Chapter C: G. S (2)

Commutator. In general an apparatus for changing. It is used on electric current generators, and motors, and on induction coils, and elsewhere, for changing the direction of currents, and is of a great variety of types.

Synonym--Commuter (but little used).

Fig. 106. DYNAMO OR MOTOR COMMUTATOR.

Commutator Bars. The metallic segments of a dynamo or motor commutator.

Commutator, Flats in. A wearing away or lowering in level of one or more metallic segments of a commutator. They are probably due in many cases to sparking, set up by periodic springing in the armature mounting, or by defective commutator connections.

Commutator of Current Generators and Motors. In general a cylinder, formed of alternate sections of conducting and non-conducting material, running longitudinally or parallel with the axis. Its place is on the shaft of the machine, so that it rotates therewith. Two brushes, q. v., or pieces of conducting material, press upon its surface.

141 STANDARD ELECTRICAL DICTIONARY.

As a part of electric motors and generators, its function is to collect the currents produced by the cutting of lines of force so as to cause them all to concur to a desired result. The cut shows the simplest form of commutator, one with but two divisions. Its object may be to enable a current of constant direction to be taken from a rotating armature, in which the currents alternate or change direction once in each rotation. It is carried by the shaft A of the armature and rotates with it. It consists of two leaves, S S, to which the terminals of the armature are connected. Two springs, W W, the terminals of the outer circuit, press against the leaves. The springs which do this take off the current. It is so placed, with reference to the springs and armature, that just as the current changes in direction, each leaf changes from one spring to the other. Thus the springs receive constant direction currents. The changing action of this commutator appears in its changing the character of the current from alternating to constant. Were two insulated collecting rings used instead of a commutator, the current in the outer circuit would be an alternating one. On some dynamos the commutator has a very large number of leaves.

Taking the Gramme ring armature, there must be as many divisions of the commutator as there are connections to the coils. In this case the function of the commutator is simply to lessen friction, for the brushes could be made to take current from the coils directly outside of the periphery of the ring.

Commutator, Split Ring. A two-division commutator for a motor; it consists of two segments of brass or copper plate, bent to arcs of a circle, and attached to an insulating cylinder. They are mounted on the revolving spindle, which carries the armature, and acts as a two part commutator. For an example of its application, see Armature, Revolving, Page's. (See also Fig. 107.)

Fig. 107. SECTION OF SPLIT RING COMMUTATOR, WITH BRUSHES.

Compass. An apparatus for utilizing the directive force of the earth upon the magnetic needle. It consists of a circular case, within which is poised a magnetized bar of steel. This points approximately to the north, and is used on ships and elsewhere to constantly show the direction of the magnetic meridian. Two general types are used. In one the needle is mounted above a fixed "card" or dial, on which degrees or points of the compass, q. v., are inscribed. In the other the card is attached to the needle and rotates with it. The latter represents especially the type known as the mariner's compass. (See Compass, Mariner's--Compass, Spirit, and other titles under compass, also Magnetic Axis--Magnetic Elements.) The needle in good compasses carries for a bearing at its centre, a little agate cup, and a sharp brass pin is the point of support.

Compass, Azimuth. A compass with sights on one of its diameters; used in determining the magnetic bearing of objects.

142 STANDARD ELECTRICAL DICTIONARY.

Compass Card. The card in a compass; it is circular in shape, and its centre coincides with the axis of rotation of the magnetic needle; on it are marked the points of the compass, at the ends generally of star points. (See Compass, Points of the.) It may be fixed, and the needle may be poised above it, or it may be attached to the needle and rotate with it.

Compass, Declination. An instrument by which the magnetic declination of any place may be determined. It is virtually a transit instrument and compass combined, the telescope surmounting the latter. In the instrument shown in the cut, L is a telescope mounted by its axis, X, in raised journals with vernier, K, and arc x, for reading its vertical angle, with level n. The azimuth circle, Q, R, is fixed. A vernier, V is carried by the box, A, E, and both turn with the telescope. A very light lozenge-shaped magnetic needle, a, b, is pivoted in the exact centre of the graduated circles, Q R, and M. The true meridian is determined by any convenient astronomical method, and the telescope is used for the purpose. The variation of the needle from the meridian thus determined gives the magnetic declination.

FIG. 108. DECLINATION COMPASS.

Compass, Inclination. A magnetic needle mounted on a horizontal axis at its centre of gravity, so as to be free to assume the dip, or magnetic inclination, when placed in the magnetic meridian. It moves over the face of a vertical graduated circle, and the frame also carries a spirit level and graduated horizontal circle. In use the frame is turned until the needle is vertical. Then the axis of suspension of the needle is in the magnetic meridian. The vertical circle is then turned through 90° of the horizon, which brings the plane of rotation of the needle into the magnetic meridian, when it assumes the inclination of the place.

143 STANDARD ELECTRICAL DICTIONARY.

Compass, Mariner's. A compass distinguished by the card being attached to and rotating with the needle. A mark, the "lubber's mark" of the sailors is made upon the case. This is placed so that the line connecting it, and the axis of rotation of the card is exactly in a plane, passing through the keel of the ship. Thus however the ship may be going, the point of the card under or in line with the "lubber's mark," shows how the ship is pointing. The case of the mariner's compass is often bowl-shaped and mounted in gimbals, a species of universal joint, so as to bc always horizontal. (See Compass, Spirit-Gimbals.)

FIG. 109. MARINER'S COMPASS.

