In the nineteenth century almost all power supplies were direct current (DC). In order to step voltage up or down, the direct current had to be converted to alternating current (AC), stepped using transformers, and then converted back to DC. The standard technique developed for changing DC to AC was a mechanical interrupter or Electrotome, run at a frequency controlled by the mechanical attributes of the device. This interrupter was made by Morris E. Leeds & Co of Philadelphia, "Manufacturers of High Grade Electrical Measuring Instruments, X-Ray Equipment and other Scientific Apparatus". The date is no later than 1900-1902.
Property of the W&L Physics & Engineering Department
“Electric Whirl,” Digital Exhibits at Washington and Lee University Library, accessed November 20, 2017, http://omeka.wlu.edu/items/show/177.