A metal tube has a metal screen placed inside it a short distance from one end. Place the tube over a burner to heat up the screen and then remove the tube from the burner. With the tube in a vertical position the cooling screen sets up a sound vibration. The length of the tube picks out the resonating wave length. Turn the tube horizontally and the sound stops. The largest, ~5 ft. x 6 in., has been dubbed "The Voice of God" for its loud deep tone. Gloves are recommended for holding the tube.