Ring, Faraday.
A closed ring of iron used as the core of a transformer or induction
coil. The term is derived from Faraday's classic experiment with such an
apparatus when he produced a spark by induction in a secondary circuit.
Roaring.
A term applied to the noise sometimes produced in a voltaic arc, when
the electrodes are close together and a heavy current is passing.
Rocker.
In a dynamo the movable piece, mounted concentrically with the
commutator, and carrying the rocker-arms and brush-holders. By moving it
the brushes are adjusted for proper lead.
Rocker Arms.
The arms projecting from a rocker and each carrying one of the
brush-holders.
Roget's Spiral.
An experimental apparatus for illustrating the mutual attraction of
currents going in like direction. A cylindrical helix or spiral of wire
is suspended by one end. Its lower end just dips into a mercury cup. An
active circuit is connected, one terminal to the upper end, the other
terminal to the mercury cup, bringing the apparatus in series into the
circuit. The current as it passes causes the coil to shorten, each
spiral attracting its neighbors. This breaks the circuit by drawing the
lower end out of the mercury cup. The current being cut off the coils
cease to attract each other, and the end dips into the mercury cup
again. This closes the circuit, the coils again attract each other and
the same sequence follows and is repeated over and over again. A bright
spark is produced at each break of the mercury contact.
Rotation of Liquids, Electro-dynamic.
By passing a current through a liquid, such as dilute sulphuric acid, it
rotates if exposed to the induction of a current flowing at right angles
to it. The condition resolves itself into a liquid traversed by
horizontal currents from centre to circumference or vice versa, rotated
by a current passing through a circular conductor below it.