Editing Electrometer (section)

=== Kelvin's quadrant electrometer ===
[[Image:Lord Kelvin quadrant electrometer engraving.jpg|thumb|200px|Lord Kelvin's Quadrant Electrometer]]

Developed by [[Lord Kelvin]], this is the most sensitive and accurate of all the mechanical electrometers. The original design uses a light aluminum sector suspended inside a drum cut into four segments. The segments are insulated and connected diagonally in pairs. The charged aluminum sector is attracted to one pair of segments and repelled from the other. The deflection is observed by a beam of light reflected from a small mirror attached to the sector, just as in a [[galvanometer]]. The engraving on the right shows a slightly different form of this electrometer, using four flat plates rather than closed segments. The plates can be connected externally in the conventional diagonal way (as shown), or in a different order for specific applications.

A more sensitive form of quadrant electrometer was developed by [[Frederick Lindemann]]. It employs a metal-coated quartz fiber instead of an aluminum sector. The deflection is measured by observing the movement of the fiber under a microscope. Initially used for measuring star light,{{citation needed|date=May 2013}} it was employed for the infrared detection{{citation needed|date=May 2013}} of airplanes in the early stages of [[World War II]].

Some mechanical electrometers were housed inside a cage often referred to as a “bird cage”. This is a form of [[Faraday Cage]] that protected the instrument from external electrostatic charges.