295 STANDARD ELECTRICAL DICTIONARY.I.A symbol sometimes used to indicate current intensity. Thus Ohm's law isoften expressed I = E/R, meaning current intensity is equal toelectro-motive force divided by resistance. C is the more general symbolfor current intensity.Ideoelectrics or Idioelectrics.Bodies which become electric by friction. This was the old definition,the term originating with Gilbert. It was based on a misconception, asinsulation is all that is requisite for frictional electrification,metals being thus electrified if held by insulating handles. The term isvirtually obsolete; as far as it means anything it means insulatingsubstances such as scaling wax, sulphur, or glass.Idle Coils.Coils in a dynamo, in which coils no electro-motive force is beinggenerated. This may occur when, as a coil breaks connection with thecommutator brush, it enters a region void of lines of magnetic force, orwhere the lines are tangential to the circle of the armature.Idiostatic Method.A method of using the absolute or attracted disc electrometer. (SeeElectrometer, Absolute.) The suspended disc and guard ring are kept atthe same potential, which is that of one of the points whose potentialdifference is to be determined; the lower fixed disc is connected to theother of the points whose potential difference is to be determined. Thenwe have the formulaV = d * SquareRoot( 8 * PI * F ) / Sin which d is the distance between the discs, V is the difference ofpotential of the two points, F the force of attraction between the discsin dynes, and S the area of the suspended disc. (See HeterostaticMethod.)296 STANDARD ELECTRICAL DICTIONARY.Idle Poles.Poles of wire sealed into Crookes' tubes, not used for the dischargeconnections, but for experimental connections to test the effect ofdifferent excitation on the discharge.Idle Wire.In a dynamo the wire which plays no part in generating electro-motiveforce. In a Gramme ring the wire on the inside of the ring is idle wire.Igniter.In arc lamps with fixed parallel carbons of the Jablochkoff type (seeCandle, Jablochkoff) a strip of carbon connects the ends of the carbonsin the unused candle. This is necessary to start the current. Such stripis called an igniter. It burns away in a very short time when an arcforms producing the light, and lasts, if all goes well, until the candleburns down to its end. Without the igniter the current would not startand no arc would form.I. H. P.Symbol for indicated horse-power.Illuminating Power.The relative light given by any source compared with a standard light,and stated in terms of the same, as a burner giving an illuminatingpower of sixteen candles. For standards see Candle, Carcel--MethvenStandard--Pentane Standard.Illuminating Power, Spherical.The illuminating power of a lamp or source of light may vary indifferent directions, as in the case of a gas burner or incandescentlamp. The average illuminating power determined by photometric test orby calculation in all directions from the source of light is called thespherical illuminating power, or if stated in candles is called thespherical candle power.Illumination, Unit of.An absolute standard of light received by a surface. Preece proposed assuch the light received from a standard candle (see Candle, Standard) ata distance of 12.7 inches. The object of selecting this distance was tomake it equal to the Carcel Standard (see Carcel), which is the lightgiven by a Carcel lamp at a distance of one meter.From one-tenth to one-fiftieth this degree of illumination was found ingas-lighted streets by Preece, depending on the proximity of the gaslamps.Image, Electric.An electrified point or system of points on one side of a surface whichwould produce on the other side of that surface the same electricalaction which the actual electrification of that surface really doesproduce. (Maxwell.)The method of investigating the distribution of electricity by electricimages is due to Sir William Thomson. The conception is purely atheoretical one, and is of mathematical value and interest.297 STANDARD ELECTRICAL DICTIONARY.Impedance.The ratio of any impressed electro-motive force to the current which itproduces in a conductor. For steady currents it is only the resistance.For variable currents it may include besides resistance inductance andpermittance. It is the sum of all factors opposing a current, both ohmicand spurious resistances. It is often determined and expressed as ohms.Synonym--Apparent Resistance--Virtual Resistance.Impedance, Oscillatory.The counter-electro-motive force offered to an oscillatory discharge, asthat of a Leyden jar. It varies with the frequency of the dischargecurrent.Synonym--Impulsive Impedance.Impressed Electro-motive Force.The electro-motive force expending itself in producing current inductionin a neighboring circuit.Impulse.