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The New Student's Reference Work/Ampère

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Ampère (än̄′ pâr′).  The “practical unit” in which electric currents are measured.  The numerical value of the ampere, as established by the International Electrical Congress, held at Chicago in 1893, is “the practical equivalent of the unvarying current which, when passed through a solution of silver nitrate in water, in accordance with standard specifications, deposits silver at the rate of 0.001118 grams per second.

This definition, having been ratified by Congress, now defines the “legal ampere.”

The logical definition of the ampere, and the one which the legal unit approximates as nearly as possible, is “a current equal to one-tenth of the absolute unit of current.”  See Electricity.