The Standard Electrical Dictionary - A Popular Dictionary of Words and Terms Used in the Practice - of Electrical Engineering
by T. O'Conor Slone
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Torque. A force tending to produce torsion around an axis. An example is the pulling or turning moment of an armature of an electric motor upon its shaft. It is often expressed as pounds of pull excited at the end of a lever arm one foot long.

The expression is due to Prof. James Thompson, then of the University of Glasgow.

"Just as the Newtonian definition of force is that which produces or tends to produce motion (along a line), so torque may be defined as that which produces or tends to produce torsion (around an axis). It is better to use a term which treats this action as a single definite entity than to use terms like 'couple' and 'moment,' which suggest more complex ideas." (S. P. Thompson.)

A force, acting with radius r gives a torque equal to f X r ; f and r may be expressed in any units. S. P. Thompson gives the following equivalents :

To reduce dyne-centimeters to gram centimeters, divide by 981 dyne-centimeters to meter-kilograms divide by 981E5 dyne-centimeter, to pound-feet divide by 13.56E6 pound-feet to meter-kilograms divide by 7.23

In each of these compound units the first unit is the force and the second unit is the radius or lever arm of the torque.

Synonyms—Turning Moment—Moment of Couple—Axial Couple—Angular Force—Axial Force.

Torsion Balance, Coulomb's. Originally an apparatus in which electrostatic attraction or repulsion is measured against the torsion of a filament, often of silk-worm cocoon fibre. It consists in one form of a cylindrical glass vessel in which a light shellac needle is suspended horizontally by a fibre. This needle carries at one end a gilded disc or sphere and is suspended by a fine wire, or filament. A proof plane, q. v., is excited by touching it to the body under trial; it is then inserted in the case. The disc on the needle is first attracted and then repelled. The position finally taken by the needle is noted. The force of torsion thus produced is determined by twisting the filament by the torsion head on the top of the apparatus so as to move the needle a certain distance towards the proof plane. The more the torsion-head has to be turned to carry the needle through a specified arc the greater is the torsion effected or the greater is the repulsion exerted, The torsional force of a wire is proportional to the angle of torsion; this gives the basis for the measurement.

With magnetic needle it is used to measure magnetic repulsion and attraction. The best material for the filament is quartz, but the instrument is not very much used.

Torsion Galvanometer. A galvanometer in which the torsion required to bring the index back to zero, when the current tends to displace it, is made the measure of the current strength or of the electro-motive force. It involves the use of a torsion head, q. v., or its equivalent.


Torsion Head. The handle and disc from whose undersurface the filament depends to which the needle or magnet is attached. It is turned to measure the torsional effect, the edge of the disc being marked or graduated so as to give the angle of deflection required to overcome the effect of the torque of the needle.

Torsion Suspension. Suspension by one or more wires, fibres, or ribands, involving the restitutive force of torsion. Thus fibre suspension, q. v., is a variety of torsion suspension.

Often a single riband of steel stretched horizontally and secured at both ends is used, the suspended object, e. g., a balance beam, being attached at its own centre to the centre of the stretched riband. Quite sensitive balances are constructed on this principle. It is peculiarly available where an electric current is to be transmitted, as absolute contact is secured, as in William Thomson's ampere balances.

Touch. A term applied to methods of magnetization, as "single touch," "double touch," or "separate touch," indicating how the poles of the inducing magnet or magnets are applied to the bar to be magnetized. Under the titles of Magnetization the different methods are described.

Tourmaline. A mineral; a subsilicate; characterized by the presence of boric trioxide, which replaces aluminum oxide. It is notable for possessing pyro-electric properties. (See Pyro-electricity.)

Tower, Electric. The tower used in the tower system, q. v., of arc light illumination.

Tower System. In electric lighting the system of lighting extended areas by powerful arc lamps placed on high towers, generally of iron or steel frame-work. The lights are thus maintained at a high elevation, giving greater uniformity of illumination than if they were lower, but at the expense of considerable light which is lost. Sometimes wooden masts are employed instead of towers.

The principle involved is that the intensity of light at any place given by a source of illumination varies with the square of its distance from the place in question. Hence in using strong arc lights it is an object to have the distances of all parts of the area illuminated at as nearly uniform distances from the light as possible. An approximation to uniformity is secured by placing the lamps at a very high elevation.


Transformer. In alternate current lighting the induction coil by which the primary current with high initial electro-motive force is caused to produce a secondary current with low initial electromotive force.

A typical transformer consists of a core of thin iron sheets. The primary is of comparatively thin wire and often of ten or more times as many turns as the secondary. The latter is of thicker wire. Where the ratio of 10 to 1 as regards number of turns in the primary and secondary obtains, the initial E. M. F. of the secondary is one-tenth that of the primary circuit.

The cores are laminated, as described, to avoid the formation of Foucault currents.

The counter-electro-motive force of the transformer when the secondary circuit is open, prevents any but the slightest current from passing through the primary. In proportion as the secondary is closed and its resistance diminished, as by lighting more lamps in parallel, the counter-electro-motive force of the transformer falls and more current passes through the primary.


The economy of the apparatus is in the fact that counter-electromotive force reduces current through a conductor without absorbing any energy. A resistance coil cuts down a current, but absorbs energy equal to the current multiplied by the potential difference between the terminals of the coil. This electric energy is converted into heat energy and is wasted. But the counter-electromotive force of a transformer is exerted to reduce current without production of heat and with little waste of energy. This is one of the advantages of the alternating current system of distribution of electric energy.

The object of a transformer being to secure safety to the person or to life by the separation of the high potential primary or street circuit, and the low potential house circuit, any contact of the two circuits in the converter is a source of danger. Special care should be taken to ensure absence of leakage, as it is termed. Mica or other insulation is sometimes employed to prevent the wires from coming in contact by piercing or sparking with the core and with each other.


Transformer, Commuting. A type of continuous current transformer, resembling a dynamo with armature and field both stationary, but with revolving commutator, by which the magnetic polarity of a double wound armature is made to rotate. This secures the desired action, of a change or lowering of potential.

Transformer, Continuous Alternating. An apparatus for transforming a continuous into an alternating current or the reverse. The combination of a continuous current dynamo with an alternating current one is sometimes employed. It is a form of motor dynamo.

Another type is a regular dynamo with ordinary commutator and with, in addition thereto, two, three or four contact rings, connecting to as many symmetrically disposed points in the winding of the armature. This will give out or receive alternating currents of two, three or four phases according to the number of collecting rings. One winding serves for both alternating and continuous currents.

Transformer, Continuous Current. A machine of the dynamo type for changing the potential of a circuit. In one form two armatures are mounted on one shaft in a single field or in separate fields; one is a motor armature driven by the original current; the other generates the new current. This is a motor dynamo. In 1874 Gramme constructed a machine with ring armature with two windings, of coarse and fine wire respectively, and with independent commutators. Such dynamo could transform currents up or down.

Continuous current transformers have attained an efficiency of 83 per cent. at full load, and of 75 per cent. at half load. Owing to the balancing of the self-inductions of the two windings these machines do not spark. As the driven and driving parts are contained in one rotating part their friction is very slight.

Transformer, Core. A transformer wound upon an enclosed core, such as the hedgehog transformer (see Transformer, Hedgehog), or common induction coil.


Transformer, Hedgehog. An induction coil transformer whose iron core is composed of a bundle of iron wires, which after the wire windings are in place have their ends spread out to reduce to some extent the reluctance of the circuit, which at the best is high, as the air acts as the return circuit.

This transformer has a low degree of hysteresis; and its efficiency for very small loads or for no load is superior to that of the closed magnetic circuit transformer.


Transformer, Multiple. A transformer connected in parallel with others between the two leads of the primary circuit. The term refers to the connection only and not to any peculiarity of the transformer itself.

Transformer, Oil. A transformer with oil insulation. The advantage of this insulation is that if pierced it at once closes, so that no permanent injury ensues. It is a self-healing form of insulation.

Transformer, Series. Transformers connected in series upon the primary circuits. The term, like "multiple transformers," only applies to the connection, not to the transformer. Series transformers are but little used.

Transformer, Shell. A transformer with its iron core entirely outside of and enclosing the primary and secondary winding. It may be made by the use of outer iron wire windings as core.

Transformer, Welding. The transformer used for electric welding. (See Welding, Electric.) It is a transformer with very long primary and exceedingly short and thick secondary. It is used with the alternating current in the primary, and produces in the secondary circuit which includes the bars to be welded a very low potential difference.

Owing to the very low resistance of the secondary circuit this low electro-motive force produces a very strong current, which develops the requisite heat. The same type of transformer is used for brazing and similar purposes.


Transmitter. In general electric phraseology, any instrument which produces signals to be transmitted through a line or circuit is a transmitter. Thus the Morse key in telegraphy or the Blake transmitter in telephony are examples of such.

Transmitter, Carbon. A form of microphone used as a telephone transmitter. (See Carbon Telephone.)

Transposing. A method of laying metallic circuits for telephoning. The wires at short intervals are crossed so that alternate sections lie on opposite sides of each other. It is done to avoid induction.

Transverse Electro-motive Force. Electro-motive force in a substance in which electric displacement is taking place, produced by a magnetic field. It is sometimes assigned as the cause of the Hall effect, q. v.

Trimmer, Brush. A shears for cutting off evenly and squarely the ends of copper dynamo brushes. The brushes when uneven from wear are removed from the brush holders, and their ends are sheared off in the trimmer.

Trolley. A grooved metallic pulley or set of pulleys which runs along an active wire of a circuit, a lead from which trolley goes to earth or connects with another wire, so that the trolley takes current generally for operating a street car motor placed upon the circuit leading from it; a rolling contact with an electric lead.

