Prism

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This compound prism (pictured here with its shagreen case) was used to demonstrate the achromatic properties of the compound lens. It was patented by a Spitalfields weaver John Dollond in 1758 and probably made by him around 1760.

The outer prisms are made of crown glass, and have a green tinge. Their angles are 12-and-a-half and 25 degrees. The inner prism is made from white flint glass, with an angle of 22 degrees. Their densities and refractive powers are different.

Newton's writings had led to the belief that the chromatic aberration of reflecting telescopes could not be corrected. However, the problem was solved practically by using a 'sandwich' of two lenses, one made of crown glass, the other of flint glass.

Record details

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• Online ID: 000-100-102-694-C
• Image Rights Holder: National Museums Scotland
• Project: National Museums Scotland
  Project description   View all records in project
• Ref: National Museums Scotland  T.1955.21
• Date: Around 1760
  c. 1760
  
• Material: Brass (Prism)
  Glass (Prism)
  Shagreen (Case)
  Prism, compound, achromatic / case
  
• Dimensions: 1.50" x 0.75" (hinged element) / 2.00" x 1.25"
  
• What: Prism, compound, achromatic / case
  
• Subject: 22. PHYSICS, Light (Departmental Classification)
  
• Who: John Dollond (Probable compound prism maker)
  
• Where: England
  
• Event:
• Description: Compound prism in a shagreen case, patented by John Dollond in 1758, probably made by Dollond, England, c. 1760
  
• References:
  • Compare with the example in Turner, G. L'E., Van Marum's Scientific Instruments in Teyler's Museum. Leiden: 1966, p 292, which has a bibliography 
• Translations:
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