WHILE the possibility of vibrating a thin cord regularly in a flat plane from a tuning fork has long been known as the Melde cord, from its discoverer ; and the development of large cigar-shaped loops on a thick stretched cord, corresponding to the fundamental and harmonic frequencies, by variable-speed electric-motor drive adjusted to the natural periods of the cord, has followed as a physical laboratory demonstration ; it is not generally realized that a multiplicity of frequencies may be simultaneously developed on the same cord, by suitably designed mechanisms.