Did you ever find an answer to this question?

I have seen this demonstration in several books, videos and websites. I have tried it once, but wasn’t able to get it to work. The explanation given for how it works is always the same and, as you point out, it doesn’t actually make sense. The experiment obviously works, but the explanation that is always presented for it is clearly faulty. At one point, I asked my father, who is a renowned physicist at Stanford University, about it. He didn’t know for sure, but suggested that possibly it works because of some instability that occurs when one or the other sets of connected cans becomes charged relative to the other. Once the sets of connected cans are oppositely charged, the drops falling through the bottomless cans into the cans at the bottom evidently have the effect of increasing the existing charges, positive or negative. This is not a very good description and is certainly not complete, but I believe it is at least more satisfactory than the standard one which is always given. I am not a physicist, and electrostatics is not my father’s specific field (he’s a solid state physicist), but that is the best I have been able to come up with so far.

For Sciencebase video fans, next Monday, we’ve got a special treat (well, I think it’s special). A short global warming lecture with a difference from Austrian student Bernhard Steinerhoff.