text: In 1840, Wheatstone brought out his magneto-electric machine for generating continuous currents.
  On 4 February 1867, he published the principle of reaction in the dynamo-electric machine by a paper to the Royal Society; but Mr. C. W. Siemens had communicated the identical discovery ten days earlier, and both papers were read on the same day.
  It afterwards appeared that Werner von Siemens, Samuel Alfred Varley, and Wheatstone had independently arrived at the principle within a few months of each other. Varley patented it on 24 December 1866; Siemens called attention to it on 17 January 1867; and Wheatstone exhibited it in action at the Royal Society on the above date.