What is leaf electroscope

A device used to test the presence of charge is a Golden Leaf electroscope,A pair of thin strips made up of gold is suspended from a small metallic rod in an insulating enclosure. The rod is connected to a metal ball on top of the enclosure . When the metal ball is charged the strip separate because the charge separates out over the metallic parts and so the two strips which accumulate like charges repel . However when a charged rod is brought near the wall of the electroscope , the strips still separate even without any contact between the rod and the electroscope and as the distance between the rod and electroscope is increased drop back the strips separate even when the electroscope remains neutral because the free electrons in the different parts of electroscope are pushed away and pile up in the strips which makes them similarly charged so they repel.