| This unique piece of apparatus uses Lissajous
figures to show that the ratio of the frequency ratios in a diatonic
scale are ratios of small numbers. On the right-hand side is an air-driven
vibrating reed (a harmonica reed) with a small mirror attached to its free
end. The octagonal, revolving drum contains eight reeds, ranging up the
scale from the same frequency as the fixed reed to its octave.
In use, the box holding the fixed reed would be rotated
The apparatus is made by Newton and Company of London, and dates from the last quarter of the nineteenth century. It is in the collection of the National Museum of American History of the Smithsonian Institution.