Electrically-Driven Tuning Forks
   In his book, An Anecdotal History of Sound (The MacMillan Company, 1935) Dayton Clarence Miller notes that the electro-magnetic interrupter and driving device for [tuning] forks were first used by Helmholtz and Koenig about 1860. 

   The electrically-driven tuning fork at the left is at St. Mary's College in Notre Dame, Indiana. It is listed at 100 francs ($20) in the 1889 Koenig catalogue, where it is catalogue number 76.

   This electrically-driven tuning fork is in the Garland Collection of Classic Physics Apparatus at Vanderbilt University. It is actually part of "Helmholtz' large apparatus  for compounding timbres of 10 harmonics" that is displayed elsewhere in the collection.

   This is the master fork for the apparatus that provides the signal that drives the system. A mercury make-and-break contact (on the front, left side of the apparatus) is actuated by the vibrations of the tuning fork, which is itself electrically driven.

   "Electrically Driven Tuning Fork. Mounted on an iron support, this form is marked "60 VD" and, in script, "R.K."
(The symbols "VD" represent the French vibrations doubles and "R.K." represents Rudolph Koenig, the maker.) A reel is available, presumably to carry a tape (with blackened surface) to record the vibrations of the fork." From Robert T. Lagemann, The Garland Collection of Classical Physics Apparatus at Vanderbilt University (Folio Publishers, Nashville, Tenn., 1983) pg 86.

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