Edison built this DC generator based on his 1878 design. The two long, vertically oriented black cylinders are the field coils that generate the magnetic field in which the rotor turns. The shape of those coils led the lab workers who worked on this design – all of whom were men – to refer it as ‘The Long-legged Mary-Ann’. The rotor is on the bottom, behind an upright lever. The lever controls a switch that can be set so the power generated by the rotor flows through the field coils in a parallel circuit, allowing the generator to create its own field.
This type of generator was built in various sizes, and there are versions up to two metres high. Large horizontal versions were used for the world's first power plant, Pearl Street Central Generating Station. Several of these ‘Jumbos’ were used to power 10,000 light bulbs in a district of Manhattan. Edison's incandescent light bulbs were powered with 110 volts.