Prisms have been standard laboratory equipment since Isaac Newton used one in 1666 to study the nature of the spectrum. 

   The two Lerebours et Secretan prisms at the left are in the collection of the National Museum of American History at the Smithsonian Institution in Washington, D.C. The cost was 40 to 70 francs, depending on the type of glass (flint or crown) and on whether the glass was especially chosen to be free of striations. 


   The long, narrow prism at the at Duke University is unmarked, but is of the same overall shape and construction as one sold by E. S. Ritchie for $3.00. 

   The 1881 Ritchie catalogue lists this as a "Mounted Prism; a prism suspended by points in frame, with movable joint and stand, so that it may be adjusted to a beam of light from an opening in the shutter; six inches in width." Remember that window shutters have horizontal slats that are linked together so that a thin blade of sunlight can be directed toward this horizontal prism inside the classroom. 

   This unmarked prism is in the Jack Judson Collection at the Magic Lantern Collection in San Antonio, Texas.

   This Duboscq prism at Union College in Schenectady, New York, has a cylindrical lens mounted in front of it, thus allowing a thin blade of light to fall on it to produce a sharp spectrum. 

   In my own lecture demonstrations I use a 35 mm slide projector with a piece of cardboard with a narrow slit cut in it in place of the slide as a light source for producing spectra. 

   Everything is here but the prism! This prism holder and lens is listed in Max Kohl catalogues of the later 1920s as "Apparatus for Demonstrating the Spectrum and the Fraunhofer Lines, consisting of a flint glass prism of 40 mm side and an achromatic lens 50 mm diam., fitted together on one stand, the prism being rotary. The apparatus can be placed in front of the heliostat or the projection apparatus as it has a tall adjustable stand."

   This apparatus, quite usable today for demonstrations, is in the apparatus collection at Hobart and William Smith Colleges in Geneva, New York.

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