Surveying
In surveying the Jacob's staff, contemporaneously referred to as a jacob staff, is a single straight rod or staff made of nonferrous material, pointed and metal-clad at the bottom for penetrating the ground. It also has a screw base and occasionally a ball joint on the mount, and is used for supporting a compass, transit, or other instrument.
The term cross-staff may also have a different meaning in the history of surveying. While the astronomical cross-staff was used in surveying for measuring angles, two other devices referred to as a cross-staff were also employed.
- Cross-head, cross-sight, surveyor's cross or cross - a drum or box shaped device mounted on a pole. It had two sets of mutually perpendicular sights. This device was used by surveyors to measure offsets. Sophisticated versions had a compass and spirit levels on the top. The French versions were frequently eight-sided rather than round.
- Optical square - an improved version of the cross-head, the optical square used two mirrors at 45° to each other. This permitted the surveyor to see along both axes of the instrument at once.
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Famous quotes containing the word surveying:
“As for my own business, even that kind of surveying which I could do with most satisfaction my employers do not want. They would prefer that I should do my work coarsely and not too well, ay, not well enough. When I observe that there are different ways of surveying, my employer commonly asks which will give him the most land, not which is most correct.”
—Henry David Thoreau (1817–1862)
“Upon looking back from the end of the last chapter and surveying the texture of what has been wrote, it is necessary, that upon this page and the five following, a good quantity of heterogeneous matter be inserted, to keep up that just balance betwixt wisdom and folly, without which a book would not hold together a single year.”
—Laurence Sterne (1713–1768)