It occurred to me, while thinking about Leigh's disk, that S(r)
may be determined experimentally. Suppose the disk, suspended
by nylon threads, is charged from an electrostatic machine in a
clean room. Then it is taken to a room in which there is a lot of
dust (for example, particles of flower or oil or toner).
Returning to the clean room we discharge the disk and take a
picture of the dust distribution. This would be S(r). I suppose
others have done something like this. Any comments?
Ludwik Kowalski