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26 to 74 of 227 glossary terms
Cardan suspension: universal mounting attributed to the 16th-century Italian philosopher and physician Girolamo Cardano which, by means of gimbals, allows the supported part to remain horizontal irrespective of the orientation of the rest of the instrument.
cardinal points: the main directions on the mariner's compass, north, south, east and west.
carpenter's rule: measuring ruler carrying one or more scales for calculating the volume of timber or the surface area of board or planking.
celestial globe: globe marked with the positions of the stars.
celestial planisphere: map of the heavens, produced by geometrical projection of a sphere on to a flat surface. A common example of the use of a form of planisphere is the rete of an astrolabe.
celestial poles: diametrically opposite points of the celestial sphere about which the heavens are observed to rotate once a day.
celestial sphere: sphere in the heavens on which the celestial motions are considered to be moving for the purpose of positional measurements from earth. It is far enough away for the earth's size to be negligible in relation to the distance of the stars, so that all observers can be considered to be at the centre of the celestial sphere.
celestial spheres: system of concentric, rotating orbs centred on the earth, proposed by Aristotle and others as constituting the physical construction of the heavenly system of planets and stars.
chalice dial: sundial where the hour lines are inscribed on the inside surface of a goblet. A second set of lines can be included to allow for refraction, when the goblet is full. See also scaphe dial.
circumferentor: form of surveying compass with fixed sights, where bearings are read from the position of a magnetic compass, see also article on the theodolite.
climates: division into latitude zones of the part of the earth known to ancient geographers, used by Ptolemy.
clinometer: an instrument for measuring inclination.
common hours: system of hour reckoning, see article on time and date.
compass: instrument indicating directions by a magnetic needle, see article on compass.
compass card: card or paper with a printed, drawn or painted compass rose, usually carried above the magnetic needle of a compass.
compass dial: form of azimuth dial.
compass rose: diagram of the points of the compass, often decorated and coloured. North is usually indicated by a fleur-de-lys.
compasses: instrument for drawing circles. see article on drawing instruments.
compendium: several instruments compiled into one device; also see article on astronomical compendium.
conjunction: two planets having the same position (in longitude) in the ecliptic are said to be in conjunction. This relative position had important astrological significance.
cross-staff: instrument for measuring angles between distant objects, mostly altitudes, see article on cross-staff.
cross-staffs: see article on cross-staff
crucifix dial: form of polyhedral sundial in the shape of a crucifix, see article on sundial.
cylinder dial: type of altitude dial, see article on the sundial.
declination: angle above or below the celestial equator.
declinatory: instrument used in constructing a sundial, to find the declination of a plane.
degrees: the conventional divisions of a circle, one being the 360th part of a circle, and thus the units used to measure and express angles.
diagonals: lines used in the subdivision of divisions of an arc, also known as transversals. Each diagonal line is drawn across the division from its beginning to its end, and is divided linearly either by dots or by concentric arcs. In this way the linear division of a line can be used for the angular subdivision of an arc.
dial: instrument for telling time by the position of the sun (occasionally by the moon), see article on the sundial.
dialling quadrant: instrument in the form of a quadrant used in the construction of a sundial.
diptych dial: type of sundial which, in many cases, could be called an astronomical compendium, in the form of a folding tablet, usually in ivory, with at least a string gnomon and a horizontal dial on the inside, but often with other dials as well.
disc dial: type of sundial belonging in the class of altitude dial.
dividers: instrument with jointed legs for measuring and transferring distances, see article on the dividers.
dominical letter: letter denoting the day of the first Sunday of the year, see article on time and date.
drawing instruments: instruments used for drawing and constructing geometrical figures, see article on drawing instruments.
Easter table: table for calculating the date of Easter, see article on time and date.
ecliptic: line on the celestial sphere representing the annual path of the sun through the stars.
epacts: numbers used in the calculation of Easter, see article on time and date.
equal hours: system of hour reckoning, see article on time and date.
equator: circle on the earth's surface 90 degrees from the poles, or the circle on the celestial sphere 90 degrees from the celestial poles.
equatorial: relating to or based on the equator. Has much the same meaning as equinoctial.
equatorial dial: another name for equinoctial dial.
equatorium: instrument to determine the longitude of one or more of the planets at any given time.
equinoctial: relating to or based on the equator, or relating to the equinox.
equinoctial dial: sundial where the hour plate or circle is set parallel to the equator, see article on the sundial.
equinoctial ring dial: type of sundial, included as an equinoctial dial, comprising two pivoted rings and a bridge for adjusting for solar declination, or of three rings.
equinox: either of two points on the celestial sphere where the equator meets the ecliptic, representing the position of the sun when it is 90 degrees from the poles, or the two dates in the year when the sun is in this position in its annual cycle.
folding rule: see rule.
folding rule and level: a compound instrument combining the functions of both a folding rule and level.
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