Signedmarked on curved edge: SIR W THOMSON'S PATENT / No 135 / J WHITE GLASGOW
Inscribedon semicircular magnet: 9.14 Sept. 24th/84
FunctionThe graded galvanometer was a modification of a tangent galvanometer by Sir William Thomson in which the bar magnet supplements earth's magnetic field. Current flows through the circular coil at the end, which causes the small compass needle within the central case to deflect from the north-south line, and the current can then be measured on the scale by the amount of the needle's deflection.
ProvenanceFrom the Department of Physics, Lyman Lab, Harvard University, 1958.