A large, 3rd quarter 18th century mahogany quadrant. This example measures 20 inches tall and is signed "*Made by JOHN GILBERT on Tower Hill LONDON* for IOHN (sic) LAW * April 11th 1772." Scale division techniques had still not been perfected to allow makers (and users) the benefit of smaller instruments up to that time. Yet numerous "state-of-the-art" advances are already in evidence. The early form vernier scale is calibrated "10 - 0 - 10." The scale on the large arc is now of 2 joined pieces of ivory instead of boxwood. The evolution from the "crab claw" to the brass-tipped wooden index arm is obvious. But note that the very early form 2-shade interchangeable filter is still being used! Dated instruments such as this are invaluable in tracking the evolutionary progress of the early makers. (Private Collection. Photo West Sea Co.)