Signedon front of case: THE LEEDS & NORTHRUP CO. / SCIENTIFIC INSTRUMENTS / PHILADELPHIA
Inscribedon plaque on rear of case: 17421 / PATENTED / June 20th, 1905
on front of case: H.U. / 109-A
FunctionHigh sensitivity D'Arsonval reflecting galvanometers are used to measure very small electrical currents and voltage differences. Instead of having a scale with a pointer, in these galvanometers a small mirror turns in the presence of electrical currents. A coil of fine wire hangs between the poles of a magnet that generates a strong magnetic field. When an electric current is sent through the wires of the coil, the coil and the mirror attached to it are deflected. The change of angle can be detected by shining a light at the mirror and observing the reflection on a large scale that is placed in front of the device (see color picture on card).
ProvenanceFrom the Engineering School, Harvard University, 11/1956.