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The Siemens mercury unit is an obsolete unit of electrical resistance. It was defined by Werner von Siemens in 1860 as the resistance of a mercury column with a length of one metre and uniform cross-section of held at a temperature of zero degrees Celsius.〔 〕 It is equivalent to approximately 0.953 ohm. Because glass tube cross sections are often slightly conical, the unit was sometimes constructed by the weight of mercury in 1 m.〔(The Electric Telegraph. R Sabine. 1867 p331 )〕 In 1881, a similar unit, the siemens was formally defined by the metric system as the unit of electric conductivity, as the inverse of the ohm for resistance. The Siemens mercury unit was superseded in 1884,〔Ohm#Historical_units_of_resistance〕 but continued in use in telegraph and telephone services until World War II. ==See also== *International System of Units 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「Siemens mercury unit」の詳細全文を読む スポンサード リンク
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