
magnetic deviation: the angle between geographical north and the direction indicated by a compass needle.

magnitudes: numbers in a scale of the relative brightnesses of the stars, 1 being the brightest.

mariner's astrolabe: altitudemeasuring instrument for finding latitude at sea, having a heavy brass or bronze ring, suspended by a shackle and ring, with a degree scale and a centrallypivoted alidade.

mater: part of an astrolabe, see article on the astrolabe.

mathematical compendium: compound instrument for performing various functions in practical mathematics.

mathematical instruments: collections of instruments of assorted kinds for performing functions in practical mathematics.

measuring rod: an instrument used to measure distances or depths. See also gauging rod.

measuring rods: see measuring rod.

meridian: the plane containing the observer and both celestial poles, or containing the observer, the zenith and the pole, or, more colloquially, the northsouth line at a particular position on the earth.

meridian circle: circular scale of degrees which in use is aligned with the meridian.

mining instruments: in this period mining instruments were principally for surveying, adapted for the special conditions of working underground in mines.

nautical circle: generic term for a circular mathematical instrument of use in navigation, but likely to carry a range of mathematical and astronomical scales.

nautical hemisphere: a combination of graduated arcs and circles used for navigational calculations, see article on the nautical hemisphere.

navicula dial: type of altitude dial in the shape of a ship.

nocturnal: instrument for finding the time at night from the orientation of the stars, see article on the nocturnal.

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.

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.

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 16thcentury Portuguese mathematician Pedro Nu?ez.

Nuremberg hours: system of hour reckoning, see article on time and date.

octant: the eighth part of a circle or an instrument measuring up to 45 degrees.
