fore-staff

The Sailor's Word-Book

An instrument formerly used at sea for taking the altitudes of heavenly bodies. The fore-staff, called also cross-staff, takes its name hence, that the observer in using it turns his face towards the object, in contradistinction to the back-staff, where he turns his back to the object. The fore or cross staff consists of a straight square staff, graduated like a line of tangents, and four crosses or vanes which slide thereon. The first and shortest of these vanes is called the ten cross or vane, and belongs to that side of the instrument whereon the divisions begin at 3° and end at 10°. The next longer vane is called the thirty cross, belonging to that side of the staff on which the divisions begin at 10° and end at 30°, called the thirty scale. The next is called the sixty cross, and belongs to that side where the divisions begin at 20° and end at 60°. The last and longest, called the ninety cross, belongs to that side whereon the divisions begin at 30° and end at 90°.

The Sailor's Word-Book

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