> This whole thing reminds me of the conundrum, if that's the word, of the bird in the cage. If a bird is in an airtight cage attached to a scale and it starts to fly, will the scale read the same or less than before? I believe the answer is no as the bird still exerts downward pressure on the air below which in turn affects the scales.
> Am I right in thinking this?
>
> Bea 'Materials science degree didn't really cover this' sty

OK, I have NO IDEA on that one. Anyone else got something? (The principles seems sound... It's just very weird.)

Don