Reference

The versorium detects the presence of static electric charge by observing the movement of a test object due to the Coulomb electrostatic force. It typically consists of a lightweight needle balanced on a pivot, and when a charged object is brought near, the electrostatic force causes the needle to turn or deflect. This deflection indicates the presence of a static electric charge. The versorium was the first electroscope, invented in 1600 by William Gilbert, and it could detect the presence of static electric charge but could not differentiate between positive and negative charges. Here is an image of a versorium to help visualize its structure: .