IEE

FIRST BOOKCROSsS-STAE E.

, the Deſcription of the Staff.

lle croſ-Staff, is an Inſtrument well known to ourSeamen, and much uſed by the ancient Aſtrono-mers and others, ſerving Aſtronomically for ob-lervation of the Altitude and Angles of diſtancein the Heavens; Geometrically for Perpendi-enlar Heights and Diſtances on Land andSea. 1. The Beſcription and ſeveral Hſes of it are ex-tant in Print, by Gemma Friſius in Latine, in Engliſh by D. Hood. Idiffer ſomething from them both, in the Projection of this Staff, butſo as their Rules may be apply ed unto it, and all their Propoſitions bewrought by it; and therefore referring the Reader to their Books, Iſhall be brief in the Explanation of that which may be applied fromtheirs unto mine, and ſo come to the Uſe of thoſe Lines which aremy Addition, not extant heretofore. i 1The neceſfary parts of this Inſtrument are Five;(1.) The staff;3.) The Croſs; And(3.) the three Sights. The Staff which I made

5 own uſe, is a full Vard in lengtb, that ſo it may ſerve for

meaſure. i 5