Chapter III: Preface (2)

Angle of Declination. The angle of error of the magnetic needle or compass, measuring the extent of its deviation from the meridian in any locality. It is the angle between the plane of the magnetic axis of a magnetic needle free to take its natural position, and the geographical meridian, the needle being counterpoised if necessary, so as to hold an absolutely horizontal position. The deviation is expressed as being east or west, referring always to the north pole. (See Magnetic Elements.)

Synonym--Variation of the Compass.

[Transcriber's note: See Agonic Line.]

Angle of the Polar Span. In a dynamo or motor the angle subtended by the portion of a pole piece facing the armature, such angle being referred to the centre of the cross-section of the armature as its centre.

STANDARD ELECTRICAL DICTIONARY. 33

Angular Velocity. The velocity of a body moving in a circular path, measured with reference to the angle it passes over in one second multiplied by the radius and divided by the time. A unit angle is taken (57°.29578 = 57° 17' 44".8 nearly) such that it is subtended by a portion of the circumference equal in length to the radius. Hence, the circumference, which is 360°, is equal to 2*PI*unit angle, PI being equal to 3.1416--. "Unit angular velocity" is such as would in a circle of radius = 1 represent a path = 1, traversed in unit time = 1 second. If the radius is r and the angle passed over is theta, the distance is proportional to r*theta; if this distance is traversed in t seconds the angular velocity is theta / t. The angular velocity, if it is multiplied by r, theta expressing a distance, will give the linear velocity. The dimensions of angular velocity are an angle (= arc / radius) / a Time = (L/L)/T = (T^-1).

The velocity expressed by the rate of an arc of a circle of unit radius, which arc subtends an angle of 57° 17' 44".8, such arc being traversed in unit time, is unit angular velocity.

Animal Electricity. Electricity, notably of high tension, generated in the animal system, in the Torpedo, Gymnotus and Silurus. The shocks given by these fish are sometimes very severe. The gymnotus, or electric eel, was elaborately investigated by Faraday. It has the power of voluntarily effecting this discharge. There is undoubtedly some electricity in all animals. The contact of the spinal column of a recently killed frog with the lumbar muscles produces contraction, showing electric excitement. Currents can be obtained from nerve and muscle, or from muscle sides and muscle cut transversely, in each case one thing representing positive and the other negative elements of a couple.

Angle of Inclination or Dip. The angle which the magnetic axis of a magnet, which magnet is free to move in the vertical plane of the magnetic meridian, makes with a horizontal line intersecting such axis. To observe it a special instrument, the dipping compass, inclination compass, dipping needle, or dipping circle, as it is called, is used. (See Elements, Magnetic, --Dipping Needle,--Compass, Inclination.)

Angle of Lag. The angle expressing the displacement of the magnetic axis of the armature core of a dynamo in the direction of its rotation. (See Lag.) Lag is due to the motion of the armature core.

Angle of Lead. The angle expressing the displacement in the direction of rotation of the armature of a dynamo which has to be given the brushes to compensate for the lag. (See Lag.) This is positive lead. In a motor the brushes are set the other way, giving a negative angle of lead or angle of negative lead.

Anion. The electro-negative element or radical of a molecule, such as oxygen, chlorine or the radical sulphion. (See Ions.) It is the portion which goes to the anode, q.v., in electrolytic decomposition.

34 STANDARD ELECTRICAL DICTIONARY.

Anisotropic. (adj.) Unequal in physical properties, as in conduction and specific inductive capacity, along various axes or directions. An anisotropic conductor is one whose conductivity varies according to the direction of the current, each axis of crystallization in a crystalline body marking a direction of different conductivity. An anisotropic medium is one varying in like manner with regard to its specific inductive capacity. In magnetism an anisotropic substance is one having different susceptibilities to magnetism in different directions. The term is applicable to other than electric or magnetic subjects.

Synonym--AEolotropic.

Annealing, Electric. Annealing by the heat produced by the passage of the electric current through the body to be annealed. The object is clamped or otherwise brought into a circuit, and a current strong enough to heat it to redness, or to the desired temperature is passed through it.

Annunciator. An apparatus for announcing a call from any place to another, as from a living-room to an office in a hotel, or for announcing the entering of any given room or window in a building protected by a burglar alarm.

A usual system comprises for each annunciator an electro-magnet. Its armature is normally held away from its poles by a spring, and when in that position a latch connected to the armature holds a little shutter. When by a push-button or other device a current is sent through a circuit which includes the electro-magnet the armature is attracted, this releases the latch and the shutter drops. In dropping it displays a number, letter or inscription which indicates the locality of the push-button or other circuit-closing device. Often annunciators are connected in circuit with a bell.

Fig. 14. ANNUNCIATOR.

35 STANDARD ELECTRICAL DICTIONARY.

Annunciator Clock. A clock operating an annunciator by making contact at determined times.

Annunciator Drop. The little shutter which is dropped by some forms of annunciators, and whose fall discloses a number, character or inscription, indicating whence the call was sent.

Fig. 15. DROP ANNUNCIATOR.

Fig. 16. ANNUNCIATOR DETACHING MECHANISM.

Annunciator, Gravity Drop. An annunciator whose operations release shutters which fall by gravity.

Annunciator, Needle. A needle annunciator is one whose indications are given by the movements of needles, of which there is usually a separate one for each place of calling.

Annunciator, Swinging or Pendulum. An annunciator which gives its indications by displacing from its vertical position a pendulum or vertically suspended arm.

36 STANDARD ELECTRICAL DICTIONARY.

Anodal Diffusion. A term in electro-therapeutics; the introduction of a medicine into the animal system by using a sponge-anode saturated with the solution of the drug in question. On passing a current the desired result is secured by cataphoresis, q. v.

