Fig. 173. LINK OF FORCE INDUCED BY A
CURRENT SHOWING THE MAGNETIC WHIRLS.
The existence of the field is easily shown by passing a conductor
vertically through a horizontal card. On causing a current to go through
the wire the field is formed, and iron filings dropped upon the card,
tend, when the latter is gently tapped, to take the form of circles. The
experiment gives a version of the well-known magnetic figures, q. v. See
Fig. 171.
The cut shows by the arrows the relation of directions of current to the
direction of the lines of force, both being assumptions, and merely
indicating certain fixed relations, corresponding exactly to the
relations expressed by the directions of electro-magnetic or magnetic
lines of force
256 STANDARD ELECTRICAL DICTIONARY.
Field, Pulsatory.
A field produced by pulsatory currents. By induction such field can
produce an alternating current.
Field, Rotating.
In a dynamo the field magnets are sometimes rotated instead of the
armature, the latter being stationary. In Mordey's alternator the
armature, nearly cylindrical, surrounds the field, and the latter
rotates within it, the arrangement being nearly the exact reverse of the
ordinary one. This produces a rotating field.
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.
Field, Stray.
The portion of a field of force outside of the regular circuit;
especially applied to the magnetic field of force of dynamos expressing
the portion which contributes nothing to the current generation.
Synonym--Waste Field.
Field, Uniform.
A field of force of uniform density. (See Field Density.)
Figure of Merit.
In the case of a galvanometer, a coefficient expressing its delicacy. It
is the reciprocal of the current required to deflect the needle through
one degree. By using the reciprocal the smaller the current required the
larger is the figure of merit. The same term may be applied to other
instruments.
It is often defined as the resistance of a circuit through which one
Daniell's element will produce a deflection of one degree on the scale
of the instrument. The circuit includes a Daniell's cell of resistance
r, a rheostat R, galvanometer G and shunt S. Assume that with the shunt
in parallel a deflection of a divisions is obtained. The resistance of
the shunted galvanometer is (GS/G+S ; the multiplying power m of the
shunt is S+G/S; the formula or figure of merit is m d (r+R +G S/G+S).
The figure of merit is larger as the instrument is more sensitive.
Synonym--Formula of Merit.
257 STANDARD ELECTRICAL DICTIONARY.
Filament.
A thin long piece of a solid substance. In general it is so thin as to
act almost like a thread, to be capable of standing considerable
flexure. The distinction between filament and rod has been of much
importance in some patent cases concerning incandescent lamps. As used
by electricians the term generally applies to the carbon filament of
incandescent lamps. This as now made has not necessarily any fibres, but
is entitled to the name of filament, partly by convention, partly by its
relative thinness and want of stiffness. (See Incandescent
Lamps--Magnetic Filament.)
Fire Alarm, Electric, Automatic.
A system of telegraph circuits, at intervals supplied with thermostats
or other apparatus affected by a change of temperature, which on being
heated closes the circuit and causes a bell to ring. (See Thermostat.)
Fire Alarm Telegraph System.
A system of telegraphic lines for communicating the approximate location
of a fire to a central station and thence to the separate fire-engine
houses in a city or district. It includes alarm boxes, distributed at
frequent intervals, locked, with the place where the key is kept
designated, or in some systems left unlocked. On opening the door of the
box and pulling the handle or otherwise operating the alarm, a
designated signal is sent to the central station. From this it is
telegraphed by apparatus worked by the central station operator to the
engine houses. The engines respond according to the discipline of the
service.
Fire Cleansing.
Freeing the surface of an article to be plated from grease by heating.
Fire Extinguisher, Electric, Automatic.
A modification of the electric fire alarm (see Fire Alarm, Electric,
Automatic), in which the thermostats completing the circuits turn on
water which, escaping through the building, is supposed to reach and
extinguish a fire.
Flashing in a Dynamo or Magneto-electric Generator.
Bad adjustment of the brushes at the commutator, or other fault of
construction causes the production of voltaic arcs at the commutator of
a generator, to which the term flashing is applied.
Flashing of Incandescent Lamp Carbons.
