Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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refraction ( refractive index )

A term indicative of the bending or deflection of a ray of light from a straight course as it passes obliquely from one medium to another, e.g., form air to water, with the extent of deflection being related to the speed of light in the two mediums. The refractive index (RI), or index of refraction, of any substance is the ratio between the speed of light in air and its speed in the substance. The greater the difference between the refractive index of a substance and its surrounding medium, the more light will be reflected and the less absorbed, while the smaller the difference, the less light will be reflected and the more absorbed. (233 )

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