A tonometer consists of a series of steel cylinders that resonate at specific frequencies upon being struck with a metal hammer. They are used as standards for high frequencies, in the same manner as tuning forks. The transverse vibrational frequencies (i.e. fundamental and harmonics) of a given cylinder depend on the length, elastic modulus, and linear density of the metal.
This apparatus consists of three wires, each bent to resemble transverse waves. The wires are mounted in a rectangular brass box that was placed in front of the lens of a projector. The top two wires are identical, but positioned so that their shadows appear to move in opposite directions as a crank on the side of the box is turned. As they do this, the crests and troughs of the waves alternately lineup and overlap. The corresponding “interference” of the two waves is seen in the changing shape of the third wire.
This set of 3 tuning forks, each mounted on its’ own resonator box, was made in Paris between about 1870 and 1900. The tuning forks were each milled from a single blank of fine steel and were then precisely tuned to produce a single, specific, tone. The resonator boxes that they are bolted to are wood, made from the same spruce often used in stringed musical instruments. Spruce wood is naturally responsive to sound vibrations and is the ideal material for this application.
Koenig’s flame analyser was, next to the sound synthesizer, one of the clearest expressions of Hermann von Helmholtz’s theory that complex sounds were made up of a spectrum of elemental or pure tones. The adjustable resonators covering a range of 65 notes from sol1 to mi5 (96–1,280 Hz), could each be rendered visible with a connection to a manometric flame capsule. The resonators were connected to a gas-filled capsule with a rubber tube. If activated, the distinctive pattern would appear in the rotating mirror.
The double siren was one of Koenig’s more popular instruments. It consisted of two “polyphonic” or “multivoiced” sirens with more than one series of holes, and was an invention of the German physicist and former teacher of Hermann von Helmholtz, Heinrich Wilhelm Dove (1803–1879). It produced several pure tones simultaneously, in musical chords, and under greater pressure. It was ideal for demonstrating interference effects (when sound waves combined to amplify or diminish each other) and combination tones. [Pantalony 2009, 184-185]
This specific array of precision tuning forks are highly-specialized experimental forks that relate directly to Koenig’s long-standing disagreement with Helmholtz on the nature of combination tones. Some of them date back to Koenig's display at the 1876 Philadelphia exposition.
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:
The set of eight tuning forks was acquired by the Science Museum, London, on the closure of the Physics Department of the Royal Naval College, Greenwich. The box is marked “Standard Set of Tuning Forks.” A handwritten note in the Science Museum’s technical file T/1968-634 states that no mention of this particular box of forks can be found in the Museum’s copy of König’s 1889 catalogue (Koenig, R. Catalogue des appareils d’acoustique).
Armstrong Cork,. 1932. “Armstrong's Acoustical Products”. Corkoustic, Ceramacoustic For Acoustical Correction Of Churches, Auditoriums, And Theatres, And Noise-Quieting Of Banks, Schools, Hospitals, Offices, Sunday School Rooms, Factories, And Other Public Buildings. Lancaster, PA.
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