Trolleys are principally used on electric railroads, and are now universally of the sub-wire system, being at the end of a pole which is inclined backward and forced upward by springs, so as to press the trolley against the bottom of the wire. Thus the trolley does not increase the sagging of the wire, but tends to push it up a little in its passage.

Trolley, Double. A trolley with two rollers or grooved wheels, placed side by side, and running on two parallel leads of wire. It is adapted to systems employing through metallic trolley lines with the motors in multiple arc, connecting or across the two leads.

Trolley Section. An unbroken or continuous section of trolley wire.

Trouv's Solution. An acid exciting and depolarizing solution for a zinc-carbon battery. Its formula is as follows: Water, 80 parts; pulverized potassium bichromate, 12 parts; concentrated sulphuric acid, 36 parts; all parts by weight. The pulverized potassium bichromate is added to the water, and the acid is added slowly with constant stirring. As much as 25 parts potassium bichromate may be added to 100 parts of water. The heating produced by the acid and water dissolves nearly all the potassium salt. Use cold.


True Contact Force. A species of electro-motive force whose existence is supposed to be proved by the Peltier effect. The lowering in temperature of a contact of dissimilar metals is attributed to a force that helps the current on its way if in the direction of thermo-current proper to the junction and opposing it if in the reverse. The true contact force is taken to explain this phenomenon; thermo-electric force cannot, as there is no heat or cold applied to the junction.

Trumpet, Electric. An apparatus consisting of a vibrating tongue, kept in motion by electricity as in the buzzer, q. v., placed in the small end of a trumpet-shaped tube.

Trunking Switchboard. A telephone switchboard arranged in sections, which sections are connected by trunk lines, through which trunk lines the desired connections are made.

Trunk Lines. In telephone distribution systems, the lines connecting different stations, or different sections of a switch-board and used by anyone requiring such connections; one trunk line answers for a number of subscribers.

Tube, Electric. A tube of glass around which is pasted a series of tinfoil circles, diamonds, or little squares, or other form of interrupted conductor. The pieces generally are placed in the line of a spiral. When a static discharge of electricity takes place along the conductor a row of bright sparks is produced at the breaks in the conductor. These by reflection are multiplied apparently, and a beautiful effect of intersecting or crossing spirals of sparks is presented.

The experiment is in line with the luminous pane and lightning jar, and is used merely as a demonstration, or lecture experiment.

Synonym—Luminous Tube.

Tubular Braid. A braid woven of tissue or worsted, and tubular or hollow. Its object is to provide a covering which can be drawn over joints in covered wires. In making the joint the ends of the wires are necessarily bared, and a short piece of tubular braid is used for covering them. It is drawn by hand over the joint.

Turns. An expression applied to the convolutions of wire in a solenoid, electro-magnet, or other apparatus or construction of that kind. A turn indicates a complete encircling of the core or axis of the object. Thus a wire wound five times around a bar gives five turns.

While this is its primary meaning the term if compounded may refer to virtual turns. Thus an ampere-turn means one ampere passing through one turn. But ten ampere-turns may mean ten amperes passing through ten turns, five amperes passing through two turns, and so on. This use is analogous to a dimension of length in a compound word, as foot-pound.

[Transcriber's note: "But ten ampere-turns may mean ten amperes passing through ONE turn or one ampere through ten turns, and so on."]

There may be a number of kinds of turns qualified by descriptive adjectives, as series-turns, the turns of wire in a series circuit of a compound dynamo. In the same way there are shunt-turns. If series ampere-turns or shunt ampere-turns are meant the word ampere should be included.


Turns, Dead, of a Dynamo. The rotations of a dynamo armature while it is building itself up or exciting itself. The expression is a bad one, as it is likely to be confounded with the dead turns of armature wire.

Turns, Primary Ampere-. The ampere-turns in a primary circuit of an induction coil or transformer. In an electric welding transformer, or in the transformer used in the alternating current system, where efficiency is an important element, the ampere-turns in primary and secondary for an efficiency of 100 per cent. should be equal. In the case of an experimental induction coil other considerations outweigh that of mere efficiency. Insulation, including security from piercing, and the production of as long a spark as possible, are, in these cases, the controlling consideration.

[Transcriber's note: A 100 per cent efficient transformer is impossible, but over 99 per cent is common. At room temperature there is always some lost flux, eddy currents and resistive losses.]

Turns, Secondary Ampere-. The ampere-turns on the secondary circuit of an induction coil or transformer. These depend on the path provided for the current. If of negligible inductance, such as a number of incandescent lamps would provide, the ampere-turns should be equal to those of the primary coil. (See Turns, Primary Ampere.)

Typewriter, Electric. A typewriter in which the work of printing or of pressing the type faces against the paper, or printing ribbon, is done by electro-magnetic attraction. The keys close electric circuits, throwing the electro-magnetic action into play. This involves the use of electricity for what is ordinarily only a mechanical process. The strength of the impression, however, is independent of the touch of the operator. It has not come into very extensive use.

[Transcriber's note: IBM introduced widely used electric typewriters in 1935.]

Ultra-gaseous Matter. Gas so rarefied that its molecules do not collide or very rarely do so.

Experiments of very striking nature have been devised by Crookes and others to illustrate the peculiar phenomena that this matter presents. The general lines of this work are similar to the methods used in Geissler tube experiments, except that the vacua used are very much higher.

When the vacuum is increased so that but one-millionth of the original gas is left the radiant state is reached. The molecules in their kinetic movements beat back and forth in straight lines without colliding, or with very rare collisions. Their motions can be guided and rendered visible by electrification. A tube or small glass bulb with platinum electrodes sealed in it, is exhausted to the requisite degree and is hermetically sealed by melting the glass. The electrodes are connected to the terminals of an induction coil or other source of high tension electrification. The molecules which come in contact with a negatively electrified pole are repelled from it in directions normal to its surface. They produce different phosphorescent or luminous effects in their mutual collisions.

Thus if they are made to impinge upon glass, diamond or ruby, intense phosphorescence is produced. A piece of platinum subjected to molecular bombardment is brought to white heat. A movable body can be made to move under their effects. Two streams proceeding from one negative pole repel each other. The stream of molecules can be drawn out of their course by a magnet.

The experiments are all done on a small scale in tubes and bulbs, resembling to a certain extent Geissler tubes.

[Transcriber's note: These effects are caused by plasma—ionized gas and electrons.]


Unbuilding. The loss of its charge or excitation by a self-exciting dynamo. It is the reverse of building-up. The latter indicates the exciting of the field by the action of the machine itself; the former the spontaneous loss of charge on open circuit or from other cause.

Underground Conductor. An electric conductor insulated and placed under the surface of the earth, as distinguished from aerial conductors.

Underground Electric Subway. A subway for the enclosing of electric telegraph and other conductors under the surface, generally in the line of streets, to do away with telegraph poles and aerial lines of wire. Many systems have been devised. The general type includes tubes called ducts in sets, called conduits, bedded in concrete or otherwise protected. Every two or three hundred feet the sets lead into a cistern-like cavity called a manhole. The insulated wires or cables, generally sheathed with a lead alloy are introduced into the tubes through the man-holes. A rope is first fed through the tube. To do this short rods which screw together are generally employed. One by one they are introduced, and each end one is screwed to the series of rods already in the duct. When the end of the duct is reached the rope is fastened to the last rod, and the rods are then drawn through, unscrewed one by one and removed, the rope following them. By means of the rope a windlass or capstan may be applied to draw the cable into the duct. At least at every second man-hole the cables have to be spliced.

Each cable may contain a large number of conductors of small size for telephoning, or a smaller number for electric light and power. The tendency is now to separate the different classes of wires in important lines, placing the heavier wires on one side of the street and the telephone and telegraph wires on the other. This of course necessitates two separate conduits.

The advantage of underground distribution affects not only the appearance of streets in doing away with unsightly telegraph poles, but it also removes an element of danger at fires. Aerial wires interfere greatly with the handling of ladders at fires, and expose the firemen who attempt to cut them to danger to their lives from shock.


Unidirectional. adj. Having one direction as a "unidirectional current" or "unidirectional leak." The term is descriptive, and applicable to many cases.

Uniform. adj. Unvarying; as a uniform potential difference, uniform current or conductor of uniform resistance per unit of length. The term is descriptive, and its application and meaning are obvious.

Uniform Field of Force. A field of evenly distributed force; one in which the number of lines of force per unit of area of any equipotential surface is the same.

Unipolar. adj. Strictly speaking this term means having only one pole, and is applied to magnets, armatures and the like. In its use a solecism is involved, for there is no such condition possible as unipolar magnetism or distribution of magnetism. An example of its use is shown in unipolar magnets. (See Magnet, Unipolar.)

Unipolar Armature. An armature of a unipolar dynamo; an armature whose windings continuously cut the lines of force about the one pole, and hence whose polarity is unchanged in its rotation.

Unipolar Current Induction. Current induction produced by moving a conductor through a magnetic field of force so that it always cuts the lines in similar relation to itself. Thus it produces a constant current through its own circuit, if a closed one, and no commutator is required. As this case always in practice amounts to the cutting of lines of force in the neighborhood of a single pole the term unipolar is employed to designate the action.

The simplest representation of unipolar induction is the rotating of a conductor around the end of a bar magnet, its axis of rotation corresponding with the axis of the magnet.

Unipolar Dynamo. A dynamo in which one part of the conductor slides on or around the magnet, so as always to cut lines of force near the same pole of the magnet.

Unit. A directly or indirectly conventional and arbitrary quantity, in terms of which measurements of things with dimensions expressible in the chosen units are executed.

Thus for length the c. g. s. unit is the centimeter; the B. E. unit is the foot.


Unit, Absolute. A unit based on the three fundamental units of length, mass and time. These units are the centimeter, gram and second. Each one in itself may be termed a fundamental absolute unit. The system of such units is termed the centimeter-gram-second system.

