An ellipsoid whose three axes represent the refractive indices of an anisotropic crystal for light after various directions with respect to the crystal axes
a particular conic part supposed to be used the tangent airplane to your area, and used to figure out the accidents of curvature for the area at the point of contact. The bend is comparable to the intersection associated with the area with a parallel into the tangent jet and indefinitely near it. It really is an ellipse once the curvature is synclastic, and an hyperbola if the curvature is anticlastic.
In geometry, the bend of intersection of any surface with an airplane indefinitely near and parallel to the tangent-plane at any point.
In the theory of equations, a curve which shows the shared effectation of both center criteria of Newton's guideline, regarding an equation associated with 5th level having all its roots imaginary.
In crystallography, a surface, in general (for a biaxial crystal) an ellipsoid having axes proportional towards main refractive indexes, whose geometrical characters serve showing the optical relations associated with the crystal: for a uniaxial crystal the area becomes a spheroid as well as for an isotropic crystal a sphere.