Theory--Electro-motive Force--Electro-motive Series.)Coupling.The joining of cells of a galvanic battery, of dynamos or of otherdevices, so as to produce different effects as desired.157 STANDARD ELECTRICAL DICTIONARYCouple, Astatic.An astatic couple is a term sometimes applied to astatic needles, q.v.C. P.(a) An abbreviation of or symbol for candle power, q. v.(b) An abbreviation of chemically pure. It is used to indicate a highdegree of purity of chemicals. Thus, in a standard Daniell battery, theuse of C. P. chemicals may be prescribed or advised.Crater.The depression that forms in the positive carbon of a voltaic arc. (SeeArc, Voltaic.)Creeping.A phenomenon of capillarity, often annoying in battery jars. Thesolution, by capillarity, rises a little distance up the sides,evaporates, and as it dries more creeps up through it, and to a point alittle above it. This action is repeated until a layer of the salts mayform over the top of the vessel. To avoid it, paraffine is often appliedto the edges of the cup, or a layer of oil, often linseed oil, is pouredon the battery solution,Crith.The weight of a litre of hydrogen at 0º C. (32º F.), and 760 mm. (30inches) barometric pressure. It is .0896 grams. The molecular weight ofany gas divided by 2 and multiplied by the value of the crith, gives theweight of a litre of the gas in question. Thus a litre of electrolyticgas, a mixture of two molecules of hydrogen for one of oxygen, with amean molecular weight of 12, weighs (12/2) * .0896 or .5376 gram.Critical Speed.(a) The speed of rotation at which a series dynamo begins to excite itsown field.(b) In a compound wound dynamo, the speed at which the same potential isgenerated with the full load being taken from the machine, as would begenerated on open circuit, in which case the shunt coil is the onlyexciter. The speed at which the dynamo is self-regulating.(c) In a dynamo the rate of speed when a small change in the speed ofrotation produces a comparatively great change in the electro-motiveforce. It corresponds to the same current (the critical current) in anygiven series dynamo.Cross.(a) A contact between two electric conductors; qualified to expressconditions as a weather cross, due to rain, a swinging cross when a wireswings against another, etc.(b) vb. To make such contact.Cross-Connecting Board.A special switch board used in telephone exchanges and central telegraphoffices. Its function is, by plugs and wires, to connect the line wireswith any desired section of the main switchboard. The terminals of thelines as they enter the building are connected directly to thecross-connecting board.158 STANDARD ELECTRICAL DICTIONARY.Cross Connection.A method of disposing of the effects of induction from neighboringcircuits by alternately crossing the two wires of a metallic telephonecircuit, so that for equal intervals they lie to right and left, or oneabove, and one below.[Transcriber's note: Also used to cancel the effect of variations in theambient magnetic field, such as solar activity.]Crossing Wires.The cutting out of a defective section in a telegraph line, by carryingtwo wires from each side of the defective section across to aneighboring conductor, pressing it for the time into service and cuttingthe other wire if necessary.Cross-magnetizing Effect.A phase of armature interference. The current in an armature of a dynamoor motor is such as to develop lines of force approximately at rightangles to those of the field. The net cross-magnetizing effect is suchcomponent of these lines, as is at right angles to the lines produced bythe field alone.Cross-over Block.A piece of porcelain or other material shaped to receive two wires whichare to cross each other, and hold them so that they cannot come incontact. It is used in wiring buildings, and similar purposes. (SeeCleat, Crossing.)Cross Talk.On telephone circuits by induction or by contact with other wires soundeffects of talking are sometimes received from other circuits; sucheffects are termed cross talk.Crucible, Electric.A crucible for melting difficultly fusible substances, or for reducingores, etc., by the electric arc produced within it. Sometimes theheating is due more to current incandescence than to the action of anarc.Fig. 116. ELECTRIC FURNACE OR CRUCIBLE.Crystallization, Electric.Many substances under proper conditions take a crystalline form. Thegreat condition is the passage from the fluid into the solid state. Whensuch is brought about by electricity in any way, the term electriccrystallization may be applied to the phenomenon. A solution of silvernitrate for instance, decomposed by a current, may give crystals ofmetallic silver.159 STANDARD ELECTRICAL DICTIONARY.Cup, Porous.A cup used in two-fluid voltaic batteries to keep the solutions separateto some extent. It forms a diaphragm through which diffusion inevitablytakes place, but which is considerably retarded, while electrolysis andelectrolytic convection take place freely through its walls. Asmaterial, unglazed pottery is very generally used.In some batteries the cup