On Sat, 31 Jul 2004 23:23:31 GMT, Mark Thorson <nospam@sonic.net>
wrote:

>Quoting from INDUCTION COILS HOW TO MAKE AND USE THEM
>by Marshall and Stoye (Spon & Chamberlin, 1906),
>pages 65-66:
>
>"For ordinary sparking experiments the negative electrode should
>terminate in a fairly large brass disc, the positive being a needle
>point adjustable as to distance, but moving opposite the centre
>of the disc. By this means the longest sparks can be obtained.
>It will be noticed that the sparks constantly strike fresh places,
>and they almost invariably traverse very crooked paths through
>the air. In this respect they are like lightning flashes -- 'small
>editions' of which they really are, as a matter of fact. These
>crooked paths represent 'lines of least resistance,' the electric
>current, no doubt, finding irregularly distributed particles of
>conducting matter floating in the atmosphere."
>
>Is that really why electric arcs follow an irregular path?

Dust is not a requirement for a crooked path. The first spark's path
could follow locally high concentrations of air. The spark produces
high conductivity remnants that can move during the time between
sparks. As the concentration of conductive material increases, spark
length can increase.