Compass, Points of the. The circle of the horizon may bc and is best referred to angular degrees. It has also been divided into thirty-two equiangular and named points. A point is 11.25°. The names of the points are as follows: North, North by East, North North-east, North-east by North, North-east, North-east by East, East North-east, East by North, East, East by South, East South-east, South-east by East, South-east, South-east by South, South South-east, South by East, South, South by West, South South-west, South-west by South, South-west, South-west by West, West South-west, West by South, West, West by North, West North-west, North-west by West, North-west, North West by North, North North-west, North by West. They are indicated by their initials as N. N. W., North North-west, N. by W., North by West.

Compass, Spirit. A form of mariner's compass. The bowl or case is hermetically sealed and filled with alcohol or other nonfreezing liquid. The compass card is made with hollow compartments so as nearly to float. In this way the friction of the pivot or point of support is greatly diminished, and the compass is far more sensitive.

Compass, Surveyor's. A species of theodolite; a telescope with collimation lines, mounted above a compass, so as to be applicable for magnetic surveys. Its use is to be discouraged on account of the inaccuracy and changes in declination of the magnetic needle.

144 STANDARD ELECTRICAL DICTIONARY.

Compensating Resistances. In using a galvanometer shunt the total resistance of the circuit is diminished so that in some cases too much current flows through it; in such case additional resistance, termed as above, is sometimes introduced in series. The shunt in parallel with the galvanometer is thus compensated for, and the experimental or trial circuit does not take too much current.

Complementary Distribution. Every distribution of electricity has somewhere a corresponding distribution, exactly equal to it of opposite electricity; the latter is the complimentary distribution to the first, and the first distribution is also complimentary to it.

Component. A force may always be represented diagrammatically by a straight line, terminating in an arrow-head to indicate the direction, and of length to represent the intensity of the force. The line may always be assumed to represent the diagonal of a parallelogram, two of whose sides are represented by lines starting from the base of the arrow, and of length fixed by the condition that the original force shall be the diagonal of the parallelogram of which they are two contiguous sides; such lines are called components, and actually represent forces into which the original force may always be resolved. The components can have any direction. Thus the vertical component of a horizontal force is zero; its horizontal component is equal to itself. Its 450 component is equal to the square root of one-half of its square.

Condenser. An appliance for storing up electrostatic charges: it is also called a static accumulator. The telegraphic condenser consists of a box packed full of sheets of tinfoil. Between every two sheets is a sheet of paraffined paper, or of mica. The alternate sheets of tinfoil are connected together, and each set has its own binding post. (See Accumulator, Electrostatic.)

Condenser, Sliding. An apparatus representing a Leyden jar whose coatings can be slid past each other. This diminishes or increases the facing area, and consequently in almost exactly similar ratio diminishes or increases the capacity of the condenser.

Conductance. The conducting power of a given mass of specified material of specified shape and connections. Conductance varies in cylindrical or prismatic conductors, inversely as the length, directly as the cross-section, and with the conductivity of the material. Conductance is an attribute of any specified conductor, and refers to its shape, length and other factors. Conductivity is an attribute of any specified material without direct reference to its shape, or other factors.

Conduction. The process or act of conducting a current.

145 STANDARD ELECTRICAL DICTIONARY.

Conductivity. The relative power of conducting the electric current possessed by different substances. A path for the current through the ether is opened by the presence of a body of proper quality, and this quality, probably correlated to opacity, is termed conductivity. There is no perfect conductor, all offer some resistance, q. v., and there is hardly any perfect non-conductor. It is the reverse and reciprocal of resistance.

Conductivity, Specific. The reciprocal of specific resistance. (See Resistance--Specific.)

Conductivity, Unit of. The reciprocal of the ohm; it is a more logical unit, but has never been generally adopted; as a name the title mho (or ohm written backwards) has been suggested by Sir William Thomson, and provisionally adopted.

Conductivity, Variable. The conductivity for electric currents of conductors varies with their temperature, with varying magnetization, tension, torsion and compression.

Conductor. In electricity, anything that permits the passage of an electric current. Any disturbance in the ether takes the form of waves because the ether has restitutive force or elasticity. In a conductor, on the other hand, this force is wanting; it opens a path through the ether and a disturbance advances through it from end to end with a wave front, but with no succession of waves. This advance is the beginning of what is termed a current. It is, by some theorists, attributed to impulses given at all points along the conductor through the surrounding ether, so that a current is not merely due to an end thrust. If ether waves preclude a current on account of their restitutive force, ether waves cannot be maintained in a conductor, hence conductors should be opaque to light, for the latter is due to ether waves. This is one of the more practical every day facts brought out in Clerk Maxwell's electromagnetic theory of light. The term conductor is a relative one, as except a vacuum there is probably no substance that has not some conducting power. For relative conducting power, tables of conductivity, q. v., should be consulted. The metals beginning with silver are the best conductors, glass is one of the worst.

[Transcriber's note: See "ether" for contemporary comments on this now discarded concept.]

Conductor, Anti-Induction. A current conductor arranged to avoid induction from other lines. Many kinds have been invented and made the subject of patents. A fair approximation may be attained by using a through metallic circuit and twisting the wires composing it around each other. Sometimes concentric conductors, one a wire and the other a tube, are used, insulated, one acting as return circuit for the other.

Conductor, Conical. A prime conductor of approximately conical shape, but rounded on all points and angles. Its potential is highest at the point.