is merely a receptacle for the soliddepolarizer. Thus, in the Leclanché battery, the cup contains themanganese dioxide and graphite in which the carbon electrode isembedded, but does not separate two solutions, as the battery only usesone. Nevertheless, the composition of the solution outside and insidemay vary, but such variation is incidental only, and not an essential ofthe operation.Current.The adjustment, or effects of a continuous attempt at readjustment ofpotential difference by a conductor, q. v., connecting two points ofdifferent potential. A charged particle or body placed in a field offorce tends to move toward the oppositely charged end or portion of thefield. If a series of conducting particles or a conducting body are heldso as to be unable to move, then the charge of the field tends, as itwere, to move through it, and a current results. It is really aredistribution of the field and as long as such redistribution continuesa current exists. A current is assumed to flow from a positive to anegative terminal; as in the case of a battery, the current in the outercircuit is assumed to flow from the carbon to the zinc plate, and in thesolution to continue from zinc to carbon. As a memoria technica the zincmay be thought of as generating the current delivering it through thesolution to the carbon, whence it flows through the wire connectingthem. (See Ohm's Law--Maxwell's Theory of Light--Conductor-Intensity.)[Transcriber's note: Supposing electric current to be the motion ofpositive charge causes no practical difficulty, but the current isactually the (slight) motion of negative electrons.]Current, After.A current produced by the animal tissue after it has been subjected to acurrent in the opposite direction for some time. The tissue acts like asecondary battery. The term is used in electro-therapeutics.Current, Alternating.Usually defined and spoken of as a current flowing alternately inopposite directions. It may be considered as a succession of currents,each of short duration and of direction opposite to that of itspredecessor. It is graphically represented by such a curve as shown inthe cut. The horizontal line may denote a zero current, that is nocurrent at all, or may be taken to indicate zero electro-motive force.The curve represents the current, or the corresponding electro-motiveforces. The further from the horizontal line the greater is either, andif above the line the direction is opposite to that corresponding to thepositions below the line. Thus the current is alternately in oppositedirections, has periods of maximum intensity, first in one and then inthe opposite sense, and between these, passing from one direction to theother, is of zero intensity. It is obvious that the current may risequickly in intensity and fall slowly, or the reverse, or may rise andfall irregularly. All such phases may be shown by the curve, and a curvedrawn to correctly represent these variations is called thecharacteristic curve of such current. It is immaterial whether theordinates of the curve be taken as representing current strength orelectromotive force. If interpreted as representing electro-motiveforce, the usual interpretation and best, the ordinates above the lineare taken as positive and those below as negative.Synonyms--Reversed Current--Periodic Currents.Fig. 117. CHARACTERISTIC CURVE OF ALTERNATING CURRENT.160 STANDARD ELECTRICAL DICTIONARY.Current, Atomic.A unit of current strength used in Germany; the strength of a currentwhich will liberate in 24 hours (86,400 seconds) one gram of hydrogengas, in a water voltameter. The atomic current is equal to 1.111amperes. In telegraphic work the milliatom is used as a unit, comparableto the milliampere. The latter is now displacing it.Current, Charge.If the external coatings of a charged and uncharged jar are placed inconnection, and if the inner coatings are now connected, afterseparating them they are both found to be charged in the same manner. Inthis process a current has been produced between the outside coatingsand one between the inner ones, to which Dove has given the name ChargeCurrent, and which has all the properties of the ordinary dischargecurrent. (Ganot.)Current, Circular.A current passing through a circular conductor; a current whose path isin the shape of a circle.Current, Commuted.A current changed, as regards direction or directions, by a commutator,q. v., or its equivalent.Current, Constant.An unvarying current. A constant current system is one maintaining sucha current. In electric series, incandescent lighting, a constant currentis employed, and the system is termed as above. In arc lighting systems,the constant current series arrangement is almost universal.161 STANDARD ELECTRICAL DICTIONARY.Current, Continuous.A current of one direction only; the reverse of an alternating current.