This rack has 3 square and 3 circular brass plates of varying dimensions. It was used to demonstrate the effect of changes in the size and thickness of plates on both their tone and the Chladni figures that they produce. A plate that is the same size as the one next to it, but double the thickness, will produce a note twice as high, while a plate that is half the area of the one next to it, but double the thickness, will sound a note that is four times higher.
These instruments demonstrate the “communication of vibrations” between connected plates. This was a topic first investigated by the French scientist Felix Savart, in the 1820s. Savart experimented with a pair of identical glass disks that were connected by only a single glass rod. When the two disks were sprinkled with sand and the first one vibrated, both disks formed identical patterns.
Source: Steven Turner; Curator, Physical Sciences, National Museum of American History, Smithsonian Institution.
„This instrument was used in an Ohio high school and probably dates from the late 19th or early 20th centuries. The replication of classic experiments was a common way to teach science at this time, and Chladni’s figures were considered to be both instructive and beautiful.
This set of resonance bars, each with its’ own resonator, can be used in an interesting demonstration. First, because the bars are physically identical, they both have the same resonant frequency. And that sound is strongly amplified by the wooden resonators on which the bars are mounted. In the demonstration, the two instruments are placed some distance apart and the first bar is struck sharply to make a tone. Because the two bars are identical, the second bar will respond to the sound of the first by making the same tone.
In the second quarter of the 19th century, the French scientist Felix Savart invented this apparatus to demonstrate resonance. It consists of a “bell” (or brass bowl) and a moveable wooden resonator. In the demonstration the bell was activated by being either bowed or struck. As the bell rang, its’ loudness could be increased or diminished by moving the resonator closer or further away. When the sound of the bell became barely audible an effective demonstration was to quickly move the resonator right next to it. The increase in loudness – the 'resonant effect' – was striking.
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