The geometric compass was designed by Galileo Galilei in Padua in 1597 and made by Marcantonio Mazzoleni. It is composed of two arms, on which numerous lines are engraved, converging at the fulcrum of the opening provided with a hole for the plumb line, a graduated quadrant with different scales, and the "forked" leg, a cursor that allows both to lengthen the rod in which it is inserted, and to position the compass vertically. This calculating instrument allowed to quickly perform more than forty different types of complex geometric and arithmetic operations, based on the mechanism of proportions, and to find solutions to various problems related to civil and military needs. For example, it was possible to calculate the ballistics of artillery shots or redraw a map in a different scale, or even carry out exchange operations. Galileo described its functioning in the treatise Le operazioni del compasso geometrico et militare, which, published in Padua in 1606 in sixty copies, was sold or provided together with a copy of the compass itself. Of the original sixty compasses, currently no more than five specimens are known. In addition to the one exhibited in the Museum of Applied Arts of the Castle, the others are at the Museum of the History of Science in Florence, at the Military Geographic Institute also in Florence, at the University of Pisa, and in Cambridge, England.
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Title:Geometric military compass by Galileo Galilei