Unit, Angle. A factor or datum in angular velocity, q. v. It is the angle subtended by a portion of the circumference equal in length to the radius of the circle. It is equal very nearly to 57.29578 or 57 17' 44.8".

Unit, B. A. This term, while logically applicable to any of the British Association units, is often restricted to the ohm as formerly defined by the British Association, the B. A. Unit of Resistance, q. v.

Unit, Fundamental. The three units of length, mass and time, the centimeter, gram and second, are termed fundamental units. On them is based the absolute system of units, and on multiples of them the practical system of units.

Unit Jar. A Leyden jar which is used as a unit of measure of charge.

It consists of a Leyden jar about 4 inches long and 3/4 inch diameter, with about 6 square inches of its outer and the same of its inner surface coated with tinfoil. It is placed between a source of electricity and a larger jar or battery of jars which is to be charged. The inner coating connects with the machine; the outer coating with the jars to be charged. Short conductors terminating in knobs connect with inner and outer coatings, and the knobs are adjusted at any desired distance apart.

By the charging operation the large jar or battery of jars receives a charge by induction, and the charge of the small jar is at first equal to this quantity. After a while a spark passes from knob to knob, discharging the small jar. This indicates the reception by the large jars of the quantity of electricity represented by the charge of the small jar. The charging goes on, and for every spark approximately the same quantity of electricity is received by the larger jars.

The sparking distance m is directly proportional to the quantity of electricity, and inversely proportional to the area of coated surface, or is proportional to the potential difference of the two coats. This is only true for short sparking distance, hence for accuracy the knobs should be adjusted not too far from each other.


Unit of Supply. A commercial unit for the sale of electric energy, as defined provisionally by the English Board of Trade; 1,000 amperes flowing for one hour under an E. M. F. of 1 volt; 3,600,000 volt-coulombs, or 1,000 watt-hours, are its equivalent. It is equal to 1000/746 = 1.34 electric horse power.

Synonym—Board of Trade Unit.

[Transcriber's note: Now called a kilowatt-hour.]

Units, Circular. A system of units of cross-sectional area, designed especially for use in describing wire conductors. The cross-sectional area of such is universally a circle, and the areas of two wires of different sizes vary with the square of their radii or diameters. Hence if the area of a circle of known diameter is determined it may be used as a unit for the dimensions of other circles. Any other circle will have an area proportioned to the area of the unit circle, as the squares of the diameters are to each other.

In practise the commonest circular unit is the circular mil. This is the area of a circle one mil, 1/1000 inch, in diameter and is equal to .0000007854 square inch. A wire two mils in diameter has an area of four circular mils; one ten mils in diameter has an area of one hundred circular mils.

Thus if the resistance of a given length of wire 1 mil in diameter is stated, the corresponding resistance of the same length of wire of the same material, but of other diameter, is given by dividing the first wire's resistance by the square of the diameter in mils of the wire in question.

As it is a basic unit, most conveniently applied by multiplication, the smaller units are used; these are the circular mil, and circular millimeter.

Units, Derived. Units derived by compounding or other processes, from the three fundamental units. Such are the units of area, volume, energy and work, momentum and electric units generally. In some cases the dimensions of the derived unit may reduce to those of a simple unit as inductance reduces to length, but the unit, as deduced from the fundamental ones, is still a derived unit.

Units, Practical. A system of units employed in practical computation. The absolute units, especially in electricity, have been found too large or too small, and the attempt to make them more convenient has resulted in this system. It is based on exactly the same considerations as the absolute system of units, except that multiples of the original fundamental units of length, mass, and time have been taken as the base of the new system. These basic units are multiples of the fundamental units. They are the following: The unit of length is 1E9 centimeters; the unit of mass is 1E-11 gram; the unit of time remains 1 second.

While this has conduced to convenience in giving better sized units, micro- and mega-units and other multiples or fractions have to be used. The following are the principal practical electric units:

Electrostatic Electromagnetic C. G. S Units. C. G. S. Units. Intensity-Ampere equal to 3E9 1E-1 Quantity-Coulomb " 3E9 1E-1 Potential-Volt " (1/3)* E-2 1E8 Resistance-Ohm " (1/9)* E-11 1E9 Capacity-Farad " 9E11 1E-9


Universal Battery System. A term in telegraphy. If several equal and high resistance telegraphic circuits are connected in parallel with each other from terminal to terminal of a battery of comparatively low resistance each circuit will receive the same current, and of practically the same strength as if only one circuit was connected. This is termed the universal battery system. It is a practical corollary of Ohm's law. The battery being of very low resistance compared to the lines the joining of several lines in parallel practically diminishes the total resistance of the circuit in proportion to their own number. Thus suppose a battery of ten ohms resistance and ten volts E. M. F. is working a single line of one hundred ohms resistance. The total resistance of the circuit is then one hundred and ten ohms. The total current of the circuit, all of which is received by the one line is 10/110 = .09 ampere, or 90 milliamperes. Now suppose that a second line of identical resistance is connected to the battery in parallel with the first. This reduces the external resistance to fifty ohms, giving a total resistance of the circuit of sixty ohms. The total current of the circuit, all of which is received by the two lines in equal parts, is 10/60 = .166 amperes. But this is equally divided between two lines, so that each one receives .083 ampere or 83 milliamperes; practically the same current as that given by the same battery to the single line. It will be seen that high line resistance and low battery resistance, relatively speaking, are required for the system. For this reason the storage battery is particularly available. The rule is that the resistance of the battery shall be less than the combined resistance of all the circuits worked by it.

Unmarked End. The south-seeking pole of a magnet, so called because the other end, called the marked end, is usually marked with a scratch or notch by the maker, while the south pole is unmarked.

V. (a) Symbol for velocity.

(b) Symbol or abbreviation for volume.

(c) Symbol or abbreviation for volt.


V. A. Symbol or abbreviation for voltaic alternatives, q. v.

Vacuum. A space destitute of any substance. The great pervading substance is in general sense the atmosphere. It is the gaseous mixture which surrounds and envelopes the earth and its inhabitants. It consists of a simple mixture of oxygen, 1 part, nitrogen, 4 parts, with 4 to 6 volumes of carbonic acid gas in 10,000 volumes of air, or about one cubic inch to one cubic foot. It presses with a force of about 14.7 lbs. per square inch under the influence of the force of gravity. The term vacuum in practise refers to any space from which air has been removed. It may be produced chemically. Air may be displaced by carbonic acid gas and the latter may be absorbed by caustic alkali or other chemical. The air may be expelled and the space may be filled with steam which is condensed to produce the vacuum. Of course in all cases the space must be included in an hermetically sealed vessel, such as the bulb of an incandescent lamp. But the universal method of producing a vacuum is by air pumps. An absolute vacuum means the entire absence of gas or air, something almost impossible to produce. A high vacuum is sometimes understood to mean one in which the path of the molecules is equal in length to the diameter of the containing vessels, as in Crookes' Radiometer and other apparatus for illustrating the radiant condition of matter. The air left after exhaustion is termed residual air or residual atmosphere.

[Transcriber's note: Dry air is about .78 nitrogen, .21 oxygen, .01 argon, .00038 carbon dioxide, and trace amounts of other gases. Argon was suspected by Henry Cavendish in 1785. It was discovered in 1894 by Lord Rayleigh and Sir William Ramsay.]

Vacuum, Absolute. A space free of all material substance. It is doubtful whether an absolute vacuum has ever been produced.

Vacuum, High. An approximate vacuum, so nearly perfect that the molecules of the residual gas in their kinetic motions rarely collide, and beat back and forth between the walls of the containing vessel, or between any solid object contained in the vessel and the walls of the vessel. The gas in such a vacuum is in the radiant or ultra-gaseous state. (See Ultra-gaseous Matter.)

Vacuum, Low. A vacuum inferior to a high vacuum; a vacuum in which the molecules collide with each other and do not move directly from side to side of the containing vessel.

Vacuum, Partial. A space partially exhausted of air so as to contain less than an equal volume of the surrounding atmosphere. It really should come below a low vacuum, but is often treated as synonymous therewith.

Vacuum, Torricellian. The vacuum existing above the mercurial column in a barometer tube. The principle of this vacuum is applied in the Geissler and other air pumps. (See Pump, Geissler—Pump, Sprengel—Pump, Swinburne.)


Valency. The relative power of replacing hydrogen or combining therewith possessed by different elements; the number of atomic bonds belonging to any element. Thus oxygen has a twofold valency, is bivalent or is a dyad, and combines with two atoms of hydrogen because the latter has a unitary atomicity, is monovalent or is a monad.

Valve, Electrically Controlled. A valve which is moved by or whose movements are regulated by electricity.

In the block system of railroad signaling the semaphores are worked by weights and pneumatic cylinders and pistons. The valves for admitting or releasing the compressed air are operated by coil and plunger mechanism. There are many other instances of the control of valves by the electric current.

Vapor Globe. A protecting glass globe surrounding an incandescent lamp, when the lamp is to be used in an atmosphere of explosive vapor, as in mines or similar places; or when in a place where it is exposed to dripping water which would break the hot lamp bulb if it fell upon it.

Variable Period. The period of adjustment when a current is started through a conductor of some capacity. It is the period of duration of the variable state, q. v., in a conductor. As indicated in the next definition in a cable of high electrostatic capacity a variable period of nearly two minutes may exist. This indicates the retardation in signaling to be anticipated in cables and other lines of high capacity.

Variable State. When an electric circuit is closed the current starts through the conductor with its full strength from the point of closure, and advances with a species of wave front so that some time elapses before it attains its full strength in the most distant parts of the conductor, owing to its having to charge the conductor to its full capacity at the given potential. The state of the line while the current thus varies is called the variable state.

A long telegraph line when a message is being transmitted may be always in the variable state. The current at the receiving end may never attain its full strength.

