Sonometer, Hughes'.
A sound measurer; a modification of a portion of Hughes' induction
balance, used for testing the delicacy of the ear or for determining the
relative intensity of sounds. (See Hughes' Induction Balance.) It is the
arrangement of three coils, two mounted one at each of the ends of a
graduated bar, and the third one between them and free to slide back and
forth thereon.
Sonorescence.
The property of producing sounds under the influence of momentary light
radiations rapidly succeeding each other. It is the property utilized in
the photophone, q. v.
Fig. 306. MORSE SOUNDER.
Sounder.
In telegraphy an instrument consisting of an electromagnet with armature
attached to an oscillating bar, the range of whose movements is
restricted by adjusting screws. The armature is drawn away from the
magnet by a spring. When a current is sent through the magnet the
armature is drawn towards the poles and produces a sound as the bar
strikes a striking piece or second adjusting screw. When the current
ceases the bar and armature are drawn back, striking the first mentioned
screw with a distinct sound, the back stroke.
The sounder is used to receive Morse and analogous character messages.
The forward strokes correspond to the beginnings of the dots or dashes
of the code, the back strokes to beginnings of the intervals. The
distinction between dots and dashes is made by observing the interval
between forward and back stroke.
Various devices are used to increase the sound. Sometimes a resonance
box is used on which the sounder is mounted.
In practice sounders are generally placed on local circuits and are
actuated by relays.