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.
This important fact laid the foundation for all subsequent inventions which finally led to the production of electromagnetic or dynamo-electric machines.
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.