A term used for a large genus of astronomical and navigational instruments. In the form of a quarter-circle, it incorporates a sun or star sighting device along one of its radial edges and a plumb-bob hanging from the centre of the circle. The old quadrans vetus was originally an Islamic invention which provides seasonal hours but is only truly accurate for an observer on the equator. The quadrans novus, invented by Profatius in 1288) was more accurate, incorporating the circular scale of the astrolabe folded into a quadrant but it was difficult to read. The 1438 horary quadrant of von Gmunden was one of several attempts to improve on this. The Gunter ~ (after Edward Gunter, Gresham College, 1623) is latitude dependent and employs a stereographic projection. The navigational ~ is actually an octant (eighth of a circle) with two reflecting mirrors replacing the plumb-bob. For the Davis ~, see back-staff.
Quarter days: the first or last days of each quarter of the year on which rent or interest is due. These dates