A ring of iron wire wound with coils of insulated wire at right angles
to its circular axis, and used as the armature of a dynamo or motor. A
number of connections are taken from the coils to a central commutator.

If such a ring with its coils is rotated in a field, current can be
taken from points of the commutator on a line at right angles to the
lines of force entering the ring.

The ring was discovered in 1862 by Pacinotti, and later was
independently discovered by Gramme. It is often known as the Gramme
ring.