Fig. 200. ATTRACTION OF CONDUCTORS CARRYING SIMILAR CURRENTS.
By Ampére's theory of magnetism, (see Magnetism, Ampére's Theory of,) a
magnet is assumed to be encircled by currents moving in the direction
opposite to that of the hands of a watch as the observer faces the north
pole. A magnet near a wire tends to place the Ampérian currents parallel
to the wire, and so that the portion of the Ampérian currents nearest
thereto will correspond in direction with the current in the wire.
300 STANDARD ELECTRICAL DICTIONARY.
This is the principle of the galvanometer. A number of methods of
memoria technica have been proposed to remember it by.
Thus if we imagine a person swimming with the current and always facing
the axis of the conductor, a magnetic needle held where the person is
supposed to be will have its north pole deflected to the right hand of
the person.
Fig. 201. REPULSION OF CONDUCTORS
CARRYING OPPOSITE CURRENTS.
Again if we think of a corkscrew, which as it is turned screws itself
along with the current, the motion of the handle shows the direction of
the lines of force and the direction in which the north pole of a needle
is deflected. This much is perhaps more properly electro-dynamics, but
is necessary as a basis for the expression of induction.
If a current is varied in intensity in one conductor it will induce a
temporary current in another conductor, part of which is parallel to the
inducing current and which conductor is closed so as to form a circuit.
If the inducing current is decreased the induced current in the near and
parallel portion of the other circuit will be of identical direction; if
increased the induced current will be of opposite direction.
This is easiest figured by thinking of the lines of force surrounding
the inducing conductor. If the current is decreased these can be
imagined as receiving a twist or turn contrary to their normal
direction, as thereby establishing a turn or twist in the ether
surrounding the other wire corresponding in direction with the direction
of the original lines of force, or what is the same thing, opposite in
direction to the original twist. But we may assume that the
establishment of such a disturbance causes a current, which must be
governed in direction with the requirements of the new lines of force.
The same reasoning applies to the opposite case.
301 STANDARD ELECTRICAL DICTIONARY.
The general statement of a variable current acting on a neighboring
circuit also applies to the approach or recession of an unvarying
current, and to the cutting of lines of force by a conductor at right
angles thereto. For it is evident that the case of a varying current is
the case of a varying number of lines of force cutting or being cut by
the neighboring conductor. As lines of force always imply a current,
they always imply a direction of such current. The cutting of any lines
of force by a closed conductor always implies a change of position with
reference to all portions of such conductor and to the current and
consequently an induced current or currents in one or the other
direction in the moving conductor.
As the inducing of a current represents energy abstracted from that of
the inducing circuit, the direction of the induced current is determined
by (Lenz's Law) the rule that the new current will increase already
existing resistances or develop new ones to the disturbance of the
inducing field.
In saying that a conductor cutting lines of force at right angles to
itself has a current induced in it, it must be understood that if not at
right angles the right angle component of the direction of the wire acts
in generating the current. The case resolves itself into the number of
lines of force cut at any angle by the moving wire.
The lines of force may be produced by a magnet, permanent or electro.
This introduces no new element. The magnet may be referred, as regards
direction of its lines of force, to its encircling currents, actual or
Ampérian, and the application of the laws just cited will cover all
cases.
Induction, Coefficient of Mutual.
The coefficient of mutual induction of two circuits is the quantity of
magnetic induction passing through either of them per unit current in
the other. (Emtage.) It is also defined as the work which must be done
on either circuit, against the action of unit current in each, to take
it away from its given position to an infinite distance from the other;
and also as the work which would be done by either circuit on the other
in consequence of unit current in each, as the other moves from an
infinite distance to its given position with respect to the other
conductor. It depends on the form, size, and relative position of the
two circuits; and on the magnetic susceptibilities of neighboring
substances.
The ether surrounding two circuits of intensity i' and i" must possess
energy, expressible (Maxwell) as 1/2 L i2 + M i i + 1/2 N i12. It can be
shown that M i i1 in any given position of the two circuits is
numerically equal (1) to the mutual potential energy of the two circuits
(2) to the number of lines of induction, which being due to A, pass from
A through B, or equally being due to B, pass from B through A, and M is
styled the coefficient of mutual induction. (Daniell.)
