|This is a classic example of a piece of apparatus which can be used for two different demonstrations. In its original form, it was intended to demonstrate longitudinal waves. The left end of the bar was set into oscillation by drawing a rosined cloth down its length. The brass bar is clamped at the center, forcing a node at this point; the two ends are thus antinodes. The ivory ball, hung by two cords, rests lightly against the right-hand end of the bar, and flies out repeatedly due to the oscillating force exerted on it by the longitudinal vibrations of the bar.|
A similar apparatus in the Catalogue of Acoustic Apparatus published in 1889 by Rudolph Koenig of Paris cost 45 francs.
REFERENCE: Thomas B. Greenslade, Jr., "Nineteenth Century Textbook Illustrations XXVIII: The Ringing Bar", Phys. Teach., 17, 44 (1979)