What do you call this instrument?
The tuning fork is a narrow, two-pronged steel bar that when tuned to a specific musical pitch retains its tuning almost indefinitely. It was apparently invented by George Frideric Handel’s trumpeter John Shore shortly before the latter's death in 1752. Because it produces a nearly pure tone (without overtones), it is useful in experimental study of the physics of sound. It has also been used in musical instruments—e.g., the dulcitone, or typophone, a set of graduated tuning forks struck by felt hammers by means of a keyboard mechanism.