Two 120-turn coils are placed facing each other on the lecture table. Each of the coils are in series with a capacitor, the values of which have been chosen such that the two LC circuits have slightly different resonant frequencies. One of the coils is driven by a sine wave generator, whose output is swept over a frequency range encomapssing the resonant frequency of both LC circuits. When the voltage across the capacitor of the secondary coil is displayed on an oscilloscope, a double resonance curve caused by the resonance in each coil is observed.
for additional notes see this [PDF]
for alternate setup (r. ashoori) see this [PDF]