Epact Scientific Instruments of Medieval and Renaissance Europe

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Protractor
Signed by Erasmus Habermel
circa 1580; German
Gilt copper; 132 mm in diameter

This beautifully and carefully made protractor was intended for specialist applications by a military engineer. The central scales give the successive positions of the tangential rule for drawing the sides of regular polygons with different numbers of sides between 3 and 16. Such polygons were the basis of the plans for contemporary fortifications.

The outer degree scale is divided by diagonals so that it can be read to 2 minutes of arc. That idea that angles could be, or would need to be, drawn to this level of accuracy seems extravagant.

Museum of the History of Science, Oxford
Inventory number 54619

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