A kerosene light or candle was placed in front of the unit and, when the mirror moved in response to weak electrical signals, the reflected spot of light moved across a calibrated scale mounted on the wall of a darkened room. Due to the laws of optics, the spot of light moved over twice as large an angle as the mirror and this served to amplify the sensitivity of the instrument. This is an all brass mirror galvanometer standing on a brass tripod stand with overhead Earth's Magnetic Field compensating magnets. It was made by Elliot Brothers-London. This small mirror galvanometer has a white paper scale integrated into its design.
Light reflects from the moving mirror and onto the white scale allowing measurements to be made.
By several manufacturers, meter shunts, standard cells, standard resistors, used to measure the tiny electrical currents on telegraph lines and ground returns. The first dual-channel Prism Synchroscope. A horizontal rotating prism provides a time-base for twin high sensitivity, low mass mirror galvanometers. Used to display telegraph cable voltages as a function of time. In original wooden box.