302 STANDARD ELECTRICAL DICTIONARY.
Induction, Electrostatic.
An electrostatic charge has always an opposite and bound charge. This
may be so distributed as not to be distinguishable, in which case the
charge is termed, incorrectly but conventionally, a free charge. But
when a charge is produced an opposite and equal one always is formed,
which is the bound charge. The region between the two charges and
permeated by their lines of force, often curving out so as to embrace a
volume of cross-sectional area larger than the mean facing area of the
excited surfaces, is an electrostatic field of force. The establishing
of an electrostatic field, and the production of a bound charge are
electrostatic induction.
An insulated conductor brought into such a field suffers a
redistribution of its electricity, or undergoes electrostatic induction.
The parts nearest respectively, the two loci of the original and the
bound charges, are excited oppositely to such charges. The conductor
presents two new bound charges, one referred to the original charge, the
other to the first bound charge.
Induction, Horizontal.
In an iron or steel ship the induction exercised upon the compass needle
by the horizontal members of the structure, such as deck-beams, when
they are polarized by the earth's magnetic induction. This induction
disappears four times in swinging a ship through a circle; deviation due
to it is termed quadrantal deviation. (See Deviation, Quadrantal.)
Induction, Lateral.
A term formerly used to express the phenomenon of the alternative
discharge of a Leyden jar or other oscillatory discharge of electricity.
(See Discharge, Alternative.)
Induction, Magnetic.
The magnetization of iron or other paramagnetic substance by a magnetic
field.
On account of its permeability or multiplying power for lines of force,
a paramagnetic body always concentrates lines of force in itself if
placed in a magnetic field, and hence becomes for the time being a
magnet, or is said to be polarized.
As the tendency of lines of force is to follow the most permeable path,
a paramagnetic bar places itself lengthwise or parallel with the
prevailing direction of the lines of force so as to carry them as far on
their way as possible. Every other position of the bar is one of
unstable equilibrium or of no equilibrium. The end of the bar where the
lines of force enter (see Lines of Force) is a south pole and is
attracted towards the north pole of the magnet.
The production of magnetic poles under these conditions in the bar is
shown by throwing iron filings upon it. They adhere to both ends but not
to the middle.
Induction, Mutual, Electro-magnetic.
The induction due to two electric currents reacting on each other.
303 STANDARD ELECTRICAL DICTIONARY.
Induction, Mutual, Electrostatic.
A charged body always induces a charge upon any other body near it; and
the same charge in the second body will induce the other charge in the
first body if the latter is unexcited. In other words the second body's
induction from the first is the measure of the charge the second would
require to induce in the first its own (the second's) induced charge.
This is the law of mutual electrostatic induction.
Induction, Open Circuit.
Inductive effects produced in open circuits. By oscillatory discharges a
discharge can be produced across a break in a circuit otherwise
complete. The requirements for its production involve a correspondence
or relation of its dimensions to the inducing discharge. The whole is
analogous to the phenomena of sound resonators and sympathetic
vibrations. Synonym--Oscillatory induction.
Induction, Self-.
(a) A phenomenon of electric currents analogous to the inertia of
matter. Just as water which fills a pipe would resist a sudden change in
its rate of motion, whether to start from rest, to cease or decrease its
motion, so an electric current requires an appreciable time to start and
stop. It is produced most strongly in a coiled conductor, especially if
a core of iron is contained within it.
As in the case of two parallel wires, one bearing currents which vary,
momentary currents are induced in the other wire, so in a single
conductor a species of inertia is found which retards and prolongs the
current. If a single conductor is twisted into a helix or corresponding
shape, its separate turns react one on the other in accordance with the
general principles of electromagnetic induction. (See Induction,
Electro-magnetic.) Thus when a current is suddenly formed the coils
acting upon each other retard for an instant its passage, producing the
effect of a reverse induced current or extra current opposing the
principal current. Of course no extra current is perceptible, but only
the diminution. When the current is passing regularly and the current is
broken, the corresponding action prolongs the current or rather
intensifies it for an instant, producing the true extra current. This is
current self-induction.
[Transcriber's note: See inductance.]
