# spherometer

## Definitions

• WordNet 3.6
• n spherometer a measuring instrument for measuring the curvature of a surface
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Webster's Revised Unabridged Dictionary
• n Spherometer (Physics) An instrument for measuring the curvature of spherical surface, as of lenses for telescope, etc.
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Century Dictionary and Cyclopedia
• n spherometer An instrument for measuring the radii of spheres; a sphere-measurer. It is of especial service to opticians in determining the focal lengths, etc., of lenses. The common form (see figure) consists of a vertical screw c, with a large graduated head a a, turning in a socket supported by three legs whose hard steel points are exactly equidistant. The fixed scale b at the side, together with thegraduated screwhead, makes it possible to measure with great accuracy the distance between the extremity of the screw and the plane passing through the ends of the three supports, when, for example, all the points are in contact with the surface of the sphere. If, in addition, the distance between the ends of the supports is known, a simple calculation gives the radius of the sphere. The same instrument may also be used to determine with precision the thickness of a plate, as (in the figure) A, placed upon a horizontal surface.
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Chambers's Twentieth Century Dictionary
• Spherometer an instrument for measuring the sphericity of portions of spherical surfaces—for example, lenses
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## Etymology

Webster's Revised Unabridged Dictionary
Sphere, + -meter,: cf. F. sphéromètre,
Chambers's Twentieth Century Dictionary
Fr.,—L. sphæra—Gr. sphaira.

## Usage

### In literature:

The spherometer is accepted at all stages of the process as the final arbiter as to curvature.
"On Laboratory Arts" by Richard Threlfall
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