(a) An electro-magnetic impulse is the impulse produced upon theluminiferous ether by an oscillatory discharge or other varying type ofcurrent; the impulse is supposed to be identical, except as regardswave-length, with a light wave.(b) An electro-motive impulse is the electro-motive force which rises sohigh as to produce an impulsive or oscillatory discharge, such as thatof a Leyden jar.Incandescence, Electric.The heating or a conductor to red, or, more etymologically, to whiteheat by the passage of an electric current. The practical conditions area high intensity of current and a low degree of conductance of theconductor relatively speaking.Inclination Map.A map showing the locus of equal inclination or dips of the magneticneedle. The map shows a series of lines, each one of which follows theplaces at which the dip of the magnetic needle is identical. The mapchanges from year to year. (See Magnetic Elements.)Independence of Currents in Parallel Circuits.If a number of parallel circuits of comparatively high resistance aresupplied by a single generator of comparatively low resistance, thecurrent passed through each one will be almost the same whether a singleone or all are connected. Under the conditions named the currents arepractically independent of each other.[Transcriber's note: The current in each parallel branch depends on theresistance/impedance of that branch. Only if they all have the same
impedance
will the current be the same.]Indicating Bell.An electric bell arranged to drop a shutter or disclose in some otherway a designating number or character when rung.298 STANDARD ELECTRICAL DICTIONARY.Indicator.(a) An apparatus for indicating the condition of a distant element, suchas the water level in a reservoir, the temperature of a drying room orcold storage room or any other datum. They are of the most variedconstructions.(b) The receiving instrument in a telegraph system is sometimes thustermed.Indicator, Circuit.A galvanometer used to show when a circuit is active, and to give anapproximate measurement of its strength. It is a less accurate anddelicate form of instrument than the laboratory appliance.Inductance.The property of a circuit in virtue of which it exercises induction anddevelops lines of force. It is defined variously. As clear andsatisfactory a definition as any is the following, due to Sumpner andFleming: Inductance is the ratio between the total induction through acircuit to the current producing it. "Thus taking a simple helix of fiveturns carrying a current of two units, and assuming that 1,000 lines offorce passed through the central turn, of which owing to leakage only900 thread the next adjacent on each side, and again only 800 throughthe end turns, there would be 800 + 900 + 1000 + 900 + 800, or 4,400linkages of lines with the wire, and this being with 2 units of current,there would be 2,200 linkages with unit current, and consequently theself-inductance of the helix would be 2,200 centimetres." (Kennelly.)Inductance, as regards its dimensions is usually reduced to a length,hence the last word of the preceding quotation.The practical unit of inductance is termed the henry, from Prof. JosephHenry; the secohm, or the quad or quadrant. The latter alludes to thequadrant of the earth, the value in length of the unit in question.[Transcriber's note: (L (di/dt) = V). A current changing at the rate ofone ampere per second through a one henry inductance produces one volt.A sinusoidal current produces a voltage 90 degrees ahead of the current,a cosine (the derivative of sine is cosine). One volt across one henrycauses the current to increase at one ampere per second.]Induction, Coefficient of Self.The coefficient of self-induction of a circuit is the quantity ofinduction passing through it per unit current in it. If a given circuitis carrying a varying current it is producing a varying quantity ofmagnetic induction through itself. The quantity of induction through thecircuit due to its current is generally proportional to its current. Thequantity for unit current is the coefficient of self-induction.(Emtage.)Induction, Cross.The induction of magnetic lines of force in a dynamo armature core bythe current passing around such armature. These lines in a symmetricaltwo pole machine are at right angles to the lines of force which wouldnormally extend across the space between the two magnet poles. The jointmagnetizing effect of the field and of the cross induction produces adistorted field between the poles .Synonym--Cross-magnetizing Effect.299 STANDARD ELECTRICAL DICTIONARY.Induction, Electro-magnetic.The inter-reaction of electromagnetic lines of force with the productionof currents thereby.A current passing through a conductor establishes around it a field offorce representing a series of circular lines of force concentric withthe axis of the conductor and perpendicular