(See Current, Alternating.)Current, Critical.The current produced by a dynamo at its critical speed; at that speedwhen a slight difference in speed produces a great difference inelectro-motive force. On the characteristic curve it corresponds to thepoint where the curve bends sharply, and where the electro-motive forceis about two-thirds its maximum.Current, Daniell/U.S. , Daniell/Siemens' Unit.A unit of current strength used in Germany. It is the strength of acurrent produced by one Daniell cell in a circuit of the resistance ofone Siemens' unit. The current deposits 1.38 grams of copper per hour.It is equal to 1.16 amperes.Current, Demarcation.In electro-therapeutics, a current which can be taken from an injuredmuscle, the injured portion acting electro-negatively toward theuninjured portion.Current Density.The current intensity per unit of cross-sectional area of the conductor.The expression is more generally used for electrolytic conduction, wherethe current-density is referred to the mean facing areas of theelectrodes, or else to the facing area of the cathode only.The quality of the deposited metal is intimately related to the currentdensity. (See Burning.)Proper Current Density for ElectroplatingAmperes Per Square Foot of Cathode.--(Urquhart.)Copper, Acid Bath. 5.0 to 10.0" Cyanide Bath, 3.0 " 5.0Silver, Double Cyanide, 2.0 " 5.0Gold, Chloride dissolved in Potassium Cyanide, 1.0 " 2.0Nickel, Double Sulphate, 6.6 " 8.0Brass, Cyanide, 2.0 " 3.0Current, Diacritical.A current, which, passing through a helix surrounding an iron core,brings it to one-half its magnetic saturation, q. v.Current, Diaphragm.If a liquid is forced through a diaphragm, a potential differencebetween the liquid on opposite sides of the diaphragm is maintained.Electrodes or terminals of platinum may be immersed in the liquid, and acontinuous current, termed a diaphragm current, may be taken as long asthe liquid is forced through the diaphragm. The potential difference isproportional to the pressure, and also depends on the nature of thediaphragm and on the liquid.162 STANDARD ELECTRICAL DICTIONARY.Current, Direct.A current of unvarying direction, as distinguished from an alternatingcurrent. It may be pulsatory or intermittent in character, but must beof constant direction.Current, Direct Induced.On breaking a circuit, if it is susceptible of exercisingself-induction, q. v., an extra current, in the direction of theoriginal is induced, which is called "direct" because in the samedirection as the original. The same is produced by a current in onecircuit upon a parallel one altogether separated from it. (SeeInduction, Electro-Magnetic-Current, Extra.)Synonym--Break Induced Current.Current, Direction of.The assumed direction of a current is from positively charged electrodeto negatively charged one; in a galvanic battery from the carbon orcopper plate through the outer circuit to the zinc plate and backthrough the electrolyte to the carbon or copper plate. (See Current.)[Transcriber's note: Current is caused by the motion of negativeelectrons, from the negative pole to the positive. The electron wasdiscovered five years after this publication.]Current, Displacement.The movement or current of electricity taking place in a dielectricduring displacement. It is theoretical only and can only be assumed tobe of infinitely short duration. (See Displacement, Electric.)Currents, Eddy Displacement.The analogues of Foucault currents, hypothetically produced in the massof a dielectric by the separation of the electricity or by itselectrification. (See Displacement.)Current, Extra.When a circuit is suddenly opened or closed a current of very briefduration, in the first case in the same direction, in the other case inthe opposite direction, is produced, which exceeds the ordinary currentin intensity. A high potential difference is produced for an instantonly. These are called extra currents. As they are produced byelectro-magnetic induction, anything which strengthens the field offorce increases the potential difference to which they are due. Thus thewire may be wound in a coil around an iron core, in which case the extracurrents may be very strong. (See Induction, Self-Coil, Spark.)Current, Faradic.A term in medical electricity for the induced or secondary alternatingcurrent, produced by comparatively high electro-motive force, such asgiven by an induction coil or magneto-generator, as distinguished fromthe regular battery current.163 STANDARD ELECTRICAL DICTIONARY.Current, Foucault.A current produced in solid conductors, and which is converted into heat(Ganot). These currents are produced by moving the conductors through afield, or by altering the strength of a field in which they arecontained. They are the source of much loss of energy and otherderangement in dynamos and motors, and to avoid them the armature coresare laminated, the plane of the laminations being parallel to the linesof force. (See Core, Laminated.)The presence of Foucault currents, if of long duration, is shown by theheating of the metal in which they are produced. In dynamo armaturesthey are produced sometimes in the metal of the windings, especially ifthe latter are of large diameter.Synonyms--Eddy Currents--Local Currents--Parasitical Currents.Current, Franklinic.In