diagometer

from The Century Dictionary.

• noun A kind of electroscope, consisting of a dry pile and a magnetized needle for an indicator, used for ascertaining the conducting power of different bodies. It was first employed by Rousseau to detect adulterations in olive-oil, which is said to have less conducting power than other fixed oils.

from the GNU version of the Collaborative International Dictionary of English.

• noun A sort of electroscope, invented by Rousseau, in which the dry pile is employed to measure the amount of electricity transmitted by different bodies, or to determine their conducting power.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A kind of electroscope in which the dry pile is employed to measure the amount of electricity transmitted by different bodies, or to determine their conductive power.