Images(4)

reflecting galvanometer

Date1920-1940

Inventory Number1997-1-0323

ClassificationReflecting Galvanometer

Subject

Maker Leeds & Northrup Company 1903 - 1995

Cultural Region

Place of Origin

Dimensions22 × 12 × 12 cm (8 11/16 × 4 3/4 × 4 3/4 in.)

Material

DescriptionA cylindrical black brass case on moulded circular bakelite base with three levelling screws and two binding posts on base. The cylinder has a long, narrow, rectangular glass window with brackets to attach a focusing lens. Behind the window is a small circular mirror suspended from a thin wire above and connected to a metal cylinder below, which lies at the center of a cavity between the poles of a magnet. Attached to the top of the magnet is the structure that supports the wire, which includes a zero adjustment screw and a screw that adjusts the clamp system for locking the coil when not in use. These two screws would likely be turned by a removable knob, which is now missing.

Signedon base between the binding posts, in raised letters: LEEDS & NORTHRUP CO. / PHILADELPHIA PA

Inscribedon base, front: (serial number): 233035; moulded flap swings out from underneath the base with the meter's specifications; on case, top: MADE IN U.S.A.

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. 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. Alternatively, a scope is pointed at the mirror to see the change in the angle that the scope points to on a scale seen through the mirror. In those cases, the scales that are used are mirror-inverted.