Alfred M. Mayer (1836-1897) was a faculty member at Lehigh University from 1867 to 1871, and then spent the remainder of his life as a professor of physics at Stephens Institute of Technology in Hoboken, New Jersey. "He invented the sound-wheel in 1876, but very graciously yielded precedence to the Austrian, V. Dvorak, who, it was found later, had quite independently made the same device a few months earlier. This little instrument ... consists of four small tuned resonators attached to a small cross and balanced on a pivot. When placed near a source of continuous sound of the pitch to which the resonators are tuned, such as an electrically driven tuning fork, the reaction against the closed end by the stationary wave formed inside of each resonator causes the wheel to rotate "backwards." From Dayton Clarence Miller, Anecdotal History of the Science of Sound, (The MacMillan Company, New York, 1935), pg 73.

   This example is at the University of Toronto, and is almost surely some of the apparatus that Koenig brought to Philadelphia for the 1876 Centennial Exposition. In the 1889 Koenig catalogue it is no. 75, and is listed at 60 francs (about $15).