T. O'Conor Sloane

“ 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. ”

“ Potential.
Potential in general may be treated as an attribute of a point in space,
and may express the potential energy which a unit mass would have if
placed at that point.
This conception of potential is that of a property attributable to a
point in space, such that if a unit mass were placed there the forces
acting upon it would supply the force factor of energy, while the body
would supply the mass factor. This property is expressible in units,
which produce, if the supposed mass is a unit mass, units of work or
energy, but potential itself is neither. ”

“ When a circuit is suddenly opened or closed a current of very brief
duration, in the first case in the same direction, in the other case in
the opposite direction, is produced, which exceeds the ordinary current
in intensity. A high potential difference is produced for an instant
only. These are called extra currents. As they are produced by
electro-magnetic induction, anything which strengthens the field of
force increases the potential difference to which they are due. ”

“ Potential is not the power of doing work, although, as it is expressed
always with reference to a unit body, it is numerically equal to the
number of ergs of work which must be done in order to bring a positive
unit of electricity from a region where there is no electric
force--which is a region at an infinite distance from all electrified
bodies--up to the point in question. This includes the assumption that
there is no alteration in the general distribution of electricity on
neighboring bodies. (Daniell.)
In practice the earth is arbitrarily taken as of zero electric potential. ”

“ 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. ”

“ 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) . ”

“ To constitute a battery the zinc and copper plates must be connected
outside of the solution. This connection need not be immediate. Any
conductor which touches both plates will bring about the action, and the
current will pass through it.
The easiest way to picture the action of a battery is to accept the
doctrine of contact action. In the battery the molecules of water are
pulled apart. The hydrogen molecules go to the copper, the oxygen
molecules go to the zinc, each one, leaving its contact with the other,
comes off charged with opposite electricity. ”

“ 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. ”

“ One and the same current
passes through all parts of a series circuit when such current is
constant.
A current being produced by electro-motive force, and electromotive
force disappearing in its production in an active circuit, there must be
some source of energy which will maintain electromotive force against
the drain made upon it by the current.
The simplest conception of an active electric circuit is a ring or
endless conductor swept through a field of force so as to cut lines of
force. A simple ring dropped over a magnet pole represents the
simplification of this process. ”

“ The electric capacity of a telegraphic conductor is identical in quality
with that of any other conductor. It varies in quantity, not only for
different wires, but for the same wire under different environments, as
the wire reacting through the surrounding air or other dielectric upon
the earth, represents one element of a condenser, the earth, in general,
representing the other. Hence, a wire placed near the earth has greater
capacity than one strung upon high poles, although the wires may be
identical in length, material and diameter. ”

“ At a waterfall a
turbine water wheel is established which drives a dynamo. From the
dynamo wires are carried to a distant factory, where a motor or several
motors are established, which receive current from the dynamo and drive
the machinery. The same current, if there is enough energy, may be used
for running lamps or electroplating. As electric energy (see Energy,
Electric,) is measured by the product of potential difference by
quantity, a very small wire will suffice for the transmission of a small
current at a high potential, giving a comparatively large quantity of
energy. ”

“ The coefficient of magnetic induction varies with the material of the
induced mass, and varies with the intensity of the magnetizing force.
This variation is due to the fact that as the induced magnetism in a
body increases, the magnetizing force required to maintain such
induction, increases in a more rapid ratio. The coefficient of magnetic
induction is the same as magnetic permeability, and in a certain sense
is the analogue of conductivity. It is also termed the multiplying power
of the body or core magnetized. ”

“ In use either the prime conductor or cushions are connected by a chain
or otherwise with the earth. Assume it to be the cushions. As the
machine is worked by turning the plate, the glass and cushion being in
contact develop opposite electricities. The glass is charged with
positive electricity, and as it turns carries it off and as it reaches
the prime conductor by induction and conduction robs it of its negative
electricity. Meanwhile the cushions negatively excited deliver their
charge to the earth. The action thus goes on, the prime conductor being
charged with positive electricity. ”

“ A term in electro-therapeutics; the shock received when an electric
circuit, including the patient in series, is broken or opened.
Synonym--Opening Shock.
Shock, Electric.
The effect upon the animal system of the discharge through it of
electricity with high potential difference. Pain, nervous shock, violent
muscular contortions accompany it. Of currents, an alternating current
is reputed worse than a direct current; intermediate is the pulsatory
current.
The voltage is the main element of shock, amperage has also some direct
influence. ”

“ Field, Rotatory.
A magnetic field whose virtual poles keep rotating around its centre of
figure. If two alternating currents differing one quarter period in
phase are carried around four magnetizing coils placed and connected in
sets of two on the same diameter and at right angles to each other, the
polarity of the system will be a resultant of the combination of their
polarity, and the resultant poles will travel round and round in a
circle. In such a field, owing to eddy currents, masses of metal,
journaled like an armature, will rotate, with the speed of rotation of
the field. ”

“ There are a number of kinds of
efficiencies of an electric generator which are given below.
Efficiency, Commercial.
Practical efficiency of a machine, obtained by dividing the available
output of work or energy of a machine by the energy absorbed by the same
machine. Thus in a dynamo part of the energy is usefully expended in
exciting the field magnet, but this energy is not available for use in
the outer circuit, is not a part of the output, and is not part of the
dividend. ”

“ Thus in a shunt-wound dynamo there is a
critical resistance for the outer circuit, below which the field ceases
to be magnetized, as enough current ceases to be shunted into it to
magnetize it. The machine is said to unbuild itself, and a discharge of
magnetism occurs from the field magnet. ”

“ 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. ”

“ 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. ”

“ 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 relative power of conducting the electric current possessed by
different substances. A path for the current through the ether is opened
by the presence of a body of proper quality, and this quality, probably
correlated to opacity, is termed conductivity. There is no perfect
conductor, all offer some resistance, q. v., and there is hardly any
perfect non-conductor. It is the reverse and reciprocal of resistance. ”

“ Indicator, Circuit.
A galvanometer used to show when a circuit is active, and to give an
approximate measurement of its strength. It is a less accurate and
delicate form of instrument than the laboratory appliance.
Inductance.
The property of a circuit in virtue of which it exercises induction and
develops lines of force. It is defined variously. As clear and
satisfactory a definition as any is the following, due to Sumpner and
Fleming: Inductance is the ratio between the total induction through a
circuit to the current producing it. ”

“ It holds that the phenomena of light are due
to ether waves, identical in general factors with those produced by
electro-magnetic induction of alternating currents acting on the ether.
In a non-conductor any disturbance sets an ether wave in motion owing to
its restitutive force; electricity does not travel through such a
medium, but can create ether waves in it. Therefore a non-conductor of
electricity is permeable to waves of ether or should transmit light, or
should be transparent. ”

“ 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. ”

“ But it has a far stronger affinity for the first named
metal. If now we immerse in dilute acid two plates, one of pure zinc,
and one of copper, no action will be discernible. But if the plates are
brought in contact with each other a stream of bubbles of hydrogen gas
will escape from the surface of the copper and the zinc will dissolve.
By applying proper tests and deductions it will be found that the copper
and zinc are being constantly charged with opposite electricities, and
that these are constantly recombining. This recombination produces what
is known as an electric current. ”

“ Thus, in the discharge of the Leyden
jar a large number of oscillations of current back and forth are
produced, the current alternating like the swings of a pendulum.
These oscillations are supposed to affect the ether, producing waves in
it identical with light waves, except that we have not been able yet to
produce them short enough to affect the visual organs. The waves thus
produced can be reflected or refracted; some substances are transparent
for them and others opaque. ”