Does Air Have A Macroscopic Grain Structure?

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?
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Mark Thorson wrote:

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

Called atoms and molecules.

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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Does air have a grain structure? It would be interesting to find out!
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<snip>
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.
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EPK wrote:

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.
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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

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