Two Quadrants

Entry

Two almost identical quadrants for measuring the rolling of a ship. They are both made of brass and mounted on a backboard with the centre of the arc at the top. The scale at the bottom goes from 0 to 45 degrees on either side. The outer rim of the arc is toothed with counter-set teeth on either side of 0 degrees. The two pointers or plumb bobs have ratchets fixed to the back. They move along the arc but can only swing outward, the ratchet preventing them from going back. The ratchets can be released by means of a catch, to reset the pointers at 0 degrees. Because the teeth are interrupted in the middle, the pointers cannot occupy the same eighth of the circle. The teeth on the first quadrant (NG-MC-884-A) subdivide the arc into quarter degrees and those on the second (NG-MC-884-B) into half degrees. The movement of the pointers on the arc of the first quadrant (NG-MC-884-A) is smoothed by means of small rollers. When the ship started to roll, each pointer would swing in the direction of heel, indicating the maximum inclination of the vessel.

Although Obreen mentions only one quadrant,¹ two have been found. Jochem Pietersz Asmus (1755-1837) did mention two quadrants of his own invention in a list from 1807.²