EXCEPTIONALLY RARE MARINER’s QUADRANT. The real deal! An authentic 18th century English ship’s navigational instrument made by the most noted instrument maker of his day, George Adams (I). This incredible relic from ye olde days of sail is made of thick brass beautifully signed in engraved cursive script, “G Adams Mathematical Instrument Maker to His MAJESTY Fleet Street London.” It is the earliest form of navigational quadrant, calibrated on the arc from 0 to 90 in single degrees subdivided to quarter degrees (15 arc minutes) marked by 10’s. The precise engraving is all the more remarkable considering it was hand-engraved! It was NOT done with the yet-to-be-invented dividing engine. Each increment is less than 1/32 inch (<1 mm) wide! In use the navigator sighted the celestial object along the 0 degree limb. A string rove through a small hole at the apex supported a small plumb bob which ran across the scale. When the sighting was taken, the observer pinched the string on the arc then noted its position on the scale. The original string, long since deteriorated, is now replaced with a working silk string and brass bob. This instrument has a 7 inch radius and measures exactly 10 inches wide.