A process of treatment for the filaments of incandescent lamps. The
chamber before sealing up is filled with a hydro-carbon vapor or gas,
such as the vapor of a very light naphtha (rhigolene). A current is then
passed through the filament heating it to redness. The more attenuated
parts or those of highest resistance are heated the highest, and
decompose most rapidly the hydro-carbon vapor, graphitic carbon being
deposited upon these parts, while hydrogen is set free. This goes on
until the filament is of uniform resistance throughout. It gives also a
way of making the resistance of the filament equal to any desired number
of ohms, provided it is originally of high enough resistance. The
process increases the conductivity of the filament.
After flashing the chambers are pumped out and sealed up.
258 STANDARD ELECTRICAL DICTIONARY.
Flashing Over.
A phenomenon observed in high potential dynamos. On a sudden alteration
of the resistance of the circuit a long blue spark will be drawn out
around the surface of the commutator from brush to brush. The spark is
somewhat of the nature of an arc, and may seriously injure commutators
whose sections are only separated by mica, or other thin insulation. In
the case of commutators whose sections are separated by air spaces it is
not so injurious.
Flats.
In a commutator of a dynamo, the burning or wearing away of a commutator
segment to a lower level than the rest. Sometimes two adjacent bars will
be thus affected, causing a flat place on the commutator. It is not
always easy to account for the formation of flats. They may have their
origin in periodic vibrations due to bad mounting, or to sparking at the
particular point.
Floor Push.
A press or push button constructed to be set into the floor to be
operated by pressing with the foot. It is used to ring an alarm bell,
sound a buzzer or for similar service.
Fluid, Depolarizing.
A fluid used in voltaic batteries to dispose of the hydrogen, which goes
to the negative plate. This it does by oxidizing it. Chromic acid,
nitric acid, and chloric acids are among the constituents of liquid
depolarizers. (See Electropoion Fluid.)
Fluid, Electric.
The electric current and charge have sometimes been attributed to a
fluid. The theory, which never was much more than hypothetical, survives
to some extent in the single and double fluid theory. (See Single Fluid
Theory-Double Fluid Theory.)
Fluorescence.
The property of converting ether waves of one length, sometimes of
invisible length, into waves of another length (visible). AEsculin,
quinine salts, uranium glass and other substances exhibit this
phenomenon. The phenomenon is utilized in the production of Geissler
tubes.
Flush Boxes.
A heavy iron box covered with a heavy hand plate and laid flush (whence
the name), or even with the surface of a roadway. Into it conductors of
an underground system lead, and it is used to make connections therewith
and for examining the leakage of the conductors and for similar
purposes. It is a "man-hole" (q. v.) in miniature.
Fluviograph.
An electric registering tide gauge or water level gauge.
259 STANDARD ELECTRICAL DICTIONARY.
Fly or Flyer, Electric.
A little wheel, ordinarily poised on a point, like a compass needle. It
carries several tangentially directed points, all pointing in the same
sense. When connected with a source of electricity of high potential it
revolves by reaction. The tension of its charge is highest at the
points, the air there is highly electrified and repelled, the reaction
pushing the wheel around like a Barker's mill or Hero's steam engine.
Sometimes the flyer is mounted with its axis horizontal and across the
rails on a railroad along which it travels.
Synonym--Reaction Wheel.
Foci Magnetic.
The two points on the earth's surface where the magnetic intensity is
greatest. They nearly coincide in position with the magnetic poles.
Fog, Electric.
Fogs occurring when the atmosphere is at unusually high potential and
accompanied by frequent change of such polarity.
Following Horns.
In dynamo-electric machines the projecting ends of the pole pieces
towards which the outer uncovered perimeter of the armature turns in its
regular operations. The leading horns are those away from which the
armature rotates. In considering rotation the exposed portion of the
superficies of the armature is considered. The definition would have to
be reversed if the part facing the pole pieces were considered.
Synonym--Trailing Horns.
Foot-candle.
A unit of illuminating power; the light given by one standard candle at
a distance of one foot. The ordinary units of illuminating power are
entirely relative; this is definite. It is due to Carl Herring.
Foot-pound.
A practical unit of work or energy. The quantity of work required to
raise a pound one foot, or one hundred pounds one-hundredth of a foot,
and so on; or the potential energy represented by a weight at an
elevation under these conditions.
Foot-step.
In a dynamo with armature at the lower end of its field magnets, the
plate generally of zinc, interposed between it and the iron base plate
to prevent the leakage of lines of force outside of the circuit. Any
diamagnetic material which is mechanically suitable may be used.
