Two iron pipes with a metal mesh 1/4 way up the length of the tube. When the mesh is heated to red hot, the updraft will cause resonance in the tube. When the tube is held horizontally, the sound dies out. The sound can be affected by raising or lowering the tube fast enough to increase or decrease the flow of air.
The same effect can be achieved by cooling the lower part of the pipe with liquid nitrogen.
The two tubes are of different lengths so when sounded together, a beat frequency of about 2 hz is heard.
Question:
Which tube has the higher frequency?
Would this work on the moon?
