The Joe cell is a capacitor.
A very large and inefficient capacitor.
By putting a charge thru one of the tubes, or anything metal, piece of wire, or whatever, it creates a magnetic field.
This magnetic field is attracted to the next plate, which is attacted to the next plate and eventually the opposite polarity plate and completes the circuit.
The Joe cell charges up just like a capacitor, whether it is in water or not. It will take a charge.
You can then discharge it, and I have successfully run a 1.5 volt clock mechanism from a joe cell.
For an explanation of the "Joe Effect" on a car engine, go to this thread