Does Air Have A Macroscopic Grain Structure?

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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?
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?

 

No. there is still local un-even distributions of moisture, air motion,
molecular motion, energy level of atoms, etc.

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.

 

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.

 

I would suspect observing the operation of a "Wilson Cloud Chamber " would
be instructive, so would watching a working "Geiger Mueller Counter tube"
would have to be one with a transparent window though ! Both examples show
the path of an Ionizing particle in real time, through a gas at near
atmospheric pressure. I suspect that under the conditions described below
"For ordinary sparking ~~" if one could vary the high voltage source, I
would not be surprised to find that there was a curve very similar to the
normal operation of a GM counter with a threshold, linear, proportional, and
avalanche portion. The only difference being that the GM counter gas is
optimized for best operation.


Yukio YANO