An instrument invented by Professor Wheatstone, to illustrate the phenomena of waves of sound.
An elastic thin bar is fixed by one of its extremities, and at its free end carries a silvered or polished ball; a ray of light is reflected from this ball, and when the thin plate is put in vibration, the fine point of light describes various curves, corresponding with the musical notes produced by the vibrations.
An optical instrument, invented by David Brewster, 1814-17.
An arrangement of mirrors produces a symmetrical reflection of beautiful images, derived from the association of pieces of colored glass, which assume new relations as the tube is slowly rotated.
This instrument is first noticed by Baptista Porta in his Natural magic, under the name of polyphaton.
Kircher describes a similar invention of his own, but the application of two reflectors so inclined to each other as to form symmetrical images, changing as the instrument is rotated, was i