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A surface whose equation in rectangular coördinates is x / (1 − Ar) + y / (1 − Br) + z / (1 − Cr) = 0.
(noun)
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If upon every central section of a quadric surface be erected a perpendicular at the center, and points be taken on this perpendicular at distances from the center equal to the axes of the section, then the locus of these points will be the wave-surface. It is frequently called Fresnel's wave-surface, to distinguish it from Huygens's wave-surface, which is simply an ellipsoid—the latter being the form of the wave-front of a uniaxial crystal, the former that of a biaxial crystal.
(noun)
The Century Dictionary (Public Domain)