Sound Waves. Waves produced in an elastic medium by sonorous vibration, as in wireless telegraphy.
Sounder. In telegraphy, the instrument operated on by the key at the other end of a line. Various devices are employed to increase their resonance—as, for instance, hollow boxes. Sounders are generally placed on local circuits and are actuated by relays.
Sounder, Repeating. A telegraphic instrument which repeats a message into another circuit.
S-P. An abbreviation for single pole.
Spark-arrester. A screen of wire-netting fitted around the carbons of arc-lamps to prevent the chips or hot sparks from flying.
Spark-coil. A coil for producing a spark from a source of comparatively low electro-motive force. The induction-coil is an example.
Spark, Electric. The phenomenon observed when a disruptive charge leaves an accumulator or induction-coil and passes through an air gap.
Spark-gap. The space left between the ends of an electric resonator across which the spark springs.
Sparking. The production of sparks at the commutator, between the bars and the brushes of dynamos and motors. They are minute voltaic arcs, and should not be allowed to occur, as they cut away the metal and score the surface of the commutator.
Spark-tube. A tube used as a gauge to determine when the exhaustion of the vacuum chamber, or bulb, of an incandescent lamp is sufficiently high.