The tutor suggested an experiment using
wooden splints, by placing a splint for only a split
second in the flame you can see where the wood
begins to burn and is hottest. This took some practice,
but the students began to see that the wood that was
in the outer parts of the flame burned, while that
which had been in the center was not burnt; therefore
the center of the flame is cooler than the outer part.
The tutor then explained that in a candle flame the
outside burns hotter because there is more oxygen
available to the flame; in the center of the flame there
is not as much oxygen and it does not burn as well.