In article , Harry
Bloomfield scribeth thus
The spiral on metal chimneys that is. I used to think it was about
having the wind help draw gases out of the chimney. In fact it about
preventing wind eddies shaking the chimney to destruction.



Yes quite correct, as can be seen by some spirals here on the top of the
Emley mast in Yorkshire..


http://tx.mb21.co.uk/gallery/gallery...=336&pageid=32
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Tony Sayer