tone-variator

Century Dictionary and Cyclopedia

1. n. In experimental psychology, an instrument which permits of the variation (continuous or discrete) of the pitch of an approximately Pure tone by known amounts and at uniform rate. In its original form, the tone-variator consisted essentially of a blown bottle of which the pitch could be varied by the continuous introduction or withdrawal of mercury. Since the pitch of the bottle-tone changes, in siren fashion, … more quickly in the higher than in the lower regions, and a uniform rate of tonal change is desired, the bottle was connected with a variator trough, so constructed that the rise and fall of the mercury in the variator furnished the necessary correction to the movement of mercury in the bottle. In the most recent form of the instrument the bottle is of brass and the mercury has been replaced by a tightly fitting piston-head connected to a metal cam (the variator) cut to the shape of the required curve. Readings of tonal change (in terms of rate of vibration) are made from a circular scale placed in front of the variator cam. E. B. Titchener, Exper. Psychol., II. ii. 139.