electro-therapeutics the current produced by a frictional electricmachine.Current, Induced.The current produced in a conductor by varying the conditions of a fieldof force in which it is placed; a current produced by induction.Current Induction.Induction by one current on another or by a portion of a current onanother portion of itself. (See Induction.)Current Intensity.Current strength, dependent on or defined by the quantity of electricitypassed by such current in a given time. The practical unit of currentintensity is the ampere, equal to one coulomb of quantity per second oftime.Current, Inverse Induced.The current induced in a conductor, when in a parallel conductor or inone having a parallel component a current is started, or is increased instrength. It is opposite in direction to the inducing current and henceis termed inverse. (See Induction, Electro-magnetic.) The parallelconductors may be in one circuit or in two separate circuits.Synonyms--Make-induced Current--Reverse-induced Current.Current, Jacobi's Unit of.A current which will liberate one cubic centimeter of mixed gases(hydrogen and oxygen) in a water voltameter per minute, the gases beingmeasured at 0º C. (32º F.) and 760 mm. (29.92 inches) barometricpressure. It is equal to .0961 ampere.Current, Joint.The current given by several sources acting together. Properly, itshould be restricted to sources connected in series, thus if two batterycells are connected in series the current they maintain is their jointcurrent.Current, Linear.A current passing through a straight conductor; a current whose pathfollows a straight line.164 STANDARD ELECTRICAL DICTIONARY.Current, Make and Break.A succession of currents of short duration, separated by absolutecessation of current. Such current is produced by a telegraph key, or bya microphone badly adjusted, so that the circuit is broken at intervals.The U. S. Courts have virtually decided that the telephone operates bythe undulatory currents, and not by a make and break current. Manyattempts have been made to produce a telephone operating by ademonstrable make and break current, on account of the abovedistinction, in hopes of producing a telephone outside of the scope ofthe Bell telephone patent.[Transcriber's note: Contemporary long distance telephone service isdigital, as this item describes.]Current-meter.An apparatus for indicating the strength of current. (See Ammeter.)Current, Negative.In the single needle telegraph system the current which deflects theneedle to the left.Current, Nerve and Muscle.A current of electricity yielded by nerves or muscles. Under properconditions feeble currents can be taken from nerves, as the same can betaken from muscles.Current, Opposed.The current given by two or more sources connected in opposition to eachother. Thus a two volt and a one volt battery may be connected inopposition, giving a net voltage of only one volt, and a current due tosuch net voltage.Current, Partial.A divided or branch current. A current which goes through a singleconductor to a point where one or more other conductors join it inparallel, and then divides itself between the several conductors, whichmust join further on, produces partial currents. It produces as manypartial currents as the conductors among which it divides. The point ofdivision is termed the point of derivation.Synonym--Derived Current.Current, Polarizing.In electro-therapeutics, a constant current.Current, Positive.In the single needle telegraph system the current which deflects theneedle to the right.Current, Pulsatory.A current of constant direction, but whose strength is constantlyvarying, so that it is a series of pulsations of current instead of asteady flow.Current, Rectified.A typical alternating current is represented by a sine curve, whoseundulations extend above and below the zero line. If by a simple twomember commutator the currents are caused to go in one direction, inplace of the sine curve a series of short convex curves following oneanother and all the same side of the zero line results. The currents allin the same direction, become what is known as a pulsating current.Synonym--Redressed Current.165 STANDARD ELECTRICAL DICTIONARY.Current, Rectilinear.A current flowing through a rectilinear conductor. The action ofcurrents depending on their distance from the points where they act,their contour is a controlling factor. This contour is determined by theconductors through which they flow.Current Reverser.A switch or other contrivance for reversing the direction of acurrent in a conductor.Currents, Ampérian.The currents of electricity assumed by Ampere's theory to circulatearound a magnet. As they represent the maintenance of a current or ofcurrents without the expenditure of energy they are often assumed to beof molecular dimensions. As they all go in the same sense of rotationand are parallel to each other the result is the same as if a single setof currents circulated around the body of the magnet. More will be foundon this subject under Magnetism. The Ampérian currents are