Anode. The positive terminal in a broken metallic or true conducting circuit; the terminal connected to the carbon plate of a galvanic battery or to its equivalent in case of any other generator. In general practice it is restricted to the positive terminal in a decomposition or electrolytic cell, such as the nickel anode in a nickel-plating bath or the anode of platinum in a gas voltameter. It is the terminal out of or from which the current is supposed to flow through the decomposition cell. In electro-therapeutics the term is used simply to indicate the positive terminal. In an electrolytic cell the electro-negative substance or anion goes to the anode. Hence, it is the one dissolved, if either are attacked. The nickel, copper or silver anodes of the electroplater dissolve in use and keep up the strength of the bath. The platinum anode in a gas voltameter is unattacked because the anion cannot act upon it chemically.

Anodic Closure Contraction. A physiological change in a living subject produced by the closing of the electric current; the muscular contraction which takes place beneath the anode applied to the surface of the body when the circuit is closed, the kathode being applied elsewhere; it is due, presumably, to direct action on the motor nerve. It is a term in electro-therapeutics. It is the converse of anodic opening contraction, q. v. An abbreviation A. C. C. is often used to designate it.

Anodic Duration Contraction. A term in electro-therapeutics. On the opening or closing of an electric circuit, the anode of which is placed over a muscle, a contraction is observed (see Anodic Closure Contraction--Anodic Opening Contraction). The above term is used to designate the duration of such contraction. An abbreviation A. D. C. is often used to designate it.

Anodic Opening Contraction. The converse of Anodic Closure Contraction, q. v.; it is the contraction of living muscle beneath or near the anode where the circuit, including such anode and the body in its course, is closed; a physiological phenomenon observed in electro-therapeutics to which branch of science the term belongs. An abbreviation A. O. C. is often used to designate it.

Anodic Reactions. A term in electro-therapeutics; the diagnosis of disease by the actions of the tissue near the anode of a circuit.

Anti-Induction Conductor. A conductor constructed to avoid induction effects in the conducting element. Many kinds have been made. A tubular metal shield or envelope which may be grounded will protect an enclosed conductor to some extent. Or the conductor may be a double wire twisted around itself, one branch being used for the regular and the other for the return circuit, thus constituting a closed metallic circuit. The inductive effects are due to interrupted or varying currents in neighboring wires and circuits. Many anti-induction conductors have been invented and patented.

37 STANDARD ELECTRICAL DICTIONARY.

Anti-magnetic Shield. In general terms a hollow screen of soft iron designed to protect any mass of steel behind or enclosed by it from magnetization by any magnet near it, such as a dynamo field magnet. This it does by concentrating the lines of force within its own mass, so that the space within it or enclosed by it is comparatively free from lines of force. It is often applied to watches, and is virtually an iron case in which they are enclosed.

Antimony. A metal, one of the elements, atomic weight, 122: equivalent, 40.6 and 24.4; valency, 3 and 5; specific gravity, 6.8. It is a conductor of electricity. Relative resistance, compressed (silver = 1), 23.60 Specific resistance, 35.50 microhms. Resistance of a wire, (a) 1 foot long, weighing 1 grain, 3.418 ohms. (b) 1 foot long, 1/1000 inch thick, 213.6 " (c) 1 meter long, weighing 1 gram, 2.384 " (d) 1 meter long. 1 millimeter thick, 0.4521 "

Resistance of a 1-inch cube, 13.98 microhms.

Approximate percentage resistance per degree C. (1.8º F. at 20º C. 88º F.) 0.389 per cent.

Elcctro-chemical equivalent (hydrogen = .0105) .2560 (See Thermo-Electric Series.)

Anvil. An intermittent contact, or "make and break" of the current is sometimes produced by directly pressing a key down upon a metallic surface, the two being terminals of the circuit. The surface or stud on which such pressure is produced is called the anvil. The ordinary telegraph key, which makes a contact by the pressure of the operator's fingers does it by making a contact between a contact piece upon the front end of the key and the anvil. In the induction coil the anvil is also found. Thus in the cut representing the end of an induction coil and its circuit breaker in which O and O' and P and P' represent the secondary circuit terminal connections A is the core of soft iron wires, h is the anvil; the hammer when resting upon it so as to be in contact closes the circuit. When the current coming from the primary to the post i, passes through the hammer and anvil h, and emerges by m, it magnetizes the core; this attracts the hammer, which is made of or is armed with a mass of iron. This breaks the circuit. The hammer falls at once on the anvil, again making the circuit, and the action is repeated with great rapidity. Hammer and anvil or key and anvil connections should be made of platinum.

Fig. 17. INDUCTION COIL CIRCUIT BREAKER.

38 STANDARD ELECTRICAL DICTIONARY.

A. O. C. Abbreviation for Anodic Opening Contraction, q. v.

Aperiodic. adj. In an oscillating apparatus, or in the oscillating member of apparatus, the fact of having no reference to time of vibration; dead-beat.

Synonym. Dead-beat.

39 STANDARD ELECTRICAL DICTIONARY.

Fig. 18. ARAGO'S DISC.

Arago's Disc. An apparatus consisting of a disc of copper mounted horizontally, or on a vertical spindle, and so arranged as to be susceptible of rapid rotation. Immediately over it, and best with a pane of glass intervening, a magnetic needle is mounted on a pivot directly over the axis of the disc. If the disc is rotated the lines of force of the magnet are cut by it, and consequently currents are produced in the copper. These currents act upon the needle and cause it to rotate, although quite disconnected. It is advisable for the needle to be strong and close to the disc, which should rotate rapidly.

Arc v. To form a voltaic arc.

Arc, Compound. A voltaic arc springing across between more than two electrodes.

Arc, Metallic. The voltaic arc produced between terminals or electrodes of metal. The characteristics of such arc as contrasted with the more usual arc between carbon electrodes are its greater length for the same expenditure of energy, its flaming character and characteristic colors due to the metals employed. It is sometimes, for the latter reason, used in spectroscopic investigations.

Arc Micrometer. A micrometer for measuring the distance between the electrodes of a voltaic arc.

Arc, Simple. A voltaic arc produced, as usual, between only two electrodes.

