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No harm in attempting a simpler solution, before getting into the 
complexity of Schlieren optics. Set up a burning candle just below the top 
of the organ pipe, illuminate it using one of those low-voltage desk lamps 
with a tiny halogen bulb, and cast the shadow of the hot air above the 
flame onto a large white card. The further from the flame you put the lamp, 
the sharper (and dimmer!) the shadow.

If that prototype works, it could save a lot of hassle. If the sounding 
organ pipe shows no effect on the swirling hot-air-shadow, then the much 
clearer Schlieren pattern probably wouldn't show the effect you need either!

Pieces of dangling tissue paper must be the easiest possible solution. But 
wondering if low notes would cause the candle flame itself to move gives me 
another idea. Why not experiment with gas flames mounted close ABOVE the 
open ends of SEVERAL organ pipes? It's just possible that the flames might 
be made to dance with the music, which would be utterly awesome...

You could easily prototype this with an ordinary gas blowtorch set to a 
gentle, luminous flame, held above a sounding organ pipe.

Hey! I just typed 'flame organ' into Google and discovered that a flame 
organ or Pyrophone was invented by Frederic Kastner in the 1800's. There's 
a whole shedload of stuff about these things. The clever ones actually 
controlled internal flames to generate the sound, while less subtle 
versions apparently shot coloured flames out of the top. How cool is that? 
(Rats! Anyway, it's quicker to post a message to ASTC-L than it is to file 
a Patent...)


[log in to unmask] * http://www.interactives.co.uk
*
Give people facts and you feed their minds for an hour.
Awaken curiosity and they feed their own minds for a lifetime.
*
Ian Russell  

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