resistance standard (10 Ohms)
Date: circa 1900
Inventory Number: 1997-1-0225d
Classification: Resistance Standard
Subject:
Maker: Otto Wolff (fl. 1870 - 1920)
Associate Name: (calibrated by) Physikalisch-Technische Reichsanstalt (founded 1887)
User: Department of Physics, Harvard University (founded 1884)
Cultural Region:
Place of Origin:
Dimensions:
15 × 16.5 × 8.5 cm (5 7/8 × 6 1/2 × 3 3/8 in.)
Material:
Description:
Coil of manganin wound on a tube supported in a perforated nickel-plated case. Two heavy terminals are protruding from the hard rubber top for suspension in mercury to a standard bridge set in an oil bath. There is a thermometer inside the container as well.
The resistance is 10 Ohms and is calibrated for 20°C.
There is a gray (faded blue) triangle painted on side, which means it was used as a demonstration instrument in the physics department at Harvard.
The resistance is 10 Ohms and is calibrated for 20°C.
There is a gray (faded blue) triangle painted on side, which means it was used as a demonstration instrument in the physics department at Harvard.
Signedstamped on top: O. Wolff Berlin 1694
Inscribedon top in an elliptical metal marker: PTR 92 [above an eagle] / 1900 [below the eagle]
on the top: 10 int Ohm / bei 20°C / Manganin
on the top: 10 int Ohm / bei 20°C / Manganin
FunctionA resistance standard is not to measure the resistance of an electric conductor but rather to compare such a conductor to a temperature-fixed resistance. In other words, such a device is used to determine the value of an unknown current. To do so, a current in the conductor would pass through mercury (for the older type of standard resistance), into which the two leads from the resistor dip. The manganin wire in this instrument was baked before being dipped into paraffin so that all moisture is removed and to improve the insulation over the wire.
Curatorial RemarksThe "PTR" stands for Physikalische Technische Reichenstalt, or what was then the German Bureau of Standards.
ProvenanceFrom the Department of Physics, Jefferson Laboratory, Harvard University.
