Pour some spirit of wine into a watch-glass, and inflame it; place a
straw across this flame, and it will only be ignited and charred at the
outer edge; the middle of the straw will be uninjured, for there is no
ignited matter in the centre of the flame.
Or, introduce into the middle of the flame one end of a glass tube,
when the vapour will rise through it, and may be lighted at the other
end of the tube.