Refractive Index (of a medium)
Ratio of the velocity of light in vacuum to the velocity of light in the medium.
Note: This index is equal to the ratio of the sines of the angles of incidence (?1) and refraction (?2) when a ray crosses the surface separating vacuum and medium.
Reference: C.I.E. (modified)
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
Celsius (previously Centigrade)
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM