Fig. 197 HUGHES' ELECTRO-MAGNET.

Fig. 198. HUGHES' INDUCTION BALANCE.
Hughes' Induction Balance.
An apparatus for determining the presence of a concealed mass of metal.
The apparatus is variously connected. The cut shows a representative
form; a and a' are two primary coils, each consisting of 100 meters (328
feet) of No. 32 silk covered copper wire (0.009 inch diameter) wound on
a boxwood spool ten inches in depth; b and b' are secondary coils. All
coils are supposed to be alike. The primary coils are joined in series
with a battery of three or four Daniell cells. A microphone m is
included in the same circuit. The secondary coils are joined in series
with a telephone and in opposition with each other. The clock is used to
produce a sound affecting the microphone. If all is exactly balanced
there will be no sound produced in the telephone. This balance is
brought about by slightly varying the distance of one of the secondaries
from the primary, until there is no sound in the telephone. If now a
piece of metal is placed within either of the coils, it disturbs the
balance and the telephone sounds.
292 STANDARD ELECTRICAL DICTIONARY.
To measure the forces acting a sonometer or audiometer is used. This is
shown in the upper part of the cut. Two fixed coils, c and e are mounted
at the ends of a graduated bar. A movable coil d is connected in the
telephone circuit; c and e by a switch can be connected with the battery
and microphone circuit, leaving out the induction balance coils. The
ends of the coils c and e, facing each other are of the same polarity.
If these coils, c and e, were equal in all respects, no sound would be
produced when d was midway between them. But they are so wound that the
zero position for d is very near one of them, c.
Assume that a balance has been obtained in the induction balance with
the coil d at zero. No sound is heard whether the switch is moved to
throw the current into one or the other circuit. A piece of metal placed
in one of the balance coils will cause the production of a sound. The
current is turned into the sonometer and d is moved until the same
sound, as tested by rapid movements of the switch, is heard in both
circuits. The displacement of d gives the value of the sound.
A milligram of copper is enough to produce a loud sound. Two coins can
be balanced against each other, and by rubbing one of them, or by
breathing on one of them, the balance will be disturbed and a sound will
be produced.
Prof. Hughes has also dispensed with the audiometer. He has used a strip
of zinc tapering from a width of 4 mm. (.16 inch) at one end to a sharp
edge or point at the other. The piece to be tested being in place in one
coil, the strip is moved across the face of the other until a balance is
obtained.
As possible uses the detection of counterfeit coins, the testing of
metals for similarity of composition and the location of bullets in the
body have been suggested. Care has to be taken that no masses of metal
interfere. Thus in tests of the person of a wounded man, the presence of
an iron truss, or of metallic bed springs may invalidate all
conclusions.
The same principle is carried out in an apparatus in which the parts are
arranged like the members of a Wheatstone bridge. One pair of coils is
used, which react on each other as primary and secondary coils. One of
the coils is in series with a telephone in the member of the bridge
corresponding to that containing the galvanometer of the Wheatstone
bridge. The latter is more properly termed an induction bridge.
Synonyms--Inductance Bridge--Inductance Balance--Induction Bridge.
293 STANDARD ELECTRICAL DICTIONARY.
Hydro-electric. adj.
(a) A current produced by a voltaic couple or the couple itself is
sometimes thus characterized or designated as a "hydro-electric current"
or a "hydro-electric couple." It distinguishes them from
thermo-electric.
(b) Armstrong's steam boiler electric machine (see Hydroelectric
Machine) is also termed a hydro-electric machine.
Hydro-electric Machine.
An apparatus for generating high potential difference by the escape of
steam through proper nozzles.
It consists of a boiler mounted on four glass legs or otherwise
insulated. An escape pipe terminates in a series of outlets so shaped as
to impede the escape of the steam by forcing it out of the direct
course. These jets are lined with hard wood. They are enclosed in or led
through a box which is filled with cold water.

Fig. 199. ARMSTRONG'S HYDRO-ELECTRIC MACHINE.