146 STANDARD ELECTRICAL DICTIONARY.

Conductor, Imbricated. A conductor used in dynamo armatures for avoiding eddy currents, made by twisting together two or more strips of copper.

Conductor, Prime. A body often cylindrical or spherical in shape, in any case with no points or angles, but rounded everywhere, whose surface, if the conductor itself is not metallic, is made conducting by tinfoil or gold leaf pasted over it. It is supported on an insulating stand and is used to collect or receive and retain static charges of electricity.

Conductors, Equivalent. Conductors of identical resistance. The quotient of the length divided by the product of the conductivity and cross-section must be the same in each, if each is of uniform diameter.

Conjugate. adj. Conjugate coils or conductors are coils placed in such relation that the lines of force established by one do not pass through the coils of the other. Hence variations of current in one produce no induced currents in the other.

Connect. v. To bring two ends of a conductor together, or to bring one end of a conductor in connection with another, or in any way to bring about an electrical connection.

Connector. A sleeve with screws or other equivalent device for securing the ends of wires in electrical contact. A binding-post, q. v., is an example. Sometimes wire spring-catches are used, the general idea being a device that enables wires to be connected or released at will without breaking off or marring their ends. The latter troubles result from twisting wires together.

Consequent Poles. A bar magnet is often purposely or accidentally magnetized so as to have both ends of the same polarity, and the center of opposite polarity. The center is said to comprise two consequent poles. (See Magnet, Anomalous.)

Conservation of Electricity. As every charge of electricity has its equal and opposite charge somewhere, near or far, more or less distributed, the sum of negative is equal always to the sum of positive electrical charges. For this doctrine the above title was proposed by Lippman.

Contact Breaker. Any contrivance for closing a circuit, and generally for opening and closing in quick succession. An old and primitive form consisted of a very coarsely cut file. This was connected to one terminal, and the other terminal was drawn over its face, making and breaking contact as it jumped from tooth to tooth. (See Circuit Breaker--do. Automatic, etc.--do. Wheel-do. Pendulum.)

147 STANDARD ELECTRICAL DICTIONARY.

Contact, Electric. A contact between two conductors, such that a current can flow through it. It may be brought about by simple touch or impact between the ends or terminals of a circuit, sometimes called a dotting contact, or by a sliding or rubbing of one terminal on another, or by a wheel rolling on a surface, the wheel and surface representing the two terminals.

There are various descriptions of contact, whose names are self-explanatory. The term is applied to telegraph line faults also, and under this, includes different descriptions of contact with neighboring lines, or with the earth.

Contact Electricity. When two dissimilar substances are touched they assume different electric potentials. If conductors, their entire surfaces are affected; if dielectrics, only the surfaces which touch each other. (See Contact Theory.)

Contact Faults. A class of faults often called contacts, due to contact of the conductor of a circuit with another conductor. A full or metallic contact is where practically perfect contact is established; a partial contact and intermittent contact are self-explanatory.

Contact Point. A point, pin or stud, often of platinum, arranged to come in contact with a contact spring, q. v., or another contact point or surface, under any determined conditions.

Contact Potential Difference. The potential difference established by the contact of two dissimilar substances according to the contact theory, q. v.

Contact Series. An arrangement or tabulation of substances in pairs, each intermediate substance appearing in two pairs, as the last member of the first, and first member of the succeeding pair, with the statement of the potential difference due to their contact, the positively electrified substance coming first. The following table of some contact potentials is due to Ayrton and Perry: CONTACT SERIES. Difference of Potential in Volts. Zinc--Lead .210 Lead--Tin .069 Tin--Iron .313 Iron--Copper .146 Copper--Platinum .238 Platinum-Carbon .113

The sum of these differences is 1.089, which is the contact potential between zinc and carbon.

Volta's Law refers to this and states that--
The difference of potential produced by the contact of any two
substances is equal to the sum of the differences of potentials
between the intervening substances in the contact series.

It is to be remarked that the law should no longer be restricted to or stated only for metals.

148 STANDARD ELECTRICAL DICTIONARY.

Contact-spring. A spring connected to one lead of an electric circuit, arranged to press against another spring, or contact point, q. v., under any conditions determined by the construction of the apparatus. (See Bell, Electric--Coil, Induction.)

Contact Theory. A theory devised to explain electrification, the charging of bodies by friction, or rubbing, and the production of current by the voltaic battery. It holds that two bodies, by mere contact become oppositely electrified. If such contact is increased in extent by rubbing together, the intensity of their electrification is increased. This electrification is accounted for by the assumption of different kinetic energy, or energy of molecular motion, possessed by the two bodies; there being a loss and gain of energy, on the two sides respectively, the opposite electrifications are the result. Then when separated, the two bodies come apart oppositely electrified.

The above accounts for the frictional production of electricity. In the voltaic battery, a separation of the atoms of hydrogen and oxygen, and their consolidation into molecules occurs, and to such separation and the opposite electrification of the electrodes by the oxygen and hydrogen, the current is attributed, because the hydrogen goes to one electrode, and the oxygen to the other, each giving up or sharing its own charge with the electrodes to which it goes. If zinc is touched to copper, the zinc is positively and the copper negatively electrified. In the separation of hydrogen and oxygen, the hydrogen is positively and the oxygen negatively electrified. In the battery, the current is due to the higher contact difference of oxygen and hydrogen compared to that between zinc and copper. It will be seen that the two contact actions in a battery work against each other, and that the current is due to a differential contact action. The zinc in a battery is electrified negatively because the negative electrification of the oxygen is greater in amount than its own positive electrification due to contact with the copper.