purelyhypothetical and are predicated on the existence of a field of forceabout a permanent magnet. (See Magnetism, Ampére's Theory of.)If the observer faces the north pole of a magnet the Ampérian currentsare assumed to go in the direction opposite to that of a watch, and thereverse for the south pole.Figs. 118-119 DIRECTION OF AMPÉRIAN CURRENTS.Currents, Angular.Currents passing through conductors which form an angle with each other.Currents, Angular, Laws of.1. Two rectilinear currents, the directions of which form an angle witheach other, attract one another when both approach to or recede from theapex of the angle.2. They repel one another, if one approaches and the other recedes fromthe apex of the angle.166 STANDARD ELECTRICAL DICTIONARYCurrents, Earth.In long telegraph lines having terminal grounds or connected to earthonly at their ends, potential differences are sometimes observed thatare sufficient to interfere with their working and which, of course, canproduce currents. These are termed earth-currents. It will be noted thatthey exist in the wire, not in the earth. They may be of 40 milliamperesstrength, quite enough to work a telegraph line without any battery.Lines running N. E. and S. W. are most affected; those running N.W. andS. E. very much less so. These currents only exist in lines grounded atboth ends, and appear in underground wires. Hence they are notattributable to atmospheric electricity. According to Wilde they are theprimary cause of magnetic storms, q. v., but not of the periodicalchanges in the magnetic elements. (See Magnetic Elements.)Synonym--Natural Currents.Current, Secondary.(a) A current induced in one conductor by a variation in the current ina neighboring one; the current produced in the secondary circuit of aninduction coil or alternating current converter.(b) The current given by a secondary battery. This terminology is not tobe recommended.Current, Secretion.In electro-therapeutics, a current due to stimulation of the secretorynerves.Current Sheet.(a) If two terminals of an active circuit are connected to two points ofa thin metallic plate the current spreads over or occupies practically aconsiderable area of such plate, and this portion of the current is acurrent sheet.The general contour of the current sheet can be laid out in lines offlux. Such lines resemble lines of force. Like the latter, they arepurely an assumption, as the current is not in any sense composed oflines.(b) A condition of current theoretically brought about by the Ampériancurrents in a magnet. Each molecule having its own current, thecontiguous portions of the molecules counteract each other and give aresultant zero current. All that remains is the outer sheet of electriccurrent that surrounds the whole.Current, Sinuous.A current passing through a sinuous conductor.Currents, Multiphase.A term applied to groups of currents of alternating type whichconstantly differ from each other by a constant proportion of periods ofalternation. They are produced on a single dynamo, the winding being socontrived that two, three or more currents differing a constant amountin phase are collected from corresponding contact rings. There arevirtually as many windings on the armature as there are currents to beproduced. Separate conductors for the currents must be used throughout.Synonyms--Polyphase Currents--Rotatory Currents.167 STANDARD ELECTRICAL DICTIONARY.Currents of Motion.In electro-therapeutics, the currents produced in living muscle ornerves after sudden contraction or relaxation.Currents of Rest.In electro-therapeutics, the currents traversing muscular or nervoustissue when at rest. Their existence is disputed.Currents, Orders of.An intermittent current passing through a conductor will inducesecondary alternating currents in a closed circuit near it. Thissecondary current will induce a tertiary current in a third closedcircuit near it, and so on. The induced currents are termed as of thefirst, second, third and other orders. The experiment is carried out byHenry's coils. (See Coils, Henry's.)Currents, Thermo-electric.These currents, as produced from existing thermo-electric batteries,are generated by low potential, and are of great constancy. The oppositejunctions of the plates can be kept at constant temperatures, as bymelting ice and condensing steam, so that an identical current can bereproduced at will from a thermopile.Thermo-electric currents were used by Ohm in establishing his law. (SeeOhm's Law.)Current, Swelling.In electro-therapeutics, a current gradually increasing in strength.Current, Undulatory.A current varying in strength without any abrupt transition from actionto inaction, as in the make and break current. The current may becontinually changing in direction (see Current, Alternating), and hence,of necessity, may pass through stages of zero intensity, but suchtransition must be by a graduation, not by an abrupt transition. Suchcurrent may be represented by a curve, such as the curve of sines. It isevident that the current may pass through the zero point as it crossesthe line or changes direction without being a make and break current.When such a current does alternate in direction it is sometimes called a"shuttle current." The ordinary commercial telephone current and thealternating current is of this type. (See Current, Make and Break.)Current, Unit.Unit current is one which in a wire of unit length, bent so as to forman arc of a circle of unit length of radius, would act upon a unit pole(see Magnetic Pole, Unit,) at the center of the circle with unit force.Unit length is the centimeter; unit force is the dyne.