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.