What is "jacob's staff"

Jacob \Ja"cob\, n. [Cf. F. Jacob. See 2d Jack.] A Hebrew patriarch (son of Isaac, and ancestor of the Jews), who in a vision saw a ladder reaching up to heaven (--Gen. xxviii. 12); -- also called Israel. And Jacob said . . . with my staff I passed over this Jordan, and now I am become two bands. --Gen. xxxii. 9, 10. Thy name shall be called no more Jacob, but Israel. --Gen. xxxii. 28. Jacob's ladder.

1. (Bot.) A perennial herb of the genus Polemonium ( Polemonium c[oe]ruleum), having corymbs of drooping flowers, usually blue. Gray.

2. (Naut.) A rope ladder, with wooden steps, for going aloft.
   --R. H. Dana, Jr.

3. (Naut.) A succession of short cracks in a defective spar. Jacob's membrane. See Retina. Jacob's staff.

   1. A name given to many forms of staff or weapon, especially in the Middle Ages; a pilgrim's staff. [Obs.]
      --Spenser.

   2. (Surveying) See under Staff.

Staff \Staff\ (st[.a]f), n.; pl. Staves (st[=a]vz or st[aum]vz; 277) or Staffs (st[.a]fs) in senses 1-9, Staffs in senses 10, 1

1. [AS. st[ae]f a staff; akin to LG. & D. staf, OFries. stef, G. stab, Icel. stafr, Sw. staf, Dan. stav, Goth. stabs element, rudiment, Skr. sth[=a]pay to cause to stand, to place. See Stand, and cf. Stab, Stave, n.] 1. A long piece of wood; a stick; the long handle of an instrument or weapon; a pole or stick, used for many purposes; as, a surveyor's staff; the staff of a spear or pike.

   And he put the staves into the rings on the sides of the altar to bear it withal.
   --Ex. xxxviii. 7.

   With forks and staves the felon to pursue.
   --Dryden.

2. A stick carried in the hand for support or defense by a person walking; hence, a support; that which props or upholds. ``Hooked staves.''
   --Piers Plowman.

   The boy was the very staff of my age.
   --Shak.

   He spoke of it [beer] in ``The Earnest Cry,'' and likewise in the ``Scotch Drink,'' as one of the staffs of life which had been struck from the poor man's hand.
   --Prof. Wilson.

3. A pole, stick, or wand borne as an ensign of authority; a badge of office; as, a constable's staff.

   Methought this staff, mine office badge in court, Was broke in twain.
   --Shak.

   All his officers brake their staves; but at their return new staves were delivered unto them.
   --Hayward.

4. A pole upon which a flag is supported and displayed.

5. The round of a ladder. [R.]

   I ascended at one [ladder] of six hundred and thirty-nine staves.
   --Dr. J. Campbell (E. Brown's Travels).

6. A series of verses so disposed that, when it is concluded, the same order begins again; a stanza; a stave.

   Cowley found out that no kind of staff is proper for an heroic poem, as being all too lyrical.
   --Dryden.

7. (Mus.) The five lines and the spaces on which music is written; -- formerly called stave.

8. (Mech.) An arbor, as of a wheel or a pinion of a watch.

9. (Surg.) The grooved director for the gorget, or knife, used in cutting for stone in the bladder.

10. [From Staff, 3, a badge of office.] (Mil.) An establishment of officers in various departments attached to an army, to a section of an army, or to the commander of an army. The general's staff consists of those officers about his person who are employed in carrying his commands into execution. See ['E]tat Major.

11. Hence: A body of assistants serving to carry into effect the plans of a superintendent or manager; sometimes used for the entire group of employees of an enterprise, excluding the top management; as, the staff of a newspaper.

    Jacob's staff (Surv.), a single straight rod or staff, pointed and iron-shod at the bottom, for penetrating the ground, and having a socket joint at the top, used, instead of a tripod, for supporting a compass.

    Staff angle (Arch.), a square rod of wood standing flush with the wall on each of its sides, at the external angles of plastering, to prevent their being damaged.

    The staff of life, bread. ``Bread is the staff of life.''
    --Swift.

    Staff tree (Bot.), any plant of the genus Celastrus, mostly climbing shrubs of the northern hemisphere. The American species ( C. scandens) is commonly called bittersweet. See 2d Bittersweet, 3 (b) .

    To set up one's staff, To put up one's staff, To set down one's staff or To put down one's staff, to take up one's residence; to lodge. [Obs.]

n. 1 (context surveying English) A single straight rod or staff, pointed and iron-shod at the bottom, for penetrating the ground, and having a socket joint at the top, used, instead of a tripod, for supporting a compass. 2 ''Verbascum thapsus'', the (vern: common mullein). 3 The ocotillo, one of (taxlink Fouquieria species noshow=1), a genus of desert shrubs of southwestern United States and Mexico having slender naked spiny branches that after the rainy season put forth foliage and clusters of red flowers.

The term Jacob's staff, also cross-staff, a ballastella, a fore-staff, or a balestilha, is used to refer to several things. In its most basic form, a Jacob's staff is a stick or pole with length markings; most staffs are much more complicated than that, and usually contain a number of measurement and stabilization features. The two most frequent uses are:

• in astronomy and navigation for a simple device to measure angles, later replaced by the more precise sextants;
• in surveying (and scientific fields that use surveying techniques, such as geology and ecology) for a vertical rod that penetrates or sits on the ground and supports a compass or other instrument.

The simplest use of a Jacob's staff is to make qualitative judgements of the height and angle of an object relative to the user of the staff.