[Transcriber's note: The SI definition of an ampere: A current in twostraight parallel conductors of infinite length and negligiblecross-section, 1 metre apart in vacuum, would produce a force equal to2E-7 newton per metre of length.]168 STANDARD ELECTRICAL DICTIONARY.Current, Wattless.Whenever there is a great difference in phase in an alternating currentdynamo between volts and current, the true watts are much less than theproduct of the virtual volts and amperes, because the the watts areobtained by multiplying the product of the virtual volts and amperes bythe cosine of the angle of lag (or lead). Any alternating current may beresolved into two components in quadrature with each other, one in phasewith the volts, the other in quadrature therewith, the former is termedby S. P. Thompson the Working Current, the latter the Wattless Current.The greater the angle of lag the greater will be the wattless current.Curve, Arrival.A curve representing the rate of rise of intensity of current at the endof a long conductor when the circuit has been closed at the other end.In the Atlantic cable, for instance, it would require about 108 secondsfor the current at the distant end to attain 9/10 of its full value. Thecurve is drawn with its abscissa representing time and its ordinatescurrent strength.Curve, Characteristic.A curve indicating, graphically, the relations between any two factors,which are interdependent, or which vary simultaneously. Thus in adynamo, the voltage increases with the speed of rotation, and acharacteristic curve may be based on the relations between the speed ofrotation and voltage developed. The current produced by a dynamo varieswith the electro-motive force, and a curve can express the relationsbetween the electro-motive force and the current produced.A characteristic curve is usually laid out by rectangular co-ordinates(see Co-ordinates). Two lines are drawn at right angles to each other,one vertical, and the other horizontal. One set of data are marked offon the horizontal line, say one ampere, two amperes, and so on, in thecase of a dynamo's characteristic curve.For each amperage of current there is a corresponding voltage in thecircuit. Therefore on each ampere mark a vertical is erected, and onthat the voltage corresponding to such amperage is laid off. This givesa series of points, and these points may be connected by a curve. Suchcurve will be a characteristic curve.The more usual way of laying out a curve is to work directly upon thetwo axes. On one is laid off the series of values of one set of data; onthe other the corresponding series of values of the other dependentdata. Vertical lines or ordinates, q. v., are erected on the horizontalline or axis of abscissas at the points laid off; horizontal lines orabscissas, q. v., are drawn from the points laid off on the verticalline or axis of ordinates. The characteristic curve is determined by theintersections of each corresponding pair of abscissa and ordinate.169 STANDARD ELECTRICAL DICTIONARY.Variations exist in characteristic curve methods. Thus to get thecharacteristic of a commutator, radial lines may be drawn from a circlerepresenting its perimeter. Such lines may be of length proportional tothe voltage developed on the commutator at the points whence the linesstart. A cut giving an example of such a curve is given in Fig. 125.(See Curve of Distribution of Potential in Armature.)There is nothing absolute in the use of ordinates or abscissas. They maybe interchanged. Ordinarily voltages are laid off as ordinates, but thepractise may be reversed. The same liberty holds good for allcharacteristic curves. Custom, however, should be followed.Synonym--Characteristic.Fig. 120. CHARACTERISTIC CURVE OF A DYNAMOWITH HORSE POWER CURVES.Curve, Characteristic, of Converter.The characteristic curve of the secondary circuit of an alternatingcurrent converter. It gives by the usual methods (see Curve,Characteristic,) the relations between the electro-motive force and thecurrent in the secondary circuit at a fixed resistance. If connected inparallel a constant electro-motive force is maintained, and the curve isvirtually a straight line. If connected in series an elliptical curve isproduced.170 STANDARD ELECTRICAL DICTIONARY.Curve, Charging.In secondary battery manipulation, a curve indicating the increase ofvoltage as the charging is prolonged. The rise in voltage with theduration of the charging current is not uniform. In one case, shown inthe cut, there was a brief