Vertical Disturbance. In 1860 Melde1 showed that a stretched string could be set in strong transverse vibration by a longitudinal movement of its end with a period half that of the transverse vibration. Lord Rayleigh2 pointed out that this principle applied to many kinds of vibrations, and especially that a pendulum could be made to vibrate through a large arc by a properly‐timed vertical movement of the support. The period of the disturbance is half that of the vibration.