An electroscope is an instrument for detecting static electric charge. In this case a pair of gold leaves are attached to the bottom of a conducting rod. If a charge is transferred to or induced in the rod the leaves repel one another and swing apart by an amount that gives a qualitative measure of the charge. The device is mounted in a case with removable glass windows to screen the leaves from draughts but allow them to be observed. In this case the leaves are situated between two adjustable earthed plates to increase the sensitivity.