Which device did Pierre and Jacques Curie invent to measure small electric charges?

Pierre and Jacques Curie invented the piezoelectric electrometer to measure very small electric charges. Their instrument used a quartz crystal whose electrical response could be precisely related to an applied mechanical force.

The brothers’ work began with their 1880 discovery of piezoelectricity: certain crystals, including quartz, produce an electric charge when compressed or stretched. By attaching a small weight to a carefully prepared quartz plate, they could generate a known quantity of charge. That known charge could then be compared with an unknown charge using an electrometer.

The device became known as the Curie electrometer or piezoelectric quartz electrometer. It was crucial to Marie Curie’s early studies of radioactivity because uranium radiation ionizes air, allowing a tiny electric current to flow. She could measure that current by balancing it against the calibrated charge produced by the quartz apparatus.

It is often confused with an electroscope, which detects charge but is generally less suitable for precise quantitative measurements. The Curies’ instrument was a specialized measuring system, not a Geiger counter or cloud chamber.