Fig. 288. POLARIZED RELAY
Reluctance.
In a magnetic circuit or portion thereof, the resistance offered to the
flow of lines of force. The magnetic circuit as has already been stated
is treated like an electric circuit, and in it reluctance occupies the
place of resistance in the electric circuit. It is the reciprocal of
permeance. S. P. Thompson expresses the law thus:
Total number of magnetic lines = (magneto-motive force) / (magnetic
reluctance)
Synonyms--Magnetic Reluctance-Magnetic Resistance.
Reluctance, Unit of.
The reluctance of a circuit through which unit magnetizing power
(magneto-motive force) can produce a unit of induction or one line of
force. This value is very high; the reluctance of ordinary magnetic
circuits ranges from 1E-5 to 1E-8 unit of reluctance.
Reluctivity.
Specific reluctance; the reluctance of a cube of material whose edge
measures one centimeter in length. It is a quality bearing the same
relation to reluctance that permeability does to permeance.
It is defined as the reciprocal of magnetic permeability. (Kenelly.) If
plotted as a curve for different values of the magnetizing force it is
found to be nearly a straight line, a linear function of the magnetizing
force, H with the equation a + b H. Reluctivity is the property of a
substance; reluctance is the property of a circuit.
459 STANDARD ELECTRICAL DICTIONARY.
Remanence.
The residual magnetism left after magnetic induction, expressed in lines
of force per square centimeter.
Repeater.
In telegraphy an instrument for repeating the signals through a second
line. It is virtually a relay which is operated by the sender, and which
in turn operates the rest of the main line, being situated itself at
about the middle point of the distance covered. In the simpler forms of
repeater two relays are used, one for transmission in one direction the
other for transmission in the other. An attendant switches one or the
other in as required.
Thus a common relay is virtually a repeater for its local circuit. If
such a relay is placed half way down a line, and if the line beyond it
is connected as its local, it becomes a repeater.
Some forms of repeaters are automatic, and repeat both ways without the
need of an attendant.
It is the practice to somewhat prolong the signals sent through a
repeater.
Replenisher, Sir William Thomson's.
A static accumulating influence machine contained in Thomson's quadrant
electrometer and used to change the quadrants. The cut shows the
horizontal section and construction of the apparatus.
It contains two gilt brass inductors A B, and two eccentric sectors or
carriers, C, D, which are mounted on an ebonite spindle, which is spun
around by the fingers. The springs s s1 connect each with its inductor;
the springs S S1 connect only each other, and touch the sectors as they
turn around.
One of the inductors may be always assumed to be of slightly higher
potential than that of the other one. When the carriers are in contact
with the springs S S1 they are each charged by induction with
electricity opposite in sign to that of the nearest quadrant. As they
leave the springs S S1 in their rotation, they next touch the springs s
s1, but of the recently opposite inductor. They share each a portion of
its charge with the inductors building up their charges. The action is
repeated over and over again as they rotate.
Fig. 289. DIAGRAM OF THOMSON'S REPLENISHER.
Fig. 290. THOMSON'S REPLENISHER.
460 STANDARD ELECTRICAL DICTIONARY.
Reservoir, Common.
A term applied to the earth, because all electrified bodies discharge
into it if connected thereto.
Residual Atmosphere.
The air left in a receiver after exhaustion by an air pump. The
quantity, where good air pumps are used, is very minute.
Residue, Electric.
The residual charge of a condenser. (See Charge, Residual.)
Resin.
(a) The product obtained by non-destructive distillation of the juice of
the pitch pine. It is the solid residue left after the turpentine has
been evaporated or distilled. It is a mixture of abietic acid C44 H64 O5
and pinic acid C20 H30 O2. It is an insulator; its specific inductive
capacity is 2.55. (Baltzmann.)
Synonyms--Colophony--Rosin.
