Two systems of recent interest are compared and the dual nature of the predicted quantum oscillations is emphasized. A small one-dimensional normal loop with an Aharonov-Bohm flux through the hole of the loop, exhibits a persistent current with period hc/e in the presence of a time- independent flux and an oscillatory Josephson-like current if the flux is increased linearly in time. A small capacitance Josephson junction, coupled capacitively to an external circuit, exhibits a currentless potential drop across the junction, with period e in the presence of a time-independent induced charge, and exhibits an oscillatory voltage if the induced charge is increased linearly in time. The role of the Aharonov-Bohm flux in the loop is taken by the induced charge in the junction, and the oscillatory behavior of the current of the loop is dual to the oscillatory behavior of the voltage of the junction. The current-voltage characteristic of the two systems is compared, and the sample specific nature of the effects is discussed. © 1986 IOP Publishing Ltd.