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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. Mirror galvanometers were used extensively in scientific instruments before reliable, stable electronic amplifiers were available. The most common uses were as recording equipment for seismometers and 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. The name is often abbreviated as ''galvo''. == Kelvin's galvanometer == The mirror galvanometer was later improved by William Thomson, later to become Lord Kelvin. He would patent the device in 1858. Thomson reacted to the need for an instrument that could indicate with sensibility all the variations of the current in a long cable. This instrument was far more sensitive than any which preceded it, enabling the detection of the slightest defect in the core of a cable during its manufacture and submersion. Moreover, it proved the best apparatus for receiving messages through a long cable. The following is adapted from a contemporary account of Thomson's instrument: 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mirror galvanometer」の詳細全文を読む スポンサード リンク
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