In the case of such a conductor as the Atlantic cable, 108 seconds would be required for a current to attain 9/10 of its full strength at the distant end, and but 1/5 second to attain 1/100 of its final value. During the period of increase of current the variable state exists.

Variation of the Compass. The declination of the magnetic needle. (See Elements, Magnetic.) As the declination is subject to daily, annual and secular variations, it is unfortunate that this term is synonymous with declination. Thus the variation of the compass means its declination, while there is also the variation of the declination and of other elements. The term variation of the compass is more colloquial than the more definite expression "declination," or "magnetic declination."


Variometer. An apparatus used in determining the relative values of the horizontal component of the earth's magnetic field in different places.

Varley's Condenser. A static condenser whose conducting surfaces are platinum electrodes immersed in dilute sulphuric acid. When the potential difference is 1/50th that of a Daniell's cell, two square inches of platinum have a capacity equal to that of an air condenser whose plates have an area of 80,000,000 square inches, and separated 1/8th of an inch from each other. As the E. M. F. increases the capacity also increases.

Varley's Resistances. Variable resistances formed of discs of carbonized cloth, q. v., piled up, and pressed together more or less firmly to vary the resistance as desired.

Varnish. A glossy transparent coating of the nature of paint, applied as a protective, or ornamental coating to objects.

Varnish, Electric. Alcoholic or etherial varnishes are the best for electrical apparatus. They dry quickly and perfectly, and tend to form surfaces unfavorable to the hygroscopic collection of water. Sealing wax dissolved in alcohol, or shellac dissolved in the same solvent are used for electrical apparatus, although the first is rather a lacquer than a varnish. Etherial solution of gum-copal is used to agglomerate coils of wire. It is well to bake varnished objects to harden the coating.

Varnish, Red. A solution of sealing wax in 90 per cent. alcohol. It is best made thin and applied in several coats, each coat being allowed to dry perfectly before the next is applied. It is often seen on Leyden jars. It is a protector from surface leakage.

Vat. A vessel for chemical or other solutions. A depositing vat is one in which a plating solution is worked, for the deposition of electroplate upon articles immersed in the liquid, and electrolyzed by an electric current.

Velocity. The rate of motion of a body. It is usually expressed in distance traversed per second of time. The absolute unit is one centimeter per second or kine. The foot per second is very largely used also.

The dimensions of velocity are length (L) divided by time (T) or L/T.

Velocity, Angular. Velocity in a circle defined by the unit angle, or the angle which subtends a circular arc equal in length to itself. The radius of the circle traversed by the moving body does not enter into this definition, as the real velocity of the object is not stated. If its angular velocity and the radius of the path it travels are given its actual velocity can be deduced.


Velocity of Signaling. The speed of transmission of electric signals is affected by the nature of the line, as regards its static capacity, and by the delicacy of the receiving instruments, which may need a more or less strong current to be affected. Thus of an original current one per cent. may suffice to operate a sensitive instrument. This might give almost the velocity of light, while if the instrument would only respond to the full current nearly two minutes (see Variable State) might be required for the production of a signal.

Velocity Ratio. A term applied to the ratios existing between the electrostatic and electro-magnetic units. If we take as numerators the dimensions of the different qualities in the electrostatic system, and their dimensions in the electro-magnetic system as denominators, the fractions thus obtained reduce to expressions containing only velocity or V in some form. Thus if we divide the dimensions of the electrostatic quantity by the dimensions of electro-magnetic quantity the quotient is simply V or velocity. A like division for potential, electrostatic and electro-magnetic gives (1/V), and so on.

The value of the velocity ratio is very nearly 3E10 (sometimes given as 2.98E10) centimeters per second. This is almost exactly that of light (2.9992E10 centimeters per second.) This is one of the proofs of Clerk Maxwell's magnetic theory of light. (See Maxwell's Theory of Light.)

[Transcriber's note: The SI metre was defined in 1983 such that the speed of light in a vacuum is exactly 299,792,458 metres per second or about 186,282.397 miles per second.]

Ventilation of Armature. In a dynamo or motor ventilation of the armature is often provided for by apertures through it in order to prevent heating. This heating is caused by Foucault currents. By proper disposition of the interior of the armature with properly disposed vanes and orifices an action like that of a fan blower can be produced, which by creating a current of air cools the machine very efficiently.

Verticity, Poles of. Points upon the earth's surface where the horizontal component of magnetic force disappears, leaving only the vertical component active. The term is derived from the verticity of the dipping needle when over either of them.


Vibration Period. In electrical resonance the period of a vibration in an electrical resonator. The length of this period indicates the quality of the resonator in responding to electrical oscillations by sympathetic vibration. For conductors of small resistance the period is thus calculated. Let T be the period of one-half a full vibration; L the absolute coefficient of self-induction expressed in centimeters or in henries X 10-9; C the electrostatic capacity of the terminals, also expressed in the same unit; v the velocity of light in centimeters per second. Then we have the formula

T = PI * SquareRoot( L * C ) / v

[Transcriber's note: If the inductance is in henries and the capacitance in farads, frequency in hertz = 1/(2 * PI * squareRoot( L * C ) )]

Vibration, Sympathetic. A vibration in a cord or other body susceptible of elastic vibration produced by the vibrations of exactly the same period in a neighboring vibrating body. Thus if two tuning forks are tuned to precisely the same pitch, and are placed near each other, if one is sounded it will start the other into vibration by sympathy.

In electricity its application is found in electric resonance experiments. The resonator has a definite period of electric resonance, and is made to give a spark by the exciter of identical period. This is by what may be called electric sympathetic vibration, and is exactly analogous to the action of the tuning forks upon each other.

Vibrator, Electro-magnetic. The make and break mechanism used on induction coils, or other similar apparatus in which by alternate attractions by and releases from an electro-magnet an arm or spring is kept in motion. In most cases the work is done by a single magnet, whose armature is attracted to the magnet, when the latter is excited, but against the action of a spring which tends to pull it away from the magnet. In its motions a make and break action is produced, to give the requisite alternations of attraction and release. Two electro-magnets may be connected so as alternately to be excited and keep an arm carrying a mutual armature in vibration, or the same result may be attained by a polarized relay. The make and break is illustrated under Bell, Electric—Coil, Induction— Anvil.

Villari's Critical Value. Magnetization induced or residual in a wire is diminished on stretching, provided that the magnetization corresponds to an inducing force above a certain critical value, known as above; this being (Sir Wm. Thomson) about 24 times the terrestrial intensity. Below that critical value tension increases the magnetization of a magnetized wire. The effects of transverse expansive stress are opposed to those of longitudinal stretching. (Daniell.)

Viole's Standard of Illuminating Power. A standard authorized by the International Congress of 1881. It is the light given by one square centimeter of platinum, melted, but just at the point of solidification. It is equal to 20 English standard candles almost exactly.

It has not been very widely accepted, the tendency among photometrists being to adhere to the old standards, carcel or candle. It is obvious that actual use of the Viole would be very inconvenient and would involve expensive apparatus, difficult to work with.



Vis Viva. The kinetic energy of a body in motion; "mechanical energy."

Vitreous Electricity. Positive electricity; the electricity produced on the surface of glass by rubbing it with silk and other substances. (See Electrostatic Series.)

The term "positive electricity" should be allowed to supplant it. It is the analogue and opposite of resinous electricity.

Vitriol, Blue. A colloquial or trade name for copper sulphate (Cu SO4).

Vitriol, Green. A colloquial or trade name for ferrous sulphate (Fe SO4).

Vitriol, White. A colloquial or trade name for zinc sulphate (Zn SO4).

Volt. The practical unit of electro-motive force or potential difference. It may be referred to various data.

An electro-motive force of one volt will cause a current of one ampere to flow through a resistance of one ohm.

A condenser of one farad capacity charged with one coulomb will have a rise of potential of one volt.

The cutting of 100,000,000 lines of force per second by a conductor induces one volt E. M. F.

A Daniell's battery gives an E. M. F. of 1.07 volts; about the most familiar approximate standard that can be cited.

It is equal to 1/300 absolute electrostatic unit.

It is equal to 1E8 absolute electro-magnetic units.

[Transcriber's note: The SI definition of a volt: The potential difference across a conductor when a current of one ampere dissipates one watt of power.]

Voltage. Potential difference or electro-motive force expressed in volts; as a voltage of 100 volts. Thus voltage may express the electro-motive force absorbed in a conductor, while electro-motive force is a term generally applied where it is produced, evolved or present in the object. The term voltage of a lamp expresses simply the volts required, but does not suggest the possession of electromotive force.


Voltage, Terminal. The voltage or potential difference at the terminals of an electric current generator, such as a dynamo, as distinguished from the total electro-motive force of the dynamo or generator.

In batteries the distinction is not generally made in practice; the total electro-motive force of the battery is made the basis of calculations.

Voltaic. adj. This adjective is used to qualify a great many things appertaining to or connected with current electricity. It is derived from Volta, the inventor of the voltaic battery, and now tends to displace the term "galvanic," formerly in general use.

Voltaic Alternatives. A term used in electro-therapeutics or medical electricity to indicate an alternating battery current.

Synonym—Alternative current.

Voltaic Effect. The potential difference developed by contact of different conductors. It is the basis of the contact theory, q. v., of electricity, although it may be accepted as the expression for a condition of things by those who reject the above theory. This potential difference is slight when the conductors are separated, but it is calculated that it would be enormous could the metals be so quickly separated as to hold each its own charge.

Thus if a copper and a zinc plate are assumed to be in contact, really 1/20000000 centimeter or 1/50000000 inch apart, they may be treated as a pair of condenser plates. Being so near, their density of charge, which is a strongly bound charge, is enormous. If it were possible to separate them without permitting any discharge, their potential would rise by the separation, on the principle of Epinus' condenser, q. v., to such an extent that they would spark through twenty feet of air. (See Volta's Fundamental Experiment.)