Contractures. A muscular spasm or tetanus due to the passage of a current of electricity; a term in electro-therapeutics.

Controlling Field. The magnetic or electro-magnetic field, which is used in galvanometers to control the magnetic needle, tending to restore it to a definite position whenever it is turned therefrom. It may be the earth's field or one artificially produced.

Controlling Force. In galvanometers and similar instruments, the force used to bring the needle or indicator back to zero. (See Controlling Field--Electro-Magnetic Control--Gravity Control--Magnetic Control--Spring Control.)

149 STANDARD ELECTRICAL DICTIONARY.

Convection, Electric. The production of blasts or currents of air (convection streams) from points connected to statically charged conductors. The term is sometimes applied to electric convection of heat. (See Convection of Heat, Electric.)

Convection, Electrolytic. The resistance of acidulated water as a true conductor is known to be very, almost immeasurably, high. As an electrolytic, its resistance is very much lower. Hence the current produced between immersed electrodes is theoretically almost null, unless the difference of potential between them is high enough to decompose the liquid. Yet a feeble current too great for a true conduction current is sometimes observed when two electrodes with potential difference too low to cause decomposition are immersed in it. Such a current is termed an electrolytic convection current. It is supposed to be due to various causes. Some attribute it to the presence of free oxygen from the air, dissolved in the water with which the hydrogen combines. Others attribute it to the diffusion of the gases of decomposition in the solution; others assume a partial polarization of the molecules without decomposition. Other theories are given, all of which are unsatisfactory. The term is due to Helmholtz.

Convection of Heat, Electric. The effect of a current upon the distribution of heat in an unevenly heated conductor. In some, such as copper, the current tends to equalize the varying temperatures; the convection is then said to be positive, as comparable to that of water flowing through an unequally heated tube. In others, such as platinum or iron, it is negative, making the heated parts hotter, and the cooler parts relatively cooler.

The effect of the electric current in affecting the distribution of heat in unequally heated metal (Thomson's effect. q. v.), is sometimes so termed. If a current passes through unequally heated iron it tends to increase the difference of temperature, and the convection is negative; in copper it tends to equalize the temperature, and the convection is positive.

Converter. An induction coil used with the alternating current for changing potential difference and inversely therewith the available current. They generally lower the potential, and increase the current, and are placed between the primary high potential system that connects the houses with the central station, and the secondary low potential system within the houses. A converter consists of a core of thin iron sheets, wound with a fine primary coil of many convolutions, and a coarse secondary coil of few convolutions. The ratio of convolutions gives the ratio of maximum potential differences of their terminals between the primary and secondary coils. The coil may be jacketed with iron to increase the permeance. (See Alternating Current System.)

Fig. 110. FERRANTI'S CONVERTER OR TRANSFORMER.

Fig. 111. SWINBURNE'S HEDGEHOG TRANSFORMER.

150 STANDARD ELECTRICAL DICTIONARY.

Co-ordinates, System of. A system for indicating the position of points in space by reference to fixed lines, intersecting at a determined and arbitrary point 0, termed the origin of co-ordinates. In plane rectangular co-ordinates two lines are drawn through the origin, one horizontal, termed the axis of abscissas, or axis of X. All distances measured parallel to it, if unknown, are indicated by x, and are termed abscissas. The other axis is vertical, and is termed the axis of ordinates, or axis of Y. All distances measured parallel to it, if unknown, are indicated by y and are termed ordinates. Thus by naming its abscissa and ordinate a point has its position with reference to the axes determined, and by indicating the relation between a point, line or curve, and a system of abscissas and ordinates, the properties of a line or curve can be expressed algebraically. Co-ordinates may also be inclined to each other at any other angles, forming oblique co-ordinates; relations may be expressed partly in angles referred to the origin as a centre, giving polar co-ordinates. For solid geometry or calculations in three dimensions, a third axis, or axis of Z, is used, distances parallel to which if unknown are indicated by z.

Fig. 112. AXES OF CO-ORDINATES.

151 STANDARD ELECTRICAL DICTIONARY.

Cooling Box. In a hydroelectric machine, q. v., a conduit or chest through which the steam passes on its way to the nozzles. Its object is to partially condense the steam so as to charge it with water vesicles whose friction against the sides of the nozzles produces the electrification .

152 STANDARD ELECTRICAL DICTIONARY.

Copper. A metal; one of the elements. Symbol, Cu; atomic weight, 63.5; equivalent, 63.5 and 31.75; valency, 1 and 2; specific gravity, 8.96. It is a conductor of electricity, whose conductivity is liable to vary greatly on account of impurities.

Annealed. Hard drawn. Relative resistance (Silver = 1), 1.063 1.086 Specific resistance, 1.598 1.634 microhms.

Resistance of a wire at 0° C. (32° F.), Annealed. Hard Drawn. (a) 1 foot long, weighing 1 grain, .2041 ohms .2083 ohms. (b) 1 foot long, 1/1000 inch thick, 9.612 " 9.831 " (c) 1 meter long, weighing 1 gram, .1424 " .1453 " (d) 1 meter long, 1 millimeter thick, .02034 " .02081 "

microhm. microhm.
Resistance of 1 inch cube at 0°C. (32° F.) .6292 .6433

Percentage of resistance change, per 1° C. (1.8° F.) at about 20° C. (68° F.) = 0.388 per cent.

