William Hyde Wollaston developed optical methods for measuring the refractive index and optical dispersion of materials. His 1802 paper described determining a specimen's refractive behavior from the boundary at which total internal reflection begins in a contacting optical prism.[ref]
A Method of examining refractive and dispersive Powers, by prismatic Reflection by William Hyde Wollaston. pp. 365–366, principle and instrument
The apparatus made the boundary into a measurement. A specimen contacted a glass prism, and hinged sighting arms located the transition between transmitted and totally reflected rays. Wollaston described a square-prism arrangement with a Vernier scale for reading the required geometric quantity. This contact method avoided having to shape the specimen itself into a prism.[ref]
In modern notation, Snell's law gives the critical-angle relation for a specimen index below a prism index . As an original example, if and , then . The angle is measured inside the prism from the interface normal. These stipulated numbers illustrate the method rather than reproducing Wollaston's measurements.
Wollaston also compared oils sold under the same name and reported differing refractive values. This gave the optical measurement a practical motivation: testing material consistency with only a small specimen.[ref]
Articles by others on the same topic
William Hyde Wollaston (1766–1828) was a prominent English chemist and physicist known for his significant contributions to the fields of chemistry and crystallography. He is particularly recognized for a few key achievements: 1. **Discovery of Platinum**: Wollaston is credited with the discovery of the element palladium in 1803, which he identified while studying platinum ores. He is also known for developing techniques for refining platinum.