rapid rise of about 0.1 volt; then a longslow rise for 0.15 volt; then a more rapid rise for nearly 0.40 volt,and then the curve became a horizontal line indicating a cessation ofincrease of voltage. The charging rate should be constant.The horizontal line is laid off in hours, the vertical in volts, so thatthe time is represented by abscissas and the voltage by ordinates of thecurve.Fig. 121. CHARGING CURVE OF A SECONDARY BATTERY.Curve, Discharging.A characteristic curve of a storage battery, indicating the fall involtage with hours of discharge. The volts may be laid off on the axisof ordinates, and the hours of discharging on the axis of abscissas. Togive it meaning the rate of discharge must be constant.Curve, Electro-motive Force.A characteristic curve of a dynamo. It expresses the relation betweenits entire electromotive force, as calculated by Ohm's Law, and thecurrent intensities corresponding thereto. To obtain the data the dynamois driven with different resistances in the external circuit and thecurrent is measured for each resistance. This gives the amperes. Thetotal resistance of the circuit, including that of the dynamo, is known.By Ohm's Law the electro-motive force in volts is obtained for each caseby multiplying the total resistance of the circuit in ohms by theamperes of current forced through such resistance. Taking the voltagesthus calculated for ordinates and the corresponding amperages forabscissas the curve is plotted. An example is shown in the cut.171 STANDARD ELECTRICAL DICTIONARY.Curve, External Characteristic.A characteristic curve of a dynamo, corresponding to the electro-motiveforce curve, except that the ordinates represent the voltages of theexternal circuit, the voltages as taken directly from the terminals ofthe machine, instead of the total electro-motive force of the circuit.The dynamo is run at constant speed. The resistance of the externalcircuit is varied. The voltages at the terminals of the machine and theamperages of current corresponding thereto are determined. Using thevoltages thus determined as ordinates and the corresponding amperages asabscissas the external characteristic curve is plotted.This curve can be mechanically produced. A pencil may be moved against aconstant force by two electro-magnets pulling at right angles to eachother. One must be excited by the main current of the machine, the otherby a shunt current from the terminals of the machine. The point of thepencil will describe the curve.Fig. 122. CHARACTERISTIC CURVE OF A DYNAMO.Curve, Horse Power.Curves indicating electric horse power. They are laid out withco-ordinates, volts being laid off on the axis of ordinates, and ampereson the axis of abscissas generally. The curves are drawn through pointswhere the product of amperes by volts equals 746. On the same diagram 1,2, 3 .... and any other horse powers can be plotted if within thelimits. See Fig. 120.Curve, Isochasmen.A line drawn on the map of the earth's surface indicating the locus ofequal frequency of auroras.172 STANDARD ELECTRICAL DICTIONARY.Curve, Life.A characteristic curve showing the relations between the durability andconditions affecting the same in any appliance. It is used most forincandescent lamps. The hours of burning before failure give ordinates,and the rates of burning, expressed indirectly in volts or incandle-power, give abscissas. For each voltage or for each candle-poweran average duration is deducible from experience, so that two dependentsets of data are obtained for the construction of the curve.Curve, Load.A characteristic curve of a dynamo, expressing the relation between itsvoltage and the amount of excitation under a definite condition ofampere load, at a constant speed. The ordinates represent voltage, theabscissas ampere turns in the field, and the curves may be constructedfor a flow of 0, 50, 100, or .. , or any other number of amperes.Fig. 123. LOAD CURVES.Curve, Magnetization.A characteristic curve of an electromagnet, indicating the relation ofmagnetization to exciting current. Laying off on the axis of ordinatesthe quantities of magnetism evoked, and the corresponding strengths ofthe exciting current on the axis of abscissas, the curve can be plotted.It first rises rapidly, indicating a rapid increase of magnetization,but grows nearly horizontal as the iron becomes more saturated. Theeffect due to the coils alone, or the effect produced in the absence ofiron is a straight line, because air does not change in permeability.Curve of Distribution of Potential in Armature.A characteristic curve indicating the distribution of potentialdifference between adjoining sections of the commutator of an armaturein different positions all around it. The potential differences aretaken by a volt-meter or potential galvanometer, connection with thearmature being made by two small metal brushes, held at a distance apartequal to the distance from centre to centre of two adjoining commutatorbars. The curve is laid out as if by polar co-ordinates extending aroundthe cross-section of the commutator, with