Electro-chemical Equivalent (Hydrogen = .0105) Cuprous .6667
Cupric .3334

In electricity it has been very extensively used as the negative plate of voltaic batteries. It has its most extensive application as conductors for all classes of electrical leads.

Copper Bath. A solution of copper used for depositing the metal in the electroplating process. For some metals, such as zinc or iron, which decompose copper sulphate solution, special baths have to be used.

The regular bath for copper plating is the following:

To water acidulated with 8 to 10 percent. of sulphuric acid as much copper sulphate is added as it will take up at the ordinary temperature. The saturated bath should have a density of 1.21. It is used cold and is kept in condition by the use of copper anodes, or fresh crystals may be added from time to time.

For deposition on zinc, iron, tin and other metals more electropositive than copper, the following baths may be used, expressed in parts by weight:

Tin Iron and Steel. Cast Iron Cold Hot. and Zinc. Zinc. Sodium Bisulphate, 500 200 300 100 Potassium Cyanide, 500 700 500 700 Sodium Carbonate, 1000 500 --- --- Copper Acetate, 475 500 350 450 Aqua Ammoniae, 350 300 200 150 Water, 2500 2500 2500 2500

These are due to Roseleur.

153 STANDARD ELECTRICAL DICTIONARY.

Copper Stripping Bath. There is generally no object in stripping copper from objects. It can be done with any of the regular copper baths using the objects to be stripped as anode. The danger of dissolving the base itself and thereby injuring the article and spoiling the bath is obvious.

Cord Adjuster. A device for shortening or lengthening the flexible cord, or flexible wire supplying the current, and by which an incandescent lamp is suspended. It often is merely a little block of wood perforated with two holes through which the wires pass, and in which they are retained in any desired position by friction and their own stiffness.

Fig. 113. FLEXIBLE CORD ADJUSTER.

Cord, Flexible. A pair of flexible wire conductors, insulated lightly, twisted together and forming apparently a cord. They are used for minor services, such as single lamps and the like, and are designated according to the service they perform, such as battery cords, dental cords (for supplying dental apparatus) and other titles.

Core. (a) The conductor or conductors of an electric cable. (See Cable Core.)

(b) The iron mass, generally central in an electro-magnet or armature, around which the wire is coiled. It acts by its high permeance to concentrate or multiply the lines of force, thus maintaining a more intense field. (See Armature--Magnet, Electro--Magnet, Field--Core, Laminated). In converters or transformers (See Converter) it often surrounds the wire coils.

Core-discs. Discs of thin wire, for building up armature cores. (See Laminated Core.) The usual form of core is a cylinder. A number of thin discs of iron are strung upon the central shaft and pressed firmly together by end nuts or keys. This arrangement, it will be seen, gives a cylinder as basis for winding the wire on.

Core-discs, Pierced. Core-discs for an armature of dynamo or motor, which are pierced around the periphery. Tubes of insulating material pass through the peripheral holes, and through these the conductors or windings are carried. The conductors are thus embedded in a mass of iron and are protected from eddy currents, and they act to reduce the reluctance of the air gaps. From a mechanical point of view they are very good. For voltages over 100 they are not advised.

Synonym--Perforated Core-discs.

154 STANDARD ELECTRICAL DICTIONARY.

Core-discs, Segmental. Core-discs made in segments, which are bolted together to form a complete disc or section of the core. The plan is adopted principally on large cores. The discs thus made up are placed together to form the core exactly as in the case of ordinary one piece discs.

Fig. 114. PIERCED OR PERFORATED CORE-DISC.

Core-discs, Toothed. Core-discs of an armature of a dynamo or motor, which discs are cut into notches on the periphery. These are put together to form the armature core, with the notches corresponding so as to form a series of grooves in which the wire winding is laid. This construction reduces the actual air-gaps, and keeps the wires evenly spaced. Distance-pieces of box-wood, m, m, are sometimes used to lead the wires at the ends of the armature.

Fig. 115. TOOTHED CORE-DISC.

Core, Laminated. A core of an armature, induction coil or converter or other similar construction, which is made up of plates insulated more or less perfectly from each other. The object of lamination is to prevent the formation of Foucault currents. (See Currents, Foucault.) As insulation, thin shellacked paper may be used, or sometimes the superficial oxidation of the plates alone is relied on. The plates, in general, are laid perpendicular to the principal convolutions of the wire, or parallel to the lines of force. The object is to break up currents, and such currents are induced by the variation in intensity of the field of force, and their direction is perpendicular to the lines of force, or parallel to the inducing conductors.

A core built up of core discs is sometimes termed a tangentially laminated core. Made up of ribbon or wire wound coil fashion, it is termed a radially laminated core.

155 STANDARD ELECTRICAL DICTIONARY.

Core Ratio. In a telegraph cable the ratio existing between the diameter of the conducting core and the insulator. To get a ratio approximately accurate in practical calculations, the diameter of the core is taken at 5 per cent. less than its actual diameter. The calculations are those referring to the electric constants of the cable, such as its static capacity and insulation resistance.

Core, Ribbon. For discoidal ring-shaped cores of armatures, iron ribbon is often used to secure lamination and prevent Foucault currents.

Synonym--Tangentially Laminated Core.

Core, Ring. A core for a dynamo or motor armature, which core forms a complete ring.

Core, Stranded. In an electric light cable, a conducting core made up of a group of wires laid or twisted together.

