Signedon hard rubber top: O. Wolff Berlin / 2718 / Manganin;
Inscribedoval plate with an image of eagle inscribed: PTR. 93. / 1903;
on hard rubber top: 0.01 int. Ohm / bei. 20°C
FunctionFor suspension in mercury to a standard bridge set in an oil bath.
A 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.
ProvenanceTriangle indicates it was used for the Physics 3, Jefferson Laboratory, Harvard University.