Construct · 4 fields · 4 citations
One name. Different field. Different construct. One map.
● jingle · one word, four kinds of bending Nearest construct by meaningreflectioncompare the meaningsEvery construct on the map is compared with every other by the meaning of its definitions, and the closest one is surfaced here. The nearest construct to refraction is reflection.
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Refraction is the change in direction of a light wave as it crosses the boundary between two transparent media in which it travels at different speeds. Each medium has a refractive index, the ratio of the speed of light in a vacuum to its speed in that medium, and the amount of bending follows Snell's law, which ties the angles on either side of the boundary to the two indices. Born and Wolf's Principles of Optics derives this behaviour from the wave nature of light and the conditions a wavefront must satisfy at an interface. The referent is the geometric bending of a wave passing between media, described by angles and refractive indices, and it is not a subsurface survey, an eye examination, or a shimmer in the open air.[1]
In exploration geophysics, refraction is the bending of a seismic wave as it crosses a boundary between rock layers of different seismic velocity. When a wave meets a faster layer at a shallow enough angle it travels along that boundary and returns to the surface as a head wave, and the arrival times of these waves reveal the depth and velocity of the layers below. Palmer's An introduction to the generalized reciprocal method of seismic refraction interpretation lays out one standard way of turning forward and reverse arrival times into a picture of an undulating refractor. The referent is the bending of an elastic wave inside the ground, used to image subsurface structure, and it is distinct from the bending of light, the focusing error of an eye, or a mirage.[2]
In eye care, refraction is the clinical procedure that measures how an eye focuses light and works out the lens power that would bring images to a sharp focus on the retina. A mismatch between the eye's optical power and its length produces refractive error: myopia, where distant objects blur; hyperopia, where the eye is underpowered for its length; and astigmatism, where focusing differs across directions. Morgan, Ohno-Matsui, and Saw's review Myopia describes how these errors are defined, measured in dioptres, and corrected with lenses. The referent is a measurement of the living eye's focusing state and the correcting prescription, not the bending of light at a glass surface, a seismic survey, or an atmospheric shimmer. This entry describes the concept and is not clinical advice.[3]
Atmospheric refraction is the bending of light as it passes through air whose density, and so whose refractive index, changes with height or temperature. Because the atmosphere is layered rather than uniform, rays follow curved paths, which lifts the apparent position of stars and the setting Sun, makes starlight appear to twinkle, and produces mirages where a strong temperature gradient near the ground or over a hot road bends light into an inverted or displaced image. Vollmer's Mirrors in the air: mirages in nature and in the laboratory explains how such images arise from the vertical gradient of the refractive index. The referent is the bending of light along a curved path through the open atmosphere, seen as shifted or shimmering images, and it is not a survey of the ground, a clinical eye measurement, or refraction at a single sharp glass boundary.[4]
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