jackstaffn.1
/ˈdʒakstɑːf/, /ˈdʒakstaf/, U.S. /ˈdʒækˌstæf/ Nautical.
A short flagpole, usually at the bow of a vessel or on its bowsprit (formerly often at the head of the spritsail topmast), on which the jack (jack n.4) is flown.
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society > travel > travel by water > vessel, ship, or boat > equipment of vessel > masts, rigging, or sails > spar > [noun] > flag-pole
jackstaff1691
1691 Smith's Sea-mans Gram. & Dict. (new ed.) i. v. facing p. 18 (table) Jack staff and Jack.
1722 A. Boyer Polit. State Great Brit. Nov. 514 The said Captain arrived at Canso..with the Head of their Chiefest King and Councellor on his Ensign Staff, and another on his Jack Staff.
1794 D. Steel Elements & Pract. Rigging & Seamanship I. 175 The Jack-staff is a short staff erected on the aftside of the bowsprit-cap, to expand the jack.
1857 Ballou's Dollar Monthly Mag. Aug. 151/1 From her stem sheets arose a short jack staff, from which fluttered the remains of an old blue shirt.
1890 R. C. Leslie Old Sea Wings, Ways, & Words iii. 38 This mast [sc. the spritsail-topmast] not only had a squaresail, the spritsail-topsail, set upon it, but terminated in a pole-head or jackstaff, upon which the flag known as ‘the jack’..was hoisted.
1912 Mariner′s Mirror 2 271 The spritsail topmast had at its head a cap into which was stuck the jack staff.
1939 J. B. Connolly Navy Men xv. 139 A flag fluttered above the ramparts of a fort ashore, and slowly down from our stern jackstaff came our ensign.
2017 N.Z. Herald (Nexis) 20 June (Sport section) Strictly speaking, a flag is only a jack if it is worn at the jackstaff at the bow of a ship.
This entry has been updated (OED Third Edition, March 2018; most recently modified version published online March 2022).
jackstaffn.2
/ˈdʒakstɑːf/, /ˈdʒakstaf/, U.S. /ˈdʒækˌstæf/ Nautical.
U.S. An instrument used in navigation to measure the angles between distant and celestial objects, consisting of a graduated staff equipped with one or more movable crosspieces; = Jacob's staff n. 2a. historical.In use, one end of the staff is placed just under the eye, and one of the crosspieces moved along the staff until the two objects lie at either end. The number assigned to the graduation to which the crosspiece was moved is then looked up in a table which provides the angle.
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the world > the universe > cosmology > science of observation > astronomical instruments > measuring altitude > [noun] > cross-staff
Jacob's staff1559
cross-staff1594
fore-staff1669
radius1745
jackstaff1886
society > travel > travel by water > vessel, ship, or boat > equipment of vessel > navigational aids > [noun] > cross-staff
Jacob's staff1559
cross-staff1594
David's staff1623
back-staff1627
fore-staff1669
radiometer1728
jackstaff1886
1886 J. Winsor Narr. & Crit. Hist. Amer. II. i. 98 The cross-staff, or jackstaff,..in several modified forms for a long time served mariners as a convenient help in ascertaining the altitude of the celestial bodies.
1932 Florida Hist. Soc. Q. 11 10 The jackstaff had come into use by that time, and with it approximately correct observations were possible under favorable conditions.
1997 Luso-Brazilian Rev. 34 50 To take the height of a star (the observed height), the navigator then used a jackstaff or backstaff (now a sextant) to measure the angle from sea level to the heavenly body at a given longitude.
This entry has been updated (OED Third Edition, March 2018; most recently modified version published online March 2022).
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