The rod is indeed part of one of the two plates on a gold leaf electroscope's capacitor.
2.
The next step was when Abraham Bennet, the inventor of the gold leaf electroscope, described a " " doubler of electricity " " ( Phil.
3.
A gold leaf electroscope does not detect the relative volts between any two points along a voltage gradient, because the electroscope has only one probe ( the end of the rod ).