In telegraphy an instrument for repeating the signals through a second
line. It is virtually a relay which is operated by the sender, and which
in turn operates the rest of the main line, being situated itself at
about the middle point of the distance covered. In the simpler forms of
repeater two relays are used, one for transmission [...]

In a frictional electric machine the cushion of leather which is pressed
against the plate as it rotates.

The rotation produced in a liquid carrying centripetal or centrifugal
currents by an electromagnet. It is practically an intensification of
electro-dynamic rotation. (See 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.

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 arms projecting from a rocker and each carrying one of the
brush-holders.

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.

A term applied to the noise sometimes produced in a voltaic arc, when
the electrodes are close together and a heavy current is passing.

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.

A contact formed by a terminal clip in the shape of a ring, split or cut
at one point so that its ends tend to spring together. The other
terminal is a bar which passes into the cut and is tightly pressed by
the elastic ring.