thereto. These lines offorce have attributed to them, as a representative of their polarity,direction. This is of course purely conventional. If one is supposed tobe looking at the end of a section of conductor, assuming a current bepassing through it towards the observer, the lines of force will have adirection opposite to the motion of the hands of a watch. The idea ofdirection may be referred to a magnet. In it the lines of force areassumed to go from the north pole through the air or other surroundingdielectric to the south pole.Two parallel wires having currents passing through them in the samedirection will attract each other. This is because the oppositelydirected segments of lines of force between the conductors destroy eachother, and the resultant of the two circles is an approximation to anellipse. As lines of force tend to be as short as possible theconductors tend to approach each other to make the ellipse become of assmall area as possible, in other words to become a circle.If on the other hand the currents in the conductors are in oppositedirections the segments of the lines of force between them will havesimilar directions, will, as it were, crowd the intervening ether andthe wires will be repelled.Fig. 200. ATTRACTION OF CONDUCTORS CARRYING SIMILAR CURRENTS.By Ampére's theory of magnetism, (see Magnetism, Ampére's Theory of,) amagnet is assumed to be encircled by currents moving in the directionopposite to that of the hands of a watch as the observer faces the northpole. A magnet near a wire tends to place the Ampérian currents parallelto the wire, and so that the portion of the Ampérian currents nearestthereto will correspond in direction with the current in the wire.300 STANDARD ELECTRICAL DICTIONARY.This is the principle of the galvanometer. A number of methods ofmemoria technica have been proposed to remember it by.Thus if we imagine a person swimming with the current and always facingthe axis of the conductor, a magnetic needle held where the person issupposed to be will have its north pole deflected to the right hand ofthe person.Fig. 201. REPULSION OF CONDUCTORSCARRYING OPPOSITE CURRENTS.Again if we think of a corkscrew, which as it is turned screws itselfalong with the current, the motion of the handle shows the direction ofthe lines of force and the direction in which the north pole of a needleis deflected. This much is perhaps more properly electro-dynamics, butis necessary as a basis for the expression of induction.If a current is varied in intensity in one conductor it will induce atemporary current in another conductor, part of which is parallel to theinducing current and which conductor is closed so as to form a circuit.If the inducing current is decreased the induced current in the near andparallel portion of the other circuit will be of identical direction; ifincreased the induced current will be of opposite direction.This is easiest figured by thinking of the lines of force surroundingthe inducing conductor. If the current is decreased these can beimagined as receiving a twist or turn contrary to their normaldirection, as thereby establishing a turn or twist in the ethersurrounding the other wire corresponding in direction with the directionof the original lines of force, or what is the same thing, opposite indirection to the original twist. But we may assume that theestablishment of such a disturbance causes a current, which must begoverned in direction with the requirements of the new lines of force.The same reasoning applies to the opposite case.301 STANDARD ELECTRICAL DICTIONARY.The general statement of a variable current acting on a neighboringcircuit also applies to the approach or recession of an unvaryingcurrent, and to the cutting of lines of force by a conductor at rightangles thereto. For it is evident that the case of a varying current isthe case of a varying number of lines of force cutting or being cut bythe neighboring conductor. As lines of force always imply a current,they always imply a direction of such current. The cutting of any linesof force by a closed conductor always implies a change of position withreference to all portions of such conductor and to the current andconsequently an induced current or currents in one or the otherdirection in the moving conductor.As the inducing of a current represents energy abstracted from that ofthe inducing circuit, the direction of the induced current is determinedby (Lenz's Law) the rule that the new current will increase alreadyexisting resistances or develop new ones to the disturbance of theinducing field.In saying that a conductor cutting lines of force at right angles toitself has a current induced in it, it must be understood that if not atright angles the right angle component of the direction of the wire actsin generating the current. The case resolves itself into the number