|William Nicol optics|
- Rasmus Bartholin understood
- that Iceland spar, a transparent calcite crystal,
- produces a double refraction, that is, birefringence.
- Viking navigators called these “sunstones”
- and used them to discern
- the direction of the sun on cloudy days.
- William Nicol constructed a prism
- by gluing together two pieces of Iceland spar
- cut at exactly 68 degrees to the crystal axis.
- Nicol’s prism produces a plane polarized light,
- correcting the refraction of the extraordinary ray
- and eliminating the ordinary ray by internal reflection.
- Isaac Newton used two triangular glass prisms
- to discover his theory of color.
- Augustin-Jean Fresnel used circular arrays
- of curved glass prisms to concentrate a lighthouse beam.
- Ignazio Porro used a double Porro prism
- in his prism binoculars.
- Giovanni Battista Donati used a double-Amici prism
- to observe stellar spectra.
- Leonard R. Ingersoll used a Nicol prism
- in his Glarimeter to measure paper glossiness.
- What we perceive
- as through a sieve
- reflects bio-specifics
- more than physics.