To demonstrate that a motor and a generator are the same.
Two Genecon motor-generators.
A pair of identical motor-generators are connected together. Cranking either one as a generator makes the other one rotate as a motor. Reversing the direction of cranking the generator reverses the direction of the motor.
John A. Johnson, Franklin Miller, Jr., A Motor is a Generator and Vice Versa, TPT 14, 36-37, (1976). Instructions, Genecon- Manual Electric Generator, Nakamura Scientific Co. LTD., Tokyo, Japan.