Fig. 337. TIN SOUNDERS.
Tissandier's Solution.
A solution for bichromate batteries. It is composed as follows:
Water, 100 parts by weight
potassium bichromate, 16 parts
66° sulphuric acid, 37 parts.
Tongue of Polarized Relay.
The German silver extension of the vibrating or oscillating member of a
polarized relay, corresponding to the armature of an ordinary relay.
Tongue of Polarized Relay, Bias of.
In a Siemens' polarized relay the pole pieces are adjustable so that
they may be brought nearer to or withdrawn from the tongue. One of the
poles is adjusted so as to be nearer the tongue. This one-sided
adjustment is the bias. Its effect is that when the relay is unexcited
this pole attracts the armature so that it normally is drawn towards it.
This ensures the normal contact of the tongue either with the contact
point, or with the insulated stop piece or adjustment screw. Without
bias the armature remains in contact with or drawn towards whichever
pole it was last attracted to. In its usual use a bias is given it.
Top, Magnetic.
A toy illustrating magnetic attraction. It consists of a disc or body of
lead or other material, through which a magnetized steel spindle pointed
at its lower end is thrust. A number of short pieces of iron wire are
used with it. It is spun like an ordinary top upon the point of the
spindle and one of the pieces of iron wire is laid by the side of its
point. As it turns the magnetic adherence causes the piece of wire to be
carried along in one direction by the rotation of the spindle, until the
end is reached, when it goes over to the other side of the spindle and
travels back again.
By using bent pieces of wire of various shapes the most curious effects
are produced. Circles and S shaped pieces give good effects. To increase
the mysterious effect covered iron wire (bonnet wire) may be employed.

Fig. 338. MAGNETIC TOP.
543 STANDARD ELECTRICAL DICTIONARY.
Torpedo, Electric.
(a) A fish, the Raia Torpedo, which possesses the power of giving
electric shocks. (See Ray, Electric.)
(b) An instrument of war; a torpedo whose operations include electrical
discharge or other electric function or factor of operation.
Torpedo, Sims-Edison.
A torpedo driven by an electric motor, and also steered by electricity.
Its motions are all controlled from the shore. The torpedo proper is
carried some distance below the surface of the water by a vessel
immediately above it, from which it is suspended by two rigid bars. In
the torpedo is a cable reel on which the conducting cable is disposed.
An electric motor and controlling gear are also contained within the
torpedo. In its front the explosive is placed. It is driven by a screw
propeller actuated by the electric motor. As it moves it pays out cable
so that it has no cable to draw after it through the water, the cable
lying stationary in the water behind it. This avoids frictional
resistance to its motion. The maintenance of the torpedo at a proper
depth is one of the advantages of the system.
544 STANDARD ELECTRICAL DICTIONARY.
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.
545 STANDARD ELECTRICAL DICTIONARY.
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.
546 STANDARD ELECTRICAL DICTIONARY.
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.

Fig. 339. FERRANTI'S TRANSFORMER.
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.
547 STANDARD ELECTRICAL DICTIONARY.
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.
548 STANDARD ELECTRICAL DICTIONARY.
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.

Fig. 340. SWINBURNE'S HEDGEHOG 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.
549 STANDARD ELECTRICAL DICTIONARY.
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.
Trouvé'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.
550 STANDARD ELECTRICAL DICTIONARY.
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.
551 STANDARD ELECTRICAL DICTIONARY.
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.]

551 STANDARD ELECTRICAL DICTIONARY.
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.]
552 STANDARD ELECTRICAL DICTIONARY.
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.
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.