40 STANDARD ELECTRICAL DICTIONARY.

Arc, Voltaic. The voltaic arc is the arc between two carbon electrodes slightly separated, which is produced by a current of sufficient strength and involving sufficient potential difference. The pencils of carbon are made terminals in a circuit. They are first placed in contact and after the current is established they are separated a little. The current now seems to jump across the interval in what sometimes appears an arch of light. At the same time the carbon ends become incandescent. As regards the distance of separation with a strong current and high electro-motive force, the arc may be several inches long.

The voltaic arc is the source of the most intense heat and brightest light producible by man. The light is due principally to the incandescence of the ends of the carbon pencils. These are differently affected. The positive carbon wears away and becomes roughly cupped or hollowed; the negative also wears away, but in some cases seems to have additions made to it by carbon from the positive pole. All this is best seen when the rods are slender compared to the length of the arc.

It is undoubtedly the transferred carbon dust which has much to do with its formation. The conductivity of the intervening air is due partly, perhaps, to this, but undoubtedly in great measure to the intense heating to which it is subject. But the coefficient of resistance of the intervening air is so much higher than that of any other part of the circuit that an intense localization of resistance occurs with corresponding localization of heating effect. This is the cause of the intense light. Thus if the carbons are but 1/32 of an inch apart as in a commercial lamp the resistance may be 1.5 ohms. The poor thermal conductivity of the carbon favors the concentration of heat also. The apparent resistance is too great to be accounted for by the ohmic resistance of the interposed air. A kind of thermoelectric effect is produced. The positive carbon has a temperature of about 4,000° C. (7,232° F.), the negative from 3,000° C. (5,432° F.) to 3,500° C. (6,322° F.). This difference of temperature produces a counter-electro-motive force which acts to virtually increase the resistance of the arc. The carbon ends of an arc can be projected with the lantern. Globules are seen upon them due to melted silica from the arc of the carbon.

Fig. 19. EXPERIMENTAL APPARATUS FOR PRODUCING THE VOLTAIC ARC.

41 STANDARD ELECTRICAL DICTIONARY.

Areometer. An instrument for determining the specific gravity of a fluid. It consists of an elongated body ballasted so as to float vertically and provided with a mark or a scale. It floats deeper in a light than in a heavy liquid. If it carries but one mark weights are added until that mark is reached, when the weights required give the specific gravity. Or the scale may give the reading directly based upon the depth to which it sinks. Areometers are often made of glass, ballasted with shot or mercury enclosed in their bottom bulb as shown. They are used in regulating battery solutions, and in watching the charging and discharging of storage batteries.

Fig. 20. AREOMETER

Fig. 21. BEAD AREOMETER

Areometer, Bead. A tube of glass containing beads of different specific gravities. It has apertures at top and bottom. When immersed in a liquid, the same fills it, and the specific gravity within certain limits, depending on the factors of the beads, is shown by the beads which float and those which sink. It is used for storage batteries and other purposes where acids and solutions have to be tested.

Argyrometry. The method of ascertaining the weight and inferentially the thickness of an electroplater's deposit of silver. It is done by weighing the article before and after plating.

Arm. The four members of a Wheatstone bridge, q. v., are termed its arms. Referring to the diagram of a bridge, P, Q, R, S, are the arms.

Fig. 22. DIAGRAM OF WHEATSTONE'S BRIDGE.

Armature. (a.) A mass or piece of iron or steel, or a collection of pieces of iron designed to be acted on by a magnet. While nickel or cobalt might be used, they rarely or never are except in experimental apparatus. The armature of a permanent horse shoe magnet is simply a little bar of soft iron. When the magnet is not in use it is kept in contact with the poles with the idea of retaining its magnetism. It is then said to be used as a keeper. A bar magnet does not generally have an armature. The armature is also used to exhibit the attraction of the magnet.

Sometimes an armature is made of steel and is permanently magnetized. Such an armature, termed a polarized armature, is repelled when its like poles are opposed to like poles of the magnet and otherwise is attracted with force due to the sums of the magnetism. If the magnet is sufficiently powerful depolarization of the armature may ensue when like poles are opposed to like poles. Polarized armatures are used in various appliances, magneto generators, telegraphic instruments and others.

(b) In a dynamo or Motor the mass of laminated iron or of wire which carries the coils of insulated wires which are caused to rotate in the field of force of the field magnets in order to establish and maintain potential difference with its accompanying current, or which rotates under the effects of a current in a motor. (See Dynamo Electric Generator.)

The work of the armature core is twofold. It acts as a portion of the magnetic circuit, conducting the lines of force, and by virtue of its high permeability or multiplying power concentrating a number of the lines of force through its own substance. To enable it to act with efficiency in this direction it should be made of iron of the highest permeability, and should approach as closely as possible to the armature cores consistent with leaving space for the wire winding. It next acts as a support for the wires which are to be swept through the field of force. Thus it acts both to establish a strong field and then acts as a carrier for the wires which are to be cut by the wires in question. In connection with this subject the different definitions under Armature, Dynamo, Commutator, Induction and similar topics may be consulted.

(c) See Armature of Influence Machine.

(d) See Armature of Leyden Jar or Static Condenser.

42 STANDARD ELECTRICAL DICTIONARY.

Armature, Bar. An armature in a dynamo or motor whose winding is made up of conductors in the form of bars, round, rectangular and of other sections. This type of armature conductor is objectionable as Foucault currents are produced in it. It is found best to laminate or subdivide low resistance armature windings.

[Transcriber's Note: Foucault currents are also called eddy currents.]

Armature, Bipolar. An armature in which two poles are induced by the field. A bipolar field magnet produces a bipolar armature.

Armature Bore. The cylindrical space defined by the pole pieces of a dynamo or motor within which the armature rotates.

Synonym--Armature Chamber.

43 STANDARD ELECTRICAL DICTIONARY.

Armature, Closed Coil. An armature for a motor or dynamo, the ends of all of whose coils are united, so as to be in one closed circuit all the way around.