oflines of force cut at any angle by the moving wire.The lines of force may be produced by a magnet, permanent or electro.This introduces no new element. The magnet may be referred, as regardsdirection of its lines of force, to its encircling currents, actual orAmpérian, and the application of the laws just cited will cover allcases.Induction, Coefficient of Mutual.The coefficient of mutual induction of two circuits is the quantity ofmagnetic induction passing through either of them per unit current inthe other. (Emtage.) It is also defined as the work which must be doneon either circuit, against the action of unit current in each, to takeit away from its given position to an infinite distance from the other;and also as the work which would be done by either circuit on the otherin consequence of unit current in each, as the other moves from aninfinite distance to its given position with respect to the otherconductor. It depends on the form, size, and relative position of thetwo circuits; and on the magnetic susceptibilities of neighboringsubstances.The ether surrounding two circuits of intensity i' and i" must possessenergy, expressible (Maxwell) as 1/2 L i2 + M i i + 1/2 N i12. It can beshown that M i i1 in any given position of the two circuits isnumerically equal (1) to the mutual potential energy of the two circuits(2) to the number of lines of induction, which being due to A, pass fromA through B, or equally being due to B, pass from B through A, and M isstyled the coefficient of mutual induction. (Daniell.)302 STANDARD ELECTRICAL DICTIONARY.Induction, Electrostatic.An electrostatic charge has always an opposite and bound charge. Thismay be so distributed as not to be distinguishable, in which case thecharge is termed, incorrectly but conventionally, a free charge. Butwhen a charge is produced an opposite and equal one always is formed,which is the bound charge. The region between the two charges andpermeated by their lines of force, often curving out so as to embrace avolume of cross-sectional area larger than the mean facing area of theexcited surfaces, is an electrostatic field of force. The establishingof an electrostatic field, and the production of a bound charge areelectrostatic induction.An insulated conductor brought into such a field suffers aredistribution of its electricity, or undergoes electrostatic induction.The parts nearest respectively, the two loci of the original and thebound charges, are excited oppositely to such charges. The conductorpresents two new bound charges, one referred to the original charge, theother to the first bound charge.Induction, Horizontal.In an iron or steel ship the induction exercised upon the compass needleby the horizontal members of the structure, such as deck-beams, whenthey are polarized by the earth's magnetic induction. This inductiondisappears four times in swinging a ship through a circle; deviation dueto it is termed quadrantal deviation. (See Deviation, Quadrantal.)Induction, Lateral.A term formerly used to express the phenomenon of the alternativedischarge of a Leyden jar or other oscillatory discharge of electricity.(See Discharge, Alternative.)Induction, Magnetic.The magnetization of iron or other paramagnetic substance by a magneticfield.On account of its permeability or multiplying power for lines of force,a paramagnetic body always concentrates lines of force in itself ifplaced in a magnetic field, and hence becomes for the time being amagnet, or is said to be polarized.As the tendency of lines of force is to follow the most permeable path,a paramagnetic bar places itself lengthwise or parallel with theprevailing direction of the lines of force so as to carry them as far ontheir way as possible. Every other position of the bar is one ofunstable equilibrium or of no equilibrium. The end of the bar where thelines of force enter (see Lines of Force) is a south pole and isattracted towards the north pole of the magnet.The production of magnetic poles under these conditions in the bar isshown by throwing iron filings upon it. They adhere to both ends but notto the middle.Induction, Mutual, Electro-magnetic.The induction due to two electric currents reacting on each other.303 STANDARD ELECTRICAL DICTIONARY.Induction, Mutual, Electrostatic.A charged body always induces a charge upon any other body near it; andthe same charge in the second body will induce the other charge in thefirst body if the latter is unexcited. In other words the second body'sinduction from the first is the measure of the charge the second wouldrequire to induce in the first its own (the second's) induced charge.This is the law of mutual electrostatic induction.Induction, Open Circuit.Inductive effects produced in open circuits. By oscillatory discharges adischarge can be produced across a break in a circuit otherwisecomplete. The requirements for its production involve a correspondenceor relation of its dimensions to the inducing discharge. The whole isanalogous to the phenomena of sound resonators and sympatheticvibrations. Synonym--Oscillatory induction.Induction, Self-.