Generation of harmonics in a Rijke tube by using a single heating element

There exist excitation positions in a Rijke tube in which a heating element may be placed to produce a harmonic of the tube. These positions can be predicted from Rayleigh's criterion. A formula is derived to calculate the positions of these points for the inth harmonic. A heating element, placed in both of the two possible positions of excitation, as predicted by this formula, successfully produced the second harmonic of a Rijke tube.