The technique of showing the lines of nodes on vibrating metal plates by strewing sand on them was developed by the German physicist Ernst E. F. Chladni. The first mention of the technique is in his book Entdeckungen ueber die Theorie des Klanges, published in 1787. Until the twentieth century the standard method of setting the plates into oscillation was drawing the rosined hairs of a violin bow over the edge of the plate, which was normally clamped at its geometrical center. Today we place a loudspeaker above or below the plate, and adjust the driving frequency until the plate goes into resonance, and the sand on the surface moves toward the nodes.
The square plate on a handle from St. Mary's College is a Sympathetic Chladni Plate. When placed just about an identical fixed plate vibrating in a certain mode, it will pick up that mode of oscillation. This plate was made by Rudolph Koenig.
Almost all nineteenth century apparatus manufacturers listed Chladni
plates in their catalogues. The clamp for the Allegheny instrument is listed
at $4.00 in the 1860 E. S. Ritchie catalogue.
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"Before you is a large brass plate mounted on a
strong support, and above it is fixed a resonant tube, so adjusted that
it can lengthened and shortened at will. Sprinkling the plate with lycompodium
power, and setting it into vibrations, we get [a pattern of nodes and antinodes].
...If the resonant tube is adjusted ... so that its note is in unison with that yielded by the plane, an augmentation of sound is produced every time an [antinode] passes under the tube. When, on the other hand, a node passes under the tube, there is a corresponding diminution of sound." From J. A. Zahm, Sound and Music, second edition, (A. C. McClurg, Chicago, 1900), pg 199 I became quite excited when I looked closely at this piece
of apparatus at Dartmouth College, for it was marked "Marloye et Cie."
Albert Marloye (1785-1874) was the mentor of Rudolph
Koenig , and sold his business to Koenig in 1858. Marolye apparatus
is quite rare in the United States: I have seen examples of his organ
pipes at Union College, Harvard University and the United States Military
Academy. Glasgow University in Scotland has a Marloye tuning fork.
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The four Chladni plates below date from about 1900 and were made by James W. Queen & Co. of Philadelphia. They are in use in physics lecture demonstrations at the University of Texas in Austin. The larger plates are 20 cm square or 20 cm in diameter, and the small plate is 10 cm square. These originally sold for about $6.00 each.