(a) A phenomenon of electric currents analogous to the inertia ofmatter. Just as water which fills a pipe would resist a sudden change inits rate of motion, whether to start from rest, to cease or decrease itsmotion, so an electric current requires an appreciable time to start andstop. It is produced most strongly in a coiled conductor, especially ifa core of iron is contained within it.As in the case of two parallel wires, one bearing currents which vary,momentary currents are induced in the other wire, so in a singleconductor a species of inertia is found which retards and prolongs thecurrent. If a single conductor is twisted into a helix or correspondingshape, its separate turns react one on the other in accordance with thegeneral principles of electromagnetic induction. (See Induction,Electro-magnetic.) Thus when a current is suddenly formed the coilsacting upon each other retard for an instant its passage, producing theeffect of a reverse induced current or extra current opposing theprincipal current. Of course no extra current is perceptible, but onlythe diminution. When the current is passing regularly and the current isbroken, the corresponding action prolongs the current or ratherintensifies it for an instant, producing the true extra current. This iscurrent self-induction.[Transcriber's note: See inductance.]Synonyms--Electric Inertia--Electro-dynamic Capacity.(b) A permanent magnet is said to tend to repel its own magnetism, andthus to weaken itself; the tendency is due to magnetic self-induction.Induction Sheath.In the brush dynamo a thin sheet of copper surrounding the magnet coreswith edges soldered together. The winding is outside of it. Its objectis to absorb extra currents set up by variations in magnetic intensityin the cores. These currents otherwise would circulate in the cores.304 STANDARD ELECTRICAL DICTIONARY.Induction, Unit of Self-.The unit of self-induction is the same as that of induction in general.It is the henry, q. v.Induction, Unipolar.Induction produced in a conductor which continuously cuts the lines offorce issuing from one pole of a magnet. As the lines of force arealways cut in the same sense a continuous and constant direction currentis produced.Induction, Vertical.In an iron or steel ship the induction or attraction exercised in thecompass by vertical elements of the structure. Such vertical masses ofiron in the northern hemisphere would have their upper ends polarized assouth poles, and would affect the magnet as soon as the vessel swung outof the magnetic meridian. Thus this induction disappears twice inswinging a ship through a complete circle; deviation due to it is termedsemi-circular deviation. (See Deviation, Semi-circular.)Fig. 202. INDUCTOR DYNAMO.Inductophone.A method of train telegraphy. The train carries a circuit including acoil, and messages are picked up by it from coils along the line intowhich an alternating current is passed. A telephone is used as areceiver in place of a sounder or relay. The invention, neverpractically used, is due to Willoughby Smith.305 STANDARD ELECTRICAL DICTIONARY.Inductor.(a) In a current generator a mass of iron, generally laminated, which ismoved past a magnet pole to increase the number of lines of forceissuing therefrom. It is used in inductor dynamos. (See DynamoInductor.) In the cut Fig. 202, of an inductor dynamo i, i, are thelaminated inductors.(b) In influence machines the paper or tinfoil armatures on which theelectrification is induced.Inertia.A force in virtue of which every body persists in its state of motion orrest except so far as it is acted on by some force.Inertia, Electro-magnetic.This term is sometimes applied to the phenomena of self-induction, orrather to the cause of these phenomena.Infinity Plug.A plug in a resistance box, which on being pulled out of its seat opensthe circuit or makes it of infinite resistance. The plug seats itselfbetween two brass plates which are not connected with each other in anyway. The other plates are connected by resistance coils of varyingresistance.Influence, Electric.Electric induction, which may be either electrostatic, current, orelectro-magnetic.Insolation, Electric.Exposure to powerful arc-light produces effects resembling those ofsun-stroke. The above term or the term "electric sun-stroke" has beenapplied to them.