Wave Addition Devices
A. Thomas Young's Device. In 1802 Thomas Young published a description of a wave addition device (Thomas Young, Journal of the Royal Institution of Great Britain, 1, 262 (1802)).

   The apparatus at the right, in regular use at Kenyon College, was made by E. S. Ritchie of Boston. The 1860 Ritchie catalogue has the following description: “Dr. Young's Instrument for showing Interference of Water Waves, as improved by Prof. Snell [of Amherst College]. Fifty ebony keys, arranged in a series, and kept in place by a bar in front, constitute the upper system of waves, the lower system is simply a dark board, which can be elevated by a lever at the back of the frame: when this is raised, all the ebony keys rest on its edge, so that their tops give the resulting form of both systems combined. If the lower system s similar to the upper one, the resultant is a system of double the height, or else becomes a straight line; there are four boards with different systems; the frame of mahogany, thirty inches long................$17.50”


   If the two systems of waves have different spatial frequencies (pictures at the left), the resultant of the two waves results in a system of beats. 

REFS: Thomas B. Greenslade, Jr., "Apparatus for Natural Philosophy: Nineteenth Century Wave Machines", Phys. Teach., 18, , 510-517 (1980)

Thomas B. Greenslade, Jr., "Harmonic Sliders", Phys. Teach. 28, 568 (1990)


B. Charles Wheatstone's Device. Wheatstone, already known as the inventor of the concertina and the kaleidophone, started to develop machines to demonstrate the properties of light waves in the 1840s. Julian Holland has estimated that thirty of the machines were eventually built. The sets of pins on the side show the vertical (lower) and horizontal (upper) motions of the pins across the top. The waveshapes and their phasings are controlled by the two templates running through the length of the apparatus. The example below is in the collection of the Smithsonian Institution.
   At the left is an instrument at Wesleyan University in Middletown, Connecticut.
   The Wheatstone wave machine at the right is in the Garland Collection of Classical Physics Apparatus at Vanderbilt University. It was purchased from Rudolph Koenig of Paris about 1875. The cost in the 1889 catalogue was 1000 francs.
   This version of the Wheatstone device is at Union College in Schenectady, New York, and was made by Rudolph Koenig. In his 1889 catalogue, this is probably what is listed as the small model, and cost 600 francs. 

REF: Julian Holland, "Charles Wheatstone and the Representation of Waves, Part I", Rittenhouse, 13, 86-106 (1999); "Part II", Rittenhouse, 14, 27-46 (2000)

C. Pluecker and Fessel's Device. The 1900 catalogue of Max Kohl of Chemnitz, Germany lists the wave addition device below as a "Wave Machine after Fessel and Pluecker with 2 movable wave channels, for producing transversal, circular and elliptic waves, elegantly made, of polished mahogany, with iron feet." The cost was 100 Marks. This machine was first described by Pluecker in 1849, just as Wheatstone was perfecting his wave machine. This device, in the collection of the National Museum of American History of the Smithsonian Institution, has a metal template on top that shifts the vertical rods from side to side, and clearly has an internal template that shifts them up and down. The reference marks on the left-hand side are used to adjust the phasing of the two sets of templates to allow the various polarizations of the wave traced out by the white balls to be set. Pluecker and Fessel are better known for their form of gyroscope  that we still use today.

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