Force.
Force may be variously defined.
(a) Any cause of change of the condition of matter with respect to
motion or rest.
(b) A measurable action upon a body under which the state of rest of
that body, or its state of uniform motion in a straight line, suffers
change.
(c) It may be defined by its measurement as the rate of change of
momentum, or
(d) as the rate at which work is done per unit of space traversed.
Force is measured by the acceleration or change of motion it can impart
to a body of unit mass in a unit of time, or, calling
force, F,
mass, m
acceleration per second a
we have F = m a.
The dimensions of force are
mass (M) * acceleration (L/(T^2)) = (M*L)/(T^2).
260 STANDARD ELECTRICAL DICTIONARY.
Force de Cheval. Horse power (French).
It is the French or metric horse power.
It is equal to:
542.496 Foot lbs. per second.
.9864 English Horse Power.
75.0 Kilogram-meters per second.
Force, Electro-magnetic.
The mechanical force of attraction or repulsion acting on the
electro-magnetic unit of quantity. Its intensity varies with the square
of the distance. It may also be defined as electric force in the
electro-magnetic system.
Its dimensions are equal to
mechanical force ((M*L)/(T^2)) divided by quantity ((M^.5)*(L^.5))
= ((M^.5)*(L^.5))/(T^2).
Force, Electrostatic.
The force by which electric matter or electrified surfaces attract or
repel each other. It is also termed electric force (not good) and
electro-motive intensity. It is the mechanical force acting upon a unit
quantity of electricity. Its intensity varies with the square of the
distance.
Its dimensions are therefore equal to
(quantity * unity / (square of distance) Q. * 1 / (L^2)
= ((M^.5) * (L^1.5) )/ T*1 / (L^2)
= ((M^.5) * (L^.5)) / T
These dimensions are also those of potential difference.
[Transcriber's Note: The image of the preceding paragraph is included
for "clarity".]
The objection to the term electric force is that it may be applied also
to electro-magnetic force, and hence be a source of confusion.
Forces, Parallelogram of.
The usual method of composing forces or resolving a force. The sides of
a parallelogram of forces represent component forces and the diagonal
represents the resultant. See Component--Resultant--Forces, Composition
of--Forces, Resolution of.
Forces, Composition of.
When several forces act in a different direction upon a point they may
be drawn or graphically represented as arrows or lines emanating from
the point in the proper direction and of lengths proportional to the
force they exercise. Any two can be treated as contiguous sides of a
parallelogram and the parallelogram can be completed. Then its diagonal,
called the resultant, will represent the combined action of the two
forces, both as regards direction and intensity. This is the composition
of two forces.
If more than two forces act upon the given point the resultant can be
composed with any of the others and a new force developed. The new
resultant can be combined with another force, and the process kept up,
eliminating the components one by one until a final resultant of all is
obtained. This will give the exact direction and intensity of the
forces, however many or varied.
261 STANDARD ELECTRICAL DICTIONARY.
Forces, Resolution of.
The developing from a single force treated as a resultant, two other
forces in any desired direction. The reverse of composition of forces.
(See Forces, Composition of--Forces, Parallelogram
of--Components--Resultant.)
Force, Tubes of.
Aggregations of lines of force, either electrostatic or magnetic. They
generally have a truncated, conical or pyramidal shape and are not
hollow. Every cross-section contains the same number of lines. The name
it will seem is not very expressive.
Force, Unit of.
The fundamental or C. G. S. unit or force is the dyne, q. v.
The British unit of force is the poundal (the force which will produce
an acceleration of one foot per second in a mass of one pound). It is
equal to about 10/322 pound. A force cannot be expressed accurately in
weight units, because weight varies with the latitude.
Forming.
The process of producing secondary battery plates from lead plates by
alternately passing a charging current through the cell and then
allowing it to discharge itself and repeating the operation. (See
Battery, Secondary, Planté's.)
Foundation Ring.
In a dynamo armature the ring-shaped core on which Gramme ring armatures
and other ring armatures are wound.
Fourth State of Matter.
Gas so rarefied that its molecules do not collide, or rarely do so;
radiant matter, q. v.
[Transcriber's note: This term now refers to plasma, an ionized gas,
which contains free electrons. The ions and electrons move somewhat
independently making plasma electrically conductive. It responds
strongly to electromagnetic fields.]