Fig. 23. CLOSED COIL GRAMME RING ARMATURE.

Armature Coil, or Coils. The insulated wire wound around the core of the armature of an electric current generator or motor.

Armature Core. The central mass of iron on which the insulated wire, to be rotated in the field of an electric current generator or motor, is wound. (See Dynamo-electric Machine and Motor, Electric.)

Armature, Cylinder. An armature of the Gramme ring type, but longer in the axial direction, so that its core resembles a long hollow cylinder, the wire being wound inside and outside as in the Gramme ring. (See Gramme Ring.)

Armature, Disc. (a) An armature of a dynamo electric machine or motor in which the coils are wound so as to be flat and are carried on the face of a disc forming the core or part of the core of the armature. S. P. Thompson treats it as a modified drum armature extended radially, the outer periphery corresponding to the back end of the drum. The poles of the field are generally placed to face the side or sides of the disc.

(b) Another type of disc armature has its wire wound on bobbins arranged around the periphery of a disc.

In disc armatures there is often no iron core, their thinness enabling this to be dispensed with.

44 STANDARD ELECTRICAL DICTIONARY.

Fig. 24. DISC ARMATURE OF FRITSCHE MACHINE.

Fig. 25. PLAN OF WINDING PACINOTTI'S DISC ARMATURE.

Armature, Discoidal Ring. In a dynamo an armature of the shape of a ring of considerable radial depth of section as compared to its axial depth. It is generally made of iron ribbon or thin band wound to the proper size.

Synonym--Flat Ring Armature.

45 STANDARD ELECTRICAL DICTIONARY.

Armature, Drum. An armature for a dynamo or motor, consisting of a cylinder of iron preferably made up of discs insulated from each other by thin shellacked paper, or simply by their oxidized surfaces, and wound with wire parallel to the axis where it lies on the cylindrical periphery and crossing the heads approximately parallel to the diameter. It operates practically on the same principle as a Gramme Ring Armature. (See Gramme Ring.)

Synonym--Cylindrical Armature.

Armature Factor. The number of conductors on an armature, counted or enumerated all around its external periphery.

Armature, Hinged. An armature pivoted to the end of one of the legs of an electro-magnet so as to be free to swing and bring its other end down upon the other pole.

Fig. 26. HINGED ARMATURES OF CLUB-FOOT ELECTRO MAGNETS.

Armature, Hole. An armature whose core is perforated to secure cooling.

Synonym--perforated Armature.

Armature, Intensity. An armature wound for high electro-motive force. A term little used at the present time.

Armature Interference. A limit to the ampere turns permissible on a given armature is found in the increase of cross magnetizing effect, q. v., the increased lead necessitated, and the growth of the demagnetizing power. All such perturbing effects are sometimes expressed as armature interference.

46 STANDARD ELECTRICAL DICTIONARY.

Armature, Load of. The circumflux, q. v., of the armature, or the ampere turns of the same. The maximum load which can be carried by an armature without sparking is directly proportional to the radial depth of core and to the length of the gap, and inversely proportional to the breadth of the polar span.

Armature, Multipolar. An armature in which a number of poles greater than two is determined by the field. A multipolar field is employed for its production.

Armature, Neutral. An armature of a magnet or telegraph relay which is not polarized or magnetized.

Synonym--Non-polarized Armature--Neutral Relay Armature.

Armature of Influence Machine. Pieces of paper pasted on the stationary plate of an electric machine of the Holtz type.

Armature of Leyden Jar or Static Condenser. The inner and outer tin-foil coatings of a Leyden jar or other condenser.

Armature, Open Coil. An armature of a dynamo or motor on which the coils are not joined in one closed circuit, but have their ends or some of them separated, and connected each to its own commutator bar or each set to their own bar.

Fig. 27. OPEN COIL RING ARMATURE.

47 STANDARD ELECTRICAL DICTIONARY.

Armature, Pivoted. An armature for an electro-magnet mounted on a pivot, which is at right angles to the yoke or parallel with the legs of the magnet, so as to be free to rotate. When the magnet is excited the armature is drawn into line or approximately so with its base or yoke. The system is used in some telegraph apparatus.

Armature Pockets. Spaces or recesses in armatures provided for the reception of the coils.

Armature, Polarized. An armature made of steel or having a steel core to which permanent magnetism has been imparted. Such are used in some forms of magneto current generators, and in telegraphic instruments. (See Relay, Polarized.)

Armature, Pole. An armature having coils wound on separate poles projecting radially all around the periphery of its central hub or disc, or projecting internally from a ring-like frame, their ends facing the field magnet.

Synonym--Radial Armature.

Armature, Quantity. An armature of a dynamo or motor wound for current of large quantity. The term is now but little used.

Armature-Reactions. When an armature is running in an active dynamo a series of reactions is established, the more important of which are: I. A tendency to cross-magnetize the armature. II. A tendency to spark at the brushes. III. A tendency for the armature current to demagnetize on account of the lead which has to be given to the brushes. IV. Variations in the neutral points as more or less current is taken from the machine. V. Heating of armature, both core and conductors, and of pole pieces, which heating is due to Foucault currents.

Armature, Revolving, Page's. An early form of motor. The field is produced by a permanent magnet. Above its poles is a soft iron armature wound with a coil of insulated wire. A two-part commutator with contact springs conveys the current to the coil. The whole is so arranged that the polarity of the armature, as induced by the coil, through which a current is passed, is reversed as its ends sweep by the poles of the magnet. Then it is repelled from the poles and swings through 180° to have its polarity reversed and to go through the next 180°, and so on. Thus it rotates at a very high rate of speed.

In the cut showing the elevation A, B, is the armature; f, g, the springs or brushes; h, the commutator with its sections o, i. In the section of the commutator W, W, designate the springs or brushes, A, the vertical spindle carrying the armature and commutator, and S, S, the commutator sections.

48 STANDARD ELECTRICAL DICTIONARY.

Fig. 28. PAGE'S REVOLVING ARMATURE.