the distances from thecommutator surface to the curve proportional to the potentialdifferences as determined by shifting the pair of brushes all around thecommutator.The above is S. P. Thompson's method. Another method of W. M. Mordeyinvolves the use of a pilot brush. (See Brush, Pilot.) Otherwise themethod is in general terms identical with the above.173 STANDARD ELECTRICAL DICTIONARY.Fig. 124. MAGNETIZATION CURVE.Fig. 125. ARMATURE: CURVE.Fig. 126. DEVELOPMENT OF ARMATURE CURVE.Curve of Dynamo.The characteristic curve of a dynamo. (See Curve, Characteristic.)Curve of Sines.An undulating curve representing wave motion. It is produced bycompounding a simple harmonic motion, or a two and fro motion like thatof an infinitely long pendulum with a rectilinear motion. Along ahorizontal line points may be laid off to represent equal periods oftime. Then on each point a perpendicular must be erected. The length ofeach must be equal to the length of path traversed by the point up tothe expiration of each one of the given intervals of time. The abscissasare proportional to the times and the ordinates to the sines of anglesproportional to the times. Thus if a circle be drawn upon the line anddivided into thirty-two parts of equal angular value, the sines of theseangles may be taken as the ordinates and the absolute distance or lengthof arc of the angle will give the abscissas.Synonyms--Sine Curve--Sinusoidal Curve--Harmonic Curve.Fig. 127. CURVE OF SINES.174 STANDARD ELECTRICAL DICTIONARY.Curve of Saturation of the Magnetic Circuit.A characteristic curve whose ordinates may represent the number ofmagnetic lines of force induced in a magnetic circuit, and whoseabscissas may represent the ampere turns of excitation or otherrepresentative of the inducing force.Curve of Torque.A characteristic curve showing the relations between torque, q. v., andcurrent in a dynamo or motor.Curve, Permeability Temperature.A characteristic curve expressing the changes in permeability of aparamagnetic substance as the temperature changes. The degrees oftemperature may be abscissas, and the permeabilities correspondingthereto ordinates of the curve.Cut In. v.To connect any electric appliance, mechanism or conductor, into acircuit.Cut Out. v.The reverse of to cut in; to remove from a circuit any conductingdevice, and sometimes so arranged as to leave the circuit completed insome other way.Cut Out.An appliance for removing any apparatus from an electric circuit, sothat no more current shall pass through such apparatus, and sometimesproviding means for closing the circuit so as to leave it complete afterthe removal of the apparatus.175 STANDARD ELECTRICAL DICTIONARY.Cut Out, Automatic.(a) A mechanism for automatically shunting an arc or other lamp when itceases to work properly. It is generally worked by an electro-magnet ofhigh resistance placed in parallel with the arc. If the arc grows toolong the magnet attracts its armature, thereby completing a shunt ofapproximately the resistance of the arc, and which replaces it until thecarbons approach again to within a proper distance. Sometimes a strip orwire of fusible metal is arranged in shunt with the arc. When the arclengthens the current through the wire increases, melts it and a springis released which acts to complete or close a shunt circuit ofapproximately arc-resistance.(b) See Safety Device--Safety Fuse.(c) See below.Cut-out, Magnetic.A magnetic cut-out is essentially a coil of wire with attracted core orarmature. When the coil is not excited the core, by pressing down astrip of metal or by some analogous arrangement, completes the circuit.When the current exceeds a certain strength the core rises as it isattracted and the circuit is opened.Cut-out, Safety.A block of porcelain or other base carrying a safety fuse, which meltsand breaks the circuit before the wire connected to it is dangerouslyheated.Synonyms--Fuse Block--Safety Catch--Safety Fuse.Cut Out, Wedge.A cut out operated by a wedge. The line terminals consist of a springbearing against a plate, the circuit being completed through their pointof contact. A plug or wedge composed of two metallic faces insulatedfrom each other is adapted to wedge the contact open. Terminals of aloop circuit are connected to the faces of the wedge. Thus on sliding itinto place, the loop circuit is brought into series in the main circuit.Synonym--Plug Cut Out--Spring Jack.Cutting of Lines of Force.A field of force is pictured as made up of lines of force; a conductorswept through the field is pictured as cutting these lines. By so doingit produces potential difference or electro-motive force in itself witha current, if the conductor is part of a closed circuit.Cycle of Alternation.A full period of alternation of an alternating current. It beginsproperly at the zero line, goes to a maximum value in one sense andreturns to zero, goes to maximum in the other sense and returns to zero.Cystoscopy.Examination of the human bladder by the introduction of a specialincandescent electric lamp. The method is due to Hitze.