Core, Tubular. Tubes used as cores for electro-magnets. For very small magnetizing power, tubular cores are nearly as efficient as solid ones in straight magnets, because the principal reluctance is due to the air-path. On increasing the magnetization the tubular core becomes less efficient than the solid core, as the reluctance of the air-path becomes proportionately of less importance in the circuit.

Corpusants. The sailors' name for St. Elmo's Fire, q. v.

Coulomb. The practical unit of quantity of electricity. It is the quantity passed by a current of one ampere intensity in one second. It is equal to 1/10 the C. G. S. electro-magnetic unit of quantity, and to 3,000,000,000 C. G. S. electrostatic units of quantity. It corresponds to the decomposition of .0935 milligrams of water, or to the deposition of 1.11815 milligrams of silver.

[Transcriber's note: A coulomb is approximately 6.241E18 electrons. Two point charges of one coulomb each, one meter apart, exerts a force of 900,000 metric tons.]

Coulomb's Laws of Electrostatic Attraction and Repulsion. 1. The repulsions or attractions between two electrified bodies are in the inverse ratio of the squares of their distance.

2. The distance remaining the same, the force of attraction or repulsion between two electrified bodies is directly as the product of the quantities of electricity with which they are charged.

156 STANDARD ELECTRICAL DICTIONARY.

Counter, Electric. A device for registering electrically, or by electro-magnetic machinery, the revolutions of shafts, or any other data or factors.

Counter-electro-motive Force. A potential difference in a circuit opposed to the main potential difference, and hence, resisting the operation of the latter, and diminishing the current which would be produced without it. It appears in electric motors, which, to a certain extent, operate as dynamos and reduce the effective electro-motive force that operates them. It appears in the primary coils of induction coils, and when the secondary circuit is open, is almost equal to the main electro-motive force, so that hardly any current can go through them under such conditions. It appears in galvanic batteries, when hydrogen accumulates on the copper plate, and in other chemical reactions. A secondary battery is charged by a current in the reverse direction to that which it would normally produce. Its own potential difference then appears as a counter-electro-motive force.

Synonym--Back Electro-motive Force.

Counter-electro-motive Force of Polarization. To decompose a solution by electrolysis, enough electro-motive force is required to overcome the energy of composition of the molecule decomposed. A part of this takes the form of a counter-electromotive force, one which, for a greater or less time would maintain a current in the opposite direction if the original source of current were removed. Thus in the decomposition of water, the electrodes become covered, one with bubbles of oxygen, the others with bubbles of hydrogen; this creates a counter E. M. F. of polarization. In a secondary battery, the working current may be defined as due to this cause.

Synonym--Back Electro-motive Force of Polarization.

Couple. Two forces applied to different points of a straight line, when opposed in direction or unequal in amount, tend to cause rotation about a point intermediate between their points of application and lying on the straight line. Such a pair constitute a couple.

Couple, Voltaic or Galvanic. The combination of two electrodes, and a liquid or liquids, the electrodes being immersed therein, and being acted on differentially by the liquid or liquids. The combination constitutes a source of electro-motive force and consequently of current. It is the galvanic or voltaic cell or battery. (See Battery, Voltaic--Contact Theory--Electro-motive Force--Electro-motive Series.)

Coupling. The joining of cells of a galvanic battery, of dynamos or of other devices, so as to produce different effects as desired.

157 STANDARD ELECTRICAL DICTIONARY

Couple, 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 high degree of purity of chemicals. Thus, in a standard Daniell battery, the use of C. P. chemicals may be prescribed or advised.

Crater. The depression that forms in the positive carbon of a voltaic arc. (See Arc, Voltaic.)

Creeping. A phenomenon of capillarity, often annoying in battery jars. The solution, by capillarity, rises a little distance up the sides, evaporates, and as it dries more creeps up through it, and to a point a little above it. This action is repeated until a layer of the salts may form over the top of the vessel. To avoid it, paraffine is often applied to the edges of the cup, or a layer of oil, often linseed oil, is poured on the battery solution,

Crith. The weight of a litre of hydrogen at 0º C. (32º F.), and 760 mm. (30 inches) barometric pressure. It is .0896 grams. The molecular weight of any gas divided by 2 and multiplied by the value of the crith, gives the weight of a litre of the gas in question. Thus a litre of electrolytic gas, a mixture of two molecules of hydrogen for one of oxygen, with a mean 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 its own field.

(b) In a compound wound dynamo, the speed at which the same potential is generated with the full load being taken from the machine, as would be generated on open circuit, in which case the shunt coil is the only exciter. The speed at which the dynamo is self-regulating.

(c) In a dynamo the rate of speed when a small change in the speed of rotation produces a comparatively great change in the electro-motive force. It corresponds to the same current (the critical current) in any given series dynamo.

Cross. (a) A contact between two electric conductors; qualified to express conditions as a weather cross, due to rain, a swinging cross when a wire swings against another, etc.

(b) vb. To make such contact.

Cross-Connecting Board. A special switch board used in telephone exchanges and central telegraph offices. Its function is, by plugs and wires, to connect the line wires with any desired section of the main switchboard. The terminals of the lines as they enter the building are connected directly to the cross-connecting board.

158 STANDARD ELECTRICAL DICTIONARY.

Cross Connection. A method of disposing of the effects of induction from neighboring circuits by alternately crossing the two wires of a metallic telephone circuit, so that for equal intervals they lie to right and left, or one above, and one below.

[Transcriber's note: Also used to cancel the effect of variations in the ambient magnetic field, such as solar activity.]

