[Correction]

In the “History” column by Gerhard Neidhofer in [1], due to a production error, the number 1p25 is incorrect in the following sentence: “The Thomson-Houston Company [later the General Electric Company (General Electric) after its merger with the Edison General Electric Company] preferred 15,000 alternations/min, corresponding to 1p25 cycles/s.” The correct number is 125 cycles/s. We apologize for this error.