Chapter I: II (7)

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.

533 STANDARD ELECTRICAL DICTIONARY.

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.

554 STANDARD ELECTRICAL DICTIONARY.

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.

555 STANDARD ELECTRICAL DICTIONARY.

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

556 STANDARD ELECTRICAL DICTIONARY.

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.

557 STANDARD ELECTRICAL DICTIONARY.

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.)

558 STANDARD ELECTRICAL DICTIONARY.

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."

559 STANDARD ELECTRICAL DICTIONARY.

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.

560 STANDARD ELECTRICAL DICTIONARY.

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.

561 STANDARD ELECTRICAL DICTIONARY.

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.

Synonym--Viole.

562 STANDARD ELECTRICAL DICTIONARY.

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.

563 STANDARD ELECTRICAL DICTIONARY.

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.

564 STANDARD ELECTRICAL DICTIONARY.

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 0º (32º F.) and 76 centimeters, or 30 inches barometer.

Fig. 341. GAS VOLTAMETER.

565 STANDARD ELECTRICAL DICTIONARY.

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 + Fº - 32) ) / (h* 491)

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

FIG. 342. SILVER VOLTAMETER.

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.

566 STANDARD ELECTRICAL DICTIONARY.

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.

Fig. 343. WEIGHT VOLTAMETERS.

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.

567 STANDARD ELECTRICAL DICTIONARY.

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.

Fig. 344. VOLTA'S FUNDAMENTAL EXPERIMENT.

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.

568 STANDARD ELECTRICAL DICTIONARY.

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.

569 STANDARD ELECTRICAL DICTIONARY.

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.

570 STANDARD ELECTRICAL DICTIONARY.

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.

Fig. 345. CARDEW VOLTMETER.

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.

571 STANDARD ELECTRICAL DICTIONARY.

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.

572 STANDARD ELECTRICAL DICTIONARY.

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.

573 STANDARD ELECTRICAL DICTIONARY.

It is equal to 1E7 ergs per second.

Synonym--Volt-ampere.

(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).

Synonym--Volt-coulomb.

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.]

574 STANDARD ELECTRICAL DICTIONARY.

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.)

Fig. 346. ELECTRIC WELDING INDUCTION COIL.

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.

575 STANDARD ELECTRICAL DICTIONARY.

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.

576 STANDARD ELECTRICAL DICTIONARY.

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.

FIG. 347. WHEATSTONE BRIDGE CONNECTIONS.

FIG. 348. TOP OF BOX BRIDGE.

577 STANDARD ELECTRICAL DICTIONARY.

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.

Fig. 349. METER BRIDGE.