The field magnet of the dynamo has two gaps in it.
In this case the dynamo and ohmmeter are combined in one instrument.
This rod was connected with the positive pole of the dynamo or electric generator.
In 1873 at Vienna the fact was discovered that a dynamo machine of the Gramme type could also act as an electric motor and jwas set in rotation when a current was passed into it from another similar machine.
The massive graphite is very easily machined and is widely used for electrodes, dynamo brushes, lead pencils and the like.