This is to partly condense the steam so as to get it into the vesicular
state, which is found essential to its action. Dry steam produces no
excitation. If the boiler is fired and the steam is permitted to escape
under the above conditions the vesicles presumably, or the "steam" is
found to be electrified. A collecting comb held against the jet becomes
charged and charges any connected surface.
294 STANDARD ELECTRICAL DICTIONARY.
The boiler in the above case is negatively and the escaping "steam" is
positively charged. By changing the material of the linings of the jets,
or by adding turpentine the sign of the electricity is reversed. If the
water contains acid or salts no electricity is produced. The regular
hydro-electric machine is due to Sir William Armstrong.
Faraday obtained similar results with moist air currents.
Hydrogen.
An element existing under all except the most extreme artificial
conditions of pressure and cold as a gas. It is the lightest of known
substances. Atomic weight, 1; molecular weight, 2; equivalent, 1;
valency, 1; specific gravity, .0691-.0695. (Dumas & Boussingault.)
It is a dielectric of about the same resistance as air. Its specific
inductive capacity at atmospheric pressure is:
.9997 (Baltzman) .9998 (Ayrton)
Electro-chemical equivalent, .0105 milligram.
The above is usually taken as correct. Other values are as follows:
.010521 (Kohllrausch) .010415 (Mascart)
The electro-chemical equivalent of any element is obtained by
multiplying its equivalent by the electro-chemical equivalent of
hydrogen. The value .0105 has been used throughout this book.
Hygrometer.
An instrument for determining the moisture in the air. One form consists
of a pair of thermometers, one of which has its bulb wrapped in cloth
which is kept moist during the observation. The evaporation is more or
less rapid according to the dryness or moisture of the air, and as the
temperature varies with this evaporation the relative readings of the
two thermometers give the basis for calculating the hygrometric state of
the air. Another form determines the temperature at which dew is
deposited on a silver surface, whence the calculations are made.
Hysteresis, Magnetic.
A phenomenon of magnetization of iron. It may be attributed to a sort of
internal or molecular friction, causing energy to be absorbed when iron
is magnetized. Whenever therefore the polarity or direction of
magnetization of a mass of iron is rapidly changed a considerable
expenditure of energy is required. It is attributed to the work done in
bringing the molecules into the position of polarity.
295 STANDARD ELECTRICAL DICTIONARY.
The electric energy lost by hysteresis may be reduced by vibrations or
jarring imparted to the iron, thus virtually substituting mechanical for
electrical work.
On account of hysteresis the induced magnetization of a piece of iron or
steel for fields of low intensity will depend on the manner in which the
material has been already magnetized. Let the intensity of field
increase, the magnetization increasing also; then lower the intensity;
the substance tends to and does retain some of its magnetism. Then on
again strengthening the field it will have something to build on, so
that when it attains its former intensity the magnetization will exceed
its former value. For a moderate value of intensity of field the
magnetization can have many values within certain limits.
Synonym--Hysteresis--Hysteresis, Static--Magnetic Friction.
Hysteresis, Viscous.
The gradual increase or creeping up of magnetization when a magnetic
force is applied with absolute steadiness to a piece of iron. It may
last for half an hour or more and amount to several per cent. of the
total magnetization. It is a true magnetic lag.

295 STANDARD ELECTRICAL DICTIONARY.
I.
A symbol sometimes used to indicate current intensity. Thus Ohm's law is
often expressed I = E/R, meaning current intensity is equal to
electro-motive force divided by resistance. C is the more general symbol
for current intensity.
Ideoelectrics or Idioelectrics.
Bodies which become electric by friction. This was the old definition,
the term originating with Gilbert. It was based on a misconception, as
insulation is all that is requisite for frictional electrification,
metals being thus electrified if held by insulating handles. The term is
virtually obsolete; as far as it means anything it means insulating
substances such as scaling wax, sulphur, or glass.
Idle Coils.
Coils in a dynamo, in which coils no electro-motive force is being
generated. This may occur when, as a coil breaks connection with the
commutator brush, it enters a region void of lines of magnetic force, or
where the lines are tangential to the circle of the armature.
