The Demonstration: Wire mesh inside of a tube is heated by a blow torch. The tube begins to produce a long tone like a steam whistle.
The Physics: When the wire mesh inside of the tube is hot, the air closest to the mesh is heated and begins to rise due to convection. As long as the mesh is hot, air will continue to move through the tube like blowing air through a straw. The movement of air creates a standing wave inside of the tube. The wavelength of the standing wave is dictated by the length of the tube. If the hoot tube is long, it will produce a lower tone. If the hoot tube is short, the tone will be much higher.