Optics. a line passing through the center of the surface of a lens or spherical mirror and through the centers of curvature of all segments of the lens or mirror.
Physics. one of three mutually perpendicular axes of a body about which the moment of inertia is maximum or minimum.
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How to use principal axis in a sentence
These are at points on the principal axis that are twice as far from O, the center of the lens, as are the principal foci.Physics | Willis Eugene Tower
In the stauraxonia the vertical imaginary principal axis is cut by two or more horizontal cross-axes or radial-axes.The Wonders of Life | Ernst Haeckel
Direct nitration gives (principally) m-nitrobenzoic acid, also pseudo-tetragonal with a much shorter principal axis.
Benzoic acid is pseudo-tetragonal, the principal axis being remarkably long; there is no cleavage at right angles to this axis.
The intersection of this last line with the principal axis will give the optical center.Visual Signaling | Signal Corps United States Army
British Dictionary definitions for principal axis
the line passing through the optical centre and centres of curvature of the faces of a lens or a curved mirror
any of three mutually perpendicular axes about which the moment of inertia of a body is maximum
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012