Achromatic and Direct Vision Prisms
   The prism at the left below is from the collection at the National Museum of American History at the Smithsonian Institution, and was made by Max Kohl of Chemnitz, Germany. In the 1900 catalogue, it is listed as "Apparatus with three prisms to demonstrate the achromatic and the direct vision prism", and is priced at 45 marks. 

   The 1916 L. E. Knott catalogue shows the same apparatus at $5.75, and has the following entry: "Weinhold's Demonstration Prism for explaining dispersion and achromatism without deviation of the mean ray. This apparatus consists of a set of three prisms conveniently mounted for the greatest utility and ease of adjustment." With one setting, the spectrum was spread out on either side of the straight-through ray; with the other, there was no spectrum. The lower two curs show how the two arrangements of prisms are achieved. 

   The prism at the right, below is unmarked and in the Greenslade collection. It is missing the prism on the left-hand upright.

   This prism set was made by Leybold and imported by the firm of James G. Biddle of Philadelphia. In the 1921 Leybold catalogue is is listed as "Apparatus compromising three prisms, for demonstrating achromatic combinations and direct vision prism... $12"

   The apparatus is in the lecture demonstration room of Cornell University. 

 These identical pieces of apparatus are at Denison University (left) and in the Greenslade collection (right). Both prisms pivot about the upright so that one or the other or both may be placed in the optical path. 
   Here the three prisms may be folded up in pairs to demonstrate achromatism or constant deviation. These were made by Lerebours et Secretan of Paris, and are listed at 50 francs in the 1853 catalogue. 

   The apparatus at the left is at Washington and Lee University in Lexington, Virginia, and at the right is an example in the Garland Collection of Classic Physics Apparatus at Vanderbilt University in Nashville, Tennessee

   At the right is an unmarked set of three prisms at Colby College in Waterville, Maine. The middle prism is fixed, and constant deviation and achromatism conditions are produced by flipping up one or the other of the two side prisms. 

   The pair of prisms on the left were used for demonstrations of spectrum recombination. The prisms are identical and face in opposite directions. This apparatus, at Washington and Lee University in Lexington, Virginia, was made by Duboscq.


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