The Standard Electrical Dictionary / A Popular Dictionary of Words and Terms Used in the Practice of Electrical Engineering

by T. O'Conor Sloane

Fig. 293. RESISTANCE FRAME.
Resistance Frame.
An open frame filled with resistance coils of iron, or German silver
wire. It is used as a resistance for dynamos and the larger or working
class of plant. The coils are sometimes connected so that by a switch
moving over a row of studs one or more can be thrown into series
according to the stud the switch is in contact with.
Resistance, German Mile Unit of.
The resistance of 8,238 yards of iron wire 1/6 inch in diameter. It is
equal to 56.81 legal ohms.
466 STANDARD ELECTRICAL DICTIONARY.
Resistance, Hittorf's.
A high resistance, often a megohm, composed of Hittorf's solution, q. v.
It is contained in a vertical glass tube near whose upper and lower ends
are electrodes of metallic cadmium attached to platinum wires. The
cadmium is melted in glass tubes, the platinum wire is inserted into the
melted metal and the tube is broken after all is solid. The resistance
should show no polarization current.

Fig. 294. HITTORF'S RESISTANCE
Resistance, Inductive.
A resistance in which self-induction is present; such as a coil of
insulated wire wound around an iron core.
Resistance, Insulation.
The resistance of the insulation of an insulated conductor. It is stated
in ohms per mile. It is determined by immersing a section of the line in
water and measuring the resistance between its conductor and the water.
The section must be of known length, and its ends must both be above the
liquid.
Resistance, Internal.
The resistance of a battery, or generator in an electric circuit as
distinguished from the resistance of the rest of the circuit, or the
external resistance.
Synonym--Essential Resistance.
Resistance, Jacobi's Unit of.
The resistance of a certain copper wire 25 feet long and weighing 345
grains.
It is equal to 0.6296 legal ohm.
Resistance, Matthiessen's Meter-gram Standard.
The resistance of a pure hard drawn copper wire of such diameter that
one meter of it weighs one gram. It is equal to .1434 Legal Ohms at 0º
C. (32º F.)
Resistance, Matthiessen's Unit of.
The resistance of a standard mile of pure annealed copper wire 1/16 inch
diameter, at a temperature of 15.5º C. (60º F.).
It is equal to 13.44 legal ohms.
467 STANDARD ELECTRICAL DICTIONARY.
Resistance, Meter-millimeter Unit of.
The resistance of a wire of copper one meter long and one square
millimeter in section. It is equal to .02057 ohms at 0º C. (32º F.) The
term may also be applied to the resistance of similar sized wire of
other metals.
Resistance, Mil-foot Unit of.
The resistance of a foot of copper wire one-thousandth of an inch in
diameter. It is equal to 9.831 ohms at 0º C. (32º F.) The term may also
be applied to the resistance of similar sized wire of other metals.
Resistance, Non-essential.
The resistance of the portion of an electric circuit not within the
generator; the same as external resistance.
Synonym--External Resistance.
Resistance, Non-inductive.
A resistance with comparatively little or negligible self-induction.
Resistance of Human Body.
The resistance of the human body is largely a matter of perfection of
the contacts between its surface and the electrodes. It has been
asserted that it is affected by disease. From 350 to 8,000 ohms have
been determined as resistances, but so much depends on the contacts that
little value attaches to the results.
Resistance, Ohmic.
True resistance measured in ohms as distinguished from
counter-electro-motive force, q. v. The latter is called often spurious
resistance.
Synonym--True Resistance.
[Transcriber's note: "True" vs. "spurious" are interesting terms,
considering that today we define impedance as a combination of "real"
resistance and "imaginary" capacitive and inductive reactance.]
Resistance, Reduced.
The resistance of a conductor reduced to ohms, or to equivalent lengths
of a column of mercury, 1 square millimeter in cross area.
Resistance, Siemen's Unit of.
The resistance of a column of mercury 1 meter long and 1 square
millimeter cross-sectional area at 0º C. (32º F.)
It is equal to .9431 legal ohm.
