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 pa.s.sed 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 s.p.a.ces 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 b.u.t.ton 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 const.i.tuents 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 gla.s.s 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 compa.s.s 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 quant.i.ty 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 s.p.a.ce traversed.

Force is measured by the acceleration or change of motion it can impart to a body of unit ma.s.s in a unit of time, or, calling force, F, ma.s.s, m acceleration per second a we have F = m a.