[Transcriber's note: Operators of arc welders are prone to skin cancerfrom ultra violet rays if not properly protected.]Installation.The entire apparatus, buildings and appurtenances of a technical ormanufacturing establishment. An electric light installation, forinstance, would include the generating plant, any special buildings, themains and lamps.Insulating Stool.A support for a person, used in experiments with static generators. Ithas ordinarily a wooden top and glass legs. It separates one standing onit from the earth and enables his surface to receive an electrostaticcharge. This tends to make his hair stand on end, and anyone on thefloor who touches him will receive a shock.Insulating Tape.Prepared tape used in covering the ends of wire where stripped formaking joints. After the stripped ends of two pieces are twistedtogether, and if necessary soldered and carefully cleaned of solderingfluid, they may be insulated by being wound with insulating tape.The tape is variously prepared. It may be common cotton or other tapesaturated with any insulating compound, or may be a strip of guttapercha or of some flexible cement-like composition.306 STANDARD ELECTRICAL DICTIONARY.Insulating Varnish.Varnish used to coat the surface of glass electrical apparatus, toprevent the deposition of hygrometric moisture, and also in theconstruction of magnetizing and induction coils and the like. Shellacdissolved in alcohol is much used. Gum copal dissolved in ether isanother. A solution of sealing wax in alcohol is also used. If appliedin quantities these may need baking to bring about the last drying. (SeeShellac Varnish.)Insulator.(a) Any insulating substance.(b) A telegraph or line insulator for telegraph wires. (See Insulator,Line or Telegraph.)Synonyms--Dielectric--Non-conductor.Insulator Cap.A covering or hood, generally of iron, placed over an insulator toprotect it from injury by fracture with stones or missiles.Insulator, Fluid.(a) For very high potentials, as in induction coils or alternatingcircuits, fluid insulators, such as petroleum or resin oil, have beenused. Their principal merit is that if a discharge does take placethrough them the opening at once closes, so that they are self-healing.(b) Also a form of telegraph or line insulator in which the lower rim isturned up and inwards, so as to form an annular cup which is filled withoil.Insulator, Line or Telegraph.A support often in the shape of a collar or cap, for a telegraph orother wire, made of insulating material. Glass is generally used in theUnited States, porcelain is adopted for special cases; pottery or stoneware insulators have been used a great deal in other countries.Sometimes the insulator is an iron hook set into a glass screw, which isinserted into a hole in a telegraph bracket. Sometimes a hook is causedto depend from the interior of an inverted cup and the space between theshank of the hook and cup is filled with paraffine run in while melted.Insulators are tested by measuring their resistance while immersed in avessel of water.Intensity. Strength.The intensity of a current or its amperage or strength; the intensity orstrength of a magnetic field or its magnetic density; the intensity orstrength of a light are examples of its use. In the case of dynamicelectricity it must be distinguished from tension. The lattercorresponds to potential difference or voltage and is not an attributeof current; intensity has no reference to potential and is acharacteristic of current.Intensity of a Magnetic Field.The intensity of a magnetic field at any point is measured by the forcewith which it acts on a unit magnet pole placed at that point. Henceunit intensity of field is that intensity of field which acts on a unitpole with a force of one dyne. (S. P. Thomson.) (See Magnetic Lines ofForce.)307 STANDARD ELECTRICAL DICTIONARY.Intercrossing.Crossing a pair of conductors of a metallic circuit from side to side toavoid induction from outside sources.Intermittent.Acting at intervals, as an intermittent contact, earth, or grounding ofa telegraph wire.Interpolar Conductor.A conductor connecting the two poles of a battery or current generator;the external circuit in a galvanic circuit.Interpolation.A process used in getting a closer approximation to the truth from twovarying observations, as of a galvanometer. The process varies fordifferent cases, but amounts to determining an average or deducing aproportional reading from the discrepant observed ones.Interrupter.A circuit breaker. It may be operated by hand or be automatic. (SeeCircuit Breaker--Circuit Breaker, Automatic--and others.)Interrupter, Electro-magnetic, for a Tuning Fork.An apparatus for interrupting a current which passes through anelectromagnet near and facing one of the limbs of a tuning fork. Thecircuit is made and broken by the vibrations of another tuning forkthrough which the current passes. The second one is thus made tovibrate, although it may be very far off and may not be in exact unisonwith the first. The first tuning fork has a contact point on one of itslimbs, to close the circuit; it may be one which dips into a mercurycup.Intrapolar