3.25 x 3.5 inch, half-prism
Date: 1875-1900
Inventory Number: 1997-1-1690
Classification: Prism
Subject:
Maker: Alvan Clark and Sons ? (1846 - 1958)
Maker: John A. Brashear ? (1840 - 1920)
Cultural Region:
Dimensions:
8.7 × 9.2 × 4.9 cm (3 7/16 × 3 5/8 × 1 15/16 in.)
Material:
Description:
This right prism has a working face of 8.5 x 9 cm (3.25 x 3.5 inches) and an angle of about 30°. The corners are ground down and the polished faces are circular.
Signedunsigned
FunctionThis prism may have been one of a series of prisms in a 19th century spectroscope where the last prism was often a half-prism--i.e, a 30° rather than 60° prism. It might also been used in conjunction with a diffraction grating in a spectroscope, where it would help in dispersing and steering the light.
As a beam-steering instrument, a wedge prism deviates a light beam at a certain angle (depending on the width of the prism and its material characteristics). When one puts two similar wedge prisms in close proximity, the incoming light beam can be placed anywhere within a cone defined by the deviation angle.
For an interesting tutorial, see the following website.
As a beam-steering instrument, a wedge prism deviates a light beam at a certain angle (depending on the width of the prism and its material characteristics). When one puts two similar wedge prisms in close proximity, the incoming light beam can be placed anywhere within a cone defined by the deviation angle.
For an interesting tutorial, see the following website.
Historical AttributesThe half-prism is a prism formed by cutting an equilateral (60°) prism in half perpendicularly to one of the faces. This forms a prism with a 30° angle between the primary faces.
Harvard's observatory, physics, and chemistry departments used half-prisms in spectroscopic studies. Many of the research-quality prisms used were manufactured by Alvan Clark & Sons or Brashear.
Harvard's observatory, physics, and chemistry departments used half-prisms in spectroscopic studies. Many of the research-quality prisms used were manufactured by Alvan Clark & Sons or Brashear.