Editing Galvanometer (section)

===Poggendorff and Thomson===
[[File:Thomsons mirror galvanometer, 1858. (9663806048).jpg|thumb|320px|Thomson mirror galvanometer, patented in 1858.]]

Originally, the instruments relied on the Earth's magnetic field to provide the restoring force for the compass needle. These were called [[#Tangent galvanometer|"tangent" galvanometer]]s and had to be oriented before use. Later instruments of the "[[#Astatic galvanometer|astatic]]" type used opposing magnets to become independent of the Earth's field and would operate in any orientation.

An early [[mirror galvanometer]] was invented in 1826 by [[Johann Christian Poggendorff]].<ref>{{Cite web |title=Museum of Technology, The History of Gadgets and Gizmos |url=https://museumoftechnology.org.uk/stories/galvos.php |access-date=2025-03-10 |website=museumoftechnology.org.uk}}</ref> An astatic galvanometer was invented by [[Hermann von Helmholtz]] in 1849; a more sensitive version of that device, the Thomson ''mirror galvanometer'', was patented in 1858 by [[William Thomson, 1st Baron Kelvin|William Thomson]] (Lord Kelvin).<ref>Lindley, David, ''Degrees Kelvin: A Tale of Genius, Invention, and Tragedy'', pp. 132–133, Joseph Henry Press, 2004 {{ISBN|0309167825}}</ref> Thomson's design was able to detect very rapid current changes by using small magnets attached to a lightweight mirror, suspended by a thread, instead of a compass needle. The deflection of a light beam on the mirror greatly magnified the deflection induced by small currents. Alternatively, the deflection of the suspended magnets could be observed directly through a microscope.