Idiostatic Method.
A method of using the absolute or attracted disc electrometer. (See
Electrometer, Absolute.) The suspended disc and guard ring are kept at
the same potential, which is that of one of the points whose potential
difference is to be determined; the lower fixed disc is connected to the
other of the points whose potential difference is to be determined. Then
we have the formula
V = d * SquareRoot( 8 * PI * F ) / S
in which d is the distance between the discs, V is the difference of
potential of the two points, F the force of attraction between the discs
in dynes, and S the area of the suspended disc. (See Heterostatic
Method.)
296 STANDARD ELECTRICAL DICTIONARY.
Idle Poles.
Poles of wire sealed into Crookes' tubes, not used for the discharge
connections, but for experimental connections to test the effect of
different excitation on the discharge.
Idle Wire.
In a dynamo the wire which plays no part in generating electro-motive
force. In a Gramme ring the wire on the inside of the ring is idle wire.
Igniter.
In arc lamps with fixed parallel carbons of the Jablochkoff type (see
Candle, Jablochkoff) a strip of carbon connects the ends of the carbons
in the unused candle. This is necessary to start the current. Such strip
is called an igniter. It burns away in a very short time when an arc
forms producing the light, and lasts, if all goes well, until the candle
burns down to its end. Without the igniter the current would not start
and no arc would form.
I. H. P.
Symbol for indicated horse-power.
Illuminating Power.
The relative light given by any source compared with a standard light,
and stated in terms of the same, as a burner giving an illuminating
power of sixteen candles. For standards see Candle, Carcel--Methven
Standard--Pentane Standard.
Illuminating Power, Spherical.
The illuminating power of a lamp or source of light may vary in
different directions, as in the case of a gas burner or incandescent
lamp. The average illuminating power determined by photometric test or
by calculation in all directions from the source of light is called the
spherical illuminating power, or if stated in candles is called the
spherical candle power.
Illumination, Unit of.
An absolute standard of light received by a surface. Preece proposed as
such the light received from a standard candle (see Candle, Standard) at
a distance of 12.7 inches. The object of selecting this distance was to
make it equal to the Carcel Standard (see Carcel), which is the light
given by a Carcel lamp at a distance of one meter.
From one-tenth to one-fiftieth this degree of illumination was found in
gas-lighted streets by Preece, depending on the proximity of the gas
lamps.
Image, Electric.
An electrified point or system of points on one side of a surface which
would produce on the other side of that surface the same electrical
action which the actual electrification of that surface really does
produce. (Maxwell.)
The method of investigating the distribution of electricity by electric
images is due to Sir William Thomson. The conception is purely a
theoretical one, and is of mathematical value and interest.
297 STANDARD ELECTRICAL DICTIONARY.
Impedance.
The ratio of any impressed electro-motive force to the current which it
produces in a conductor. For steady currents it is only the resistance.
For variable currents it may include besides resistance inductance and
permittance. It is the sum of all factors opposing a current, both ohmic
and spurious resistances. It is often determined and expressed as ohms.
Synonym--Apparent Resistance--Virtual Resistance.
Impedance, Oscillatory.
The counter-electro-motive force offered to an oscillatory discharge, as
that of a Leyden jar. It varies with the frequency of the discharge
current.
Synonym--Impulsive Impedance.
Impressed Electro-motive Force.
The electro-motive force expending itself in producing current induction
in a neighboring circuit.
Impulse.
(a) An electro-magnetic impulse is the impulse produced upon the
luminiferous ether by an oscillatory discharge or other varying type of
current; the impulse is supposed to be identical, except as regards
wave-length, with a light wave.
(b) An electro-motive impulse is the electro-motive force which rises so
high as to produce an impulsive or oscillatory discharge, such as that
of a Leyden jar.
Incandescence, Electric.
The heating or a conductor to red, or, more etymologically, to white
heat by the passage of an electric current. The practical conditions are
a high intensity of current and a low degree of conductance of the
conductor relatively speaking.
Inclination Map.
