Kelvin's Astatic Galvanometer
Title
Kelvin's Astatic Galvanometer
Description
This is a very sensitive galvanometer, patterned after one built by Lord Kelvin. This type galvanometer is capable of detecting a current as small as 10 picoamperes for a deflection of 1 mm at a distance of 1 m.
Within each of the two brass cylinders are two facing coils, and in the center of the cylinder, betrween the coils, is a small piece of mica with five short magnetized needles glued to it. On each mica flake the needles are all turned the same way, but the two sets are oppositely directed in order to minimize the effect of the earth's magnetic field. The two sheets of mica are rigidly attached together and to a mirror between the cylinders, and mica and mirror are all suspended by a fine fiber. ("Astatic" refers to the fact that the design minimizes the effect of the earth's magnetic field.)
This instrument was purchased from Queen & Company for $30, probably near 1900.
Within each of the two brass cylinders are two facing coils, and in the center of the cylinder, betrween the coils, is a small piece of mica with five short magnetized needles glued to it. On each mica flake the needles are all turned the same way, but the two sets are oppositely directed in order to minimize the effect of the earth's magnetic field. The two sheets of mica are rigidly attached together and to a mirror between the cylinders, and mica and mirror are all suspended by a fine fiber. ("Astatic" refers to the fact that the design minimizes the effect of the earth's magnetic field.)
This instrument was purchased from Queen & Company for $30, probably near 1900.
Identifier
em_039
Collection
Electricity_and_Magnetism
Subject
Galvanometers
Creator
James W. Queen & Co.
Source
Display Case G1b
Date
1900