Resistance, Specific.
The relative resistance of a substance. It is expressed as the actual
resistance of a cube of the substance which is one centimeter on each
edge. For metals it is usually expressed in microhms, for liquids in
ohms.
The resistances of a specified length of wire of specified diameter of
different substances is often given, and is really a particular way of
stating specific resistances.
Synonym--Specific Conduction Resistance.
Resistance, Spurious.
The counter-electro-motive force, q. v., operating to prevent a current
being produced of what should be its full strength were the true
resistance and actuating electro-motive force only concerned. Such
counter-electro-motive force may be treated as a spurious resistance and
such a value in ohms assigned to it as would correspond to its proper
effect.
468 STANDARD ELECTRICAL DICTIONARY.
In its effect on opposing a current and in resisting its formation it
differs from true resistance. The latter in diminishing current strength
absorbs energy and develops heat; spurious resistance opposes and
diminishes a current without absorption of energy or production of heat.
[Transcriber's note: "Spurious resistance" is now called reactance,
consisting of capacitive reactance and inductive reactance. The
combination of reactance and (Ohmic/true) resistance is called
impedance. The calculation of impedance requires complex algebra, not
just real values used in DC circuit analysis.]
Resistance, Steadying.
When arc lamps are connected in parallel or multiple arc a small
resistance coil is sometimes placed in series with each lamp for
steadying purposes. It reduces the percentage of variation of resistance
in each lamp, which may be caused by a change in the position of the
carbons.
Resistance, Swiss Unit of.
A unit constructed by the "Administration Suisse," based on the same
data as the Breguet and the Digney Units. (See Resistance, Digney Unit
of)
It is equal to 10.30 legal ohms.
Resistance, Thomson's Unit of.
A unit of resistance based on the foot and second.
It is equal to 0.3166 legal ohm.
Resistance, Unit.
Unit resistance is that of a conductor in which unit current is produced
by unit electro-motive force.
Resistance, Varley's Unit of.
The resistance of a standard mile of a special copper wire 1/16 inch
diameter.
It is equal to 25.33 ohms.
Resistance, Weber's Absolute Unit.
A metric system unit; (meter / second) * 1E7
It is equal to 0.9089 legal ohm.
Resonance, Electric.
A set of phenomena known as the Hertz experiments are grouped under this
title, which phenomena are incidents of and depend on the propagation of
electric waves through wires or current conductors, as well as through
the ether. Ordinarily a wire is only a seat of current, and is in its
nature inconsistent with wave propagation through its mass. Such waves
are virtually confined to the exterior of the wire. The point is that
the current-producing force is supposed to enter the wire at all points
from without, the current not being produced by an end-push. Hence in
rapidly recurring waves which are produced by a rapidly pulsatory or
alternating current, no time is afforded for the current-producing
force, in this case the wave-producing force, to penetrate into the
substance of the wire. In one of his experiments Dr. Hertz surrounded a
wire by a glass tube chemically silvered. The coating was so thin as to
be translucent. Through this metallic layer a current could be induced
in the wire in its interior. Any mechanical layer of metal took up the
induction itself, and protected the central wire. This gave a clue to
the thickness of metal penetrated by the rapid induced waves used by Dr.
Hertz.
469 STANDARD ELECTRICAL DICTIONARY.

Fig. 295. ELECTRICAL RESONANCE EXCITER.
The method used for the production of rapid oscillations is the
following. To the terminals of an induction coil two metal spheres AA1
are connected as shown. This apparatus is termed the exciter; in its
discharge a series of isochronous discharges takes place, alternating in
direction. The period of duration T of a single one is given by the
formula T= 2* PI * squareRoot( LC ), in which C is the capacity and L
is the self-induction. The spheres may be 30 centimeters (11.8 inches)
in diameter, connected each to conductors 0.5 centimeter (.2 inch) in
diameter and 40 centimeters (15.7 inches) long each. For the length of
an undulation the formula gives for this apparatus 4.8 meters (15.75
feet) as the length of a wave, assuming for them the velocity of
propagation equal to that of light. The exciter may have 10,000 times
the rate of oscillation possessed by the plain induction coil.