Fig. 29. SECTION OF COMMUTATOR OF PAGE'S REVOLVING ARMATURE. W, W, Brushes; A, Spindle; S, S, Armature Segments.

Armature, Ring. An armature whose core is in the shape of a ring, as the Gramme Ring Armature. (See Figs. 23 & 27.)

49 STANDARD ELECTRICAL DICTIONARY.

Armature, Rolling. (a) An armature for a permanent horseshoe magnet consisting of a straight cylinder of soft iron on which a heavy wheel is mounted. When the legs of the magnet are inclined downward and the bar is laid across them it rolls down to the poles, across their ends, and back up the under side. It is merely a magnetic toy or illustrative experiment.

Synonym--Wheel Armature.

(b) Another form consists of little bars of iron with brass discs attached to the ends. On placing two of these together and bringing the poles of a magnet near them, as shown, they become magnetized with like polarity by induction and repel each other, rolling away in opposite directions.

Fig. 30. ROLLING OR WHEEL ARMATURE.

Fig. 31. ROLLING ARMATURES.

Armature, Shuttle. The original Siemens' armature, now discarded. The core was long and narrow, and its cross section was nearly of the section of an H. The grooves were wound full of wire, so that the whole formed almost a perfect cylinder, long and narrow comparatively. (See Winding Shuttle.)

Synonym--Siemens' Old Armature--Girder Armature--H Armature.

Fig. 32. SHUTTLE OR H ARMATURE.

Armature, Spherical. An armature of a dynamo which is wound on a spherical core, so as to be almost a sphere. It is employed in the Thomson-Houston dynamo, being enclosed in a cavity nearly fitting it, formed by the pole pieces.

Armature, Stranded Conductor. A substitute for bar-armatures in which stranded copper wire conductors are substituted for the solid bar conductors, to avoid Foucault currents. (See Armature, Bar.)

50 STANDARD ELECTRICAL DICTIONARY.

Armature, Unipolar. An armature of a unipolar dynamo. (See Dynamo Unipolar.)

Armor of Cable. The metal covering, often of heavy wire, surrounding a telegraph or electric cable subjected to severe usage, as in submarine cables.

Synonym--Armature of Cable.

Arm, Rocker. An arm extending from a rocker of a dynamo or motor, to which arm one of the brushes is attached. (See Rocker.) Ordinarily there are two arms, one for each brush.

Articulate Speech. Speech involving the sounds of words. It is a definition which has acquired importance in the Bell telephone litigations, one contention, concerning the Bell telephone patent, holding that the patentee did not intend his telephone to transmit articulations, but only sound and music.

Astatic. adj. Having no magnetic directive tendency due to the earth's magnetism. Examples are given under Astatic Needle; Circuit, Astatic; and Galvanometer Astatic.

Fig. 33. NOBILI'S PAIR.

FIG. 34. VERTICAL PAIR ASTATIC COMBINATION.

Astatic Needle. A combination of two magnetic needles so adjusted as to have as slight directive tendency as possible. Such a pair of needles when poised or suspended will hardly tend to turn more to one point of the compass than another. The combination is generally made up of two needles arranged one above the other, with their poles in opposite directions. This combination is usually called Nobili's pair. If of equal strength and with parallel magnetic axes of equal length they would be astatic. In practice this is very rarely the case. A resultant axis is generally to be found which may even be at right angles to the long axis of the magnets, causing them to point east and west. Such a compound needle requires very little force to turn it one way or the other. If one of the needles is placed within a coil of insulated wire a feeble current will act almost as strongly to deflect the system as if the other was absent, and the deflection will only be resisted by the slight directive tendency of the pair of needles. This is the basis of construction of the astatic galvanometer. Sometimes coils wound in opposite directions and connected in series, or one following the other, surround both needles, thus producing a still greater effect of deflection.

Other astatic needles are shown in the cuts below. [Figures 33 to 35.]

51 STANDARD ELECTRICAL DICTIONARY.

FIG. 35. SIMPLE ASTATIC NEEDLE.

Asymptote. A line continuously approached by a curve, but which the curve, owing to its construction or nature of curvature, can never touch, be tangent to, or intersect.

Atmosphere. (a) A term applied to the atmospheric pressure as a practical unit of pressure equal to 15 lbs. to the square inch as generally taken. It is really about 14.7 lbs. per square inch, or 1,033 grams per square centimeter.

(b) Air, q. v.

Atmosphere Residual. The atmosphere left in a vessel after exhaustion. The term may be applied to any gas. In an incandescent lamp after flashing the residual atmosphere consists of hydro-carbons.

Atmospheric Electricity. The electricity of the atmosphere, rarely absent, but often changing in amount and sign. Benjamin Franklin, in a memoir published in 1749, indicated the method of drawing electricity from the clouds by pointed conductors. In June, 1752, he flew a kite and by its moistened cord drew an electric spark from the clouds, confirming his hypothesis that lightning was identical with the disruptive discharge of electricity. To observe electricity in fine weather a gold-leaf or other electroscope may be connected to the end of a long pointed insulated conductor. The electricity during thunderstorms can be shown by a similar arrangement, or burning alcohol or tinder gives an ascending current of warm air that acts as a conductor. Quite elaborate apparatus for observing and recording it have been devised. Atmospheric electricity is usually positive, but occasionally negative. When the sky is cloudless it is always positive, increasing with the elevation and isolation of the place. In houses, streets, and under trees no positive electricity can be found. In the Isle of Arran, Scotland, a rise of 24 to 48 volts per foot of increase in elevation was found by Sir William Thomson. At sunrise the electrification of the air is feeble, it increases towards noon and decreases again to reach a second maximum a few hours after sunset. It increases with the barometric pressure generally. In cloudy weather it is sometimes negative and the sign often changes several times in the same day. In a thunderstorm the changes in sign and potential are very rapid. The cause of atmospheric electricity is far from clear. Tait attributes it to a contact effect between air and water vapor, Solmeke to friction of water vesicles against ice particles in the upper atmosphere, he first showing that the two may coexist. The cause of the enormous increase of potential producing lightning is attributed to the decreased capacity due to the change of water from cloud vesicles to drops, thus diminishing the electrostatic capacity of the water in question. (See Lightning.)