Synonyms--Electric Inertia--Electro-dynamic Capacity.
(b) A permanent magnet is said to tend to repel its own magnetism, and
thus to weaken itself; the tendency is due to magnetic self-induction.
Induction Sheath.
In the brush dynamo a thin sheet of copper surrounding the magnet cores
with edges soldered together. The winding is outside of it. Its object
is to absorb extra currents set up by variations in magnetic intensity
in the cores. These currents otherwise would circulate in the cores.
304 STANDARD ELECTRICAL DICTIONARY.
Induction, Unit of Self-.
The unit of self-induction is the same as that of induction in general.
It is the henry, q. v.
Induction, Unipolar.
Induction produced in a conductor which continuously cuts the lines of
force issuing from one pole of a magnet. As the lines of force are
always cut in the same sense a continuous and constant direction current
is produced.
Induction, Vertical.
In an iron or steel ship the induction or attraction exercised in the
compass by vertical elements of the structure. Such vertical masses of
iron in the northern hemisphere would have their upper ends polarized as
south poles, and would affect the magnet as soon as the vessel swung out
of the magnetic meridian. Thus this induction disappears twice in
swinging a ship through a complete circle; deviation due to it is termed
semi-circular deviation. (See Deviation, Semi-circular.)
Fig. 202. INDUCTOR DYNAMO.
Inductophone.
A method of train telegraphy. The train carries a circuit including a
coil, and messages are picked up by it from coils along the line into
which an alternating current is passed. A telephone is used as a
receiver in place of a sounder or relay. The invention, never
practically used, is due to Willoughby Smith.
305 STANDARD ELECTRICAL DICTIONARY.
Inductor.
(a) In a current generator a mass of iron, generally laminated, which is
moved past a magnet pole to increase the number of lines of force
issuing therefrom. It is used in inductor dynamos. (See Dynamo
Inductor.) In the cut Fig. 202, of an inductor dynamo i, i, are the
laminated inductors.
(b) In influence machines the paper or tinfoil armatures on which the
electrification is induced.
Inertia.
A force in virtue of which every body persists in its state of motion or
rest except so far as it is acted on by some force.
Inertia, Electro-magnetic.
This term is sometimes applied to the phenomena of self-induction, or
rather to the cause of these phenomena.
Infinity Plug.
A plug in a resistance box, which on being pulled out of its seat opens
the circuit or makes it of infinite resistance. The plug seats itself
between two brass plates which are not connected with each other in any
way. The other plates are connected by resistance coils of varying
resistance.
Influence, Electric.
Electric induction, which may be either electrostatic, current, or
electro-magnetic.
Insolation, Electric.
Exposure to powerful arc-light produces effects resembling those of
sun-stroke. The above term or the term "electric sun-stroke" has been
applied to them.
[Transcriber's note: Operators of arc welders are prone to skin cancer
from ultra violet rays if not properly protected.]
Installation.
The entire apparatus, buildings and appurtenances of a technical or
manufacturing establishment. An electric light installation, for
instance, would include the generating plant, any special buildings, the
mains and lamps.
Insulating Stool.
A support for a person, used in experiments with static generators. It
has ordinarily a wooden top and glass legs. It separates one standing on
it from the earth and enables his surface to receive an electrostatic
charge. This tends to make his hair stand on end, and anyone on the
floor who touches him will receive a shock.
Insulating Tape.
Prepared tape used in covering the ends of wire where stripped for
making joints. After the stripped ends of two pieces are twisted
together, and if necessary soldered and carefully cleaned of soldering
fluid, they may be insulated by being wound with insulating tape.
The tape is variously prepared. It may be common cotton or other tape
saturated with any insulating compound, or may be a strip of gutta
percha or of some flexible cement-like composition.
306 STANDARD ELECTRICAL DICTIONARY.
Insulating Varnish.
Varnish used to coat the surface of glass electrical apparatus, to
prevent the deposition of hygrometric moisture, and also in the
construction of magnetizing and induction coils and the like. Shellac
dissolved in alcohol is much used. Gum copal dissolved in ether is
another. A solution of sealing wax in alcohol is also used. If applied
in quantities these may need baking to bring about the last drying. (See
Shellac Varnish.)
