catflap.org Online Dictionary Query

  Micrometer \Mi*crom"e*ter\, n. [Micro- + -meter: cf. F.
     microm[`e]tre.]
     An instrument, used with a telescope or microscope, for
     measuring minute distances, or the apparent diameters of
     objects which subtend minute angles. The measurement given
     directly is that of the image of the object formed at the
     focus of the object glass.
     [1913 Webster]
  
     Circular micrometer, or Ring micrometer, a metallic ring
        fixed in the focus of the object glass of a telescope, and
        used to determine differences of right ascension and
        declination between stars by observations of the times at
        which the stars cross the inner or outer periphery of the
        ring.
  
     Double image micrometer, a micrometer in which two images
        of an object are formed in the field, usually by the two
        halves of a bisected lens which are movable along their
        line of section by a screw, and distances are determined
        by the number of screw revolutions necessary to bring the
        points to be measured into optical coincidence. When the
        two images are formed by a bisected object glass, it is
        called a divided-object-glass micrometer, and when the
        instrument is large and equatorially mounted, it is known
        as a heliometer.
  
     Double refraction micrometer, a species of double image
        micrometer, in which the two images are formed by the
        double refraction of rock crystal.
  
     Filar micrometer, or Bifilar micrometer. See under
        Bifilar.
  
     Micrometer caliper or Micrometer gauge (Mech.), a caliper
        or gauge with a micrometer screw, for measuring dimensions
        with great accuracy.
  
     Micrometer head, the head of a micrometer screw.
  
     Micrometer microscope, a compound microscope combined with
        a filar micrometer, used chiefly for reading and
        subdividing the divisions of large astronomical and
        geodetical instruments.
  
     Micrometer screw, a screw with a graduated head used in
        some forms of micrometers; turning the head one full
        revolution advances the position of the tip of the screw
        only by a little.
  
     Position micrometer. See under Position.
  
     Scale micrometer, or Linear micrometer, a minute and very
        delicately graduated scale of equal parts used in the
        field of a telescope or microscope, for measuring
        distances by direct comparison.
        [1913 Webster]

  Bifilar \Bi*fi"lar\, a. [Pref. bi- + filar.]
     Two-threaded; involving the use of two threads; as, bifilar
     suspension; a bifilar balance.
     [1913 Webster]
  
     Bifilar micrometer (often called a bifilar), an
        instrument form measuring minute distances or angles by
        means of two very minute threads (usually spider lines),
        one of which, at least, is movable; -- more commonly
        called a filar micrometer.
        [1913 Webster]

  Bifilar \Bi*fi"lar\, a. [Pref. bi- + filar.]
     Two-threaded; involving the use of two threads; as, bifilar
     suspension; a bifilar balance.
  
     Bifilar micrometer (often called a bifilar), an
        instrument form measuring minute distances or angles by
        means of two very minute threads (usually spider lines),
        one of which, at least, is movable; -- more commonly
        called a filar micrometer.