52 STANDARD ELECTRICAL DICTIONARY.

Atom. The ultimate particle or division of an elementary substance; the smallest part that can exist in combination, and one which cannot exist alone. An elementary substance is composed of molecules just as truly as a compound one, but the atoms in the molecule of an elementary substance are all precisely alike. Hence atoms are the units of chemistry, they have to do with combinations, but the physical unit, the smallest particle of matter that can have an independent existence, is the molecule. The two are often confounded, especially by writers of a few years ago, so that by "atom" the molecule is often meant. There is nothing to be said of their size or mass. All such calculations refer to the molecule, q. v., often spoken of and called the atom.

[Transcriber's note: Yet to be discovered: electron--1897 (5 years), proton--1920 (28 years), neutron--1932 (30 years), quark--1961 (69 years).]

Atomic Attraction. The attraction of atoms for each other, in virtue of which they combine into molecules; chemical affinity, q. v., treats principally of this, although molecular attraction also plays a part in it.

Atomic Heat. The product of the atomic weight of a substance by its specific heat. This product is approximately the same, 6.4; this approximation is so close that it is of use in determining the valency and atomic weights of substances. The atomic weight of a substance therefore represents the approximate number of gram-calories required to raise one gram-atom, q. v., of such substance through 1° C. (1.8° F.)

Atomicity. The quantivalence or valency of the atoms; the number of combination bonds, or bonds of affinity, possessed by the atoms of any substance. Thus two atoms of hydrogen combine with one atom of oxygen, and three of oxygen with one of sulphur, forming saturated compounds. Therefore, taking hydrogen as of single atomicity or a monad, oxygen is of double atomicity or a dyad, and sulphur is of six-fold atomicity, or a hexad. The elements are thus classified into seven orders of atomicities, thus:

1, Monads or Univalent elements, Hydrogen, etc.
2, Dyads or Bivalent " Oxygen, etc.
3, Triads or Trivalent " Nitrogen, etc.
4, Tetrads or Quadrivalent " Lead, etc.
5, Pentads or Quinquivalent " Phosphorous, etc.
6, Hexads or Sexivalent " Chromium, etc.
7, Heptads or Septivalent " Chromium, etc.

The same element often possesses several atomicities. Barium is generally a dyad, sometimes a tetrad; nitrogen acts as a monad, dyad, triad, tetrad and pentad. The familiar electrolysis of water, giving two volumes of hydrogen to one of oxygen, is one of the illustrations of the theory indicating that two atoms of hydrogen are combined with one of oxygen.

53 STANDARD ELECTRICAL DICTIONARY.

Atomic Weight. The number expressing the relative weight of the atom of any substance, that of hydrogen being generally taken as unity. This is the universal system, although any other element might be taken as the basis of the system. The whole theory of atomic weights is based on the indivisibility of the atom and on the theory of atomicity, q. v. (See Equivalents.)

[Transcriber's note: The standard is now the isotope carbon-12 as exactly 12.]

Attraction. The tendency to approach and adhere or cohere, shown by all forms of matter. It includes gravitation, cohesion, adhesion, chemical affinity and other forms, and is opposed by repulsion, and is sometimes overcome by it, although it may be assumed to be always present. See the different kinds of attractions under their titles: Atomic Attraction, Electro-magnetic Attraction and Repulsion, Electro Static Attraction and Repulsion, Electro-dynamic Attraction and Repulsion; Magnetic Attraction and Repulsion; Molar Attraction.

Audiometer. An apparatus for obtaining a balance of induction from two coils acting upon a third. The third is placed between the other two and is free to move towards either. A scale is provided to show the extent of its movement. A varying or interrupted current being passed through the two outer coils, the preponderating current will produce the most induction if the central coil is equidistant. It can always be moved to such a point that there will be no inductive effect, one counteracting the other. Thus its position measures the relative induction. A telephone is in circuit with the intermediate coil and is used to determine when its position is such that no current is induced in it. It is sometimes used as a direct test of hearing. (See Hughes' Induction Balance.)

Synonym--Acoutemeter.

Aura, Electrical. The blast of air produced at highly electrified points.

Aurora. A luminous display seen in the northern heavens in the northern hemisphere, where it is the Aurora Borealis, and seen in the southern heavens in the southern hemisphere, where it is called Aurora Australis, or indifferently for either, the Aurora Polaris. It takes the form of pale luminous bands, rays and curtains varying in color. Near the poles they are very numerous. A French commission observed 150 auroras in 200 days. Their height is variously estimated at from 90 to 460 miles; they are most frequent at the equinoxes and least so at the solstices. There is a secular variation also, they attain a maximum of occurrence every 11 years together with sun spots, with a minimum 5 or 6 years after the maximum. There is also a period of 60 years, coincident with disturbances in the earth's magnetism. Various attempts have been made to account for them. They have a constant direction of arc with reference to the magnetic meridian (q. v.) and act upon the magnetic needle; in high latitudes they affect telegraph circuits violently. There is a strong probability that they represent electric currents or discharges. De la Rive considers them due to electric discharges between the earth and atmosphere, which electricities are separated by the action of the sun in equatorial regions. According to Balfour Stewart, auroras and earth currents.(q. v.) may be regarded as secondary currents due to small but rapid changes in the earth's magnetism. The subject is very obscure. Stewart treats the earth as representing the magnetic core of an induction coil, the lower air is the dielectric, and the upper rarefied and therefore conducting atmosphere is the secondary coil. This makes the aurora a phenomenon of induced currents. Then the sun may be regarded as the instigator of the primary changes in the earth's lines of force representing the primary of an induction coil.

