The mounted wire loop, with enclosed compass needle and terminal mercury cups, is clearly identical in principle with the devices of Schweigger and Poggendorf, and is called a "Galvanoscope."
"The Earliest Electromagnetic Instruments"
Robert A. Chipman
His note that "for the more minute effects a compass was employed in the Galvanoscope, having its terrestrial magnetism neutralized ..."
"The Earliest Electromagnetic Instruments"
Robert A. Chipman