannon.They have never been satisfactorily explained. Sometimes the phenomenonis probably subjective and due to persistence of vision.Lightning Jar.A Leyden jar whose coatings are of metallic filings dusted on to thesurface while shellacked, and before the varnish has had time to dry. Inits discharge a scintillation of sparks appears all over the surface.Line of Contact.The line joining the points of contact of the commutator brushes in adynamo or motor.Synonym--Diameter of Commutation.Lines of Force.Imaginary lines denoting the direction of repulsion or attraction in afield of force, q. v. They may also be so distributed as to indicate therelative intensity of all different parts of the field. They are normalto equipotential surfaces. (See Electro-magnetic Lines ofForce--Electrostatic Lines of Force--Magnetic Lines of Force.)Lines of Induction.Imaginary lines within a body marking the direction taken within it bymagnetic induction. These are not necessarily parallel to lines offorce, but may, in bodies of uniform agglomeration, or in crystallinebodies, take various directions.Synonym--Lines of Magnetic Induction.Lines of Slope.Lines in a field of force which mark the directions in which theintensity of force in the field most rapidly falls away.Links, Fuse.Links made of more or less easily fusible metal, for use as safetyfuses.Listening Cam.In a telephone exchange a cam or species of switch used to connect theoperator's telephone with a subscriber's line.331 STANDARD ELECTRICAL DICTIONARY.Lithanode.A block of compressed lead binoxide, with platinum connecting foils foruse as an electrode in a storage battery. It has considerable capacity,over 5 ampere-hours per pound of plates, but has not met with anyextended adoption.Load.In a dynamo the amperes of current delivered by it under any givenconditions.Local Action.(a) In its most usual sense the electric currents within a battery, dueto impurities in the zinc, which currents may circulate in exceedinglyminute circuits, and which waste zinc and chemicals and contributenothing to the regular current of the battery. Amalgamated or chemicallypure zinc develops no local action.(b) The term is sometimes applied to currents set up within the armaturecore or pole pieces of a dynamo. (See Currents, Foucault.)Local Battery.A battery supplying a local circuit (q. v.); in telegraphy, where it isprincipally used, the battery is thrown in and out of action by a relay,and its current does the work of actuating the sounder and any otherlocal or station instruments. (See Relay.)Local Circuit.A short circuit on which are placed local apparatus or instruments. Suchcircuit is of low resistance and its current is supplied by a localbattery, q. v. Its action is determined by the current from the mainline throwing its battery in and out of circuit by a relay, q. v., orsome equivalent.Local Currents.Currents within the metal parts of a dynamo. (See Currents, Foucault.)In a galvanic battery. where there is local action, q. v., there arealso local currents, though they are not often referred to.Localization.Determining the position of anything, such as a break in a cable, or agrounding in a telegraph line. In ocean cables two typical cases are thelocalization of a break in the conductor and of a defect in theinsulation admitting water. The first is done by determining the staticcapacity of the portion of the line which includes the unbroken portionof the conductor; the other by determining the resistance of the line ona grounded circuit.Locus.A place. The word is used to designate the locality or position of, orseries of positions of definite conditions and the like. Thus anisogonic line is the locus of equal declinations of the magnetic needle;it is a line passing through all places on the earth's surface where thecondition of a given declination is found to exist.332 STANDARD ELECTRICAL DICTIONARY.Lodestone.Magnetic magnetite; magnetite is an ore of iron, Fe3 04 which isattracted by the magnet. Some samples possess polarity and attract iron.The latter are lodestones.Synonym--Hercules StoneLogarithm.The exponent of the power to which it is necessary to raise a fixednumber to produce a given number. The fixed number is the base of thesystem. There are two systems; one, called the ordinary system, has 10for its base, the other, called the Naperian system, has 2.71828 for itsbase. The latter are also termed hyperbolic logarithms, and are onlyused in special calculations.Log, Electric.An apparatus for measuring the speed of a ship. A rotating helical vaneof known pitch is dragged behind the vessel. As the helix rotates itsmovements may actuate electric machinery for registering its rotations.The number of these in a given time, multiplied by the pitch of thevane, gives the distance traversed in such time.Loop.A portion of a circuit introduced in series into another circuit. Thelatter circuit is opened by a spring-jack, q. v. or other device, andthe loop inserted. By loops any number of connections can be insertedinto a circuit in series therewith, and in series or in parallel withone another.Loop Break.A double bracket or similar arrangement for holding on insulators theends of a conductor which is cut between them, and to which areconnected the ends of a loop. The space between the insulators may beabout a foot.Luces.This may be used as the plural of lux, q. v. It is the Latin plural.Luminous Jar.A Leyden jar whose coatings are of lozenge-shaped pieces of tinfoilbetween which are very short intervals. When discharged, sparks appearall over the surface where the lozenges nearly join.Lux.A standard of illumination, q. v., as distinguished from illuminatingpower.It is the light given by one candle at a distance of 12.7 inches--by acarcel, q. v., at a distance of one meter---or by 10,000 candles at105.8 feet.It was proposed by W. H. Preece. All the above valuations are identical.