zenith-sectorhttp://www.oed.com/dictionary/zenith-sector_n%3Ftab%3Dmeaning_and_usezenith sector, n.
Revised 2018

zenith sectornoun

Now historical.
  1. 1775–
    A type of zenith telescope formerly favoured, having a heavily built mount with fine adjustments for accurate alignment.
    1. 1775
      Which quantities are not too small to be measured and demonstrated by an accurate zenith sector, such as that belonging to the Royal Society.
      Philosophical Transactions (Royal Society) vol. 65 499
    2. 1829
      The zenith sector..can be used only on the meridian; and its measures are referred to the zenith point of the place of observation. Its principal uses are to determine the latitude of the place of observation by a star of known zenith distance; to measure the zenith distance of a star..; and to ascertain the zenith point.
      W. Pearson, Practical Astronomy vol. II. 531
    3. 1970
      A 5-foot portable zenith sector was found to be difficult both to manipulate and to rectify.
      Notes & Rec. Royal Society vol. 24 266
    4. 2006
      The expedition was equipped with a 9-foot-tall zenith sector constructed by the London instrument maker George Graham.
      E. Danson, Weighing World iv. 33

Originally published as part of the entry for zenith, n. & adj.

zenith, n. & adj. was revised in June 2018.