Crossing Wires. The cutting out of a defective section in a telegraph line, by carrying two wires from each side of the defective section across to a neighboring conductor, pressing it for the time into service and cutting the other wire if necessary.

Cross-magnetizing Effect. A phase of armature interference. The current in an armature of a dynamo or motor is such as to develop lines of force approximately at right angles to those of the field. The net cross-magnetizing effect is such component of these lines, as is at right angles to the lines produced by the field alone.

Cross-over Block. A piece of porcelain or other material shaped to receive two wires which are to cross each other, and hold them so that they cannot come in contact. It is used in wiring buildings, and similar purposes. (See Cleat, Crossing.)

Cross Talk. On telephone circuits by induction or by contact with other wires sound effects of talking are sometimes received from other circuits; such effects are termed cross talk.

Crucible, Electric. A crucible for melting difficultly fusible substances, or for reducing ores, etc., by the electric arc produced within it. Sometimes the heating is due more to current incandescence than to the action of an arc.

Fig. 116. ELECTRIC FURNACE OR CRUCIBLE.

Crystallization, Electric. Many substances under proper conditions take a crystalline form. The great condition is the passage from the fluid into the solid state. When such is brought about by electricity in any way, the term electric crystallization may be applied to the phenomenon. A solution of silver nitrate for instance, decomposed by a current, may give crystals of metallic silver.

159 STANDARD ELECTRICAL DICTIONARY.

Cup, Porous. A cup used in two-fluid voltaic batteries to keep the solutions separate to some extent. It forms a diaphragm through which diffusion inevitably takes place, but which is considerably retarded, while electrolysis and electrolytic convection take place freely through its walls. As material, unglazed pottery is very generally used.

In some batteries the cup is merely a receptacle for the solid depolarizer. Thus, in the Leclanché battery, the cup contains the manganese dioxide and graphite in which the carbon electrode is embedded, but does not separate two solutions, as the battery only uses one. Nevertheless, the composition of the solution outside and inside may vary, but such variation is incidental only, and not an essential of the operation.

Current. The adjustment, or effects of a continuous attempt at readjustment of potential difference by a conductor, q. v., connecting two points of different potential. A charged particle or body placed in a field of force tends to move toward the oppositely charged end or portion of the field. If a series of conducting particles or a conducting body are held so as to be unable to move, then the charge of the field tends, as it were, to move through it, and a current results. It is really a redistribution of the field and as long as such redistribution continues a current exists. A current is assumed to flow from a positive to a negative terminal; as in the case of a battery, the current in the outer circuit is assumed to flow from the carbon to the zinc plate, and in the solution to continue from zinc to carbon. As a memoria technica the zinc may be thought of as generating the current delivering it through the solution to the carbon, whence it flows through the wire connecting them. (See Ohm's Law--Maxwell's Theory of Light--Conductor-Intensity.)

[Transcriber's note: Supposing electric current to be the motion of positive charge causes no practical difficulty, but the current is actually the (slight) motion of negative electrons.]

Current, After. A current produced by the animal tissue after it has been subjected to a current in the opposite direction for some time. The tissue acts like a secondary battery. The term is used in electro-therapeutics.

Current, Alternating. Usually defined and spoken of as a current flowing alternately in opposite directions. It may be considered as a succession of currents, each of short duration and of direction opposite to that of its predecessor. It is graphically represented by such a curve as shown in the cut. The horizontal line may denote a zero current, that is no current at all, or may be taken to indicate zero electro-motive force. The curve represents the current, or the corresponding electro-motive forces. The further from the horizontal line the greater is either, and if above the line the direction is opposite to that corresponding to the positions below the line. Thus the current is alternately in opposite directions, has periods of maximum intensity, first in one and then in the opposite sense, and between these, passing from one direction to the other, is of zero intensity. It is obvious that the current may rise quickly in intensity and fall slowly, or the reverse, or may rise and fall irregularly. All such phases may be shown by the curve, and a curve drawn to correctly represent these variations is called the characteristic curve of such current. It is immaterial whether the ordinates of the curve be taken as representing current strength or electromotive force. If interpreted as representing electro-motive force, the usual interpretation and best, the ordinates above the line are 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 current which will liberate in 24 hours (86,400 seconds) one gram of hydrogen gas, in a water voltameter. The atomic current is equal to 1.111 amperes. In telegraphic work the milliatom is used as a unit, comparable to the milliampere. The latter is now displacing it.

Current, Charge. If the external coatings of a charged and uncharged jar are placed in connection, and if the inner coatings are now connected, after separating them they are both found to be charged in the same manner. In this process a current has been produced between the outside coatings and one between the inner ones, to which Dove has given the name Charge Current, and which has all the properties of the ordinary discharge current. (Ganot.)

Current, Circular. A current passing through a circular conductor; a current whose path is in 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 such a current. In electric series, incandescent lighting, a constant current is 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 speed when a slight difference in speed produces a great difference in electro-motive force. On the characteristic curve it corresponds to the point where the curve bends sharply, and where the electro-motive force is 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 a current produced by one Daniell cell in a circuit of the resistance of one 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 injured muscle, the injured portion acting electro-negatively toward the uninjured portion.

Current Density. The current intensity per unit of cross-sectional area of the conductor. The expression is more generally used for electrolytic conduction, where the current-density is referred to the mean facing areas of the electrodes, or else to the facing area of the cathode only.

