Excellent work describing the construction and function of an articulated pendulum and how it creates uniform complex motions when drawing magnificently beautiful waveforms. The basis of which are music ratios - fully explained and graphically demonstrated. A chord of music notes can and does form mathematically correct waveforms. This device was very "in" during the 1880s and 1890s. Explains very well the numerical relations of vibrations. The Pendulograph is the same as the Harmonograph. 8.5" X 11"