Voltaic Electricity. Electricity of low potential difference and large current intensity; electricity such as produced by a voltaic battery; current or dynamic electricity as opposed to static electricity.

Voltameter. In general an apparatus for determining the quantity of electricity passing through a conductor by measuring the electrolytic action it can perform.

Voltameter, Copper. An apparatus which may be of similar construction with the silver voltameter (see Voltameter, Silver), but in which a copper anode and a solution of copper sulphate are substituted for the silver anode and silver nitrate solution. One coulomb corresponds to .329 milligram or .005084 grain of copper deposited. It is not accepted as of as high a standard as the silver voltameter.

The electrodes should be placed half an inch from each other. Two square plate electrodes may conveniently be used, and not less than two square inches on each plate should be the area per ampere of current.


Voltameter, Differential, Siemens'. A volume or gas voltameter with duplicate eudiometers and pairs of electrodes. It is used for determining the resistance of the platinum conductor used in his pyrometer. A current divides between the two voltameters; in one branch of the circuit the platinum conductor is placed, in the other a known resistance. The current strength varying inversely with the resistance, the resistances of the two conductors are inversely proportional to the gas evolved.

Voltameter, Gas. A voltameter whose indications are based on the electrolysis of water, made an electrolyte by the addition of sulphuric acid. The gases evolved are measured. It may take several forms.

In one form it is an apparatus consisting of a single eudiometer or graduated glass tube with upper end closed and its lower end or mouth open, collecting the mixture of hydrogen and oxygen.

In the form shown in the cut three tubes are connected, the side tubes representing eudiometers. For each side tube there is a platinum electrode. In this apparatus the oxygen and hydrogen are connected in opposite tubes. A is an open tube filled with dilute sulphuric acid. By opening the cocks on B and C they can both be completely filled with acid. As shown in the cut, this operation is not yet completed. The hydrogen alone may in this case be measured.

The mixed gas voltameter has only one eudiometer.

The exact equivalents are only approximately known. The volume of mixed gases per coulomb is given as .1738 cubic centimeters (Ayrton); .172 cubic centimeters (Hospitalier); and other values by other authorities. The hydrogen is equal to 1/3 of the mixed gases almost exactly.

Synonyms—Volume Voltameter—Sulphuric Acid Voltameter.

The gas is measured at 0 (32 F.) and 76 centimeters, or 30 inches barometer.



If the gas is measured in cubic inches, the temperature in degrees F., and the barometric height in inches, the following formula may be used for reduction to standard pressure and temperature. It is the volume corresponding to one coulomb. ( .01058 * 30 * (491 + F - 32) ) / (h* 491)

For the metric measurements and degrees C. (.1738 * 76 * (273 + C)) / (h X 273)

Voltameter, Silver. An apparatus consisting of a platinum vessel containing a solution of silver nitrate into which solution a silver anode dips, whose end is wrapped in muslin to prevent the detachment of any particles. When a current is passed by connecting one terminal to the dish and the other to the rod, securing a proper direction of current, silver will be deposited on the dish and the same amount will be dissolved from the rod. The dish is weighed before and after the test. Its increase in weight gives the silver deposited.


In the cut Ag is the silver anode, Pt is the platinum dish, r is the conducting rod, p is a wooden standard, Cu is a copper plate on which the dish rests and which also serves as a conductor and contact surface, b is a muslin cloth to place over the silver plate to prevent detached particles falling in the dish; s s' are the binding screws.

The weight of silver corresponding to a coulomb is given variously by different authorities. Ayrton and Daniell take 1.11815 milligrams or .017253 grain of metallic silver. Other determinations are as follows: 1.1183 milligrams (Kohlrausch). 1.124 " (Merscart).

The solution of silver nitrate should be from 15 to 30 per cent. of strength. The current should not exceed one ampere per six square inches; or in other words not more than about 3/1000 grain of silver should be deposited per second on a square inch area of the dish. The edge of the silver disc or anode should be about equidistant from the side and bottom of the dish. The latter notes are due to Lord Rayleigh.


Voltameter, Weight. A voltameter in which the amount of decomposition is determined by weighing the products, or one of the products of the electrolysis. The titles Voltameter, Copper, and Voltameter, Silver, may be cited.


In the cuts are shown examples of weight gas voltameters. These are tubes light enough to be weighed when charged. Each contains a decomposition cell T, with its platinum electrodes, and charged with dilute sulphuric acid, while t is calcium chloride or other drying agent to collect any water carried off as vapor or as spray by the escaping gases; c are corks placed in position when the weighing is being executed, so as to prevent the calcium chloride from absorbing moisture from the air.

In use the tubes are weighed. They are then connected to the circuit, after removal of the corks, and the decomposition proceeds. After a sufficient time they are removed, the corks put in place, and they are weighed again. The loss gives the water decomposed.

The water corresponding to one coulomb is .09326 milligram .001430 grain, Ayrton, .092 " Hospitalier, .0935 " Daniell.


Voltametric Law. The law on which voltameters are based. The amount of chemical decomposition produced by an electric current in a given electrolyte is proportional to the quantity of electricity passed through the solution.


Volta's Fundamental Experiment. The moistened finger is placed on the upper plate of a condensing or electrophorous electroscope. The other hand holds a plate of zinc z, soldered to a plate of copper c. The lower plate is touched with the copper. On removing the cover the gold leaves l diverge and with negative electricity. Hence zinc is supposed to be positively electrified when in contact with copper. The experiment is used to demonstrate the contact theory of electricity.


Volta's Law of Galvanic Action. The electro-motive force between any two metals in an electro-chemical series (see Electro-Chemical Series) is equal to the sum of the electro-motive forces between all the intervening metals.

Volta's Law of Thermo-electricity. In a compound circuit, consisting of a number of different metals, all points of which are at the same temperature, there is no current.

Volt, B. A. The volt based on the B. A. ohm. It is equal to .9889 legal volt.

Volt, Congress. The volt based upon the congress or legal ohm; the legal volt.

Volt-coulomb. The unit of electric work; the watt-second; it is equivalent to 1.0E7 ergs. .24068 gram degree C. (calorie) .737337 foot lbs., .00134 horse power seconds.

Volt Indicator. A form of easily read voltameter for use in electric light stations and for similar work.

Volt, Legal. The legal volt based upon the legal ohm. It is equal to 1.00112 B. A. volt.

Voltmeter. An instrument for determining the potential difference of any two points.

In many cases it is a calibrated galvanometer wound with a coil of high resistance. The object to be attained is that it shall receive only an insignificant portion of current and that such portion shall suffice to actuate it. If connected in parallel with any portion of a circuit, it should not noticeably diminish its resistance.

The divisions into which ammeters range themselves answer for voltmeters. In practice the same construction is adopted for both. The different definitions of ammeters in disclosing the general lines of these instruments are in general applicable to voltmeters, except that the wire winding of the coils must be of thin wire of great length. The definitions of ammeters may be consulted with the above understanding for voltmeters.

In the use made of voltmeters there is a distinction from ammeters. An ammeter is a current measurer and all the current measured must be passed through it. But while a voltmeter is in fact a current measurer, it is so graduated and so used that it gives in its readings the difference of potential existing between two places on a circuit, and while measuring the current passing through its own coils, it is by calibration made to give not the current intensity, but the electro-motive force producing such current.

In use it may be connected to two terminals of an open circuit, when as it only permits an inconsiderable current to pass, it indicates the potential difference existing between such points on open circuit. Or it may be connected to any two parts of a closed circuit. Owing to its high resistance, although it is in parallel with the intervening portion of the circuit, as it is often connected in practice, it is without any appreciable effect upon the current. It will then indicate the potential difference existing between the two points.


Voltmeter, Battery. A voltmeter for use in running batteries. In one form (Wirt's) it is constructed for a low range of voltage, reading up to two and a half volts and having exactly one ohm resistance, thus giving the battery some work to do.

Voltmeter, Cardew. A voltmeter in which the current passing through its conductor heats such conductor, causing it to expand. Its expansion is caused to move an index needle. By calibration the movements of the needle are made to correspond to the potential differences producing the actuating currents through it. The magnetic action of the current plays no part in its operation. It is the invention of Capt. Cardew, R. E.

The construction of the instrument in one of its most recent forms is shown in the cut. On each side of the drum-like case of the instrument are the binding screws. These connect with the blocks m and n. To these the fine wire conductor is connected and is carried down and up over the two pulleys seen at the lowest extremity, its centre being attached to c. From c a wire is carried to the drum p, shown on an enlarged scale on the left of the cut. A second wire from the same drum or pulley connects to the spring S. The winding of the two wires is shown in the separate figure of c, where it is seen that they are screwed fast to the periphery of the little drum, and are virtually continuations of each other. By the screw A the tension of the spring S is adjusted.

On the shaft of the little drum p is a pinion, which works into the teeth of the cog-wheel r. The shaft of r is extended through the dial of the instrument, and carries an index. The dial is marked off for volts; g g and h h are standards for carrying the pulleys.


The action of the instrument is as follows. The current passing through the wire heats it. This current by Ohm's law is proportional to the electro-motive force between the terminals. As it is heated it expands and as it cools contracts, definite expanding and contracting corresponding to definite potential differences. As the wire expands and contracts the block or pin c moves back and forth, thus turning the drum p and cogwheel r one way or permitting it to turn the other way under the pull of the spring S.


In this construction for a given expansion of the wire the piece c only moves one half as much. The advantage of using a wire twice as long as would be required for the same degree of movement were the full expansion utilized is that a very thin wire can be employed. Such a wire heats and cools more readily, and hence the instrument reaches its reading more quickly or is more deadbeat, if we borrow a phraseology properly applicable only to instruments with oscillating indexes.

