Mirror galvanometer
![A mirror galvanometer](/Images/godic/202501/26/Spot_Galvanometer_picture4840.png")
![Thomson mirror galvanometer of tripod type, from around 1900](/Images/godic/202501/26/Thomson_mirror_galvanometer4840.jpg")
![Galvanometer by H.W. Sullivan, London. Late 19th or early 20th century. This galvanometer was used at the transatlantic cable station, Halifax, NS, Canada](/Images/godic/202501/26/H.W.Sullivan_Galavanometer_London4840.jpg")
![Modern mirror galvanometer from Scanlab](/Images/godic/202501/26/DynAXIS_L4840.jpg")
A mirror galvanometer is an electromechanical instrument that indicates that it has sensed an electric 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.