Insulator.
(a) Any insulating substance.
(b) A telegraph or line insulator for telegraph wires. (See Insulator,
Line or Telegraph.)
Synonyms--Dielectric--Non-conductor.
Insulator Cap.
A covering or hood, generally of iron, placed over an insulator to
protect it from injury by fracture with stones or missiles.
Insulator, Fluid.
(a) For very high potentials, as in induction coils or alternating
circuits, fluid insulators, such as petroleum or resin oil, have been
used. Their principal merit is that if a discharge does take place
through them the opening at once closes, so that they are self-healing.
(b) Also a form of telegraph or line insulator in which the lower rim is
turned up and inwards, so as to form an annular cup which is filled with
oil.
Insulator, Line or Telegraph.
A support often in the shape of a collar or cap, for a telegraph or
other wire, made of insulating material. Glass is generally used in the
United States, porcelain is adopted for special cases; pottery or stone
ware insulators have been used a great deal in other countries.
Sometimes the insulator is an iron hook set into a glass screw, which is
inserted into a hole in a telegraph bracket. Sometimes a hook is caused
to depend from the interior of an inverted cup and the space between the
shank of the hook and cup is filled with paraffine run in while melted.
Insulators are tested by measuring their resistance while immersed in a
vessel of water.
Intensity. Strength.
The intensity of a current or its amperage or strength; the intensity or
strength of a magnetic field or its magnetic density; the intensity or
strength of a light are examples of its use. In the case of dynamic
electricity it must be distinguished from tension. The latter
corresponds to potential difference or voltage and is not an attribute
of current; intensity has no reference to potential and is a
characteristic of current.
Intensity of a Magnetic Field.
The intensity of a magnetic field at any point is measured by the force
with which it acts on a unit magnet pole placed at that point. Hence
unit intensity of field is that intensity of field which acts on a unit
pole with a force of one dyne. (S. P. Thomson.) (See Magnetic Lines of
Force.)
307 STANDARD ELECTRICAL DICTIONARY.
Intercrossing.
Crossing a pair of conductors of a metallic circuit from side to side to
avoid induction from outside sources.
Intermittent.
Acting at intervals, as an intermittent contact, earth, or grounding of
a telegraph wire.
Interpolar Conductor.
A conductor connecting the two poles of a battery or current generator;
the external circuit in a galvanic circuit.
Interpolation.
A process used in getting a closer approximation to the truth from two
varying observations, as of a galvanometer. The process varies for
different cases, but amounts to determining an average or deducing a
proportional reading from the discrepant observed ones.
Interrupter.
A circuit breaker. It may be operated by hand or be automatic. (See
Circuit Breaker--Circuit Breaker, Automatic--and others.)
Interrupter, Electro-magnetic, for a Tuning Fork.
An apparatus for interrupting a current which passes through an
electromagnet near and facing one of the limbs of a tuning fork. The
circuit is made and broken by the vibrations of another tuning fork
through which the current passes. The second one is thus made to
vibrate, although it may be very far off and may not be in exact unison
with the first. The first tuning fork has a contact point on one of its
limbs, to close the circuit; it may be one which dips into a mercury
cup.
Intrapolar Region.
A term in medical electricity, denoting the part of a nerve through
which a current is passing.
Ions.
The products of decomposition produced in any given electrolysis are
termed ions, the one which appears at the anode or negative electrode is
the anion. The electrode connected to the carbon or copper plate of a
wet battery is an anode. Thus in the electrolysis of water oxygen is the
anion and hydrogen is termed the kation. In this case both anion and
kation are elements. In the decomposition of copper sulphate the anion
is properly speaking sulphion (S O4), a radical, and the kation is
copper, an element. Electro-negative elements or radicals are anions,
such as oxygen, sulphion, etc., while electro-positive ones are kations,
such as potassium. Again one substance may be an anion referred to one
below it and a kation referred to one above it, in the electro-chemical
series, q. v. Anion means the ion which goes to the anode or positive
electrode; kation, the ion which goes to the kathode or negative
electrode.