The quality of the deposited metal is intimately related to the current density. (See Burning.)

Proper Current Density for Electroplating Amperes Per Square Foot of Cathode.--(Urquhart.) Copper, Acid Bath. 5.0 to 10.0 " Cyanide Bath, 3.0 " 5.0 Silver, Double Cyanide, 2.0 " 5.0 Gold, Chloride dissolved in Potassium Cyanide, 1.0 " 2.0 Nickel, Double Sulphate, 6.6 " 8.0 Brass, Cyanide, 2.0 " 3.0

Current, 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 difference between the liquid on opposite sides of the diaphragm is maintained. Electrodes or terminals of platinum may be immersed in the liquid, and a continuous current, termed a diaphragm current, may be taken as long as the liquid is forced through the diaphragm. The potential difference is proportional to the pressure, and also depends on the nature of the diaphragm and on the liquid.

162 STANDARD ELECTRICAL DICTIONARY.

Current, Direct. A current of unvarying direction, as distinguished from an alternating current. It may be pulsatory or intermittent in character, but must be of constant direction.

Current, Direct Induced. On breaking a circuit, if it is susceptible of exercising self-induction, q. v., an extra current, in the direction of the original is induced, which is called "direct" because in the same direction as the original. The same is produced by a current in one circuit upon a parallel one altogether separated from it. (See Induction, Electro-Magnetic-Current, Extra.)

Synonym--Break Induced Current.

Current, Direction of. The assumed direction of a current is from positively charged electrode to negatively charged one; in a galvanic battery from the carbon or copper plate through the outer circuit to the zinc plate and back through the electrolyte to the carbon or copper plate. (See Current.)

[Transcriber's note: Current is caused by the motion of negative electrons, from the negative pole to the positive. The electron was discovered five years after this publication.]

Current, Displacement. The movement or current of electricity taking place in a dielectric during displacement. It is theoretical only and can only be assumed to be of infinitely short duration. (See Displacement, Electric.)

Currents, Eddy Displacement. The analogues of Foucault currents, hypothetically produced in the mass of a dielectric by the separation of the electricity or by its electrification. (See Displacement.)

Current, Extra. When a circuit is suddenly opened or closed a current of very brief duration, in the first case in the same direction, in the other case in the opposite direction, is produced, which exceeds the ordinary current in intensity. A high potential difference is produced for an instant only. These are called extra currents. As they are produced by electro-magnetic induction, anything which strengthens the field of force increases the potential difference to which they are due. Thus the wire may be wound in a coil around an iron core, in which case the extra currents may be very strong. (See Induction, Self-Coil, Spark.)

Current, Faradic. A term in medical electricity for the induced or secondary alternating current, produced by comparatively high electro-motive force, such as given by an induction coil or magneto-generator, as distinguished from the 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 a field, or by altering the strength of a field in which they are contained. They are the source of much loss of energy and other derangement in dynamos and motors, and to avoid them the armature cores are laminated, the plane of the laminations being parallel to the lines of force. (See Core, Laminated.)

The presence of Foucault currents, if of long duration, is shown by the heating of the metal in which they are produced. In dynamo armatures they are produced sometimes in the metal of the windings, especially if the latter are of large diameter.

Synonyms--Eddy Currents--Local Currents--Parasitical Currents.

Current, Franklinic. In electro-therapeutics the current produced by a frictional electric machine.

Current, Induced. The current produced in a conductor by varying the conditions of a field of 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 on another portion of itself. (See Induction.)

Current Intensity. Current strength, dependent on or defined by the quantity of electricity passed by such current in a given time. The practical unit of current intensity is the ampere, equal to one coulomb of quantity per second of time.

Current, Inverse Induced. The current induced in a conductor, when in a parallel conductor or in one having a parallel component a current is started, or is increased in strength. It is opposite in direction to the inducing current and hence is termed inverse. (See Induction, Electro-magnetic.) The parallel conductors 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 being measured at 0º C. (32º F.) and 760 mm. (29.92 inches) barometric pressure. It is equal to .0961 ampere.

Current, Joint. The current given by several sources acting together. Properly, it should be restricted to sources connected in series, thus if two battery cells are connected in series the current they maintain is their joint current.

Current, Linear. A current passing through a straight conductor; a current whose path follows a straight line.

164 STANDARD ELECTRICAL DICTIONARY.

Current, Make and Break. A succession of currents of short duration, separated by absolute cessation of current. Such current is produced by a telegraph key, or by a microphone badly adjusted, so that the circuit is broken at intervals. The U. S. Courts have virtually decided that the telephone operates by the undulatory currents, and not by a make and break current. Many attempts have been made to produce a telephone operating by a demonstrable make and break current, on account of the above distinction, in hopes of producing a telephone outside of the scope of the Bell telephone patent.

[Transcriber's note: Contemporary long distance telephone service is digital, 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 the needle to the left.

Current, Nerve and Muscle. A current of electricity yielded by nerves or muscles. Under proper conditions feeble currents can be taken from nerves, as the same can be taken from muscles.

Current, Opposed. The current given by two or more sources connected in opposition to each other. Thus a two volt and a one volt battery may be connected in opposition, giving a net voltage of only one volt, and a current due to such net voltage.

Current, Partial. A divided or branch current. A current which goes through a single conductor to a point where one or more other conductors join it in parallel, and then divides itself between the several conductors, which must join further on, produces partial currents. It produces as many partial currents as the conductors among which it divides. The point of division 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 the needle to the right.