In the most recent instruments about thirteen feet of wire .0025 inch in diameter, and made of platinum-silver alloy is used.


If the potential difference to be measured lies between 30 and 120 volts the wire as described suffices. But to extend the range of the instrument a resistance in series is required. If such resistance is double that of the instrument wire, and remains double whether the latter is hot or cold the readings on the scale will correspond to exactly twice the number of volts. This is brought about in some instruments by the introduction in series of a duplicate wire, precisely similar to the other wire, and like it, carried around pulleys and kept stretched by a spring.

[Transcriber's note: If the series resistance is twice that of the voltmeter, the indicated voltage will be ONE THIRD of the total voltage.]

Thus whatever ratio of resistance exists between the two wires cold, it is always the same at any temperature, as they both increase in temperature at exactly the same rate. Tubes are provided to enclose the stretched wires and pulleys, which tubes are blackened.

The voltmeter is unaffected by magnetic fields, and, as its self-induction is very slight, it is much used for alternating currents. The tubes containing the wire may be three feet long.

Its disadvantages are thus summarized by Ayrton. It absorbs a good deal of energy; it cannot be constructed for small potential differences, as the wire cannot be made thicker, as it would make it more sluggish; there is vagueness in the readings near the zero point and sometimes inaccuracy in the upper part of the scale.

Volts, Lost. The volts at the terminals of a dynamo at full load fall short of their value on open circuit. The difference of the two values are termed lost volts.

Voltmeter, Electrostatic. A voltmeter based on the lines of the quadrant electrometer. It includes two sets of quadrants, each oppositely excited by one of the two parts, whose potential difference is to be determined. They attract each other against a controlling force as of gravity.

One form has the two sets poised on horizontal axes, bringing the parts so that the flat quadrants move in vertical planes.

In another form a number of quadrants are used in each set, the members of the two sets alternating with each other. One set is fixed, the others move and carry the index.

Vulcanite. Vulcanized india rubber which by high proportion of sulphur and proper vulcanization has been made hard. It is sometimes distinguished from ebonite as being comparatively light in color, often a dull red, while ebonite is black. For its electrical properties see Ebonite.

Both substances have their defects, in producing surface leakage. Washing with weak ammonia, or with dilute soda solution, followed by distilled water, is recommended for the surface, if there is any trouble with surface leakage. It may also be rubbed over with melted paraffine wax.


W. (a) A symbol or abbreviation for watt.

(b) A symbol or abbreviation for work.

(c) A symbol or abbreviation for weight.

Wall Bracket. A telegraph bracket to be attached to the external walls of buildings to which wires are attached as they come from the poles to reach converters, or for direct introduction into a building.

Wall Sockets. Sockets for incandescent lamps constructed to be attached to a wall.

Ward. Direction in a straight line; a term proposed by Prof. James Thompson. The words "backward" and "forward" indicate its scope.

Water. A compound whose molecule consists of two atoms of hydrogen and one atom of oxygen; formula, H2 O.

Its specific gravity is 1, it being the base of the system of specific gravities of solids and liquids.

If pure, it is almost a non-conductor of electricity. If any impurity is present it still presents an exceedingly high, almost immeasurable true resistance, but becomes by the presence of any impurity an electrolyte.

Water Equivalent. In a calorimeter of any kind the weight of water which would be raised as much as is the calorimeter with its contents by the addition of any given amount of heat received by the calorimeter.

Waterproof Lamp Globe. An outer globe for incandescent lamps, to protect them from water.

Watt. (a) The practical unit of electric activity, rate of work, or rate of energy. It is the rate of energy or of work represented by a current of one ampere urged by one volt electro-motive force; the volt-ampere.

It is the analogue in electricity of the horse power in mechanics; approximately, 746 watts represent one electric horse power.

Ohm's law, taken as C = E/R, gives as values for current, C and E/R, and for electro- motive force C R. In these formulas, C represents current strength, R represents resistance and E represents electro-motive force. Then a watt being the product of electro-motive force by current strength, we get the following values for rate of electric energy, of which the watt is the practical unit: (1) E2/R — (2) C*E — (3) C2 * R.

The equivalents of the watt vary a little according to different authorities. Ayrton gives the following equivalents: 44.25 foot pounds per minute—.7375 foot pounds per second—1/746 horse power. These values are practically accurate. Hospitalier gives .7377 foot pounds per second. Hering gives .737324 foot pounds per second, and 1000/745941 horse power.


It is equal to 1E7 ergs per second.


(c) It has been proposed to use the term as the unit of energy, instead of activity or rate of energy (Sir C. W. Siemens, British Association, 1882); this use has not been adopted and may be regarded as abandoned.

[Transcriber's note; Watt is a unit of POWER—energy per unit of time.]

Watt-hour. A unit of electric energy or work; one watt exerted or expended for one hour.

It is equivalent to : 866.448 gram-degrees C. (calories) 2654.4 foot lbs. 3600 watt-seconds or volt-coulombs. 60 watt-minutes.

Watt-minute. A unit of electric energy or work; one watt exerted or expended for one minute.

It is equivalent to 14.4408 gram-degrees C. (calories), 44.240 foot pounds, 60 watt seconds or volt-coulombs, 1/60 watt hour.

Watts, Apparent. The product in an alternating current dynamo of the virtual amperes by the virtual volts. To give the true watts this product must be multiplied by the cosine of the angle of lead or lag. (See Current, Wattless.)

[Transcriber's note: This is now called a volt-amp. The usual usage is KVA, or kilovolt-ampere.]

Watt-second. A unit of electric energy or work. One watt exerted or expended for one second.

It is equivalent to .24068 gram degree C. (calorie), .000955 lb. degree F., .737337 foot lbs., .0013406 horse power second (English), .0013592 horse power second (metric).


Waves, Electro-magnetic. Ether waves caused by electromagnetic disturbances affecting the luminiferous ether. (See Discharge, Oscillatory—Maxwell's Theory of Light—Resonance. Electric.)

[Transcriber's note: The Michaelson-Morley experiment (1887) had already called ether into question, but quantum theory and photons are decades in the future.]


Weber. (a.) A name suggested by Clausius and Siemens to denote a magnet pole of unit strength. This use is abandoned.

(b.) It has been used to designate the unit of quantity—the coulomb. This use is abandoned.

(c.) It has been used to designate the unit of current strength the ampere. This use is abandoned.

[Transcriber's note: Definition (a) is now used. One weber of magnetic flux linked to a circuit of one turn produces an electromotive force of 1 volt if it is reduced to zero at a uniform rate in 1 second.]

Weber-meter. An ampere-meter or ammeter. The term is not used since the term "weber," indicating the ampere or coulomb, has been abandoned.

Welding, Electric. Welding metals by heat produced by electricity. The heat may be produced by a current passing through the point of junction (Elihu Thomson) or by the voltaic arc. (Benardos & Olzewski.)


The current process is carried out by pressing together the objects to be united, while holding them in conducting clamps. A heavy current is turned on by way of the clamps and rapidly heats the metals at the junction, which is of course the point of highest resistance. As the metal softens, it is pressed together, one of the clamps being mounted with feed motion, flux is dropped on if necessary, and the metal pieces unite.

The most remarkable results are thus attained; almost all common metals can be welded, and different metals can be welded together. Tubes and other shapes can also be united. In many cases the weld is the strongest part.


The alternating current is employed. A special dynamo is sometimes used to produce it. This dynamo has two windings on the armature. One is of fine wire and is in series with the field magnets and excites them. The other is of copper bars, and connects with the welding apparatus, giving a current of high intensity but actuated by low potential.

Where the special dynamo is not used, an induction coil or transformer is used. The primary includes a large number of convolutions of relatively fine wire; the secondary may only be one turn of a large copper bar.

The cut shows in diagram an electric welding coil. P is the primary coil of a number of turns of wire; S S is the secondary, a single copper bar bent into an almost complete circle. It terminates in clamps D D for holding the bars to be welded. B C, B' C are the bars to be welded. They are pressed together by the screw J. The large coil I of iron wire surrounding the coils represents the iron core.

The real apparatus as at present constructed involves many modifications. The diagram only illustrates the principle of the apparatus.

In welding by the voltaic arc the place to be heated is made an electrode of an arc by connection with one terminal of an electric circuit. A carbon is connected to the other terminal. An arc is started by touching and withdrawal of the carbon. The heat may be used for welding, soldering, brazing, or even for perforating or dividing metal sheets.

Welding Transformer. The induction coil or transformer used in electric welding. For its general principles of construction, see Welding, Electric.

Wheatstone's Bridge. A system of connections applied to parallel circuits, including resistance coils for the purpose of measuring an unknown resistance. A single current is made to pass from A through two parallel connected branches, joining together again at C. A cross connection B D has a galvanometer or other current indicator in circuit. In any conductor through which a current is passing, the fall of potential at given points is proportional to the resistance between such points. Referring to the diagram a given fall of potential exists between A and C. The fall between A and B is to the fall between A and C as the resistance r between A and B is to the resistance r + r' between A and C. The same applies to the other branch, with the substitution of the resistances s and S' and the point D for r r' and B. Therefore, if this proportion holds, r : r' : : s : S'. No current will go through B D , and the galvanometer will be unaffected. Assume s' to be of unknown resistance, the above proportion will give it, if r, r' and s are known, or if the ratio of r to r' and the absolute value of s is known.


In use the resistances r, r', and s are made to vary as desired. To measure an unknown resistance it is introduced at S', and one of the other resistances is varied until the galvanometer is unaffected. Then the resistance of S' is determined by calculation as just explained. The artificial resistances may be resistance coils, q. v., or it is enough to have one unknown resistance at s. Then if the length of wire ABC is accurately known, the point B can be shifted along it until the balance is attained. The relative lengths A B, and B C, will then give the ratio r : r' needed for the calculation. This assumes the wire ABC to be of absolutely uniform resistance. This is the principle of the meter-bridge described below. The use of coils is the more common method and is carried out by special resistance boxes, with the connections arranged to carry out the exact principle as explained. The principle of construction and use of a resistance box of the Wheatstone bridge type, as shown in the cut, is described under Box Bridge, q. v.




