The Collaborative International Dictionary
Rheoscope
Rheoscope \Rhe"o*scope\ (r[=e]"[-o]*sk[=o]p), n. [Gr. "rei^n to flow + -scope.] (Physics) An instrument for detecting the presence or movement of currents, as of electricity.
Wikipedia
Rheoscope
A rheoscope is an instrument for detecting or measuring currents, such as fluid currents or electric currents. The word rheoscope as a detector of electrical currents was coined by Sir Charles Wheatstone about 1840 but is no longer used to describe electrical instruments. The word makeup is similar to that of rheostat (also coined by Wheatstone) which was a device used to adjust the current in a circuit. Rheostat is a historical term for a variable resistance, though unlike rheoscope may still be encountered.