A 50 mm dish of steel in mineral oil. A live pin, a grounded cup, and no wire between them — until the bearings build one.
THE TWO MECHANISMS
Bearings polarise in the field and stick head-to-tail, so chains grow out from
the pin along the field lines — fastest at a chain's tip, where the field
concentrates. Touch the cup and the circuit closes: current flows, the supply
sags, and the assembly goes quiet. Turn contact charging up and the
cell switches regime — bearings take charge off the pin and get thrown across
the oil instead of building anything.
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