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nautical circle: generic term for a circular mathematical instrument of use in navigation, but likely to carry a range of mathematical and astronomical scales.
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nautical hemisphere: a combination of graduated arcs and circles used for navigational calculations, see article on the nautical hemisphere.
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navicula dial: type of altitude dial in the shape of a ship.
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nocturnal: instrument for finding the time at night from the orientation of the stars, see article on the nocturnal.
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nocturnal and quadrant: compound instrument which combines both the functions of a nocturnal and quadrant, usually on two different sides of the same instrument, with equal importance given to each.
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nocturnal and sundial: compound instrument which combines both the functions of a nocturnal and sundial, usually on two different sides of the same instrument, with equal importance given to each.
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nonius: a way of subdividing a quadrant of a circle to provide fine discrimination of parts of degrees, comparable in purpose to the later vernier scale. The name comes from the latinized surname of the 16th-century Portuguese mathematician Pedro Nu?ez.
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Nuremberg hours: system of hour reckoning, see article on time and date.
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octant: the eighth part of a circle or an instrument measuring up to 45 degrees.
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old quadrant: type of horary quadrant, see article on the quadrant.
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opposition: two planets 180? from each other in the ecliptic are said to be in opposition. This relative position had important astrological significance.
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ordinary hours: system of hour reckoning, see article on time and date.
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orthographic planisphere: flat map produced by orthographic projection.
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pedometer: device worn by a walker to measure distance by counting paces.
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pendant sundial: a form of sundial suspended by a cord and possibly hung around the neck.
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perpetual calendar: calendar covering a number of years, see article on time and date.
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phase of the moon: the changing appearance of the moon throughout its approximately monthly cycle, from the thin crescent of new moon to the complete circle of full moon and back again.
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pillar dial: type of altitude dial, see article on the sundial.
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pin gnomon: the part of a sundial which casts the shadow, where this part is in the form of a pin.
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plane table: type of surveying instrument, see article on the plane table.
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plane table alidade: an alidade specially adapted for use with a plane table.
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planetary hours: system of hour reckoning, see article on time and date.
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planetary temperaments: astrological character of the fixed stars; as assigned in classical astrology, each star had a nature and effect similar to one or more of the planets.
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planisphere: a representation of a spherical body on a flat surface, commonly a map of the earth or of the heavens.
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planispheric astrolabe: astronomical instrument based on a planispheric projection of the heavens, see article on the astrolabe.
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plate: part of an astrolabe with a projection of altitude and azimuth lines on to the equatorial plane, see article on the astrolabe.
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plumb level: device for determining a horizontal level or an angle of elevation by a plumb line or plummet.
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plumb line: a suspended thread with a weight at its end, indicating the vertical.
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plummet: a form of plumb line in which the 'line' and weight are a single rigid piece.
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polar dial: type of sundial, see article on the sundial.
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polyhedral dial: sundial with hour lines on various faces of a solid figure, see article on the sundial.
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prime vertical: celestial great circle passing through the east and west points and the zenith.
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primum mobile: instrument for finding the sines and versed signs of angles, see article on the primum mobile.
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projection: translation of a figure on to a plane or curved surface using straight lines in a systematic way. For example, a spherical surface can be projected on to a plane (the plane of projection) by means of straight lines drawn from all points on the surface to a certain defined point (the point of projection) and marking where they intersect the plane. In a stereographic projection, such as is used for the ordinary astrolabe, points on a containing circle are projected on to an equatorial plane from one pole; in an orthographic projection, such as is used in a Rojas design of universal astrolabe, the point of projection is at infinity and the projection lines are parallel.
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proportional compasses: drawing instrument consisting of two legs each with points at either end; used for transferring dimensions in enlarged or reduced ratio.
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proportional dividers: drawing instrument consisting of two legs each with points at either end; used for transferring dimensions in enlarged or reduced ratio.
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proportional instrument: unusual instrument used to mechanically perform functions in trigonometry.
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protractor: instrument for setting out and measuring degrees.
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quadragesima: the 40 days of Lent or the first Sunday in Lent.
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quadrans vetus: type of horary quadrant, see article on the quadrant.
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quadrant: instrument based on a quarter of a circle, see article on the quadrant.
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quadratum nauticum: diagram for finding course directions from latitudes and longitudes, see article on the astrolabe.
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quatrefoil: decorative form with four leaves or petals.
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radio latino: instrument for measuring angles in surveying and gunnery, see article on the radio latino.
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ramming rods: long rods, often in wood, intended for use in gunnery and used to push the projectile inside a cannon, or to compress the powder in an arquebus.
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reduction compass: a drafting instrument with two pivoting arms which sits parallel to a drawing surface, held up by its fixed points. The arms have no scales but can be divided at any given position by moveable points.
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Regiomontanus-type dial: design of portable altitude dial adjustable for any latitude.
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rete: skeletal star map representing the rotation of the heavens on an astrolabe. The rete normally features a projection of the ecliptic and pointers for prominent stars, and can be rotated over a chosen latitude plate. see article on the astrolabe.
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right ascension: angle parallel to the celestial equator, measured eastwards from the spring equinox.
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ring dial: simple form of altitude dial in the shape of a ring, for use in one latitude.
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rule (or ruler): an instrument of multifarious functions in the form of a straight rod of metal, wood or other material; a folding rule is an alternative form with two or more jointed legs.
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Saints' days: anniversary days for Christian saints.
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scaphe dial: sundial where the hour lines are marked on a concave hemisphere or part hemisphere.
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sector: calculating instrument using pairs of lines on the faces of two hinged arms, see article on the sector.
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sexagenarium: an instrument in the form of a volvelle for planetary calculations.
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shadow square: a form of geometrical quadrant, where two sides of a square are divided into equal parts and a plumb line or alidade from the opposite corner is used for measuring angles in terms of ratios (that is, tangents). Where a plumb line is used, one side has a pair of fixed sights. The name comes from the fact that a measurement of the altitude of the sun, expressed as a ratio, applied to the length of the shadow cast by an upright structure, yields its height. See also under astrolabe.
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sight: a device through which an object of interest can be viewed. Sights appear on surveying and astronomical instruments and in a more specialised form in the gunner's sight.
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simple theodolite: surveying instrument for measuring horizontal angles, see article on the theodolite.
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sinical quadrant: a quarter of a circle with a scale of degrees at its circumference which carries a pattern of criss-crossing vertical and horizontal lines. The ratio of the length of a given line to the quadrant's radius gives the sine or cosine of the corresponding angle.
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solar time: time measured directly from the position of the sun, see article on the sundial.
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