Galileo, illustration of the use of the compass, from Le Operazione del Compasso Geometrico et Militare (The Operation of the Geometric and Military Compass), Padua, 1606
Galileo designed his geometric and military compass ("compasso geometrico e militare") in 1597. Known in English as the sector, the compass was widely used until the invention of logarithmic tables. In Galileo's model, an arc could be inserted between the two arms of the compass to make the instrument into a quadrant. A plumb bob could be attached.
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