The Davis quadrants are usually made of ebony, rosewood, or other dark woods, with boxwood scale arcs and could be made by expert wood-workers. The numerous examples preserved attest the skill of the old cabinet-makers, for they are never warped or twisted while their jointing is a Chinese puzzle. Probably the _Mayflower_ carried a Davis quadrant and quite likely an astrolabe, and of course, a compass, for the compass had been in use for two centuries. Whether the compass was independently invented in Europe or was borrowed from the Chinese is uncertain. The old marine compasses were set in gimbals. The magnet was a thin bar attached, usually with sealing wax, to the under side of the compass card, the whole mounted in a thin bowl of turned wood. These were the compasses of the eighteenth century. There is one in the Salem collection inscribed,--"Benjamin King Salem in New England", with the date "1770" cut in the box; another has the mark of Benjamin King, 1790. A surveyor's compass, wooden throughout, including wooden sights, is inscribed,--"Made by James Halsey near ye draw bridge Boston." The liquid compass first suggested by Francis Crow in 1813 and improved by E. S. Ritchie of Boston, has largely displaced the older devices. The "nocturnal", used at night, as its name signifies, appeared at an early date, exactly when it does not seem possible to say. One in the Salem collection is marked,--"Nathaniel Viall 1724". By adjusting the movable discs to the date on the scale for the day of the month, sighting the north star through the hole in the center and then bringing the arm against the "guard stars", the hour was indicated with reasonable accuracy. Good pictures and descriptions of the nocturnal may be found in old books on navigation. In 1730, John Hadley in England and Thomas Godfrey in Philadelphia, independently invented the octant, known for nearly two hundred years as Hadley's quadrant. Both Hadley and Godfrey received awards for their devices. Although called quadrant in this country it is generally known elsewhere as octant, which is the better name, for the instrument represents but one eighth of the circle. By the principle of reflection, however, it covers ninety degrees and the scale is so marked. The Davis quadrant with its two arcs does represent one fourth of the circle and for that instrument the name is correct.