Region.A term in medical electricity, denoting the part of a nerve throughwhich a current is passing.Ions.The products of decomposition produced in any given electrolysis aretermed ions, the one which appears at the anode or negative electrode isthe anion. The electrode connected to the carbon or copper plate of awet battery is an anode. Thus in the electrolysis of water oxygen is theanion and hydrogen is termed the kation. In this case both anion andkation are elements. In the decomposition of copper sulphate the anionis properly speaking sulphion (S O4), a radical, and the kation iscopper, an element. Electro-negative elements or radicals are anions,such as oxygen, sulphion, etc., while electro-positive ones are kations,such as potassium. Again one substance may be an anion referred to onebelow it and a kation referred to one above it, in the electro-chemicalseries, q. v. Anion means the ion which goes to the anode or positiveelectrode; kation, the ion which goes to the kathode or negativeelectrode.[Transcriber's note: An ion is an atom or molecule that has lost orgained one or more valence electrons, giving it a positive or negativeelectrical charge. A negatively charged ion, with more electrons thanprotons in its nuclei, is an anion. A positively charged ion, with fewerelectrons than protons, is a cation. The electron was discovered fiveyears after this publication.]308 STANDARD ELECTRICAL DICTIONARY.Iron.A metal; one of the elements; symbol, Fe; atomic weight, 56;equivalent, 28 and 14, ; valency, 4 and 2.It is a conductor of electricity. The following data are at0° C. 32° F., with annealed metal.Specific Resistance, 9.716 microhms.Relative Resistance. 6.460Resistance of a wire,(a) 1 foot long weighing 1 grain, 1.085 ohms.(b) 1 foot long 1/1000 inch thick, 58.45 "(c) 1 meter long weighing 1 gram, .7570 "(d) 1 meter long, 1 millimeter thick, .1237 "Percentage increase in resistance per degree C. (1.8° F.)at about 20° C. (68°F.), about 0.5 per cent.Resistance of a 1 inch cube, 3.825 microhms.Electro-chemical equivalent (Hydrogen = .0105), .147 and .294Iron, Electrolytic.Iron deposited by electrolytic action. Various baths are employed forits formation. (See Steeling.) It has very low coercive power, onlyseven to ten times that of nickel.Ironwork Fault of a Dynamo.A short circuiting of a dynamo by, or any connection of its coils with,the iron magnet cores or other iron parts.Isochronism.Equality of periodic time; as of the times of successive beats of atuning fork, or of the times of oscillations of a pendulum.Isoclinic Lines.The lines denoting the locus of sets of equal dips or inclinations ofthe magnetic needle upon the earth's surface, the magnetic parallels, q.v. These lines are very irregular. (See Magnetic Elements.)Isoclinic Map.A map showing the position of isoclinic lines.Isodynamic Lines.Lines marking the locus of places of equal magnetic intensity on theearth's surface. (See Magnetic Elements, Poles of Intensity.)Isodynamic Map.A map showing the position of isodynamic lines. (See Poles ofIntensity.)Isogonic Lines.Lines on a map marking the locus of or connecting those points where thedeclination or variation of the magnetic needle is the same. (SeeMagnetic Elements--Declination of Magnetic Needle.)Synonyms--Isogonal Lines--Halleyan Lines.309 STANDARD ELECTRICAL DICTIONARY.Isogonic Map.A map showing the isogonic lines. On such a map each line ischaracterized and marked with the degrees and direction of variation ofthe compass upon itself.Synonym--Declination Map.[Transcriber's note: The file Earth_Declination_1590_1990.gif providedby the U.S. Geological Survey (http://www.usgs.gov) is an animation ofthe declination of the entire earth.]Isolated Plant, Distribution or Supply.The system of supplying electric energy by independent generatingsystems, dynamo or battery, for each house, factory or other place, ascontra-distinguished from Central Station Distribution or Supply.Isotropic.(Greek, equal in manner.)Having equal properties in all directions; the reverse of anisotropic,q. v. Thus a homogeneous mass of copper or silver has the same specificresistance in all directions and is an isotropic conductor. Glass hasthe same specific inductive capacity in all directions and is anisotropic medium or dielectric. The same applies to magnetism. Iron isan isotropic paramagnetic substance. (See Anisotropic.) The term appliesto other branches of physics also.I. W. G.Contraction for Indian Wire Gauge--the gauge adopted in British India.