Frame.
In a dynamo the bed-piece is sometimes called the frame.
Franklin's Experiment.
Franklin proved the identity of lightning and electricity by flying a
kite in a thunder storm. The kite was of silk so as to endure the
wetting. When the string became wet sparks could be taken from a key
attached to its end. The main string was of hemp; at the lower end was a
length of silk to insulate it. The key was attached near the end of and
to the hemp string.
Franklin's Plate.
A simple form of condenser. It consists of a plate of glass coated on
each side with tinfoil with a margin of about an inch of clear glass.
One coating may be grounded as indicated in the cut, and the plate
charged like a Leyden jar. Or one side may be connected with one
terminal, and the other with the other terminal of an influence machine
and the pane will be thus charged.
Synonym--Fulminating Pane.
262 STANDARD ELECTRICAL DICTIONARY.
Fig. 174. FRANKLIN'S PLATE.
Franklin's Theory.
The single fluid theory, q. v., of electricity.
Frequency.
The number of double reversals or complete alternations per second in an
alternating current.
Synonym--Periodicity.
Frictional Electricity.
Electricity produced by friction of dissimilar substances. (See
Electrostatic Series.) The contact theory holds that friction plays only
a secondary rôle in this process; that it increases the thoroughness of
contact, and tends to dry the rubbing surfaces, but that the charges
induced are due to contact of dissimilar substances, not to friction of
one against the other.
Frictional Heating.
The heating of a conductor by the passage of a current; the Joule
effect, q. v.
Fringe.
The outlying edge of a magnetic field.
Frog, Galvani's Experiment With.
A classic experiment in electricity, leading to the discovery of current
or dynamic electricity. If a pair of legs of a recently killed frog are
prepared with the lumbar nerves exposed near the base of the spinal
column, and if a metallic conductor, one half-length zinc and the other
half-length copper, is held, one end between the lumbar nerves and the
spine, and the other end against one of the muscles of the thigh or
lower legs, the moment contact occurs and the circuit is completed
through the animal substance the muscles contract and the leg is
violently drawn upwards. Galvani, in 1786, first performed, by accident,
this famous experiment, it is said, with a scalpel with which he was
dissecting the animal. He gave his attention to the nerves and muscles.
Volta, more happily, gave his attention to the metals and invented the
voltaic battery, described by him in a letter to Sir Joseph Banks, dated
1800.
Frog, Rheoscopic.
If the nerve or living muscle of a frog is suddenly dropped upon another
living muscle so as to come in contact with its longitudinal and
transverse sections, the first muscle will contract on account of the
stimulation of its nerve due to the passage of a current derived from
the second muscle (Ganot). The experiment goes under the above title.
263 STANDARD ELECTRICAL DICTIONARY.
Frying.
A term applied to a noise sometimes produced in a voltaic arc due to too
close approach of the carbons to each other. It has been suggested that
it may be due to volatilization of the carbon. (Elihu Thomson.)
Fulgurite.
An irregular and tubular mass of vitrified quartz, believed to be formed
by melting under the lightning stroke.
Fig. 175. CRUCIBLE, ELECTRIC.
Furnace, Electric.
A furnace in which the heat is produced by the electric current. It has
hitherto been practically used only in the extraction of aluminum and
silicium from their ores. The general principle involves the formation
of an arc between carbon electrodes. The substances to be treated are
exposed to the heat thus produced. Sometimes the substances in the arc
form imperfect conductors, and incandescence takes a part in the action.
Sometimes the substances are merely dropped through the arc.
[Transcriber's note: Silicium is silicon.]
Fuse Board.
A tablet on which a number of safety fuses are mounted. Slate is
excellent material for the tablet, as it is incombustible, and is easily
drilled and worked.
Fuse Box.
A box containing a safety fuse. Porcelain is an excellent material for
its base. No combustible material should enter into its composition.
Fuse, Cockburn.
A safety fuse or cut off which consists of a wire of pure tin running
from terminal to terminal, to whose centre a leaden ball is secured by
being cast into position. The connection with the terminals is made by
rings at the ends of the wire through which the terminal screws are
passed and screwed home. When the tin softens under too heavy a current
the weight of the shot pulls it apart.
Fig. 176 COCKBURN SAFETY FUSE.
264 STANDARD ELECTRICAL DICTIONARY.