Refractare

Refractare is a term historically used to denote the act of refraction, particularly in Latin-language scientific writings. In modern English usage, the verb is refract and the noun refraction, so refractare appears mainly in historical or philological contexts. The root comes from Latin refractus, meaning bent back or broken, reflecting the way a wave changes direction when crossing media with different optical densities.

In optics, refractare describes the process by which light or other waves bend as they pass from one medium to another. The bending occurs because the speed of the wave changes in different materials. The relationship governing this behavior is Snell's law: n1 sin theta1 = n2 sin theta2, where n1 and n2 are the refractive indices of the two media, and theta1 and theta2 are the angles of incidence and refraction relative to the boundary.

Applications of refraction include the design of lenses and prisms, which use bending of light to focus or disperse it. Atmospheric refraction affects the apparent positions of stars and planets, especially near the horizon. In modern science and engineering, refraction is central to imaging systems, microscopy, astronomy, and fiber-optic communications, where precise control of light paths is essential.

Related concepts include refractive index, dispersion, critical angle, and total internal reflection. While refractare as a term is mainly of historical interest, its modern equivalents—refract and refraction—remain foundational in optics and wave physics.