When this apparatus is worked it produces induced waves in every
neighboring conductor. The resonance effects appear in the size of the
spark induced. Thus a wire bent into a circle with its ends nearly
touching will give a spark, but if made of proper electrostatic
capacity, corresponding with the particular waves employed, the spark
will be very much larger. The ring, with its spark gap is termed a
resonator. It is used as an explorer to trace the waves.
Waves thus produced are transmitted by stone walls and nonconductors in
general. A plate of zinc reflects part and transmits part. The reflected
waves can be traced by the resonator, their angle of reflection being
equal to their angle of incidence. They can be received by one parabolic
reflector, reflected to another and brought to a focus. They can be
reflected so as to produce interference or loops and nodes, and the
loops and nodes can be traced by the resonator. By a prism of asphalt
they are refracted exactly like light.
From all this it is concluded that an additional proof is furnished of
the identity of light and electro-magnetic waves, and a very strong
experimental proof of Maxwell's theory of light is furnished.
Synonym--Hertz's Experiments.
470 STANDARD ELECTRICAL DICTIONARY.

Fig. 296. ELECTRICAL RESONATOR.
Resonator, Electric.
A small open electric circuit, with ends nearly touching. When exposed
to electric resonance, or to a sympathetic electric oscillatory
discharge, a spark passes from across the gap. The production of this
spark is altogether a matter of the inductance of the resonator. The
simplest form is a circle of copper wire with its ends nearly touching.
The length of the gap is adjustable by bending. A screw adjustment may
also be provided. Another form is shown in the cut, Fig. 296. Here
sheets of tinfoil are used to regulate the electrostatic capacity, while
at m is shown the finger piece for regulating the size of the spark gap
a.
Synonym--Spark Micrometer.
Resultant.
The line indicating the result of the application of two or more forces
to a point. Its direction and length give the elements of direction and
intensity. (See Forces, Resolution of Forces, Composition of
Components.)
Resultant Polarity.
The magnetic polarity imparted to a mass of iron acted on by two or more
separate inducing forces or currents. It appears in dynamos and motors.
The final polarity is the resultant of the inducing effect of the field
magnet poles and of the windings.
Retardation.
In telegraphy a retardation of the rate of transmission of signals. It
is due to several causes.
(a) The self-induction of the circuit, especially if it includes many
electro-magnets, produces extra currents (see Currents, Extra.) These
are opposed to the main current on closing it and hence retard the
action. They are in the same direction on opening it and hence again
retard the action.
(b) Every line has a certain static capacity. This is affected by the
proximity of the lines to the earth. For each signal electricity has to
be charged upon the line until the line is charged to its end with a
certain proportion of the initial density. This charging takes time and
hence introduces retardation.
(c) The cores of the electro-magnets of the relays or sounders are not
instantly magnetized and demagnetized. This magnetic lag, q. v.,
introduces retardation.
471 STANDARD ELECTRICAL DICTIONARY.
Retardation of Phase.
The fractional lagging behind of waves or alternating currents; by
lagging behind a portion of a wave length the corresponding phases, as
of full amplitude, are kept back or retarded. The phase of current
intensity may be retarded with reference to the electro-motive force by
the introduction of transformers of high capacity with high resistance
on open secondary circuits.
[Transcriber's note: Capacitors are used to correct current phase lag.]
Retentivity.
Coercitive or coercive force; by virtue of which steel retains its
magnetism. It is the more modern name, "coercive force" as a term being
rejected by many.
Synonyms--Coercive Force--Coercitive Force.
Retort Carbon.
Carbon deposited in coal gas retorts from decomposition of the
hydrocarbons. It is a very hard, pure form, and is of graphitic
modification. Owing to its great hardness it is little used for
electrical purposes, the molded carbons being easier to make. The
deposition occurs in the regular gas-making process, and is a
disadvantage to the working.
Return.
