Definition of mirror galvanometer in English:

mirror galvanometer

noun

  • A sensitive galvanometer in which the reading is indicated by a beam of light reflected from a mirror attached to the magnetic coil which responds to the current, especially that developed in around 1860 by William Thomson (Lord Kelvin) to detect signals carried by the transatlantic undersea telegraph cable.

Origin

Late 19th century; earliest use found in Scribner's Monthly.