(b) The name is also generally applied to similar substances obtained
from the sap of other trees; thus shellac is a resin. The resins are a
family of vegetable products; the solid portions of the sap of certain
trees. Common resin, lac, dragons blood, are examples. They are all
dielectrics and sources of resinous or negative electricity when rubbed
with cotton, flannel, or silk. (See Electrostatic Series.)
461 STANDARD ELECTRICAL DICTIONARY.
Resinous Electricity.
Negative electricity; the electricity produced upon the surface of a
resinous body by rubbing it; such a body is shellac or sealing wax;
flannel and other substances may be used as the rubbing material. (See
Electrostatic Series.)
Resistance.
(a) The quality of an electric conductor, in virtue of which it opposes
the passage of an electric current, causing the disappearance of
electro-motive force if a current passes through it, and converting
electric energy into heat energy in the passage of a current through it.
If a current passes through a conductor of uniform resistance there is a
uniform fall of potential all along its length. If of uneven resistance
the fall in potential varies with the resistance. (See Potential, Fall
of.)
The fall of potential is thus expressed by Daniell. "In a conductor, say
a wire, along which a current is steadily and uniformly passing, there
is no internal accumulation of electricity, no density of internal
distribution; there is, on the other hand, an unequally distributed
charge of electricity on the surface of the wire, which results in a
potential diminishing within the wire from one end of the wire to the
other."
Resistance varies inversely with the cross section of a cylindrical or
prismatic conductor, in general with the average cross-section of any
conductor, and in the same sense directly with its true or average or
virtual length. It varies for different substances, and for different
conditions as of temperature and pressure for the same substance. A rise
of temperature in metals increases the resistance, in some bad
conductors a rise of temperature decreases the resistance.
462 STANDARD ELECTRICAL DICTIONARY.
Approximately, with the exception of iron and mercury, the resistance of
a metallic conductor varies with the absolute temperature. This is very
roughly approximate.
Except for resistance energy would not be expended in maintaining a
current through a circuit. The resistance of a conductor may be supposed
to have its seat and cause in the jumps from molecule to molecule, which
the current has to take in going through it. If so a current confined to
a molecule would, if once started, persist because there would be no
resistance in a molecule. Hence on this theory the Ampérian currents
(see Magnetism, Ampere's Theory of) would require no energy for their
maintenance and Ampére's theory would become a possible truth.
When metals melt their resistance suddenly increases.
Light rays falling on some substances, notably selenium, q. v., vary the
resistance.
Longitudinal stretching of a conductor decreases it, it increases with
longitudinal compression, and increases in iron and diminishes in tin
and zinc when a transverse stress tends to widen the conductor.
(b) The term resistance is used to express any object or conductor used
in circuit to develop resistance.
[Transcriber's note: At room temperatures, the thermal motion of ions in
the conductor's crystal lattice scatters the electrons of the current.
Imperfections of the lattice contribute slightly. At low temperatures
superconductivity (zero resistance) can occur because an energy gap
between the electrons and the crystal lattice prevents any interaction.
At the time of this book, none of this was known. "Jumps from molecule
to molecule" is a good guess.]
Resistance, Apparent.
Impedance; the virtual resistance of a circuit including the spurious
resistance due to counter-electromotive force. It may be made up of true
resistance and partly of an inductive reaction, as it represents the net
factor, the entire obstruction to the passage of a current, and not
merely a superadded resistance or counter-electro-motive force.
Synonym--Impedance.
[Transcriber's note: Impedance can also have a component due to
capacitance.]
Resistance, Asymmetrical.
Resistance which varies in amount in different directions through a
conductor. It implies a compound or composite conductor such as the
human system. The presence of counter-electro-motive force in different
parts of a conductor may bring about asymmetrical resistance.
Resistance, B. A. Unit of.
The British Association Ohm. (See Ohm, B. A.)
463 STANDARD ELECTRICAL DICTIONARY.
Resistance Box.