A line or conductor which is supposed to carry current back to its
starting point, after it has traversed a line. It may be a wire or the
grounding of the ends of a line [or] may make the earth act as a return,
termed ground- or earth-return. The best distinction of a return is to
so term the portion of a circuit on which no apparatus is placed.
Reversibility.
The principal in virtue of which a device for producing a given form of
energy can absorb the same and do work. The reversibility of the dynamo
is its quality in virtue of which it can act as a current generator,
thereby converting mechanical energy into electric energy, or if a
current is passed through it, it rotates, doing work, and thereby
converting electric energy into mechanical energy. The knowledge of this
principle can be traced back to Jacobi in 1850.
Reversible Bridge.
A form of Wheatstone's Bridge adapted for reversal of the positions or
interchange of the proportionate arms, v., so that the accuracy of the
coils can be tested.
Rheochord.
An apparatus by means of which variable quantities of wire are thrown
into the circuit; a rheostat using wire. (See Rheostat, Wheatstone's.)
Rheometer.
A galvanometer. (Obsolete.)
472 STANDARD ELECTRICAL DICTIONARY.
Rheomotor.
A source of current; a current generator; a producer of potential
difference. (Obsolete.)
Rheophore.
The portion of an active circuit capable of deflecting a magnetic
needle. This properly includes all of the metallic conductor of a
circuit. (Obsolete.)
Rheoscope.
A galvanoscope; an instrument for qualitatively detecting potential
difference, fall or rise. (See Galvanoscope.)
Rheostat.
An adjustable resistance; an apparatus for changing the resistance
without opening the circuit. Its action may depend on the introduction
of variable lengths of mercury column, of some other liquid, or of wire
into a circuit. (See Rheostat, Wheatstone's.)
Rheostat Arm.
The third arm of known resistance in a Wheatstone bridge. (See
Proportionate Arms.)
Rheostatic Machine.
An apparatus for increasing potential difference. It consists of a
number of static condensers. They are charged in multiple arc or in
parallel, and are discharged in series. Secondary batteries may be used
for the charging; thus a static effect is produced from a galvanic
battery.
Rheostat, Wheatstone's.
This apparatus consists of two cylinders, one, A, made of brass, the
other, B, of wood, with a spiral groove. At its end is a copper ring a.
A fine brass wire has one end attached to this ring. Its other end is
fastened at e, and it is wound as shown; n and o are binding screws
connected, one with the cylinder-ring a, the other with the brass
cylinder, A. The current entering at o, traverses the wire on B, as
there the windings are insulated by the grooves, thence it passes to m
and by A, whose metal short circuits all the wire on it, to the
binding-post n. The handle, d, is turned one way or the other to
regulate the length of the wire through which the current must pass. On
each cylinder there is a square head, one of which is shown at c, so
that the handle can be shifted from one to the other as required; to A
if the wire is to be wound on that cylinder, to B if the reverse is
desired.

Fig. 297. WHEATSTONE'S RHEOSTAT.
473 STANDARD ELECTRICAL DICTIONARY.
Rheotome.
An automatic circuit breaker, one which rapidly opens and closes a
circuit, as in the case of the primary of an induction coil an
interrupter. (Obsolete.)
Rheotrope.
A pole changer, current reverser, or commutator, g., such as the
commutator of an induction coil. (Obsolete.)
Rhigolene.
A petroleum product; a hydrocarbon of low boiling point. Its vapor is
used in flashing (q. v.) carbon filaments for incandescent lamps.
Rhumbs.
In a mariners' compass, the thirty-two points, designated, north, north
by east, north north east, etc. (See Compass Mariner's-Compass, Points
of the.)
Rhumkorff Coil.
The induction coil, q. v.
Rigidity, Molecular.
The tendency of molecules to resist rotation or change of position; the
assumed cause of magnetic coercive force, or retentivity.
Ring Contact.
A contact formed by a terminal clip in the shape of a ring, split or cut
at one point so that its ends tend to spring together. The other
terminal is a bar which passes into the cut and is tightly pressed by
the elastic ring.