What detector was attached to the pail in Faraday's ice pail experiment?

The detector attached to the pail in Faraday's ice pail experiment was a gold-leaf electroscope.

Faraday connected the insulated pail by a wire to a delicate gold-leaf detector. As a charged ball descended into the container, the leaves diverged, indicating that electrostatic induction had produced charge on the pail. When the ball was removed, the leaves collapsed again, showing that the induced effect disappeared.

The original 1844 account used the related historical term “gold-leaf electrometer,” but gold-leaf electroscope is the standard description commonly used for the apparatus. Both instruments rely on the movement or divergence of lightweight gold leaves in response to electric charge; an electrometer is generally intended to provide more measurement capability.

Modern classroom versions often replace the fragile gold leaves with electronic electrometers, which are more sensitive and can give quantitative readings. A photomultiplier tube, Wheatstone bridge, or Geiger counter belongs to a different type of measurement and was not Faraday's detector.