A map showing the locus of equal inclination or dips of the magnetic
needle. The map shows a series of lines, each one of which follows the
places at which the dip of the magnetic needle is identical. The map
changes from year to year. (See Magnetic Elements.)
Independence of Currents in Parallel Circuits.
If a number of parallel circuits of comparatively high resistance are
supplied by a single generator of comparatively low resistance, the
current passed through each one will be almost the same whether a single
one or all are connected. Under the conditions named the currents are
practically independent of each other.
[Transcriber's note: The current in each parallel branch depends on the
resistance/impedance of that branch. Only if they all have the same

impedance

will the current be the same.]
Indicating Bell.
An electric bell arranged to drop a shutter or disclose in some other
way a designating number or character when rung.
298 STANDARD ELECTRICAL DICTIONARY.
Indicator.
(a) An apparatus for indicating the condition of a distant element, such
as the water level in a reservoir, the temperature of a drying room or
cold storage room or any other datum. They are of the most varied
constructions.
(b) The receiving instrument in a telegraph system is sometimes thus
termed.
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. "Thus taking a simple helix of five
turns carrying a current of two units, and assuming that 1,000 lines of
force passed through the central turn, of which owing to leakage only
900 thread the next adjacent on each side, and again only 800 through
the end turns, there would be 800 + 900 + 1000 + 900 + 800, or 4,400
linkages of lines with the wire, and this being with 2 units of current,
there would be 2,200 linkages with unit current, and consequently the
self-inductance of the helix would be 2,200 centimetres." (Kennelly.)
Inductance, as regards its dimensions is usually reduced to a length,
hence the last word of the preceding quotation.
The practical unit of inductance is termed the henry, from Prof. Joseph
Henry; the secohm, or the quad or quadrant. The latter alludes to the
quadrant of the earth, the value in length of the unit in question.
[Transcriber's note: (L (di/dt) = V). A current changing at the rate of
one ampere per second through a one henry inductance produces one volt.
A sinusoidal current produces a voltage 90 degrees ahead of the current,
a cosine (the derivative of sine is cosine). One volt across one henry
causes the current to increase at one ampere per second.]
Induction, Coefficient of Self.
The coefficient of self-induction of a circuit is the quantity of
induction passing through it per unit current in it. If a given circuit
is carrying a varying current it is producing a varying quantity of
magnetic induction through itself. The quantity of induction through the
circuit due to its current is generally proportional to its current. The
quantity for unit current is the coefficient of self-induction.
(Emtage.)
Induction, Cross.
The induction of magnetic lines of force in a dynamo armature core by
the current passing around such armature. These lines in a symmetrical
two pole machine are at right angles to the lines of force which would
normally extend across the space between the two magnet poles. The joint
magnetizing effect of the field and of the cross induction produces a
distorted field between the poles .
Synonym--Cross-magnetizing Effect.
299 STANDARD ELECTRICAL DICTIONARY.
Induction, Electro-magnetic.
The inter-reaction of electromagnetic lines of force with the production
of currents thereby.
A current passing through a conductor establishes around it a field of
force representing a series of circular lines of force concentric with
the axis of the conductor and perpendicular thereto. These lines of
force have attributed to them, as a representative of their polarity,
direction. This is of course purely conventional. If one is supposed to
be looking at the end of a section of conductor, assuming a current be
passing through it towards the observer, the lines of force will have a
direction opposite to the motion of the hands of a watch. The idea of
direction may be referred to a magnet. In it the lines of force are
assumed to go from the north pole through the air or other surrounding
dielectric to the south pole.
Two parallel wires having currents passing through them in the same
direction will attract each other. This is because the oppositely
directed segments of lines of force between the conductors destroy each
other, and the resultant of the two circles is an approximation to an
ellipse. As lines of force tend to be as short as possible the
conductors tend to approach each other to make the ellipse become of as
small area as possible, in other words to become a circle.
If on the other hand the currents in the conductors are in opposite
directions the segments of the lines of force between them will have
similar directions, will, as it were, crowd the intervening ether and
the wires will be repelled.