astatic pair for galvanometer
Date: circa 1890
Inventory Number: 0171
Classification: Galvanometer Needle
Subject:
Maker: American ?
User: Department of Physics, Harvard University (founded 1884)
Cultural Region:
City of Use:
Dimensions:
9.1 × 16 × 1 cm (3 9/16 × 6 5/16 × 3/8 in.)
Description:
A pair of adjustable compass needles mounted in parallel on a copper rod.
Signedunsigned
FunctionAn astatic pair consists of two compass needles arranged parallel to each other on the same pivot, with inverse polarities.
Such an arrangement will be indifferent to external magnetic fields as the needles are trying to turn in opposite directions. However, if a current circulates between the two needles, the magnetic field created by the current will be detected by the pair, as in that case both needles turn in the same direction. This makes astatic pairs very sensitive for measuring electric currents.
Such an arrangement will be indifferent to external magnetic fields as the needles are trying to turn in opposite directions. However, if a current circulates between the two needles, the magnetic field created by the current will be detected by the pair, as in that case both needles turn in the same direction. This makes astatic pairs very sensitive for measuring electric currents.
Curatorial RemarksWas in box of 0374a-c. Now stored separately.
Primary SourcesSilvanus P. Thompson, , Elementary Lessons in Electricity and Magnetism (London, 1882), 155. Fig. 181, 102.
Unnamed source: (London, 1895), p.20, fig. 15, p.186, fig.111
Unnamed source: (London, 1895), p.20, fig. 15, p.186, fig.111
ProvenanceFrom Harvard University physics department.