"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?
Is the mechanism for this phenomenon known?
Is it the presence of dust, or something? Would an arc
struck in dust-free air follow a smooth path?
Or could there be an invisible grain structure in air?
Such as local pockets with different chemical composition,
as compared to the matrix? Would an arc struck in
pure nitrogen behave any differently than an arc struck
in air?
> 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?
Yes
> Is the mechanism for this phenomenon known?
Yes.
> Is it the presence of dust, or something? Would an arc
> struck in dust-free air follow a smooth path?
No. there is still local un-even distributions of moisture, air motion,
molecular motion, energy level of atoms, etc.
>
> Or could there be an invisible grain structure in air?
Called atoms and molecules.
> Such as local pockets with different chemical composition,
> as compared to the matrix? Would an arc struck in
> pure nitrogen behave any differently than an arc struck
> in air?
Arcs in pure nitrogen (or helium) do behave differently, But probably not in
the way you are thinking.
One explanation for the jagged paths of lightning is that it follows charge
paths left by cosmic radiation.
--
Russ Lyttle
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http://home.earthlink.net/~lyttlec/philosophy/logos.html
Does air have a grain structure? It would be interesting to find out!
> A "grain structure" implies crystallinity, so .. no.
> There is a substructure, which changes on fine scales (less than cm),
> which would be the length scale of interest for these effects.
Wood has a grain structure, but it is not crystalline.
I meant inhomogeneities on the scale of millimeters
to centimeters that could be responsible for the
crooked path of electric arcs.
Yukio YANO
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