detachable spherical iron shell for reflecting galvanometer with moving magnet

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detachable spherical iron shell for reflecting galvanometer with moving magnet

Date1858-1865

Inventory Number0179a

ClassificationReflecting Galvanometer

Subject

Maker Siemens, Halske & Company 1858 - 1865

User Department of Physics, Harvard University founded 1884

Cultural Region

Place of Origin

Place of Use

Dimensions6 × 12 × 12 cm (2 3/8 × 4 3/4 × 4 3/4 in.)

Material

DescriptionReflecting galvanometer with moving magnet and extra pair of coils. Demountable coils (with replacements, parts d and e) in pressed rubber and brass mounting. Pair of adjustable compensating magnets above. Heavy detachable spherical iron shell (parts a and b) with etched "A" on interior encloses entire galvanometer. Viewing window below shell shows small round mirror and round metal plate in case with etched "5" behind plate. Three-legged brass base with leveling screws (c) has an extension on top which is missing in the black & white photos but visible in the color photo. Similar to instrument 0185a-f in this collection.

One coil affixed to galvanometer marked 20° C / 16670 U / 2228 ohms. Other coil affixed to galvanometer marked 20° C / 16910 U / 2168 ohms. One extra coil marked 20° C / 2032.3 ohms. Other extra coil marked 20° C / 2074.7 ohms.

Signedon base: SIEMENS & HALSKE

Inscribedon base (serial number): 69020 underneath brass knobs on front: A1 [and] E1

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.

ProvenanceFrom the Department of Physics, Harvard University, 11/19/56.