principal axis

noun

1. 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.
2. Physics. one of three mutually perpendicular axes of a body about which the moment of inertia is maximum or minimum.

principal axis

noun

1. the line passing through the optical centre and centres of curvature of the faces of a lens or a curved mirror
2. any of three mutually perpendicular axes about which the moment of inertia of a body is maximum

Word History and Origins

Origin of principal axis¹

First recorded in 1875–80

Example Sentences

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.

From Project Gutenberg

In the stauraxonia the vertical imaginary principal axis is cut by two or more horizontal cross-axes or radial-axes.

From Project Gutenberg

Direct nitration gives (principally) m-nitrobenzoic acid, also pseudo-tetragonal with a much shorter principal axis.

From Project Gutenberg

Benzoic acid is pseudo-tetragonal, the principal axis being remarkably long; there is no cleavage at right angles to this axis.

From Project Gutenberg

The intersection of this last line with the principal axis will give the optical center.

From Project Gutenberg