[Transcriber's note: Solar wind, streams of electrons and protons, interacting with the earth's magnetic field causes aurora. Neither electrons (1897) nor protons (1920) were known in 1892. The Soviet satellite Luna first measured the solar wind in 1959. Even today increased understanding of solar and auroral phenomenon continues.]

54 STANDARD ELECTRICAL DICTIONARY.

Austral Pole. The north pole of the magnet is thus called sometimes in France; the austral pole of a magnet is the one which points towards the north polar regions As unlike magnetic poles attract each other, it is but rational to call the north-seeking pole of the magnet the south or Austral Pole. In the same nomenclature the south pole of a magnet, or the south-seeking pole, is called the Boreal Pole.

A. W. G. Abbreviation for American Wire Gauge, q. v.

Axis, Electric. The electric axis of a pyroelectric crystal, such as a tourmaline crystal; the line connecting the points of greatest pyroelectric excitability.

Axis of Abscissa. In a system of rectilinear, or right angle co-ordinates, the horizontal axis. (See Co-ordinates.)

Synonym--Axis of X.

Axis of Ordinates. In a system of rectilinear right angle co-ordinates, the vertical axis. (See Co-ordinates.)

Synonym--Axis of Y.

Azimuth. The angle between the plane of the meridian and the plane of an azimuth circle, q. v.

Azimuth Circle. A great circle, whose plane passes through the zenith or point of the heavens directly overhead; any great circle in whose plane the vertical at the point of observation is included.

Each celestial body has or determines an azimuth circle.

55 STANDARD ELECTRICAL DICTIONARY.

B. (a) Abbreviation for Baumé, a hydrometer scale. (See Baumé.) Thus 10º B. means "ten degrees Baumé."

(b) Symbol for the coefficient of induced magnetization, or the number of lines per square centimeter induced in a magnetic circuit or in any specified part of it.

B. A. Abbreviation for British Association. It is prefixed to standards fixed by the committee of the British Association for the Advancement of Science. Thus the B. A. ohm means the British Association ohm, a measure of resistance which is equal to the resistance of a column of mercury 104.9 centimeters long and one square millimeter area of cross-section. (See Ohm.)

Back Induction. A demagnetizing force produced in a dynamo armature when a lead is given the brushes. The windings by such setting of the brushes are virtually divided into two sets, one a direct magnetizing set, the other a cross magnetizing set. The latter have a component due to the obliqueness of the neutral line, which component is demagnetizing in its action.

Back Shock or Stroke of Lightning. A lightning stroke received after the main discharge of the lightning, and caused by a charge induced in neighboring surfaces by the main discharge. The discharge affects the evenness of distribution of surrounding surfaces so that a species of secondary discharge is required to make even the distribution, or to supply charge where needed to bind an opposite one. The effects are much lese severe as a rule than those of the main charge, although the back stroke has caused death. The back stroke is sometimes felt a considerable distance from the place of the original lightning stroke.

Synonym--Return Stroke.

Back Stroke. (a) In telegraphy the return stroke of the lever in a telegraph sounder, striking the end of the regulating screw with a sound distinct from that which it produces on the forward stroke as it approaches the magnet poles. It is an important factor in receiving by ear or sound reading.

(b) See Back Shock or Stroke of Lightning.

Balance. (a) Wheatstone's Bridge, q. v., is sometimes termed the Electric Balance.

(b) A suspension or torsion balance is one which includes a filament or pair of filaments to whose lower end or ends are attached a horizontal indicator often called a needle, or a magnetic needle. (See Torsion Balance.)

(c) See Induction Balance, Hughes'.

(d) For Thermic Balance, see Bolometer.

(e) See Balance, Ampere.

56 STANDARD ELECTRICAL DICTIONARY.

Balance, Ampere. A class of electrical measuring instruments due to Sir William Thomson may be grouped under this head.

The instrument is a true balance or scales such as used for weighing. It is supported by a torsional wire support in place of knife edges. At each end it carries a circle of wire through which the current to be tested is passed. The torsional wire support enables the current to be carried to these wire rings. Above and below each of these rings are two similar rings, also connected so as to receive the current. They are so connected that the current shall go through them in opposite senses. When a current passes, therefore, one of these rings repels and one attracts the balanced ring.

The extent of this action measures the intensity of the current. A sliding weight moving along a graduated scale on the balance is used to bring the balance beam into equilibrium when the current is passing. The degree of displacement of this weight gives the strength of the current in amperes.

These balances are made for different currents. Thus there is a centi-ampere balance, deka-ampere balance and others, as well as an ampere balance.

Balata. A gum used as an insulating material. It is the inspissated juice of a sapotaceous tree, the bullet tree, Mimusops globosa, of tropical America, from the Antilles to Guiana. It is intermediate in character between caoutchouc and gutta percha. It is superior to gutta percha in some respects, being very slightly acted on by light.

Synonym--Chicle.

B. & S.. W. G. Abbreviation for Brown & Sharpe Wire Gauge; the regular American Wire Gauge. (See Wire Gauge, American.)

Barad. An absolute or fundamental unit of pressure, equal to one dyne per square centimeter.

Barometer. An apparatus for measuring the pressure exerted by the atmosphere. It consists, in the mercurial form, of a glass tube, over 31 inches long, closed at one end, filled with mercury and inverted, with its open end immersed in a cistern of mercury. The column falls to a height proportional to the pressure of the atmosphere from 30 to 31 inches at the sea level. The "standard barometer" is a height of the mercury or of the "barometric column" of 30 inches or 760 centimeters, measured from the surface of the mercury in the cistern.

The column of mercury is termed the barometric column. Above it in the tube is the Torricellian vacuum.

[Transcriber's note: More accurately, 29.92 inches of mercury or 14.696 PSI.]

Bars of Commutators. The metal segments of a commutator of a dynamo or motor. They are made of bars of copper, brass or bronze insulated from one another. (See Commutator.)

Synonyms--Segments, Commutator Segments, Commutator Bars.