A box filled with resistance coils. The coils are connected in series so
that a circuit including any given number has their aggregate resistance
added to its own. The terminals of consecutive coils are connected to
short blocks of brass which are secured to the top of the box, lying
flatwise upon it, nearly but not quite in contact with each other. Plugs
of brass are supplied which can go in between pairs of blocks, which
have a pair of grooves reamed out to receive them. Such plugs short
circuit the coil below them when in position. The cut shows how such
coils are connected and the use of plugs to short circuit them. The
diagram shows the top of a Wheatstone bridge, q. v., resistance box with
connections for determining resistances.
Fig. 291. RESISTANCE BOX.
Resistance Box, Sliding.
A resistance box whose coils are set in a circle. Two metal arms with
handles are pivoted at the centre of the circle and by moving them
around they make and break contacts so as to throw the coils in and out
of circuit. The object is to permit an operator to adjust resistance
without looking at the box--an essential in duplex telegraphy.
Resistance, Breguet Unit of.
The same in origin as the Digney Unit. (See Resistance, Digney Unit of.)
It is equal to 9.652 Legal Ohms.
Resistance, Carbon.
A resistance, a substitute for a resistance coil; it is made of carbon,
and is of various construction. In the Brush dynamo regulator a set of
four vertical piles of plates of retort carbon, q. v., is used as a
resistance, whose resistance is made to vary by changing the pressure.
This pressure automatically increases as the current strength increases,
thus reducing the resistance.
464 STANDARD ELECTRICAL DICTIONARY.
Resistance Coil, Standard.
A standard or resistance issued by the Electric Standard Committee of
Great Britain. The cut shows the standard ohm. It is formed either of
German silver, or of an alloy of silver, 66.6 per cent. and platinum,
33.4 per cent. The wire is insulated and doubled before winding as
described before. (See Coil, Resistance.) The two ends of the wire are
soldered, each one to a heavy copper wire or rod r. The whole coil is
enclosed in a brass case, and is enclosed with paraffine melted in at A.
A place for a thermometer is provided at t. By immersing the lower part
of the case B in water of different degrees of heat any desired
temperature can be attained.
Fig. 292. STANDARD OHM COIL.
Resistance, Combined.
The actual resistance of several parallel conductors starting from the
same point and ending at the same point. If the individual resistance be
a b c d .. and the combined resistance be x then we have
x = 1 / (( 1/a) + (1/b) + (1/c) + (1/d) + …)
Synonym--Joint Resistance.
Resistance, Critical.
In a series wound dynamo the resistance of the outer circuit above which
the machine will refuse to excite itself.
Resistance, Dielectric.
The mechanical resistance of a dielectric to the tendency to perforation
or to the strains due to electrification. This is a phase of mechanical
resistance, and is distinct from the electrical or ohmic resistance of
the same substance.
Resistance, Digney Unit of.
The resistance of an iron wire, 1 kilometer long, 4 millimeters
diameter, temperature unknown.
It is equal to 9.163 legal ohms.
Resistance, Electrolytic.
The resistance of an electrolyte to the passage of a current decomposing
it. It is almost entirely due to electrolysis and is added to by
counter- electro-motive force, yet it is not treated specifically as
such, but as an actual resistance. When a current of a circuit of too
low voltage to decompose an electrolyte is caused by way of immersed
terminals to pass through an electrolyte the resistance appears very
high and sometimes almost infinite. If the voltage is increased until
the electrolyte is decomposed the resistance suddenly drops, and what
should be termed electrolytic resistance, far lower than the true
resistance, appears.
465 STANDARD ELECTRICAL DICTIONARY.
Resistance, English Absolute or Foot-Second Unit of.
A unit based on the foot and second. It is equal to (( foot / second ) *
1E7) , being based on these dimensions.
It is equal to 0.30140 legal ohm.
Resistance, Equivalent.
A resistance equivalent to other resistances, which may include
counter-electro-motive force.
Resistance, Essential.
The resistance of the generator in an electric circuit; the same as
internal resistance.
Resistance, External.
In an electric circuit the resistance of the circuit outside of the
generator, or battery.
Synonym--Non-essential Resistance.