The next cut shows the sliding form of bridge called the meter bridge, if the slide wire is a meter long or a half- or a quarter-meter bridge, etc., according to the length of this wire. It is described under Meter Bridge, q. v. Many refinements in construction and in proper proportion of resistances for given work apply to these constructions.

Synonyms—Electric Balance—Resistance Bridge—Wheatstone's Balance.


Whirl, Electric. (a) A conductor carrying an electric current is surrounded by circular lines of force, which are sometimes termed an electric whirl.

(b) The Electric Flyer. (See Flyer, Electric.)

Wimshurst Electric Machine. An influence machine for producing high potential or static electricity.

Two circular discs of thin glass are mounted on perforated hubs or bosses of wood or ebonite. Each hub has a groove turned upon it to receive a cord. Each disc is shellacked. They are mounted on a horizontal steel spindle so as to face and to be within one-eighth of an inch of each other. On the outside of each disc sixteen or eighteen sectors of tinfoil or thin metal are cemented.


Two curved brass rods terminating in wire brushes curved into a semi-ellipse just graze the outer surfaces of the plates with their brushes. They lie in imaginary planes, passing through the axis of the spindle and at right angles from each other.

Four collecting combs are arranged horizontally on insulating supports to collect electricity from the horizontal diameters of the discs. These lie at an angle of about 45 with the other equalizing rods. Discharging rods connect with the collecting combs.

The principle of the machine is that one set of sector plates act as inductors for the other set. Its action is not perfectly understood.

It works well in damp weather, far surpassing other influence machines in this respect. On turning the handle a constant succession or stream of sparks is produced between the terminals of the discharging rods.

Windage. In a dynamo the real air gap between the armature windings and pole pieces is sometimes thus termed.

Wind, Electric. The rush of air particles from a point connected to a statically charged condenser.

Winding, Compound. A method of winding a generator or motor in which a shunt winding is used for the field magnets and in which also a second winding of the magnet is placed in series with the outer circuit. (See Winding, Series—Winding, Shunt.)


The object of compound winding is to make a self-regulating dynamo and this object is partly attained for a constant speed.

The characteristic curves of shunt and series winding are of opposite natures. The first increases in electro-motive force for resistance in the outer circuit, the latter decreases under the same conditions. If the windings are so proportioned that these conditions for each one of the two windings are equal and opposite, it is evident that the characteristic may be a straight line. This, however, it will only be at a single speed of rotation.


Winding, Disc. A winding which (S. P. Thompson) may be treated as a drum winding extended radially, the periphery corresponding to the back end of the drum. The magnet poles are generally placed so as to face the side or sides of the disc.

Winding, Lap. A method of winding disc and drum armatures. It consists in lapping back each lead of wire towards the preceding lead upon the commutator end of the armature. Thus taking the letter U as the diagrammatical representation of a turn of wire in connecting its ends to the commutator bars they are brought towards each other so as to connect with contiguous commutator bars. This carries out the principle of keeping the two members of the U moving in regions of opposite polarity of field, so that the currents induced in them shall have opposite directions, thus producing a total current in one sense through the bent wire.

Winding, Long Shunt. A system of compound winding for dynamos and motors. The field is wound in series and, in addition thereto, there is a shunt winding connected across from terminal to terminal of the machine, and which may be regarded either as a shunt to the outer circuit, or as a shunt to the series-field and armature winding. (See Winding, Short Shunt.)

Synonyms—Series and Long Shunt Winding.

Winding, Multiple. A winding of an electro-magnet, in which separate coils are wound on the core, so that one or any number may be used as desired in parallel or in series. For each coil a separate binding post should be provided.

Winding, Multipolar. Winding adapted for armatures of multi-polar dynamos or motors.

Winding, Series. A method of winding a generator or motor, in which one of the commutator-brush connections is connected to the field-magnet winding; the other end of the magnet winding connects with the outer circuit. The other armature-brush connects with the other terminal of the outer circuit.

Winding, Series and Separate Coil. A method of automatic regulation applied to alternating current dynamos.

Winding, Short Shunt. A method of compound winding for dynamos and motors. The field is wound in series, and in addition thereto there is a shunt winding connected from brush to brush only, thus paralleling the armature. (See Winding, Long Shunt.)

Synonyms—Series and Short Shunt Winding.


Winding, Shunt. A method of winding a generator or motor. Each commutator-brush has two connections. One set are the terminals of the outer circuit, the other set are the terminals of the field-magnet windings. In other words, the field-magnet windings are in shunt or in parallel with the outer circuit.

Winding, Shuttle. A method of dynamo or motor-armature winding. A single groove passes longitudinally around the core and in this the wire is continuously wound. The system is not now used. The old Siemens' H armature illustrates the principle.

Winding, Wave. A method of winding disc and drum armatures. It consists in advancing the commutator ends of the U shaped turns progressively, so that as many commutator bars intervene between any two consecutive commutator connections of the wire as there are leads of wire on the drum between consecutive leads of the wire. This is carried out with due regard to the principle that taking the letter U as the diagrammatical representation of a turn of wire, its two members must move through regions of the field of opposite polarity.

Wire Finder. A galvanometer or other instrument used for identifying the ends of a given wire in a cable containing several.

Work. When a force acts upon a body and the body moves in the direction of the force, the force does work. Hence, work is the action of a force through space against resistance.

It is generally expressed in compound units of length and weight, as foot-pounds, meaning a pound raised one foot.

Work, Electric, Unit of. The volt-coulomb, q. v., or watt-second, as it is often termed.

Working, Diode. In multiplex telegraphy the transmission of two messages, simultaneously, over one wire. (See Telegraphy, Multiple.)

Working, Contraplex. A variety of duplex telegraphy in which the messages are sent from opposite ends of the line, simultaneously, so as to be transmitted in opposite directions. (See Working, Diplex.)

Working, Diplex. In duplex telegraphy the sending of two independent messages from the same end of the line in the same direction.


Working, Double Curb. A method of working telegraph lines. When a signal is sent the line is charged. This has to be got rid of, and is an element of retardation. In double curb working it is disposed of by sending a momentary current first in the reverse, and then in the same, and finally in the reverse direction. This is found to reduce the charge to a very low point.

Working, Hexode. In multiplex telegraphy the transmission of six messages simultaneously over one wire. (See Telegraphy, Multiplex.)

Working, Pentode. In multiplex telegraphy the transmission of five messages simultaneously over one wire. (See Telegraphy, Multiplex.)

Working, Reverse Current. A method of telegraphy, in which the currents are reversed or alternated in direction.

Working, Single Curb. A simpler form of telegraph signaling than double curb working. It consists in sending a reverse current through the line for each signal by reversing the battery connection.

Working, Tetrode. In multiplex telegraphy the transmission of four messages simultaneously over the same line. (See Telegraphy, Multiplex.)

Working, Triode. In multiplex telegraphy the transmission of three messages simultaneously over the same wire. (See Telegraphy, Multiplex.)

Work, Unit of. The erg, q. v. It is the same as the unit of energy, of which work is the corelative, being equal and opposite to the energy expended in doing it. There are many other engineering units of work, as the foot-pound and foot-ton.

Yoke. In an electro-magnet, the piece of iron which connects the ends furthest from the poles of the two portions of the core on which the wire is wound.

Zamboni's Dry Pile. A voltaic pile or battery. It is made of discs of paper, silvered or tinned on one side and sprinkled on the other with binoxide of manganese. Sometimes as many as 2,000 of such couples are piled up in a glass tube and pressed together with two rods which form the terminals. They maintain a high potential difference, but having very high resistance and slight polarization capacity, give exceedingly small quantities.

Zero. (a) The origin of any scale of measurement.

(b) An infinitely small quantity or measurement.


Zero, Absolute. From several considerations it is believed that at a certain temperature the molecules of all bodies would touch each other, their kinetic motion would cease, and there would be no heat. This temperature is the absolute zero. It is put at -273 C. (-459 F.)

[Transcriber's note; The modern value is 0 Kelvin, -273.15 C, or -459.67 F. The lowest reported temperature observed is 1E-10 K.]

Zero, Potential. Conventionally, the potential of the earth. True zero potential could only exist in the surface of a body infinitely distant from other electrified bodies.

Zero, Thermometric. There are three thermometric zeros. In the Raumur and centigrade scales, it is at the temperature of melting ice; in the Fahrenheit scale, it is 32 F. below that temperature, or corresponds to -17.78 C.

The third is the absolute zero. (See Zero, Absolute.)

Zinc. A metal; one of the elements; atomic weight, 65.1; specific gravity, 6.8 to 7.2.

microhms. Resistance at 0 C. (32 F.), per centimeter cube, 5.626 Resistance at 0 C. (32 F.), per inch cube, 2.215

Relative resistance (silver = 1), 3.741

ohms. Resistance of a wire, 1 foot long, weighing 1 grain, .5766 (a) 1 foot long, 1 millimeter diameter, 33.85 (b) 1 meter long, weighing 1 gram, .4023 (c) 1 meter long, 1 millimeter diameter, .07163

Zinc is principally used in electrical work as the positive plate in voltaic batteries.

Zincode. The terminal connecting with the zinc plate, or its equivalent in an electric circuit; the negative electrode; the kathode. A term now little used.

Zinc Sender. An apparatus used in telegraphy for sending a momentary reverse current into the line after each signal, thus counteracting retardation.

Zone, Peripolar. In medical electricity, the region surrounding the polar zone, q. v.

