| The term "compass" or "compasses" denotes
a wide range of instruments for drawing, measurement,
and proportional calculation. Besides the more
common compasses for drawing circumferences,
widespread since antiquity, the Renaissance
has left us a great number of special compasses,
whose names reflect their specific functions:
oval compasses to draw ellipses, hyperbolas
and parabolas; two-point compasses—also
called dividers—to divide lines
and transfer measurements; nautical compasses,
to track routes on sea-charts; compasses with
curved points, called gunner's compasses, to
measure mouths of cannons, cannon balls, and
columns; three-legged compasses to reproduce
maps; four-point compasses, or reduction compasses,
to enlarge or reduce drawings, divide lines
and circumferences proportionally, and draw
polygons; eight-point compasses to measure
fractions of degrees and carry out proportional
calculations; proportional compasses to perform
arithmetic, geometric, and trigonometric calculations
and to measure weights, gradients, and distances
for military use; and sophisticated surveying
compasses that combined a magnetic compass,
a windrose, and optical sights for surveying
and for drawing topographic maps. |
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