Assume two masses A and B at the end of a weightless rod, suspended by
the parallel cords a A, b B. Let the rod be rotated through an angle
theta. Consider the cord a A. Its lower end is swung through the angle
theta, as referred to the center O; the cord is deflected from the
vertical by an angle psi, such that a A tang(psi)= O A 2 sin (theta/2).
The component of gravitation tending to restore A to A, acting towards A
is equal to m g tan(psi). Its moment around O is equal to (m g tan(psi))
* (O A cos(theta/2). The whole moment of the couple is 2 m g tan(psi).
0 A. cos(theta/2) = 2 m g (O A2/ a A) 2 sin(theta/2). Cos(theta/2) =
2mgl(OA2/aA) sin(theta). The moment of the restoring force is thus
proportional to the sine of the angle of deflection, and the
oscillations of such a system are approximately simple harmonic.
(Daniell.)
If the twisting is carried so far as to cause the threads to cross and
come in contact with each other the suspension ceases to be a bifilar
suspension, but assumes the nature of a torsional suspension.
[Transcriber's note: This is the image of the first paragraph.]
Swaging, Electric.
Mechanical swaging in which the objects to be swaged are heated by an
electric current as in electric welding.
S. W. G.
Abbreviation for Standard Wire Gauge.
Fig. 309. SIMPLE SWITCH.
Switch.
A device for opening and closing an electric circuit.
A simple type is the ordinary telegrapher's switch. A bar of metal is
mounted horizontally by a pivot at one end, so as to be free to rotate
through an arc of a circle. In one position its free end rests upon a
stud of metal. One terminal of a circuit is attached to its journal, the
other to the stud. Resting on the stud it closes the circuit, in other
positions it opens the circuit.