Editing Mirror galvanometer (section)

{{Short description|Type of ammeter}}
[[File:Thomson mirror galvanometer.jpg|thumb|upright|Thomson mirror galvanometer of tripod type, from around 1900]]
[[File:H.W.Sullivan Galavanometer London.jpg|thumb|upright|Galvanometer by H.W. Sullivan, London. Late 19th or early 20th century. This galvanometer was used at the transatlantic cable station, Halifax, NS, Canada]]
[[File:DynAXIS L.jpg|thumb|upright|Modern mirror galvanometer from Scanlab]]

A '''mirror galvanometer''' is an [[ammeter]] that indicates it has sensed an electric [[Current (electricity)|current]] by deflecting a light beam with a [[mirror]].  The beam of light projected on a scale acts as a long massless pointer.  In 1826, [[Johann Christian Poggendorff]] developed the mirror galvanometer for detecting electric currents. The apparatus is also known as a ''spot galvanometer'' after the spot of light produced in some models.

Mirror galvanometers were used extensively in scientific instruments before reliable, stable [[electronic amplifier]]s were available.  The most common uses were as recording equipment for [[seismometer]]s and [[submarine communications cable|submarine cables]] used for telegraphy.

In modern times, the term ''mirror galvanometer'' is also used for devices that move [[laser]] beams by rotating a mirror through a galvanometer set-up, often with a [[Servomechanism|servo]]-like control loop. The name is often abbreviated as ''galvo''.