Quote from J. A. Zahm, Sound and Music, second edition (A. C. McClurg & Co., Chicago, 1900) pp 29-30

   "In this connection permit me to show your a still more remarkable way of producing sound... The instrument used consists of a peculiarly shaped brass bar and a block of lead. It is named Trevelyan's rocker, from Mr. Trevelyan, who invented it and first gave an explanation of its mode of action. The brass bar is made so as to move from side to side, under the influence of slight impulses. [The bottom surface of the bar has two parallel knife-edges.] The rocker is heated, and on placing it upon this cold lead block, you at once hear a musical note. By pressing on the rocker with the point of a pencil, the pitch of the sound is made higher, and any variations in the pressure, however slight, give rise to a corresponding change of pitch."

   The reference is to Arthur Trevelyan, who described the device to the Royal Society of Edinburg in 1829.

   This example is at Yale University.

REFERENCES: Ira M. Freeman, "What is Trevelyan's Rocker", Phys. Teach., 12, 382 (1974); John Tyndall, "Heat Considered as a Mode of Motion" (D. Appleton and Company, New York, 1873), pp 114-118