Thomson's reflecting galvanometer with moving magnet
Date: circa 1883
Inventory Number: 0245
Classification: Reflecting Galvanometer
Subject:
Maker: Electric Manufacturing Company (1884 - 1930s ?)
User: Department of Physics, Harvard University (founded 1884)
Cultural Region:
Place of Origin:
Troy,
City of Use:
Dimensions:
48.4 × 21.6 × 21.6 cm (19 1/16 × 8 1/2 × 8 1/2 in.)
Description:
Moving magnet with a mirror hung in the center of a coil mounted in a cylindrical brass case with glass in one end and glass peep hole in other. Vertical tube supports adjustable curved magnet above case for zero adjustment. Tripod brass base with leveling screws.
A blue triangle signifies that it was used in the Physics 3 laboratory course at Harvard in the late 1920s.
A blue triangle signifies that it was used in the Physics 3 laboratory course at Harvard in the late 1920s.
Signedon back of case: Electric Mfg. Co. / Troy, N.Y.
FunctionReflecting 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.
This reflecting astatic galvanometer neutralizes the disturbing effect of Earth's magnetic field through the use of a curved neutralizing magnet above the instrument.
This reflecting astatic galvanometer neutralizes the disturbing effect of Earth's magnetic field through the use of a curved neutralizing magnet above the instrument.
Curatorial RemarksProbably part of an exhibit of electrical meters at the Taft School curated by David P. Wheatland.
ProvenanceFrom the Department of Physics, Harvard University.