What instrument did Curie use to measure electric charge in samples?

Marie Curie used an electrometer to measure the tiny electrical effects produced by radioactive samples. The device allowed her to quantify how radiation ionized the air around substances containing uranium.

The instrument was especially valuable because it measured weak electric currents rather than merely recording radiation on photographic plates. Pierre Curie and his brother Jacques had developed a sensitive piezoelectric electrometer, and Marie used it with an ionization chamber and piezoelectric quartz in her early investigations.

Her measurements showed that uranium compounds’ activity depended on the amount of uranium present, not simply on their chemical form. Pitchblende and chalcolite were unexpectedly more active than uranium itself, leading her to suspect unknown radioactive substances. That line of reasoning helped lead to the discovery of polonium and radium.

A barometer measures atmospheric pressure, a calorimeter measures heat, and a spectroscope analyzes light. None was the key charge-measuring instrument in this experiment.