The forks give the notes ciii, civ, div, eiv, fiv, the 11th harmonic of c1, the 13th harmonic of c1, aiv, the 14th harmonic of c1, bv, and cv (ciii and cv have vibration frequencies of 1024 and 4096 respectively).
These forks are constructed to prove the following law:
Barlow, W. H. (1873) 1873. “On The Pneumatic Action Which Accompanies The Articulation Of Sounds By The Human Voice, As Exhibited By A Recording Instrument”. Proceedings Of The Royal Society Of London 22: 277-286.
The Stimmeinstellungszeichen, literally “voice disposition indicators,” are metal shapes about 10 cm in diameter. Polished brass wire is bent to form abstract curves and lines. The linguist Eduard Sievers invented them to support his system of sound analysis (Schallanalyse).
Having developed several glass harmonicas, in March 1790 Chladni announced the invention of a new instrument that he called the euphone. Resembling an organ and piano, and unlike the harmonica from which it was derived, the euphone was composed of glass strips (as opposed to bowls or vessels). Each strip was a different length and generated a different tone. Chladni discussed the relationship between the lengths and the tones in his Entdeckungen über die Theorie des Klanges.