309 STANDARD ELECTRICAL DICTIONARY.J.Symbol for the unit joule, the unit of electric energy.Jacobi's Law.A law of electric motors. It states that the maximum work of a motor isperformed when the counter-electromotive force is equal to one-half theelectro-motive force expended on the motor.Jewelry.Small incandescent lamps are sometimes mounted as articles of jewelry inscarf-pins or in the hair. They may be supplied with current fromstorage or from portable batteries carried on the person.Joint, American Twist.A joint for connecting telegraph wires, especially aerial lines. Itsconstruction is shown in the cut. The end of each wire is closely woundaround the straight portion of the other wire for a few turns.Fig. 203. AMERICAN TWIST JOINT.310 STANDARD ELECTRICAL DICTIONARY.Joint, Britannia.A joint for uniting the ends of telegraph and electric wires. The endsof the wires are scraped clean and laid alongside each other for twoinches, the extreme ends being bent up at about right angles to thewire. A thin wire is wound four or five times around one of the wires,back of the joint, the winding is then continued over the lappedportion, and a few more turns are taken around the other single wire.The whole is then soldered.Fig. 204. BRITANNIA JOINT.Joint, Butt.A joint in belting or in wire in which the ends to be joined are cut offsquare across, placed in contact and secured. It ensures even runningwhen used in belting. Any irregularity in thickness of a belt affectsthe speed of the driven pulley. As dynamos are generally driven bybelts, and it is important to drive them at an even speed to preventvariations in the electro-motive force, butt joints should be used onbelting for them, unless a very perfect lap joint is made, which doesnot affect either the thickness or the stiffness of the belt.When a butt joint is used in wire a sleeve may be used to receive theabutting ends, which may be secured therein by soldering. This speciesof joint has been used on lightning rods and may more properly be termeda sleeve joint.Joint, Lap.(a) In belting a joint in which the ends are overlapped, and riveted orotherwise secured in place. If made without reducing the thickness ofthe ends it is a bad joint for electrical work, as it prevents evenrunning of machinery to which it is applied. Hence dynamo belts shouldbe joined by butt joints, or if by lap joints the ends should be shavedoff so that when joined and riveted, there will be no variation in thethickness of the belt.(b) In wire lap joints are made by overlapping the ends of the wire andsoldering or otherwise securing. The Britannia joint (see Joint,Britannia,) may be considered a lap-joint.Joint, Marriage.A joint for stranded conductors used for Galende's cables. It is madesomewhat like a sailor's long splice. Each one of the strands is woundseparately into the place whence the opposite strand is unwound and theends are cut off so as to abutt. In this way all are smoothly laid inplace and soldering is next applied.Fig. 205. MARRIAGE JOINT.311 STANDARD ELECTRICAL DICTIONARY.Joint, Sleeve.A joint in electric conductors, in which the ends of the wires areinserted into and secured in a metallic sleeve or tube, whose internaldiameter is just sufficient to admit them.Joint, Splayed.The method of joining the ends of stranded conductors. The insulatingcovering is removed, the wires are opened out, and the center wire,heart or core of the cable is cut off short. The two ends are broughttogether, the opened out wires are interlaced or crotched like thefingers of the two hands, and the ends are wound around the body of thecable in opposite directions. The joint is trimmed and well soldered.Tinned wire with rosin flux for the soldering is to be recommended.Insulating material is finally applied by hand, with heat if necessary.Joints in Belts.Belt-joints for electric plants where the belts drive dynamos should bemade with special care. The least inequality affects the electro-motiveforce. Butt joints are, generally speaking, the best, where the ends ofthe belt are placed in contact and laced. Lap-joints are made byoverlapping the belt, and unless the belt is carefully tapered so as topreserve uniform strength, the speed of the dynamo will vary and alsothe electromotive force.Joulad.A name proposed to be substituted for "joule," q. v. It has not beenadopted.Joule.This term has been applied to several units.(a) The practical C. G. S. unit of electric energy and work--thevolt-coulomb. It is equal to 1E7 ergs--0.73734 foot pound.--.00134 horsepower seconds. A volt-ampere represents one joule per second.(b) It has also been used as the name of the gram-degree C. thermalunit--the small calorie.Synonym--Joulad.Joule Effect.The heating effect of a current passing through a conductor. It varieswith the product of the resistance by the square of the current, or with(C^2)*R.Joule's Equivalent.The mechanical equivalent of heat, which if stated in foot-pounds perpound-degree F. units, is 772 (772.55). (See Equivalents.)Junction Box.In underground distribution systems, an iron casing or box in which thefeeders and mains are joined, and where other junctions are made.Synonym--Fishing Box.