The versorium is a needle constructed out of metal which is allowed to pivot freely on a pedestal. It is similar to a compass needle, but unmagnetized. The needle is attracted to charged bodies brought near it, turning towards the charged object.

What is an electroscope and how does it work?

The electroscope is an early scientific instrument used to detect the presence of electric charge on a body. It detects charge by the movement of a test object due to the Coulomb electrostatic force on it. The amount of charge on an object is proportional to its voltage.

What do you think causes the versorium needle to turn?

The needle is made from unmagnetised metal. When rubbed amber is brought towards the versorium, the needle will turn accusingly until it points towards the amber. The Greeks believed that amber alone could be charged by rubbing.