Harper's Electricity Book for Boys
CHAPTER VI.--CURRENT-DETECTORS AND GALVANOMETERS 102
HOW TO MAKE DETECTORS -- AN ASTATIC CURRENT-DETECTOR -- AN ASTATIC GALVANOMETER -- A TANGENT GALVANOMETER
Harper's Electricity Book for Boys
HOW TO MAKE DETECTORS -- AN ASTATIC CURRENT-DETECTOR -- AN ASTATIC GALVANOMETER -- A TANGENT GALVANOMETER