Answer
The Lippmann electrometer is a capillary electrometer invented by Gabriel Lippmann in 1873. It measures electrical potential by observing the movement of a mercury meniscus in a glass capillary tube. When a voltage is applied across the electrodes, the surface tension of the mercury changes, causing the meniscus to move. The amount of movement is proportional to the applied voltage, allowing for precise measurements of electrical potential.