Sound Reading.
The art or method of receiving telegraph messages by ear. It is now
universally used by all expert Morse operators. It can only be applied
to telegraph systems producing audible sounds; in some cases, as in
needle telegraphy, it may be quite inapplicable.
Space, Clearance.
The space between faces of the pole pieces and the surface of the
armature in a dynamo. It is really the air gap, but in calculating
dynamo dimensions the thickness of the insulated copper wire windings of
the commutator are counted in as part of the air gap, because copper is
almost the same as air in impermeability. Clearance space is a
mechanical factor; the air gap is an electric or magnetic factor.
Synonym--Inter-air Space.
Space, Crookes' Dark.
In an exhausted tube, through which an electric discharge is caused to
pass, the space surrounding the negative electrode of the tube. This
space is free from any luminous effect, and by contrast with the light
of the discharge appears dark. The vacuum may be made so high that the
dark space fills the whole space between the electrodes. It is less for
a less vacuum and varies for other factors, such as the temperature of
the negative electrode from which it originates, the kind of residual
gas present, and the quality of the spark.
Space, Faraday's Dark.
The space in an exhausted tube between the luminous glows about the two
electrodes.
Space, Interferric.
A term for the air-gap in a magnetic circuit. It is etymologically more
correct than air-gap, for the latter is often two-thirds or more filled
with the insulating material and copper wire of the armature windings.
(See Space, Clearance.)
Spark Arrester.
A screen of wire netting fitting around the carbons of an arc lamp above
the globe to prevent the escape of sparks from the carbons.
Spark Coil.
A coil for producing a spark from a source of comparatively low
electro-motive force. It consists of insulated wire wound round a core
of soft iron, best a bundle of short pieces of wire. Such a coil may be
eight inches long and three inches thick, and made of No. 18-20 copper
wire, with a core one inch in diameter. On connecting a battery
therewith and opening or closing the circuit, a spark is produced by
self-induction, q. v. It is used for lighting gas.