Hello all:
I've thought about this problem for a while, and have come to the conclusion
that the tube works like a horn. In a typical wind instrument, the musician
creates a vibration which then resonates and causes the instrument itself to
resonate. In the Rijke tube, there is no musician to cause a vibration,
thus, I believe the gauze must create random vibrations(a 'buzzing') in the
air, which then causes the tube itself to resonate at it's natural
frequency. The reason it stops when turned sideways is because the hot
grating doesn't have enough 'power' (i.e. it can only cause hot air to rise
when in a favorable upright position) to keep the air flow up. Does anyone
have comments/objections/nasty messages to respond?