57 STANDARD ELECTRICAL DICTIONARY.

Bath. (a) In electro-plating the solution used for depositing metal as contained in a vat or tank; as a silver, copper, or nickel bath used for plating articles with silver, copper, or nickel respectively.

(b) In electro-therapeutics a bath with suitable arrangements, electrodes and connections for treating patients with electricity. It is termed an electric bath or electro-therapeutic bath.

Bath, Bipolar Electric. In electro-therapeutics a bath in which the electrodes are both immersed in the water. The patient placed between them receives part of the discharge. The electrodes are large copper plates, termed shovel electrodes.

Bath, Electric Shower. An electro-medical shower bath. The patient is placed on a metallic stove or support connected to one of the electric terminals. Water slightly alkaline is showered upon him. The other electrode is in connection with the water. The rain of drops and streamlets is the conductor of the current or discharge.

Bath, Multipolar Electric. An electro-medical bath with a number of electrodes instead of two.

Bath, Stripping. In electro-plating a solution used for dissolving and thus removing the plating from any object. The stripping bath is of the same general type as the plating bath for the same metal as the one to be dissolved. The object to be "stripped" is made the anode of a plating circuit, and as the current acts the old plating is attacked and dissolves, leaving the body of the article bare. It is simply the operation of plating reversed. The same term is applied to baths acting by simple solution. Stripping baths are described under the different metals as Silver Bath, Stripping--Gold Bath, Stripping.

Bath, Unipolar Electric. An electro-medical bath, in which only one electrode connects with the water of the bath. The second electrode is supported above the bath. The patient touches this while in the water whenever electric action is desired.

FIG. 36. THREE WIRE MOULDING OR BATTEN.

FIG. 37. TWO WIRE MOULDING OR BATTEN.

58 STANDARD ELECTRICAL DICTIONARY.

Batten. A strip of wood grooved longitudinally for holding wires in wiring apartments for electric light or power. In use they are fastened to the wall, grooves inward, or else grooves outward, with the wires lying in the grooves and covered with the covering strip. For two wire work each batten contains two grooves; for the three wire system it contains three grooves.

Synonym--Moulding.

Battery. A combination of parts or elements for the production of electrical action. The term is principally applied to voltaic batteries, but there are also magnetic batteries, batteries of Leyden jars, and other combinations, described in their places, which come under this category.

[Transcriber's note: A group of similar items such as questions, machines, parts, guns, or electric cells.]

Battery, Acetic Acid. A battery whose active solution or excitant is acetic acid or vinegar. This acid has been used by Pulvermacher in his medical battery, as being a substance found in every household in the form of vinegar. It is now but little used.

Battery, Alum. A battery using as excitant a solution of alum. This battery has had some application for electric clocks, but only to a limited extent.

Fig. 38. BALLOON OR FLASK BATTERY.

Battery, Aluminum. A battery in which aluminum is the negative plate and aluminum sulphate the excitant. It is mounted like the gravity battery. Its electro-motive force is 0.2 volt.

59 STANDARD ELECTRICAL DICTIONARY.

Battery, Bagration. A battery with zinc and carbon electrodes immersed in earth sprinkled with sal ammoniac (ammonium chloride). The copper is preferably first immersed in sal ammoniac solution and dried, until a green layer is formed on its surface.

The battery is highly praised for its constancy by De la Rive, but may be regarded as obsolete.

Battery, Balloon. A form of gravity battery into whose centre a globular flask, B, is inverted, which is filled before inversion with copper sulphate, of which 2 lbs. are used, and water, so as to remain full. This acts as a reservoir of copper sulphate, which it constantly supplies. The glass jar is closed with a perforated wooden cover.

Battery, Banked. (a) A battery arranged to feed a number of separate circuits.

(b) A battery connected in parallel or in multiple arc.

Battery, Bichromate. A battery with amalgamated zinc and carbon plates, with an exciting fluid composed of sulphuric acid, water, and potassium bichromate. For formula of such solutions see Electropoion Fluid--Kookogey's Solution--Poggendorff's Solution--Trouvé's Solution--Delaurier's Solution, and others. (See Index.)

Battery, Bunsen. A two fluid porous cell battery. The negative plate is carbon, the positive plate, amalgamated zinc. The depolarizer is nitric acid or electropoion fluid, q.v., in which the carbon is immersed. The last named depolarizer or some equivalent chromic acid depolarizing mixture is now universally used. The excitant is a dilute solution of sulphuric acid. Originally the carbon was made cylindrical in shape and surrounded the porous cups, in which the zinc was placed. This disposition is now generally reversed. The electro-motive force is 1.9 volts. The depolarizing solution is placed in the compartment with the carbon. The excitant surrounds the zinc.

Fig. 39. BUNSEN'S BATTERY.

60 STANDARD ELECTRICAL DICTIONARY.

Battery, Cadmium. A battery in which cadmium is the negative plate, sulphate of cadmium solution the excitant and depolarizer, and zinc the positive plate. Electro-motive force, .31 volt or about one third of a Daniell cell. It is mounted like a gravity battery.

Battery, Callan. A modification of Grove's battery. Platinized lead is used for the negative plate, and as a depolarizer a mixture of 4 parts concentrated sulphuric acid, 2 parts of nitric acid, and 2 parts of a saturated solution of potassium nitrate. (See Battery, Grove's.)

Battery, Camacho's. A battery with carbon negative and amalgamated zinc positive electrodes. The carbon is contained in a porous cup, packed with loose carbon. Electropoion or other fluid of that type serves as excitant and depolarizer, and is delivered as shown from cell to cell by syphons.

Fig. 40. CAMACHO'S BATTERY.

Battery, Carré's. A Daniell battery for whose porous cup a vessel or species of sack made of parchment paper is substituted. The battery has been used for electric light, and has been run for 200 successive hours, by replacing every 24 hours part of the zinc sulphate solution by water.

61 STANDARD ELECTRICAL DICTIONARY.

Battery, Cautery. A battery used for heating a platinum wire or other conductor used for cauterization in electro-therapeutics. The term is descriptive, not generic.