An Etymological Dictionary of Astronomy and Astrophysics

A crystal device made of two → quartz  → prisms
with equal acute angles assembled in a rhombus that is used in analyzing → polarized light. The wedge-shaped prisms are placed against each other and can be displaced along their plane of contact by a → micrometer. Thus they form a parallel plate of variable thickness allowing the optical retardation to be adjusted.

See also: Jacques Babinet (1794-1872), French physicist; → compensator.