Zone, Polar. In medical electricity, the region surrounding the electrode applied to the human body.

583-624 INDEX.

Page A 7 Absolute 7 Absolute Calibration 97 Absolute Electric Potential 429 Absolute Electrometer 222 Absolute Galvanometer 266 Absolute Measurement 8 Absolute Potential 428 Absolute Temperature 8 Absolute Unit 554 Absolute Unit Resistance, Weber's 468 Absolute Vacuum 557 Absolute Zero 581 Abscissa 7 Abscissas, Axis of 54 Absorption, Electric 8 A. C. C. 8 Acceleration 8 Accumulator 8 Accumulator, Electrostatic 8 Accumulator, Water Dropping 9 Acetic Acid Battery 58 Acheson Effect 208 Acid, Carbonic 108 Acid, Chromic, Battery 61 Acid, Hydrochloric, Battery 66 Acid, Spent 491 Acid, Sulphuric 497 Acidometer 10 Acierage 494 Aclinic Line 10 Acoustic Telegraphy 10 Acoutemeter 10, 53 Action, Electrophoric 230 Action, Local 331 Action, Magne-crystallic 335 Action, Refreshing 454 Action, Secondary 477 Actinic Photometer 411 Actinic Rays. 11 Actinism 11 Actinometer, Electric 11 Active Electric Circuit, 123 Activity 11 Actual Horse Power 290 Adapter 11 A. D. C., 11 Adherence, Electro-magnetic 11 Adherence, Magnetic 338 Adjuster, Cord 152 Adjustment of Brushes 90 Admiralty Rules of Heating 12 AEolotropic 34 Aerial Cable 95 Aerial Conductor 12 Affinity 12 Affinity, Molecular 380 After Current,. 159 Agglomerate Leclanch Battery 66 Agir Motor 13 Agone 13 Agonic Line, 13 Air 13 Air Blast 13 Air Condenser 14 Air Field 252 Air Gaps 15 Air Line Wire 15 Air Pump, Heated 15 Air Pump, Mercurial 16 Air Pumps, Short Fall 16 Alarm, Burglar 16 Alarm, Electric 17 Alarm, Fire, Electric Automatic 257 Alarm, Fire and Heat 17 Alarm, Overflow 18 Alarm, Water Level 18 Alcohol, Electric Rectification of 18 Alignment, 18 Allotropy 18 Alloy 18 Alloy, Platinum 419 Alloy, Platinum-Silver 419 Alloys, Paillard 400 Alphabet, Telegraphic 19 Alternating 23 Alternating Current 159 Alternating Current Arc 23 Alternating Current Dynamo 193 Alternating Current Generator or Dynamo 24 Alternating Current Meter 373 Alternating Current System 23 Alternating Field 252 Alternative Current 563 Alternative Path 24 Alternatives, Voltaic 563 Alternator 24 Alternator, Constant Current 24 Alternator, Dead Point of an 177 Alternation 23 Alternation, Complete 23 Alternation, Cycle of 175 Alum Battery 58 Aluminum 24 Aluminum Battery 58 Amalgam 24 Amalgamation 25 Amber 25 American Twist Joint 309 Ammeter 26 Ammeter, Ayrton 26 Ammeter, Commutator 26 Ammeter, Cunynghame's 26 Ammeter, Eccentric Iron Disc 27 Ammeter, Electro-magnetic 27 Ammeter, Gravity 27 Ammeter, Magnetic Vane 27 Ammeter, Magnifying Spring 28 Ammeter, Permanent Magnet 28 Ammeter, Reducteur for 453 Ammeter, Solenoid 28 Ammeter, Spring 28 Ammeter, Steel Yard 28 Ammunition Hoist, Electric 29 Amperage 29 Ampere 29 Ampere- and Volt-meter Galvanometer 274 Ampere Arc 30 Ampere Balance 56 Ampere Currents 30 Ampere Feet 30 Ampere-hour 30 Amperes, Lost 30 Ampre's Memoria Technica 30 Ampere Meters 26, 30 Ampere Meter, Balance 391 Ampere Meter, Neutral Wire 391 Ampere-minute 30 Ampere Ring 30 Ampere-second 30 Ampere's Theory of Magnetism 354 Ampere-turns 31 Ampere-turns, Primary 31 Ampere-turns, Secondary 31, 551 Ampere Windings 31 Amprian Currents 165 Amplitude of Waves 31 Analogous Pole 31, 425 Analysis 31 Analysis, Electric 32 Analysis, Electrolytic 214 Analyzer, Electric 32 Anelectrics 32 Anelectrotonus 32 Angle of Declination 32, 177 Angle of the Polar Span 32 Angle of Inclination or Dip 33 Angle of Lag 33-318 Angle of Lead 33 Angle of Maximum Sensitiveness 479 Angle of Polar Span 423 Angle, Polar 423 Angle, Unit 554 Angular Currents 165 Angular Currents, Laws of 165 Angular Force 544 Angular Velocity 32, 559 Animal Electricity 33 Animal System, Electric Excitability of 247 Anion 33 Anisotropic 34 Annealing, Electric 34 Annular Electro-magnet 216 Annunciator 34 Annunciator Clock 35 Annunciator Clock, Electric 127 Annunciator Drop 35 Annunciator, Gravity Drop 35 Annunciator, Needle 35 Annunciator, Swinging or Pendulum 35 Anodal Diffusion 35 Anode 36 Anodic Closure Contraction 36 Anodic Duration Contraction 36 Anodic Opening Contraction 36 Anodic Reactions 36 Anomalous Magnet 335 Anti-induction Conductor 36, 145 Anti-magnetic Shield 37 Antilogous Pole, 425 Antimony 37 Anvil 37 A. O. C. 38 Aperiodic 38 Aperiodic Galvanometer 266 Apparent Coefficient of Magnetic Induction 346 Apparent Resistance 297, 462 Apparent Watts 573 Arago's Disc 88 Arc 39 Arc, Ampere 30 Arc, Compound. 39 Arc, Electric Blow-pipe 84 Arc, Metallic 39 Arc, Micrometer 39, 376 Arc, Multiple 387 Arc, Simple 39 Arc, Voltaic 39 Arc Box, Multiple 387 Arc Lamp 319 Arc Lamp, Differential 320 Arc Lamp, Double Carbon 191 Areometer 41 Areometer, Bead 41 Argyrometry 41 Arm 41 Armature 41 Armature, Bar 42 Armature, Bipolar 42 Armature Bore 42 Armature Chamber 42 Armature, Closed Coil 43 Armature Coil, or Coils 43 Armature Conductors, Lamination of 319 Armature Core 43 Armature, Cylinder 43 Armature, Cylindrical 45 Armature, Disc 43 Armature, Drum 45 Armature Factor 45 Armature, Flat Ring 45 Armature, Girder 49 Armature, H 49 Armature, Hinged 45 Armature, Hole 45 Armature, Intensity 45 Armature Interference 45 Armature, Load of 46 Armature, Multipolar 46 Armature, Neutral 46 Armature, Neutral Relay 46, 390 Armature, Non-polarized 46 Armature of Influence Machine 46 Armature of Leyden Jar or Static Condenser 46 Armature, Open Coil 46 Armature, Perforated 45 Armature, Pivoted 47 Armature Pockets 47 Armature, Polarized 47 Armature, Pole 47 Armature, Quantity 47 Armature, Radial 47 Armature Reactions 41 Armature, Revolving, Page's 47 Armature, Ring 48 Armature, Rolling 49 Armatures, Gyrostatic Action of 288 Armature, Shuttle 49 Armature, Siemens' Old 49 Armature, Spherical 49 Armature, Stranded Conductor 49 Armature, Unipolar 50, 553 Armature, Ventilation of 560 Armor of Cable 50 Arm, Rheostat 472 Arms, Proportionate 436 Arms, Ratio 437 Arms, Rocker 50-474 Arrester, Lightning 328 Arrester, Lightning, Counter-electro-motive Force 329 Arrester, Lightning, Plates 329 Arrester, Lightning, Vacuum. 329 Arrester Plate 417 Arrester, Spark 489 Arrival Curve 168 Articulate Speech 50 Artificial Carbon 106 Artificial Magnet 335 Ascending Lightning 330 Assymmetrical Resistance 462 Astatic 50 Astatic Circuit 12 Astatic Couple 157 Astatic Galvanometer 266 Astatic Needle 50 Astronomical Meridian, 372 Asymptote 51 Atmosphere 51 Atmosphere, Residual 51, 460 Atmospheric Electricity 51 Atom 52 Atomic Attraction 52 Atomic Current 160 Atomic Energy 238 Atomic Heat 52-285 Atomic Weight 53 Atomicity 52 Attracted Disc Electrometer 223 Attraction 53 Attraction, Atomic 52 Attraction, Magnetic 338 Attraction, Molar 380 Attraction, Molecular 380 Attraction and Repulsion, Electro-dynamic 211 Attraction and Repulsion, Electro-magnetic 217 Attraction and Repulsion, Electro-static 234 Attraction and Repulsion, Electro-static, Coulomb's Law of 155 Audiometer 53 Aura, Electrical 53 Aurora 53 Austral Pole 54 Autographic Telegraph 510 Automatic Circuit Breaker 121 Automatic Cut Out 175, 475 Automatic Drop 192 Automatic Electric Bell 78 Automatic Electric Fire Alarm 257 Automatic Switch 500 Automatic Telegraph 504 A. W. G., 54 Axial Couple 514 Axial Force 544 Axial Magnet 336 Axis, Electric 54 Axis, Magnetic 338 Axis of Abscissas 54 Axis of Ordinates 54, 397 Axis of X 54 Axis of Y 54, 397 Ayrton's Ammeter 26 Azimuth 54 Azimuth Circle 54 Azimuth Compass 141 Azimuth, Magnetic 338

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