A rod with static electric charge is brought near a gold leaf electroscope that has been placed inside a Faraday cage. A second electroscope is connected to the cage itself. The electroscope inside the cage responds to the charged rod only when the lid is left off of the cage. When the lid covers the cage the electroscope inside is unaffected by the charged rod but the electroscope connected to the cage deflects.

J4, J5

PIRA DCS 5B20.30