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An
arc of flame marks the path of an electric current. When the button
is pressed one side of each pair of electrodes becomes positively
charged, and the other side becomes negatively charged. Since
opposite charges attract one another, when the electrodes are
moved close enough together, the charges will jump across the
gap. The glowing light—the visible arc-shaped flame—marks
the path that the current takes. The flame is arc-shaped because
of the heat it creates. Warm air rises: The heat can be felt above
the chamber. The drafts of hot air made by the heat of the arc
not only pull the flame upward in the middle, they also make it
possible for the flame to jump up from the bottom pair of electrodes
to the top pair.
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