[Transcriber's note: An ion is an atom or molecule that has lost or
gained one or more valence electrons, giving it a positive or negative
electrical charge. A negatively charged ion, with more electrons than
protons in its nuclei, is an anion. A positively charged ion, with fewer
electrons than protons, is a cation. The electron was discovered five
years after this publication.]
308 STANDARD ELECTRICAL DICTIONARY.
Iron.
A metal; one of the elements; symbol, Fe; atomic weight, 56;
equivalent, 28 and 14, ; valency, 4 and 2.
It is a conductor of electricity. The following data are at
0° C. 32° F., with annealed metal.
Specific Resistance, 9.716 microhms.
Relative Resistance. 6.460
Resistance of a wire,
(a) 1 foot long weighing 1 grain, 1.085 ohms.
(b) 1 foot long 1/1000 inch thick, 58.45 "
(c) 1 meter long weighing 1 gram, .7570 "
(d) 1 meter long, 1 millimeter thick, .1237 "
Percentage increase in resistance per degree C. (1.8° F.)
at about 20° C. (68°F.), about 0.5 per cent.
Resistance of a 1 inch cube, 3.825 microhms.
Electro-chemical equivalent (Hydrogen = .0105), .147 and .294
Iron, Electrolytic.
Iron deposited by electrolytic action. Various baths are employed for
its formation. (See Steeling.) It has very low coercive power, only
seven to ten times that of nickel.
Ironwork Fault of a Dynamo.
A short circuiting of a dynamo by, or any connection of its coils with,
the iron magnet cores or other iron parts.
Isochronism.
Equality of periodic time; as of the times of successive beats of a
tuning fork, or of the times of oscillations of a pendulum.
Isoclinic Lines.
The lines denoting the locus of sets of equal dips or inclinations of
the magnetic needle upon the earth's surface, the magnetic parallels, q.
v. These lines are very irregular. (See Magnetic Elements.)
Isoclinic Map.
A map showing the position of isoclinic lines.
Isodynamic Lines.
Lines marking the locus of places of equal magnetic intensity on the
earth's surface. (See Magnetic Elements, Poles of Intensity.)
Isodynamic Map.
A map showing the position of isodynamic lines. (See Poles of
Intensity.)
Isogonic Lines.
Lines on a map marking the locus of or connecting those points where the
declination or variation of the magnetic needle is the same. (See
Magnetic Elements--Declination of Magnetic Needle.)
Synonyms--Isogonal Lines--Halleyan Lines.
309 STANDARD ELECTRICAL DICTIONARY.
Isogonic Map.
A map showing the isogonic lines. On such a map each line is
characterized and marked with the degrees and direction of variation of
the compass upon itself.
Synonym--Declination Map.
[Transcriber's note: The file Earth_Declination_1590_1990.gif provided
by the U.S. Geological Survey (http://www.usgs.gov) is an animation of
the declination of the entire earth.]
Isolated Plant, Distribution or Supply.
The system of supplying electric energy by independent generating
systems, dynamo or battery, for each house, factory or other place, as
contra-distinguished from Central Station Distribution or Supply.
Isotropic.
(Greek, equal in manner.)
Having equal properties in all directions; the reverse of anisotropic,
q. v. Thus a homogeneous mass of copper or silver has the same specific
resistance in all directions and is an isotropic conductor. Glass has
the same specific inductive capacity in all directions and is an
isotropic medium or dielectric. The same applies to magnetism. Iron is
an isotropic paramagnetic substance. (See Anisotropic.) The term applies
to other branches of physics also.
I. W. G.
Contraction for Indian Wire Gauge--the gauge adopted in British India.
309 STANDARD ELECTRICAL DICTIONARY.
J.
Symbol for the unit joule, the unit of electric energy.
Jacobi's Law.
A law of electric motors. It states that the maximum work of a motor is
performed when the counter-electromotive force is equal to one-half the
electro-motive force expended on the motor.
Jewelry.
Small incandescent lamps are sometimes mounted as articles of jewelry in
scarf-pins or in the hair. They may be supplied with current from
storage or from portable batteries carried on the person.
Joint, American Twist.
A joint for connecting telegraph wires, especially aerial lines. Its
construction is shown in the cut. The end of each wire is closely wound
around the straight portion of the other wire for a few turns.